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Purpose:
To compare the accuracy of the Barrett True-K formula with other methods available on the American Society of Cataract and Refractive Surgery (ASCRS) post-refractive surgery intraocular lens (IOL) power calculator for the prediction of IOL power after previous myopic laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK).
Setting:
Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA.
Design:
Retrospective case series.
Methods:
The accuracy of the Barrett True-K formula was compared with the Adjusted Atlas (4.0 mm zone), Masket, modified-Masket, Wang-Koch-Maloney, Shammas, and Haigis-L methods to calculate IOL power. A separate analysis of 2 no-history methods (Shammas and Haigis-L) was performed and compared with the Barrett True-K no-history option.
Results:
Eighty-eight eyes were available for analysis. The Barrett True-K formula had a significantly smaller median absolute refraction prediction error than all other formulas except the Masket, smaller variances compared with the Wang-Koch-Maloney, Shammas, and Haigis-L, and a greater percentage of eyes within ±0.50 diopter (D) of predicted error in refraction compared with the Adjusted Atlas, Masket, and modified Masket methods (all P < .05). In eyes with no historical data, the Barrett True-K no-history formula had a significantly smaller median absolute refraction prediction error and a greater percentage of eyes within ±0.50 D of the predicted error in refraction than the Shammas and the Haigis-L formulas (both P < .05).
Conclusion:
The Barrett True-K formula was either equal to or better than alternative methods available on the ASCRS online calculator for predicting IOL power in eyes with previous myopic LASIK or PRK.

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... Following this study, other methods that do not require the patient's clinical history have been published, and are among the most utilized [19][20][21][22]. ...

... Hoffer et al. suggested to avoid multiple IOLs in a study when reporting a method accuracy [24]. This is acceptable but obtaining a large database in most of the studies regarding IOL power calculation after refractive surgery is difficult, hence multiple IOL models were analyzed [22,25,[41][42][43][44]. As reported by Abulafia et al. [48] more than one IOL model is appropriate when limited data are available. ...

... Although the primary objective of this paper was to study and to verify if ALMA approach could be used to improve the R factor results, additional limitation relates to the inability to compare ALMA with other methods, such as Barrett True-K formula [22]. Unfortunately, this comparison was not possible because many other formulas are not published in the literature and hence zeroing out mean error to compare refractive errors was unreliable. ...

Purpose
To test a new method to calculate the Intraocular Lens (IOL) power, that combines R Factor and ALxK methods, that we called Advance Lens Measurement Approach (ALMA).
Design
Retrospective, Comparative, Observational study.
Setting
Department of Medicine and Surgery, University of Salerno, Italy.
Methods
Ninety one eyes of 91 patients previously treated with Photorefractive Keratectomy (PRK) or Laser-Assisted in Situ Keratomileusis (LASIK) that underwent phacoemulsification and IOL implantation in the capsular bag were analyzed. For 68 eyes it was possible to zero out the Mean Errors (ME) for each formula and for selected IOL models, in order to eliminate the bias of the lens factor (A-Costant). Main outcome, measured in this study, was the median absolute error (MedAE) of the refraction prediction.
Results
In the sample with ME zeroed (68 eyes) both R Factor and ALxK methods resulted in MedAE of 0.67 D. For R Factor 33 eyes (48.53%) reported a refractive error <0.5D, and 53 eyes (77.94%) reported a refractive error <1D, For ALxK method, 32 eyes (47.06%) reported a refractive error <0.5 D, and 53 eyes (77.94%) reported a refractive error <1 D. ALMA method, reported a MedAE of 0.55 D, and an higher number of patients with a refractive error <0.5 D (35 eyes, 51.47%), and with a refractive error <1 D (54 eyes, 79.41%).
Conclusions
Based on the results obtained from this study, ALMA method can improve R Factor and ALxK methods. This improvement is confirmed both by zeroing the mean error and without zeroing it.

... These include selecting a medical school and residency program, choosing between academic and private practice, whether to pursue fellowship training and/or additional advanced degrees such as a Master of Public Health (MPH), Master of Business Administration (MBA), or Doctor of Philosophy (PhD). These options can be instrumental in facilitating a fruitful academic career [1][2][3][4]. Previous studies have described the characteristics of American ophthalmology residency program directors [1], department chairs [2], and clinician-scientists receiving National Institute of Health (NIH) grants [3]. ...

... These options can be instrumental in facilitating a fruitful academic career [1][2][3][4]. Previous studies have described the characteristics of American ophthalmology residency program directors [1], department chairs [2], and clinician-scientists receiving National Institute of Health (NIH) grants [3]. Gershoni et al. investigated the impact of subspecialty choice on research productivity, ...

... Ocular biometry parameters, which are basic elements in planning for cataract surgery, include axial length (AL), anterior chamber depth (ACD), corneal curvature, and white-to-white (WTW) [2]. Accordingly, appropriate implanted intraocular lens (IOL) power selection results in an acceptable uncorrected distance visual acuity, with greater patient satisfaction [3]. Different formulas have been recommended for the calculation of IOL power, all of which require specific biometric data and constants [4]. ...

Background: This study was conducted to investigate ocular biometry parameters in cataract surgery candidates in northern Tehran, Iran using OA-2000 biometry device. Methods: In this cross-sectional study, values of ocular biometry parameters, including axial length (AL), anterior chamber depth (ACD), mean corneal curvature (mean K), lens thickness (LT), corneal astigmatism (CA), and white-to-white (WTW) of 818 eyes with cataracts, were measured using the OA-2000 biometry device (Tomey, Nagoya, Japan). The participants were divided into six age subgroups, in 10-year intervals. Finally, the values of the biometry parameters were calculated, and the trend of changes was examined for both age and sex subgroups. Results: The mean ± standard deviation (SD) of age of the participants was 63.82 ± 13.25 years. Mean ± SD of biometry parameters were as follows: AL, 23.36 ± 1.55 mm; ACD, 3.09 ± 0.40 mm; LT, 4.45 ± 0.55 mm; mean K, 44.51 ± 1.72 D; CA, 1.06 ± 0.94 D; and WTW, 11.81 ± 0.45 mm. Most of the parameters showed significant age-related changes in the total population. There was an increase in LT (P < 0.001) and mean K (P = 0.001), as well as a decrease in AL (P < 0.001) and ACD (P < 0.001) with age. Moreover, AL had a negative negligible correlation with LT (r = -0.24, P < 0.001) and mean K (r = -026, P < 0.001), as well as a weak positive correlation with ACD (r = 0.44, P < 0.001). Conclusions: Our study revealed that the mean values of most biometric parameters varied across age and sex subgroups. Moreover, most of the parameters showed significant age-related changes in the total population. Keywords: ocular biometry, cataract, axial length, anterior chamber depth, keratometry, lens thickness, corneal astigmatism, white to white

... 5,[7][8][9][10] However, recent publications have suggested that the Barrett True-K formula (and the Barrett True-K No History [Barrett TKNH] formula for those eyes without data from before refractive surgery available) 11 may be one of the most accurate formulas for eyes with a history of myopic laser refractive surgery. [12][13][14] Use of posterior corneal measurements and total corneal power has also modernized lens calculation methods, especially in the subgroup of eyes with prior myopic laser refractive surgery. 15 These data refine outcomes by improving on assumptions about the ratio of anterior to posterior corneal curvature and its effect on the index of refraction. ...

... The Barrett True-K formula has non-inferior or superior results when compared to many of the other formulas used for eyes with previous refractive surgery. [12][13][14] Benefits of this formula include that it is freely available online, can be used with standard biometry values, and can be further improved if data from prior to refractive surgery are input. 12 Although the methodology remains unpublished, the Barrett True-K formula uses ocular biometry measurements to calculate modi- The ratio of anterior to posterior corneal curvature changes after myopic laser refractive surgery; therefore, the standard keratometric index of refraction cannot be accurately used in these eyes. ...

... [12][13][14] Benefits of this formula include that it is freely available online, can be used with standard biometry values, and can be further improved if data from prior to refractive surgery are input. 12 Although the methodology remains unpublished, the Barrett True-K formula uses ocular biometry measurements to calculate modi- The ratio of anterior to posterior corneal curvature changes after myopic laser refractive surgery; therefore, the standard keratometric index of refraction cannot be accurately used in these eyes. 16 Optical coherence tomography-based IOL calculation formulas use total corneal power and have demonstrated promising results for eyes with previous refractive surgery using RTVue (Optovue, Inc). ...

Purpose:
To assess the accuracy of intraoperative aberrometry, the Barrett True-K No History (Barrett TKNH), Barrett TKNH with posterior corneal measurements (Barrett TKNH with PC), Shammas-PL, and Haigis-L formulas in patients with cataract who had prior myopic refractive surgery.
Methods:
This was a retrospective consecutive case series of patients with prior myopic refractive surgery undergoing cataract extraction. Mean absolute error (MAE) and median absolute error (MedAE) of refraction prediction were compared for each formula. Interactions of each biometry measurement were modeled for each formula to evaluate those with the most significant impact on refraction prediction.
Results:
One hundred sixteen eyes of 79 patients were analyzed. MAE was 0.40 ± 0.33 diopters (D) for intraoperative aberrometry and 0.42 ± 0.31 D for the Barrett TKNH, 0.38 ± 0.30 D for the Barrett TKNH with PC, 0.47 ± 0.38 D for the Shammas-PL, and 0.56 ± 0.39 D for the Haigis-L formulas. Comparisons between formulas were significant for Barrett TKNH versus Barrett TKNH with PC formulas (P = .046), Barrett TKNH with PC versus Shammas-PL formulas (P = .023), and for all comparisons with the Haigis-L formula (P < .001), and not significant for all other comparisons (P > .05). Eyes were within ±0.50 D of prediction 73%, 72%, 69%, 62%, and 52% of the time for intraoperative aberrometry, the Barrett TKNH with PC, Barrett TKNH, Shammas-PL, and Haigis-L formulas, respectively. Corneal asphericity (Q value) was significantly associated with prediction error for all five methods. Changes in anterior chamber depth had a significant impact on Shammas-PL prediction errors.
Conclusions:
Newer technology using information from the posterior cornea modestly improved outcomes when compared to established methods for intraocular lens selection in eyes that had previous laser refractive surgery for myopia. [J Refract Surg. 2021;37(1):60-68.].

... Intraocular lens (IOL) power calculation for cataract surgery in eyes with previous laser refractive surgery has been a challenge for many years [1]. Indeed, a great variety of formulas and algorithms have been described and validated for IOL power calculation in this type of eyes, with some requiring previous laser refractive surgery clinical history [2][3][4][5][6] and some without [2,[7][8][9]. No clinical history methods are popular due to their ease of use, the difficulty in patients obtaining their previous clinical history, and the variability in the accuracy of the clinical data. ...

... Intraocular lens (IOL) power calculation for cataract surgery in eyes with previous laser refractive surgery has been a challenge for many years [1]. Indeed, a great variety of formulas and algorithms have been described and validated for IOL power calculation in this type of eyes, with some requiring previous laser refractive surgery clinical history [2][3][4][5][6] and some without [2,[7][8][9]. No clinical history methods are popular due to their ease of use, the difficulty in patients obtaining their previous clinical history, and the variability in the accuracy of the clinical data. ...

... The Haigis-L [7] and Shammas-PL [8] formulas are examples of commonly used no-history methods. Recently, the Barrett True-K no-history formula has also been shown to be accurate [2,10,11]. ...

This comparative study aimed to determine if total keratometry (TK) from IOLMaster 700 could be applied to conventional formulas to perform IOL power calculation in eyes with previous myopic laser refractive surgery, and to evaluate their accuracy with known post-laser refractive surgery formulas.
Sixty-four eyes of 49 patients with previous myopic laser refractive surgery were evaluated 1 month after cataract surgery. A comparison of the prediction error was made between no clinical history post-laser refractive surgery formulas (Barrett True-K, Haigis-L, Shammas-PL) and conventional formulas (EVO, Haigis, Hoffer Q, Holladay I, and SRK/T) using TK values obtained with the optical biometer IOLMaster 700 (Carl Zeiss Meditec), as well as Barrett True-K with TK.
The mean prediction error was statistically different from zero for Barrett True-K, Barrett True-K with TK, Haigis-L, Shammas-PL, and Holladay I with TK. The mean absolute error (MAE) was 0.424, 0.671, 0.638, 0.439, 0.408, 0.424, 0.479, 0.647, and 0.524, and median absolute error (MedAE) was 0.388, 0.586, 0.605, 0.298, 0.294, 0.324, 0.333, 0.438, and 0.377 for Barrett True-K, Haigis-L, Shammas-PL, Barrett True-K TK, EVO with TK, Haigis with TK, Hoffer Q with TK, Holladay I with TK, and SRK/T with TK, respectively. EVO TK followed by Barrett True-K TK and Haigis TK achieved the highest percentages of patients with absolute prediction error within 0.50 and 1.00 D (68.75%, 92.19%, and 64.06%, 92.19%, respectively)
Formulas combined with TK achieve similar or better results compared to existing no-history post-myopic laser refractive surgery formulas.

... [1][2][3][4][5][6] The introduction of more advanced formulas and methods for IOL power calculation and new technologies for corneal power and anterior eye segment measurements have enabled more accurate predictions. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] Among these methods, ray-tracing calculations have demonstrated very good outcomes after excimer laser corneal refractive surgery when no historical data are available. The measurements could be performed with the OKULIX software (Panopsis GmbH), the PhacoOptics software (IOL Innovations Aps), and the internal software of the Sirius topography instrument (Costruzioni Strumenti Oftalmici). ...

... The commonly used methods and formulas in such cases are the method by Savini and Hoffer, the Masket formula, and the Barrett true-K formula. 1,10,15 However, when no preoperative records are available, an accurate IOL power calculation might become more challenging. Several formulas and methods have been introduced to overcome this problem. ...

Purpose: To evaluate and compare the predictability of intraocular lens (IOL) power calculation after small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism.
Setting: Department of Ophthalmology, Philipps University of Marburg, Marburg, Germany.
Design: Retrospective comparative case series.
Methods: The study included 204 eyes that underwent SMILE. Preoperative evaluation included optical biometry using IOLMaster 500 and corneal tomography using Pentacam HR. The corneal tomography measurements were repeated at 3 months postoperatively. The change of spherical equivalent due to SMILE was calculated by the manifest refraction at corneal plane (SMILE-Dif). A theoretical model, involving the virtual implantation of the same IOL before and after SMILE, was used and the IOL power calculations were performed using ray-tracing (Okulix, Version 9.06), third- (Hoffer Q, Holladay-1, SRK/T) and fourth-generation formulas (Haigis-L, Haigis). The difference between the IOL-induced refractive error at corneal plane before and after SMILE (IOL-Dif) was compared to SMILE-Dif. The prediction error (PE) was calculated as the difference between SMILE-Dif–IOL-Dif.
Results: The PE with ray tracing was -0.06±0.40 diopters (D), Haigis-L -0.39±0.62 D, Haigis 0.70±0.48 D, Hoffer Q 0.84±0.47 D, Holladay-1 1.21±0.51 D and SRK/T 1.46±0.54 D. The PE with ray tracing was significantly smaller compared with all formulas (P≤0.001). The PE variance with ray tracing was σ²=0.159, being significantly more homogenous compared with all formulas (P≤0.011, F≥6.549). Ray tracing resulted in an absolute PE ≤0.5 D in 81.9% of the cases, followed by Haigis-L (53.4%), Haigis (35.3%), Hoffer Q (25.5%), Holladay-1 (6.4%) and SRK/T (2.9%).
Conclusions: Ray-tracing was the most accurate approach for IOL power calculation after myopic SMILE.

... Selecting an IOL power calculation formula of high accuracy is a direct and convenient way for most ophthalmologists. In recent years, new formulas, such as the Haigis-L and Barrett True-K formulas, have improved the outcomes of these challenging eyes [1,3]. However, the percentage of patients reaching the emmetropic range (± 0.5 D) after cataract surgery hardly exceeds 60% [4]. ...

... This rate was consistent with the 28.21% to 68% for no history methods reported by previous studies [2,[10][11][12][13], but significantly lower than the 69.6% to 80.8% in virgin eyes [14]. While underestimation of IOL power and consequent hyperopic outcomes after cataract surgery often occur in post-myopic-LASIK eyes when using normal formulas [15], myopic prediction errors were frequently reported with some modified formulas [3,11,13]. In this study, the proportion of eyes with prediction error greater than − 1.0 D was high and almost coincident between the two formulas, indicating their common defect in avoiding great refractive surprises thereby not being able to detected some underlying influential factors. ...

Purpose
To evaluate the influence of corneal ablation patterns on the prediction error after cataract surgery in post-myopic-LASIK eyes.
Methods
Eighty-three post-myopic-LASIK eyes of 83 patients that underwent uneventful cataract surgery were retrospectively included. Predicted postoperative spherical equivalence (SE) was calculated for the implanted lens using the Haigis-L and Barrett True-K formula. Prediction error at one month postsurgery was calculated as actual SE minus predicted SE. For each eye, area and decentration of the ablation zone was measured using the tangential curvature map. The associations between prediction errors and corneal ablation patterns were investigated.
Results
The mean prediction error was − 0.83 ± 1.00 D with the Haigis-L formula and − 1.00 ± 0.99 D with the Barrett True-K formula. Prediction error was positively correlated with keratometry (K) value and negatively correlated with ablation zone area using either formula, and negatively correlated with decentration of the ablation zone using the Barrett True-K formula (all P < 0.05). In the K < 37.08 D group, prediction error was negatively correlated with decentration of the ablation zone with both formulas (all P < 0.05). Multivariate analysis showed that with the Haigis-L formula, prediction error was associated with axial length (AL), K value and decentration, and with the Barrett True-K formula, prediction error was associated with AL and decentration (all P < 0.05).
Conclusion
A flatter cornea, larger corneal ablation zone and greater decentration will lead to more myopic prediction error after cataract surgery in post-myopic-LASIK eyes.

... It requires keratometric measurements before and after laser refractive treatment. In addition, the formula can predict lens power when no Barrett True-K No History formula is available for eyes with no historical data 14 . This formula can be accessed from the Asia-Pacific Association of Cataract and Refractive Surgeons (www.apacrs.org) ...

... In 2007, Awwad et al. 22 published findings of the double-K adjusted Holladay 1 formula in patients undergoing RK surgery, achieving good prediction of IOL power. In 2016, Abulafia et al. 14 compared the accuracy of the Barrett True-K formula of the ASCRS calculator in patients with a history of myopic LASIK/PRK refractive surgery with other available methods and found that the Barrett's calculation was equal to or better than alternative methods for IOL selection. Turnbull et al. 17 compared seven formulas in 2020 for IOL calculation in cataract surgery patients with a history of RK, with the best results in those using the Barrett True-K formula. ...

Introduction:
The challenge of calculating intraocular lens (IOL) power after refractive surgery such as radial keratotomy (RK) remains unresolved after two decades. At present, there is an increase in patients with this history.
Objectives:
The objectives of the study were to determine the difference in refractive error after surgery between the Barrett True-K No History and Panacea formulas, for the calculation of IOL in cataract operated patients with a history of RK.
Materials and methods:
An observational, analytical, cross-sectional, and retrospective study was conducted. The power of the IOL was calculated, with the Barrett True-K No History and Panacea formulas, and the IOLMaster 500 biometer. Two groups were studied. The predicted spherical equivalent was adjusted to obtain the power of the final implanted lens. The result of the predicted spherical equivalent was subtracted from the actual spherical equivalent, thus the refractive error was obtained for each formula. Student's t-test was used for independent groups.
Results:
The error with the Barrett True-K No History formula was −0.16 ± 1.12, whereas the error with the Panacea formula was −0.93 ± 1.22. p = 0.346.
Conclusion:
There was no statistically significant difference when comparing these two formulas, which showed that Panacea is as effective as Barrett True-K No History in cataract-operated patients with a history of RK.

... The Shammas-PL formula calculates IOL power based upon estimated postoperative anterior chamber depth (pACD), axial length (AL) and post-refractive surgery keratometry (1). The Barrett True-K formula (version 2.0) is based on the Barrett Universal II formula and is accessed online (7,8). Many studies have been published on monofocal IOL power calculation after refractive surgery, but to the best of our knowledge there have been few reports on multifocal IOL (mIOL) power calculation after refractive surgery. ...

... However, the keratometry used in both formulas were not measured values, but expected values developed by using regression analysis (a no-history method). As a result, IOL power calculations with Shammas-PL and Haigis-L have shown more myopic PE in eyes with prior corneal refractive surgery than those preoperatively expected (7). Recently published meta-analysis concluded that the ASCRS average based on ASCRS calculator (available at: http://www.ascrs. ...

Background:
This study aimed to compare the clinical outcomes of implantation of various multifocal intraocular lenses (mIOLs) and the prediction accuracy of two intraocular lens (IOL) power calculation formulas for eyes that underwent previous corneal refractive surgery.
Methods:
Four types of mIOLs [TECNIS Symfony (Group I), AcrySof IQ PanOptix (Group II), LENTIS Mplus (Group III), and TECNIS ZLB00 (Group IV)] were used and the IOL power was calculated with the two no-history methods, Shammas-PL and Barrett True-K. Visual acuity and refractive outcomes including manifest refraction, prediction error (PE), absolute error (AE), and median absolute error (MedAE) were evaluated at three months after the cataract surgery.
Results:
For all groups the Barrett True-K formula produced a narrower range of PEs and lower MedAE than Shammas-PL. Eyes of lower predictive accuracy (group B, AE >0.5D) showed weak uncorrected distance visual acuity resulting from myopic refractive error and target refraction when compared to that of higher predictive accuracy (group A, AE ≤0.5 D).
Conclusions:
Targeting emmetropia using the Barrett True-K, which considers both anterior and posterior corneal curvature is recommended in patients undergoing mIOL implantation with prior corneal refractive surgery. Additionally, history of prior large amount of laser ablation seems to be an important factor related to low predictive accuracy.

... However, the Haigis-L formula has been reported to show greater myopic shift after cataract surgery compared to the Barrett True-K no-history and Shammas methods [5,24]. The Barrett True-K formula uses the modified K value and applies the double K method based on the Barrett Universal II formula [25]. Previous studies have shown that the Barrett True-K formula yields the highest percentage of eyes with refractive errors within 0.50 D in IOL power calculation with anterior keratometry values [25,26]. ...

... The Barrett True-K formula uses the modified K value and applies the double K method based on the Barrett Universal II formula [25]. Previous studies have shown that the Barrett True-K formula yields the highest percentage of eyes with refractive errors within 0.50 D in IOL power calculation with anterior keratometry values [25,26]. In a meta-analysis, the average ASCRS online calculator result or the Barrett True-K no-history method was recommended for IOL power calculation [23]. ...

Purpose
To evaluate the prediction accuracy of the intraocular lens (IOL) power calculation using adjusted corneal power according to the posterior/anterior corneal curvature radii ratio in the Haigis formula (Haigis-E) in patients with a history of prior myopic laser vision correction.
Methods
Seventy eyes from 70 cataract patients who underwent cataract surgery and had a history of myopic laser vision correction were enrolled. The adjusted corneal power obtained with conventional keratometry (K) was calculated using the posterior/anterior corneal curvature radii ratio measured by a single Scheimpflug camera. In eyes longer than 25.0 mm, half of the Wang-Koch (WK) adjustment was applied. The median absolute error (MedAE) and the percentage of eyes that achieved a postoperative refractive prediction error within ± 0.50 diopters (D) based on the Haigis-E method was compared with those in the Shammas, Haigis-L, and Barrett True-K no-history methods.
Results
The MedAE predicted using the Haigis-E (0.33 D) was significantly smaller than that obtained using the Shammas (0.44 D), Haigis-L (0.43 D), and Barrett True-K (0.44 D) methods (P < 0.001, P = 0.001, and P = 0.014, respectively). The percentage of eyes within ± 0.50 D of refractive prediction error using the Haigis-E (78.6%) was significantly greater than that produced using the Shammas (57.1%), Haigis-L (58.6%), and Barrett True-K (61.4%) methods (P = 0.025).
Conclusion
IOL power calculation using the adjusted corneal power according to the posterior/anterior corneal curvature radii ratio and modified WK adjustment in the Haigis formula could improve the refraction prediction accuracy after cataract surgery in eyes with prior myopic laser vision correction.

... The predictability of the ISS method was compared with the Shammas no-history method [15,22], Haigis-L formula [24], Potvin-Hill pentacam method [25], and Barrett True K no-history formula [28,29]. These IOL calculation formulas or methods do not require preoperative data and were performed using the ASCRS IOL power calculator. ...

... In 246 eyes with previous LASIK/PRK, Ianchulev et al. reported a median absolute refractive error of 0.53 D for Haigis-L and 0.51 D for Shammas [32]. In 58 eyes with previous LASIK/PRK, Abulafia et al. reported a median absolute refractive error of 0.46 D for Shammas, 0.58 D for Haigis-L, and 0.33 D for Barrett True-K [29]. Our study showed better results than these reports, but this difference is probably due to differences in the population groups studied and whether or not the type of IOL was standardized. ...

Background:
A new method, the Iida-Shimizu-Shoji (ISS) method, is proposed for calculating intraocular lens (IOL) power that combines the anterior-posterior ratio of the corneal radius of the curvature after laser in situ keratomileusis (LASIK) and to compare the predictability of the method with that of other IOL formulas after LASIK.
Methods:
The estimated corneal power before LASIK (Kpre) in the double-K method was 43.86 D according to the American Society of Cataract and Refractive Surgery calculator, and the K readings of the IOL master were used as the K values after LASIK (Kpost). The factor for correcting the target refractive value (correcting factor [C-factor]) was calculated from the correlation between the anterior-posterior ratio of the corneal radius of the curvature and the refractive error obtained using this method for 30 eyes of 30 patients.
Results:
Fifty-nine eyes of 59 patients were included. The mean values of the numerical and absolute prediction errors obtained using the ISS method were -0.02 ± 0.45 diopter (D) and 0.35 ± 0.27 D, respectively. The prediction errors using the ISS method were within ±0.25, ±0.50, and ±1.00 D in 49.2%, 76.3%, and 96.6% of the eyes, respectively. The predictability of the ISS method was comparable to or better than some of the other formulas.
Conclusions:
The ISS method is useful for calculating the IOL power in eyes treated with cataract surgery after LASIK.

... the EKR of the Holladay Report module at 3.00 mm, 4.00 mm and 4, 50 mm, which are effective after photoablative CRS [13][14][15] . The corneal power used by the Pentacam-AXL to calculate the IOL was also analyzed with the Barret formula 11,12,16 , named True-K, and that calculated by the MRM [2][3][4]14,15 , which uses the formula K = Kpre + Rpre -Rpo, where Kpre is the preoperative corneal power, Rpre is the preoperative refraction and Rpo is the postoperative refraction. This method, as had previously been stated, is still considered by many authors [2][3][4]14,15 the standard method to obtain corneal power after CRS, which is why it was used as a reference in this study for comparisons. ...

... The TRCP provides the new Pentacam-AXL with the total data of the cornea, in a study area of 4 mm (effective pupillary area), considering the true refractive indices (air = 1, cornea = 1.376 and aqueous = 1.336) and the "true" total dioptric power of the cornea, since it considers the true optical conditions of the cornea, taking into account the anterior and posterior surfaces with their correct refractive indices, in addition to pachymetry and central and peripheral corneal aberrations. Both EKR and TRCP make Pentacam ideal in patients with previous CRS [3][4][5][6][7][8][9][10][11][12][13][14][15] . ...

... 11 The accuracy of Barrett True-K no-history was tested against Shammas and Haigis-L by Abulafia et al in 2016. 15 They found no significant differences in the variance of numerical refractive PE between the different methods, hence suggested that the Barrett True-K nohistory is at least as accurate as the other. 15 All of the aforementioned studies looked at combination of formulae requiring and not requiring refraction data prior to LASIK unlike Yang et al 6 and our study that just looked at the formulae not requiring refraction data prior to LASIK. ...

... 15 They found no significant differences in the variance of numerical refractive PE between the different methods, hence suggested that the Barrett True-K nohistory is at least as accurate as the other. 15 All of the aforementioned studies looked at combination of formulae requiring and not requiring refraction data prior to LASIK unlike Yang et al 6 and our study that just looked at the formulae not requiring refraction data prior to LASIK. Similar to Yang et al, 6 we found that using 'minimum' IOL power on the ASCRS calculator gives less variance and higher chances of having postoperative refraction within ±1.0 D in post-LASIK eyes. ...

Aim
To compare intraocular lens (IOL) calculation methods not requiring refraction data prior to myopic laser-assisted in situ keratomileusis (LASIK) and radial keratotomy (RK).
Methods
In post-LASIK eyes, the methods not requiring prior refraction data were Hagis-L; Shammas; Barrett True-K no-history; Wang-Koch-Maloney; ‘average’, ‘minimum’ and ‘maximum’ IOL power on the American Society of Cataract and Refractive Surgeons (ASCRS) IOL calculator. Double-K method and Barrett True-K no-history, ‘average’, ‘minimum’ and ‘maximum’ IOL power on ASCRS IOL calculator were evaluated in post-RK eyes. The predicted IOL power was calculated with each method using the manifest postoperative refraction. Arithmetic and absolute IOL prediction errors (PE) (implanted–predicted IOL powers), variances in arithmetic IOL PE and percentage of eyes within ±0.50 and ±1.00 D of refractive PE were calculated.
Results
Arithmetic or absolute IOL PE were not significantly different between the methods in post-LASIK and post-RK eyes. In post-LASIK eyes, ‘average’ showed the highest and ‘minimum’ showed the least variance, whereas ‘average’ and ‘minimum’ had highest percentage of eyes within ±0.5 D and ‘minimum’ had the highest percentage of eyes within ±1.0 D. In the post-RK eyes, ‘minimum’ had highest variance, and ‘average’ had the least variance and highest percentage of eyes within ±0.5 D and ±1.0 D.
Conclusion
In post-LASIK and post-RK eyes, there are no significant differences in IOL PE between the methods not requiring prior refraction data. ‘Minimum’ showed least variance in PEs and more chances of eyes to be within ±1.0 D postoperatively in post-LASIK eyes. ‘Average’ had least variance and more chance of eyes within ±1.0 D in post-RK eyes.

... The American Society of Cataract and Refractive Surgery (ASCRS) online calculator (https://ascrs.org/tools/iol-calculator) is recommended for the calculation of IOL power after refractive surgery in patients with prior myopic LASIK/PRK or RK, 7,10 including seven myopic LASIK/PRK previously. 11 When no refractive history is available in eyes with RK, Barrett True-K (post-RK) also performs well. 7 However, few reports have discussed the suitable formula to predict IOL power for the patients who have undergone RK combined with LASIK/PRK corneal refractive surgeries. ...

... 10,15,16 The Barrett True-K formula with or without previous data (post-LASIK/PRK or post-RK) gave better results in comparison with various methods and formulas from the ASCRS online calculator. 11,12,[15][16][17][18] In case 1, the Barrett True-K (no history, post-RK) formula from the ASCRS online calculator predicted more accurately with the data (AL, K, ACD) from both IOL Master 500 and Lenstar LS900, with the differences from the actual IOL power less than 1D. For the right eye of case 1, our results showed that Barrett True-K (no history, post-RK) was better than Barrett True-K (no history, post-PRK) when using AL/K/ACD either with or without the lens thickness (LT) measured by the Lenstar LS900. ...

Purpose
To report two challenging intraocular lens power calculation cases with patients each underwent different successive corneal refractive surgeries, respectively.
Observations
Biometry data, including the Back to Front corneal radii ratio (B/F ratio), were collected by Lenstar, IOL Master, and Pentacam AXL for Case 1 (received radial keratotomy (RK) and photorefractive keratectomy (PRK)) and Case 2 (received RK and laser-assisted in situ keratomileusis (LASIK)). The IOL power calculation was determined by several methods, including Shammas, Haigis-L, and Barrett True-K, which are available in the American Society of Cataract and Refractive Surgery online calculator and Pentacam AXL. The Barrett True-K (no history, post-RK) was more accurate in Case 1 (increased B/F ratio), whereas the Shammas, Haigis-L, and Barrett True-K (no history, post-LASIK/PRK) were more accurate in Case 2 (decreased B/F ratio).
Conclusion and importance
The B/F ratio may be a factor to be considered when selecting the IOL power calculation formula for patients who undergo two different corneal refractive surgeries. The further study focusing on this issue should be performed to clarify the results in the future.

... Accurate assessment of the corneal curvature is essential for IOL power prediction. Conventionally, the corneal power was estimated with a theoretical algorithm, using anterior corneal curvature only [7]. Now, total Open Access † Ling Wei and Kaiwen Cheng contributed equally to this work *Correspondence: zhuxiangjia1982@126.com; luyieent@163.com ...

... The newer IOLMaster 700 obtains Table 2 The absolute prediction errors of different formulas using total keratometry or standard keratometry in highly myopic eyes a reading of total corneal power, taking both corneal thickness and actual values for the radius of the posterior cornea into account, using telecentric 3-zone K and swept-source OCT technology. By replacing hypotheses and modeling with actual measurements, the IOLMaster 700 may provide reliable data on corneal power in some challenging cases, such as surgically modified [7,28,29,34] and high astigmatic corneas [17,35,36]. Here, we found no significant difference between TK and standard K in highly myopic eyes within this certain range of corneal thickness. ...

Background
The accuracy of using total keratometry (TK) value in recent IOL power calculation formulas in highly myopic eyes remained unknown.
Methods
Highly myopic patients who underwent uneventful cataract surgery were prospectively enrolled in this prospective comparative study. At one month postoperatively, standard deviation (SD) of the prediction errors (PEs), mean and median absolute error (MedAE) of 103 highly myopic eyes were back-calculated and compared among ten formulas, including XGboost, RBF 3.0, Kane, Barrett Universal II, Emmetropia Verifying Optical 2.0, Cooke K6, Haigis, SRK/T, and Wang-Koch modifications of Haigis and SRK/T formulas, using either TK or standard keratometry (K) value.
Results
In highly myopic eyes, despite good agreement between TK and K ( P > 0.05), larger differences between the two were associated with smaller central corneal thickness ( P < 0.05). As to the refractive errors, TK method showed no differences compared to K method. The XGBoost, RBF 3.0 and Kane ranked top three when considering SDs of PEs. Using TK value, the XGboost calculator was comparable with the RBF 3.0 formula ( P > 0.05), which both presented smaller MedAEs than others (all P < 0.05). As for the percentage of eyes within ± 0.50 D or ± 0.75 D of PE, the XGBoost TK showed comparable percentages with the RBF 3.0 TK formula (74.76% vs. 66.99%, or 90.29% vs. 87.38%, P > 0.05), and statistically larger percentages than the other eight formulas ( P < 0.05).
Conclusions
Highly myopic eyes with thinner corneas tend to have larger differences between TK and K. The XGboost enhancement calculator and RBF 3.0 formula using TK showed the most promising outcomes in highly myopic eyes.

... Table 1 summarizes details of the 11 studies included in this assessment [15][16][17][18][19][20][21][22] All studies relied exclusively on retrospective data on which to perform refractive outcomes analysis, except for Helaly et al, 13 in which some of the eyes included were prospectively enrolled. The abstracted refractive outcomes from these studies are organized in 3 separate tables. ...

Purpose
To review the literature to evaluate the outcomes of intraocular lens (IOL) power calculation in eyes with a history of myopic LASIK or photorefractive keratectomy (PRK).
Methods
Literature searches were conducted in the PubMed database in January 2020. Separate searches relevant to cataract surgery outcomes and corneal refractive surgery returned 1169 and 162 relevant citations, respectively, and the full text of 24 was reviewed. Eleven studies met the inclusion criteria for this assessment; all were assigned a level III rating of evidence by the panel methodologist.
Results
When automated keratometry was used with a theoretical formula designed for eyes without previous laser vision correction, the mean prediction error (MPE) was universally positive (hyperopic), the mean absolute errors (MAEs) and median absolute errors (MedAEs) were relatively high (0.72–1.9 diopters [D] and 0.65–1.73 D, respectively), and a low (8%–40%) proportion of eyes were within 0.5 D of target spherical equivalent (SE). Formulas developed specifically for this population requiring both prerefractive surgery keratometry and manifest refraction (i.e., clinical history, corneal bypass, and Feiz-Mannis) produced a proportion of eyes within 0.5 D of target SE between 26% and 44%. Formulas requiring only preoperative keratometry or no history at all had lower MAEs (0.42–0.94 D) and MedAEs (0.30–0.81 D) and higher (30%–68%) proportions within 0.5 D of target SE. Strategies that averaged several methods yielded the lowest reported MedAEs (0.31–0.35 D) and highest (66%–68%) proportions within 0.5 D of target SE. Even after using the best-known methods, refractive outcomes were less accurate in eyes that had previous excimer laser surgery for myopia compared with those that did not have it.
Conclusions
Calculation methods requiring both prerefractive surgery keratometry and manifest refraction are no longer considered the gold standard. Refractive outcomes of cataract surgery in eyes that had previous excimer laser surgery are less accurate than in eyes that did not. Patients should be advised of this refractive limitation when considering cataract surgery in the setting of previous corneal refractive surgery. Conclusions are limited by the small sample sizes and retrospective nature of nearly all existing literature in this domain.

... [5][6][7][8] Over the past decade, several formulas were developed to improve the precision of IOL power calculation in post-corneal refractive surgery eyes, including the Haigis-L, 9 Shammas, 10 Masket, 11 and Barrett True-K formulas. 12 Several studies have reported on the superiority of the Barrett formulas (Barrett Universal II and Barrett True-K) compared to other preoperative calculation methods in predicting IOL power in eyes with or without previous refractive surgery. [13][14][15][16] Intraoperative aberrometry (IA) was designed to increase the accuracy of IOL power calculation and to reduce residual refractive error after cataract surgery. ...

Purpose:
To compare the refractive predictability of intraoperative aberrometry (IA, ORA, Alcon) and Barrett True-K/Universal II formulas for intraocular lens (IOL) power calculations in post-corneal refractive surgery and normal eyes.
Methods:
Retrospective study of normal and post-corneal refractive surgery eyes that underwent cataract surgery with IA at tertiary academic center. Preoperatively, IOL power calculations were performed using Barrett Universal II (normal eyes) or Barrett True-K (post-corneal refractive surgery eyes) formulas. Intraoperatively, aphakic IA measurements were used for IOL power calculations. Mean absolute refractive prediction error (MAE) and the percentage of eyes with prediction error within ±0.50, ±0.75 and ±1.00 D were calculated. Refractive predictability was also evaluated in short, normal, and long eyes.
Results:
Two hundred and seventy-three eyes were included in the analysis. No statistically significant differences were observed between the MAE of preoperative formulas and IA for post-hyperopic laser vision correction (LVC), post-myopic LVC, post-radial keratotomy (RK) and normal eyes. For prediction error within ±0.5 D in post-corneal refractive surgery eyes, range of agreement between Barrett True-K and IA ranged from 28% (7/25) of the time in post-RK eyes to 49% (40/81) of the time in post-hyperopic LVC; the corresponding value for Barrett Universal II/IA was 62% (64/103) in normal eyes. When there was disagreement, IA outperformed Barrett True-K in post-hyperopic LVC eyes and Barrett formula outperformed IA in post-myopic LVC, post-RK, and normal eyes.
Conclusion:
IA appears to be comparable to Barrett formulas for IOL power calculations in post-corneal refractive surgery and normal eyes. In post-hyperopic LVC, IA yields better results compared to Barrett True-K formula; in real-life scenarios, IA reveals statistical advantage over the Barrett True-K no history formula for eyes post-hyperopic LVC.

... Barrett True-K TK Toric Calculator can be of help in these eyes because it incorporates the direct measurements of the posterior cornea avoiding estimation errors. [22] In eyes with keratoconus there is an irregular surface, and the apex is offset. TIOL implantation can be deferred in such situations. ...

Currently toric intraocular lens (TIOL) implantation is the most reliable method to correct pre-existing corneal astigmatism of 1D or more at the time of cataract surgery. A good surgical outcome depends on proper patient selection, accurate preoperative measurements, precise intraocular lens (IOL) power calculation and execution of proper surgical plan. Accurate keratometry measurement on a pristine cornea is crucial in TIOL power calculation. The recognition of the importance of posterior corneal astigmatism and its inclusion into various formulas and recent methods to measure it directly have resulted in better postoperative refractive outcomes. Fine-tuning of surgery with digital guidance in TIOL alignment and new lens designs with better rotational stabilities have helped achieve more predictable outcomes. Postoperative IOL rotation is the major cause of patient dissatisfaction after TIOL surgery. However, various correction algorithms and formulas are available which can help optimal corrective re rotation to address this problem satisfactorily.

... The Shammas-PL formula calculates IOL power based upon anterior chamber depth (ACD), axial length (AL) and post-refractive surgery keratometry 1 . The Barrett True-K formula (version 2.0) is based on the Barrett Universal II formula and is accessed online 7,8 . Many studies have been published on monofocal IOL power calculation after refractive surgery, but to the best of our knowledge there have been few reports on multifocal IOL (mIOL) power calculation after refractive surgery. ...

This study aimed to compare the clinical outcomes of implantation of various multifocal intraocular lenses (mIOLs) and the prediction accuracy of two intraocular lens (IOL) power calculation formulas for eyes that underwent previous corneal refractive surgery. Four types of mIOLs (TECNIS Symfony (Group I), AcrySof IQ PanOptix (Group II), LENTIS Mplus (Group III), and TECNIS mIOL (Group IV)) were used and the IOL power was calculated with the two no-history methods, Shammas-PL and Barrett True-K. Visual acuity and refractive outcomes including manifest refraction, prediction error (PE), absolute error (AE), and median absolute error (MedAE) were evaluated at three months after the cataract surgery. For all groups the Barrett True-K formula produced a narrower range of PEs and lower MedAE than Shammas-PL. Eyes of lower predictive accuracy (group B, AE > 0.5D) showed weak uncorrected distance visual acuity resulting from myopic refractive error and target refraction when compared to that of higher predictive accuracy (group A, AE ≤ 0.5 D). Targeting emmetropia using the Barrett True-K is recommended in patients undergoing mIOL implantation with prior corneal refractive surgery. Additionally, history of prior large amount of laser ablation seems to be an important factor related to low predictive accuracy.

... La TRCP facilita al novedoso Pentacam-AXL los datos totales de la córnea, en una zona de estudio de 4 mm (zona efectiva pupilar), teniendo en cuenta los índices refractivos reales (aire = 1, córnea = 1.376 y medio acuoso = 1.336) y el poder dióptrico total «real» de la córnea, ya que considera condiciones reales ópticas de la córnea, tomando en cuenta la cara anterior y posterior con sus correctos índices refractivos, además de la paquimetría y las aberraciones corneales centrales y periféricas. Tanto las EKR como la TRCP hacen al Pentacam ideal en pacientes con CRC previa [3][4][5][6][7][8][9][10][11][12][13][14][15] . ...

Objetivo:
Comparar el poder de la lente intraocular calculada con la potencia refractiva total corneal (TRCP), las lecturas queratométricas efectivas (EKR) aportadas por el Holladay Report del topógrafo Pentacam-AXL y el poder corneal real (True K) utilizado por la fórmula de Barret True K incorporada en el propio equipo, con los valores obtenidos por el método de historia clínica (MHC) en pacientes con cirugía fotoablativa previa para corregir la miopía.
Método:
Se realizó un estudio transversal en 99 ojos de 52 pacientes miopes poscirugía fotoablativa en el Servicio de Cirugía Refractiva del Instituto Ramón Pando Ferrer, de noviembre de 2018 a noviembre de 2019. Se estudiaron características demográficas, refractivas y biométricas que incluyeron poderes corneales aportados por el Pentacam-AXL. Se compararon el poder corneal y el poder de la lente intraocular calculada.
Resultados:
La edad media fue de 25.71 ± 4.46, hubo predominio femenino (67.3%), y el equivalente esférico fue de −0,06 ± 0,34 dioptrías. Solo hubo diferencias significativas en la queratometría media (p =0.02) y el poder de la lente calculado con esta (p < 0.01) al compararlo con el obtenido por el MHC; no así con la EKR, la TRCP y el True K.
Conclusiones:
Las lecturas queratométricas efectivas que aporta el módulo Holladay Report del Pentacam, la potencia refractiva total corneal y el poder corneal real utilizado por la fórmula de Barret True K no difieren del poder corneal obtenido por el MHC en ojos con cirugía fotoablativa previa para corregir la miopía, por lo cual pueden emplearse en el cálculo de la lente intraocular.

... [6] In a study conducted by Abulafia et al., it was found that in patients with previous refractive surgery, the Barrett True-K formula showed a mean absolute refraction prediction error level significantly lower than the other alternative formulas including Masket, Wang-Koch-Maloney, Shammas, and Haigis-L. [7] In addition to a higher percentage of eyes within the range ± 0.50D of error predicted in refraction compared with the methods of adjusted Atlas, Masket, and Modified Masket. In eyes with no prior historical data, Barrett True-K had a smaller median absolute refraction prediction error and a higher percentage of eyes within <0.50D of the predicted error in refraction than the Shammas and Haigis-L formulas. ...

Radial keratotomy (RK) was a popular refractive procedure in the 90s. However, more reproducible laser-assisted surgeries are currently preferred. Furthermore, RK patients who undergo cataract surgery experience variable refractive and keratometric changes during the early postoperatory period. Unfortunately, those post-RK patients currently require cataract surgery. A 58-year-old male with a history of RK in both eyes (OU) presented with a 2-year history of night glare and progressive vision loss due to a subcapsular cataract in OU. Using the double-K Holladay formula, bilateral phacoemulsification was performed. At 1 week, refraction was + 2.25/-1.00/27° (power [Pwr]: 39.25D) in oculus dextrus (OD) and + 3.00/−0.75/171° in oculus sinister (OS) (Pwr: 37.41D), achieving a best-corrected visual acuity (BCVA) of 20/30 OU. At 6 weeks, refraction was + 0.75/−0.75/18° (Pwr: 39.71D) in OD and + 1.00/−0.25/180° (Pwr: 38.33) in OS. BCVA remained 20/30 OU. The resulting transitory hyperopic shift after surgery demands a careful and comprehensive intraocular lens calculation preferably aiming toward myopic overcorrection.

... The details of this formula are not published, but it uses an internal regression formula to calculate an estimated change in manifest refraction. 17 Other formulas, like the Potvin-Shammas-Hill formula, the Galilei-formula and the OCT-formula are based on theoretical formulas, but instead of keratometry, uses total corneal power from instruments that provide actual measurements of the posterior cornea. 15,18,19 The most commonly used post-LVC formulas are available with an online calculator from the ASCRS website. ...

Purpose:
To compare the refractive predictability of ray tracing IOL calculations based on OCT data versus traditional IOL calculation formulas based on reflectometry in patients with a history of previous myopic laser vision correction (LVC).
Patients and methods:
This was a prospective interventional single-arm study of IOL calculations for cataract and refractive lens exchange (RLE) patients with a history of myopic LVC. Preoperative biometric data were collected using an optical low coherence reflectometry (OLCR) device (Haag-Streit Lenstar 900) and two optical coherence tomography (OCT) devices (Tomey Casia SS-1000 and Heidelberg Engineering Anterion). Traditional post LVC formulas (Barret True-K no-history and Haigis-L) with reflectometry data, and ray tracing IOL calculation software (OKULIX, Panopsis GmbH, Mainz, Germany) with OCT data were used to calculate IOL power. Follow-up examination was 2 to 3 months after surgery. The main outcome measure, refractive prediction error (RPE), was calculated as the achieved postoperative refraction minus the predicted refraction.
Results:
We found that the best ray tracing combination (Anterion-OKULIX) resulted in an arithmetic prediction error statistically significantly lower than that achieved with the best formula calculation (Barret True-K no-history) (-0.13 D and -0.32 D, respectively, adjusted p = 0.01), while the Barret TK NH had the lowest SD. The absolute prediction error was 0.26 D and 0.35 D for Anterion-OKULIX and Barret TK NH, respectively, but this was not statistically significantly different. The Anterion-OKULIX calculation also had the highest percentage of eyes within ± 0.25, compared to both formulas and within ±0.50 and ±0.75 compared to the Haigis-L (p = 0.03).
Conclusion:
Ray tracing calculation based on OCT data from the Anterion device can yield similar or better results than traditional post LVC formulas. Ray tracing calculations are based on individual measurements and do not rely on the ocular history of the patient and are therefore applicable for any patient, also without previous refractive surgery.

... Several methods have been introduced to address these sources of error and to reduce refractive surprises after keratorefractive surgery [2][3][4][5][6][7][8][9]. New technologies for corneal power measurements that incorporate measurements of the anterior and posterior corneal radii (e.g., total keratometry [10]) were established to enable more accurate predictions. ...

Small incision lenticule extraction (SMILE), with over 5 million procedures globally performed, will challenge ophthalmologists in the foreseeable future with accurate intraocular lens power calculations in an ageing population. After more than one decade since the introduction of SMILE, only one case report of cataract surgery with IOL implantation after SMILE is present in the peer-reviewed literature. Hence, the scope of the present multicenter study was to compare the IOL power calculation accuracy in post-SMILE eyes between ray tracing and a range of empirically optimized formulae available in the ASCRS post-keratorefractive surgery IOL power online calculator. In our study of 11 post-SMILE eyes undergoing cataract surgery, ray tracing showed the smallest mean absolute error (0.40 D) and yielded the largest percentage of eyes within ±0.50/±1.00 D (82/91%). The next best conventional formula was the Potvin–Hill formula with a mean absolute error of 0.66 D and an ±0.50/±1.00 D accuracy of 45 and 73%, respectively. Analyzing this first cohort of post-SMILE eyes undergoing cataract surgery and IOL implantation, ray tracing showed superior predictability in IOL power calculation over empirically optimized IOL power calculation formulae that were originally intended for use after Excimer-based keratorefractive procedures.

... Various studies have reported wide ranges of outcomes. [16][17][18][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] The key outcomes are summarized as follows: ...

In eyes with previous corneal refractive surgery, difficulties in accurately determining corneal refractive power and in predicting the effective lens position create challenges in intraocular lens (IOL) power calculations. There are three categories of methods proposed based on the use of historical data acquired prior to the corneal refractive surgery. The American Society of Cataract and Refractive Surgery postrefractive IOL calculator incorporates many commonly used methods. Accuracy of refractive prediction errors within ± 0.5 D is achieved in 0% to 85% of eyes with previous myopic LASIK/photorefractive keratectomy (PRK), 38.1% to 71.9% of eyes with prior hyperopic LASIK/PRK, and 29% to 87.5% of eyes with previous radial keratotomy. IOLs with negative spherical aberration (SA) may reduce the positive corneal SA induced by myopic correction, and IOLs with zero SA best match corneal SA in eyes with prior hyperopic correction. Toric, extended-depth-of-focus, and multifocal IOLs may provide excellent outcomes in selected cases that meet certain corneal topographic criteria. Further advances are needed to improve the accuracy of IOL power calculation in eyes with previous corneal refractive surgery.

... The Barrett True-K formula is one of the more recently developed methods and can be used without historical data. Studies comparing it to other formulas in patients with previous LASIK or PRK suggest it was at least equal to and often better than other methods with accurate refractive results 11,[21][22][23][24]28 . However, studies comparing the Barrett True-K formula to IA may reveal conflicting results. ...

To compare the predictive refractive accuracy of intraoperative aberrometry (ORA) to the preoperative Barrett True-K formula in the calculation of intraocular lens (IOL) power in eyes with prior refractive surgery undergoing cataract surgery at the Loma Linda University Eye Institute, Loma Linda, California, USA. We conducted a retrospective chart review of patients with a history of post-myopic or hyperopic LASIK/PRK who underwent uncomplicated cataract surgery between October 2016 and March 2020. Pre-operative measurements were performed utilizing the Barrett True-K formula. Intraoperative aberrometry (ORA) was used for aphakic refraction and IOL power calculation during surgery. Predictive refractive accuracy of the two methods was compared based on the difference between achieved and intended target spherical equivalent. A total of 97 eyes (69 patients) were included in the study. Of these, 81 eyes (83.5%) had previous myopic LASIK/PRK and 16 eyes (16.5%) had previous hyperopic LASIK/PRK. Median (MedAE)/mean (MAE) absolute prediction errors for preoperative as compared to intraoperative methods were 0.49 D/0.58 D compared to 0.42 D/0.51 D, respectively (P = 0.001/0.002). Over all, ORA led to a statistically significant lower median and mean absolute error compared to the Barrett True-K formula in post-refractive eyes. Percentage of eyes within ± 1.00 D of intended target refraction as predicted by the preoperative versus the intraoperative method was 82.3% and 89.6%, respectively (P = 0.04). Although ORA led to a statistically significant lower median absolute error compared to the Barrett True-K formula, the two methods are clinically comparable in predictive refractive accuracy in patients with prior refractive surgery.

... Para obtener la refracción aspirada, la selección debe realizarse basándose tanto en parámetros anatómicos y ópticos del ojo como en la elección de la fórmula más adecuada para su cálculo 4-7 . Uno de los parámetros más importantes para el cálculo de la LIO es el largo axial (LA) [7][8] . Una medición errónea de, por ejemplo, 1 mm produce un defecto refractivo de aproximadamente 2,35 dioptrías (D) en un ojo de 23,5 mm, de 1,75D en un ojo de 30 mm, y de hasta 3,75D en un ojo de 20 mm 8 . ...

Resumen Objetivos: Determinar los resultados refractivos poscirugía de catarata en pacientes mayores de 40 años y la influencia del largo axial y de la edad en ellos. Métodos: Estudio observacional, retrospectivo y analítico. Se estudiaron los pacientes mayores de 40 años sometidos a cirugía de catarata mediante facoemulsificación e implante de lente intraocu-lar entre el 1º de enero de 2017 y el 31 de julio de 2018. Se analizó la agudeza visual y refracción subjetiva al mes de la cirugía, el error refractivo posquirúrgico, el largo axial y la edad de los pa-cientes al momento de la cirugía. Se utilizó el test de Mann-Whitney y la correlación de Spearman para la asociación de variables, con una p<0.05 de significancia estadística. Resultados: Se incluyeron 87 ojos de 62 pacien-tes con una edad media de 72,89 ± 9,38 años. La agudeza visual promedio no corregida al mes de la cirugía fue 0,20 ± 0,22 logMAR. El error refrac-tivo promedio fue +0,34 ± 0,38 dioptrías (D) y el promedio de su valor absoluto fue 0,42 ± 0,29D. La prevalencia de un error refractivo menor o igual a 1D fue del 96,5%. El error refractivo pos-quirúrgico absoluto no tuvo asociación estadísti-camente significativa con el largo axial (p= 055) ni con la edad (p= 0,91). En cambio, la agudeza visual posquirúrgica se asoció estadísticamen-te con el largo axial (p= 0,01) y con la edad (p< 0,02). Conclusiones: En este trabajo encontramos que la edad y el largo axial influyeron en la agudeza ARTÍCULO ORIGINAL Resultados refractivos poscirugía de catarata con implante de lente intraocular en pacientes mayores de 40 años

... As for the statistics, data were verified for non-normality using the Kolmogorov-Smirnov test. The percentages of eyes within ±0.25 D, ±0.50 D, and ±1.00 D of PE were compared using Fisher's exact test and Bonferroni correction, following the methods used in previous reports [8,9]. ...

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... 10 It uses a telecentric technique for keratometric measurements, which is distance-independent, 11 and incorporates the influence of the posterior corneal curvature with the measurement of the total corneal power, total keratometry (TK ® ). 12 IOLMaster 700 uses a keratometric index of 1.3375 to convert the anterior corneal curvature measurements in millimeters to corneal power in diopters (D). It can even provide information on the central corneal shape by using the central topography software feature, which is based on telecentric 3-zone keratometry and SS-OCT. ...

Background
Cataract surgery in keratoconic patients is challenging because of the corneal distortion, which can lead to inaccurate keratometry readings. This study is a comparison of the accuracy of keratometry readings by two types of devices in a tertiary hospital.
Purpose
To evaluate the comparability of corneal power measurements, anterior chamber depth (ACD), and white-to-white (WTW) distance between Scheimpflug-based tomography (Pentacam AXL; OCULUS GmbH, Wetzlar, Germany) and swept-source optical biometry (IOLMaster 700; Carl Zeiss Meditec AG, Jena, Germany) in patients with keratoconus.
Methods
This pilot, prospective, interinstrument reliability study included 30 keratoconic eyes of 15 individuals who had not undergone any kind of corneal surgery. Standard K and total refractive power (TK ® ) of the flattest and steepest axes of the IOLMaster 700 were compared with the standard keratometry (SimK), true net power (TNP), equivalent keratometer readings (EKR), and total corneal refractive power (TCRP) of the Pentacam. The Bland–Altman analysis was used to evaluate the agreement between the measurements of both devices. The paired-samples t-test and the Wilcoxon signed-rank test were performed to compare the mean values of the variables obtained with the devices.
Results
The K1 value of the IOLMaster 700 was significantly higher from EKR K1 along the 3-mm (mean difference: 0.79 diopters, p = 0.01), 4-mm (mean difference: 1.01 D, p = 0.01), and 4.5-mm zones (mean difference: 1.20 D, p = 0.01) and TNP K1 along the 3-mm (mean difference: 0.88 D, p < 0.001) and 4-mm zones (mean difference: 0.97 D, p < 0.001). The TK1 value was significantly higher from EKR K1 along the 2-mm (mean difference: 0.42 D, p = 0.04), 3-mm (mean difference: 0.83 D, p = 0.003), 4-mm (mean difference: 1.05 D, p = 0.004), and 4.5-mm zones (mean difference: 1.24 D, p = 0.005) and TNP K1 along the 3-mm (mean difference: 0.92 D, p < 0.001) and 4-mm zones (mean difference: 1.01 D, p < 0.001). The K2 value of the IOLMaster 700 was significantly higher from TK2 (mean difference: 0.11 D, p = 0.04) and all the corresponding variables of the Pentacam device. The TK2 value was significantly higher from all the corresponding variables of the Pentacam device. The Pentacam also yielded significantly lower values for the WTW distance (mean difference: 0.31 mm, p < 0.001) and no significant difference in terms of ACD values ( p = 0.9).
Conclusion
The IOLMaster measured significantly greater keratometry readings in the steep axis for all the variables studied. The keratometry and WTW measurements of the investigated devices cannot be used interchangeably in keratoconus.

... Wang et al. suggested that the OCT and True-K No History (TKNH) were promising formulas for post-corneal refractive surgery eyes, which were included in the latest update of the ASCRS IOL calculator (48). For cataract eyes with previous LASIK or PRK, Barrett True-K formula provided more stable predictions than alternative methods (18,49). Similar results were obtained in a prospective study on the IOL calculations in patients undergoing cataract surgery after SMILE (50). ...

Purpose
To assess the efficacy, safety, and predictability of presbyopia-correcting intraocular lenses (IOLs) in cataract patients with previous corneal refractive surgery.
Methods
A systematic literature search was performed to identify studies evaluating the clinical outcomes of presbyopia-correcting IOLs implantation in cataract surgery after laser refractive surgery. Outcomes were efficacy, safety and predictability parameters.
Results
The authors identified 13 studies, involving a total of 128 patients and 445 eyes. Presbyopia-correcting IOLs were effective at improving distance, intermediate and near visual acuity aftercataract surgery. The proportion of post-laser surgery eyes with uncorrected distance visual acuity (UDVA) ≥ 20/25 was 0.82 [95% confidence interval (CI), 0.74-0.90] and the pooled rates of spectacle independence at near, intermediate, and far distances were 0.98 (95% CI, 0.94-1.00), 0.99 (95% CI, 0.95-1.00) and 0.78 (95% CI, 0.65-0.94) respectively. The percentage of participants who suffered from halos and glare was 0.40 (95% CI, 0.25-0.64) and 0.31 (95% CI, 0.16-0.60), respectively. The predictability had a percentage of 0.66 (95% CI, 0.57-0.75) and 0.90 (95% CI, 0.85-0.96) of eyes within ±0.5 diopters (D) and ±1.0 D from the targeted spherical equivalent.
Conclusions
Presbyopia-correcting IOLs provide satisfactory results in terms of efficacy, safety and predictability in patients with previous corneal refractive surgery, but have a higher risk of photopic side effects such as halos and glare.

... Varios estudios avalan la obtención de resultados refractivos precisos y se considera en la actualidad una de las mejores opciones en pacientes con antecedentes de cirugía refractiva. (25,26,27,28,29,30,31,32,33) Esta fórmula se encuentra disponible en el equipo Pentacam AXL adquirido por la institución (único en el país). Este tomógrafo de alta resolución tiene múltiples prestaciones; entre ellas, la del cálculo de la LIO con gran variedad de fórmulas. ...

Objetivo:
Determinar los resultados refractivos en pacientes operados de catarata con cirugía refractiva corneal, según el cálculo del poder dióptrico de la lente intraocular con la fórmula Barrett True K.
Métodos:
Se realizó un estudio pre-experimental, del tipo antes y después, en el cual fueron incluidos 18 pacientes (31 ojos). En ellos se analizaron variables demográficas y clínicas. La principal variable de salida fue la predictibilidad del componente esférico ± 0,50 D, ± 1,0 D según la longitud axial.
Resultados:
Fueron estudiados pacientes con un promedio de edad de 59,4 años, predominantemente del sexo femenino (66,7 %). El 77,4 % fue operado con queratotomía radial. Con la cirugía de catarata se produjo una mejora ostensible de la agudeza visual no corregida (mediana preoperatoria: 0,12 y mediana posoperatoria: 0,60). Solo el 9,7 % de los ojos analizados presentó una agudeza visual sin corregir de 20/20 y el 90,3 % de 20/40 o más. La cantidad de ojos con un equivalente esférico de ± 0,50 disminuyó en la medida en que aumentó la longitud axial (corta: 100 %; normal: 57,1 %; larga: 22,7 %), no así la predictibilidad del componente esférico de ± 0,50, que aumentó (corta: 50,0 %; normal: 57,1 %; larga: 63,6 %).
Conclusiones:
La fórmula Barrett True K resulta útil para el cálculo de la lente intraocular en pacientes operados de catarata y cirugía refractiva corneal previa.

The intraocular lens (IOL) selection process for patients is a thoughtful one which requires objective assessment of patient-specific ocular characteristics, including the quality and quantity of the corneal astigmatism, the health of the ocular surface, and other ocular comorbidities. Potential issues that could be considered complications following surgery, including dry eye disease, anterior or epithelial basement membrane dystrophy, Salzmann nodular degeneration, and pterygium should be proactively addressed. Aspheric IOLs are designed to eliminate the positive spherical aberration (SA) added by traditional IOLs to the pseudophakic visual axis. SA may be a consideration with patient selection. Patients' desire for increased spectacle independence after surgery is one of the main drivers for the development of multifocal IOLs and extended depth of focus (EDOF) IOLs. There is not one single multifocal or EDOF IOL; however, that suits all patients' needs. The wide variety of multifocal and EDOF IOLs, their optics, and their respective impact on patient quality of vision have to be fully understood to choose the appropriate IOL for each individual and surgery has to be customized. Patients with previous laser-assisted in situ keratomileusis, radial keratotomy and ocular pathologies including glaucoma, age-related macular degeneration, and epiretinal membrane require specific considerations for IOL selection. Subjectively, patient-centered considerations, including visual goals, lifestyle, personality, profession, and hobbies are key elements for the surgeon to assess and factor into an IOL recommendation. This holistic approach will help surgeons achieve optimal surgical outcomes and meet (hopefully exceed) the high expectations of patients.

Purpose:
To assess the accuracy of the following intraocular lens (IOL) power formulas: Barrett True-K No History (BTKNH), Emmetropia Verifying Optical 2.0 Post Myopic LASIK/PRK (EVO 2.0), Haigis-L, American Society of Cataract and Refractive Surgery (ASCRS) average, and Shammas, designed for patients who have undergone previous myopic refractive surgery, independent of preexisting clinical history and corneal tomographic measurements.
Methods:
Data from 302 eyes of 302 patients who previously underwent myopic refractive surgery and had cataract surgery done by a single surgeon with only one IOL type inserted were included. The predicted refraction was calculated for each of the formulas and compared with the actual refractive outcome to give the prediction error. Subgroup analysis based on the axial length and mean keratometry was performed.
Results:
On the basis of mean absolute prediction error (MAE), the formulas were ranked as follows: Haigis-L (0.61 diopters [D]), ASCRS average (0.63 D), BTKNH (0.67 D), EVO 2.0 (0.68 D), and Shammas (0.69 D). The Haigis-L had a statistically significant lower MAE compared with all formulas (P < .05) except the ASCRS average. Hyperopic mean prediction errors were seen in all formulas for axial lengths of greater than 30 mm or mean keratometry values of 35.00 diopters or less.
Conclusions:
The Haigis-L and the ASCRS average formulas provided the most accurate results in the overall population evaluated in this study. Moreover, according to data observed, it is important to be careful handling very long eyes and very flat corneas because hyperopic refractions could be more common. [J Refract Surg. 2022;38(7):443-449.].

IOL power calculation after keratorefractive surgery is an important applied aspect of cataract surgery. The probability of refractive error is especially high when calculating in patients with a history of radial keratotomy. There is no unified approach to the tactics and methodology of calculation for this category of patients at the moment. The studies were conducted in a group of 17 patients (26 eyes) with a history of RK. The Haigis formula, which does not use keratometry to predict ELP, was chosen as the main one for the calculation. IOL calculation and biometrics were carried out on the IOL-Master, but corrected TCP IOL (Ray Traced) data obtained on the Galilei keratotomograph were manually entered into the optional keratometry fields. Thу Burrett True-K and Hoffer Q were used as verification formulas, the calculation was also carried out on IOL-Master, using corrected Galilei data. In all cases, postoperative refraction close to emmetropic was obtained. The spherical component of refraction ranged from +0.5 to -1.0 D, cylindrical — from 0.0 to 4.0 D, according to autorefractometry. Visual acuity without correction ranged from 0.4 to 1.0. Uncorrected visual acuity of 0.8 and higher was obtained in 65.38% of cases. The calculation algorithm implemented by us using the Haigis formula in combination with the use of individually adjusted keratometric TCP IOL data (Ray Traced, Galilei), allowed us to significantly improve the accuracy of IOL power calculating in patients with a history of RK and achieve target refraction even in cases of complex and irregular corneal topography.

Purpose:
To assess the predictive accuracy of 4 No-History intraocular lenses (IOLs) power formulas in eyes with prior myopic excimer laser surgery, classified in 4 groups according to their axial length (AL), and investigate the relationship between AL and predictive accuracy.
Setting:
Seoul St. Mary's Hospital, Republic of Korea.
Design:
Retrospective case series.
Methods:
IOL power was calculated with the Barrett True-K, Haigis-L, Shammas-PL and Triple-S formulas in 4 groups classified according to AL. Primary outcomes were the median absolute error (MedAE) and percentage of eyes with a prediction error (PE) within ±0.50 diopter (D).
Results:
This study included 107 eyes of 107 patients. The Barrett True-K had the lowest MedAE when AL was < 26.0 mm (0.30 D) and between 26.0 and 28.0 mm (0.54 D); in these subgroups, it had the highest percentages with a PE within ±0.50 D (71.4% and 46.2%). For AL between 28.0 and 30.0 mm, the Triple-S method showed the lowest MedAE (0.43 D) and highest percentage with a PE within ±0.50 D (58.3%). For AL ≥ 30.0 mm, the Shammas-PL formula produced the lowest MedAE (0.41 D) and highest percentage with a PE within ±0.50 D (58.3%). The Barrett True-K was the only formula with a correlation between AL and PE (r=-0.219/P=0.023).
Conclusions:
The predictive accuracy of No-History IOL formulas depends on the AL. The Barrett True-K had the highest accuracy when AL was < 28.0 mm and the Triple-S when it ranged from 28.0 mm to 30.0 mm, while the Shammas-PL was more accurate when AL was ≥ 30.0 mm.

Purpose:
To objectively determine which formula/keratometry combination was best for calculating intraocular lens (IOL) sphere power in eyes with a history of prior myopic laser in situ keratomileusis (LASIK).
Setting:
One practice in the United States.
Design:
Retrospective, unmasked, nonrandomized chart review.
Methods:
Consecutive patients undergoing cataract surgery after prior myopic LASIK were included. Eyes had to have a postoperative refraction at least 3 weeks after surgery. IOL power was calculated with the ASCRS Online Post-Refractive IOL Calculator using anterior keratometry and recalculated using total corneal power (TK). The accuracy of treatment was calculated and compared between different formulas and keratometry methods including intraoperative aberrometry (IA).
Results:
Data from 101 eyes, 44 of which had TK available, were analyzed. Using TK, the Wang-Koch-Maloney formula had the highest percentages of eyes with expected spherical equivalent refractive errors within 0.50 diopter (D) and 1.00 D of plano (57% and 87%, respectively). With anterior keratometry, the Barrett True K formula had the highest percentages (64% and 92%, respectively) but was not significantly better than Wang-Koch with TK within 0.50 D and 1.00 D (McNemar test, p > 0.2). Expected sphere results based on IA were not significantly different than for Barrett True K within 0.50 D or within 1.00 D (McNemar test, p > 0.2).
Conclusion:
Using TK in existing post-LASIK formulas did not appear beneficial. The formulas may have to be optimized for use with TK. The best expected results were obtained with the Barrett True K and Haigis L formulas using anterior keratometry. IA did not appear to materially improve results.

Purpose
To compare prediction errors of the Barrett True K No History (Barrett TKNH) formula and intraoperative aberrometry (IA) in eyes with prior radial keratotomy (RK).
Methods
A retrospective, non‐randomized study of all patients with RK who underwent cataract surgery using IA at the UCHealth Sue Anschutz‐Rodgers Eye Center from 2014 to 2019 was conducted. Refraction prediction error (RPE) for IA and Barrett TKNH was compared. General linear modelling accounting for the correlation between eyes was used to determine whether absolute RPE differed significantly between Barrett TKNH and IA. Outcome by number of RK cuts was also compared between the two methods.
Results
Forty‐seven eyes (31 patients) were included. The mean RPEs for Barrett TKNH and IA were 0.04 ± 0.92D and 0.01 ± 0.92D, respectively, neither was significantly different than zero (p = 0.77, p = 0.91). The median absolute RPEs were 0.50D and 0.48D, respectively (p = 0.70). The refractive outcome fell within ± 0.50D of prediction for 51.1% of eyes with Barrett TKNH and 55.3% with IA, and 80.8% were within ± 1.00D for both techniques. Mean absolute RPE increased with a higher number of RK cuts (grouped into < 8 cuts and ≥ 8 cuts) for both Barrett TKNH (0.35D and 0.74D, p = 0.008) and IA (0.30D and 0.80D, p = 0.0001).
Conclusions
There is no statistically significant difference between Barrett TKNH and IA in predicting postoperative refractive error in eyes with prior RK. Both are reasonable methods for choosing intraocular lens power. Eyes with more RK cuts have higher prediction errors.

Purpose:
To describe and evaluate a method for calculating intraocular lens (IOL) power in the second operative eye of patients with a history of keratorefractive surgery.
Methods:
All eyes had undergone cataract surgery by a single surgeon from 2015 to 2018. Postoperative outcomes on the first eye (eg, IOL power implanted and postoperative refractive error) were used to back calculate a "Real K" for the first eye. The difference (delta) between the second and first eye topographic simulated keratometry values was then added to the first eye Real K to calculate the second eye Real K. This Real K value was inputted into the Holladay IOL Consultant software as an "alternate K" to derive an accurate IOL power for the second eye. Mean absolute error, mean error, and percentage of eyes on target using the Delta K method were compared with results obtained with intraoperative abserrometry and the Haigis-L and Barrett True-K No History formulas.
Results:
The mean error for the Delta K method was significantly better than the Haigis-L (P = .00001) and Barrett True-K No History (P = .027) formulas, and on par with intra-operative aberrometry (P = .25). The mean absolute error of the Delta K method was significantly better than the Haigis-L formula (P = .03). The Delta K mean absolute error was on par with intraoperative aberrometry (P = .81) and the Barrett True-K No History formula (P = .56).
Conclusions:
The Delta K mean absolute error is comparable to the Barrett True-K No History formula. The mean error is lower than that calculated with the Barrett True-K No History formula and comparable to intraoperative aberrometry. [J Refract Surg. 2020;36(12):826-831.].

Purpose:
To compare the accuracy of intraocular lens (IOL) power calculation in patients with previous radial keratotomy using the Haigis and Barrett True-K formulas.
Methods:
In a retrospective cases series of patients with previous radial keratotomy and minimum follow-up of 1.2 months, preoperative data from an IOLMaster 500 or 700 (Carl Zeiss Meditec AG), the IOL power implanted, and the postoperative refraction were used to calculate the refractive prediction error. The primary outcomes were the mean absolute and arithmetic refractive prediction errors and the percentage of eyes with a refractive prediction error within ±0.50 and ±1.00 diopters (D).
Results:
One hundred eight eyes were evaluated with a mean follow-up of 6.9 ± 4.9 months. The Haigis formula yielded a mean arithmetic refractive prediction error of -0.29 ± 1.00 D, which was significantly different than that of the Barrett True-K formula, which was -0.03 ± 0.96 D (P < .001). The mean absolute refractive prediction error was 0.80 ± 0.67 for the Haigis formula and 0.74 ± 0.60 for the Barrett True-K formula (P > .05). The percentages of eyes with a refractive prediction error within ±0.50 and ±1.00 D were 43.5% and 65.7% for the Haigis formula and 42.6% and 75.9% for the Barrett True-K formula, respectively (all P > .05). The subgroup analysis revealed that for flat corneas (K1 < 38.00 D), the Barrett True-K formula resulted in more hyperopic results than the Haigis formula.
Conclusions:
The Barrett True-K formula exhibited better arithmetic predictability than the Haigis formula; however, it showed a tendency for hyperopic results in very flat corneas. [J Refract Surg. 2020;36(12):832-837.].

Purpose:
To compare the accuracy of the methods for calculation of intraocular lens (IOL) power in eyes with previous myopic laser refractive surgery.
Setting:
EENT Hospital of Fudan University, Shanghai, China.
Design:
Network meta-analysis.
Methods:
A literature search of MEDLINE and Cochrane Library from January 2000 to July 2019 was conducted for studies that evaluated methods of calculating IOL power in eyes with previous myopic laser refractive surgery. Outcomes measurements were the percentages of prediction error within ±0.50 diopters (D) and ±1.00 D of the target refraction (% ±0.50 D and % ±1.00 D). Traditional and network meta-analysis were conducted.
Results:
Nineteen prospective or retrospective clinical studies, including 1217 eyes and 13 calculation methods, were identified. A traditional meta-analysis showed that compared with the widely used Haigis-L method, the Barrett True-K formula, optical coherence tomography (OCT), and Masket methods showed significantly higher % ±0.50 D, whereas no difference was found in the % ±1.00 D. A network meta-analysis revealed that compared with the Haigis-L method, the OCT, Barrett True-K formula, and optiwave refractive analysis (ORA) methods performed better on the % ±0.50 D, whereas the Barrett True-K formula and ORA methods performed better on the % ±1.00 D. Based on the performances of both outcomes, the Barrett True-K formula, OCT, and ORA methods showed highest probability to rank the top 3 among the 13 methods.
Conclusions:
The Barrett True-K formula, OCT, and ORA methods seemed to offer greater accuracy than others in calculating the IOL power for postrefractive surgery eyes.

Purpose of review:
We review recent studies comparing intraocular lens (IOL) formulas with an emphasis on selection of the highest performing formulas based on patient axial length, age, and history of previous corneal refractive surgery.
Recent findings:
The Barrett Universal II formula based on a theoretical model has consistently demonstrated high accuracy. The Olsen four-factor formula using ray tracing optics and the Hill-RBF calculator using artificial intelligence have also demonstrated good prediction results after being updated. Notably, the Kane formula, incorporating artificial intelligence, has overall shown the best performance for all axial lengths. Although newly developed and updated IOL formulas have improved refractive prediction in patients with short or long axial length eyes or prior history of corneal refractive surgery, these challenging cases still require special consideration. The Barrett True-K formula has shown accurate results regardless of preoperative data in eyes with previous myopic refractive surgery.
Summary:
Advancements in optical biometry and IOL calculation formulas continue to improve refractive outcomes. The clinician can optimize refractive outcomes in the majority of patients with the use of formulas that have shown consistent results and accuracy in several large studies.

This chapter deals with complex cataract surgery, which are also known as challenging cases. For the novice surgeon to become proficient requires graded challenge, adequate time allocated, and supervision from a trainer or mentor. The chapter gives the book knowledge necessary for this progression, and serves as a reminder to master cataract surgeons when dealing with or teaching small pupil surgery, floppy iris, intumescent, dense or soft nuclei, zonular weakness, corneal endothelial weakness, vitreous loss and so on. The authors hope the contents of this chapter, along with reflection, will promote surgical safety, efficiency and proficiency in the operating theatre.

Purpose:
To compare the accuracy of intraocular lens (IOL) calculation methods for extended depth-of-focus (EDoF) IOLs in eyes with a history of myopic laser-assisted in situ keratomileusis (LASIK)/photorefractive keratectomy (PRK) surgery lacking historical data.
Setting:
Changsha Aier Eye Hospital, Changsha, and Wuhan Aier Eye Hospital, Wuhan, China.
Design:
Retrospective case series.
Methods:
Patients with axial lengths (ALs) ≥25.0 mm and a history of myopic LASIK/PRK surgery who underwent cataract surgery with implantation of EDoF IOLs were enrolled. A comparison was performed of the accuracy of 10 IOL methods lacking historical data, including Barrett True-K no history (Barrett TKNH), Haigis-L, Shammas, and Potvin-Hill formulas and average, minimum, and maximum IOL power on the ASCRS online postrefractive IOL calculator; Seitz/Speicher/Savini (Triple-S) formula; and Schuster/Schanzlin-Thomas-Purcell (SToP) formulas based on Holladay 1 and SRK/T formulas. IOL power was calculated with the abovementioned methods in 2 groups according to AL (Group 1: 25.0 mm ≤ AL < 28.0 mm and Group 2: AL ≥ 28.0 mm).
Results:
64 eyes were included. Excellent outcomes were achieved with the minimum, Barrett TKNH, SToP (SRK/T), and Triple-S formulas in the whole sample and subgroups, which led to similar median absolute error, mean absolute error, and the percentage of eyes with a prediction error within ±0.5 diopters (D). In the whole sample, the Haigis-L and maximum formulas had a significantly higher absolute error than minimum, SToP (SRK/T), and Barrett TKNH formulas. The maximum formula also had a significantly lower percentage of eyes within ±0.5 D than the Barrett TKNH, and SToP (SRK/T) formulas (15.6% vs 50% and 51.5%, all P < .05 with Bonferroni adjustment).
Conclusions:
Predicting the EDoF IOL power in postmyopic refractive eyes by no-history IOL formulas remains challenging. The Barrett TKNH, Triple-S, minimum, and SToP (SRK/T) formulas achieved the best accuracy when AL ≥ 25.0 mm, while the Barrett TKNH and SToP (SRK/T) formulas were recommended when AL ≥ 28.0 mm.

Purpose:
To evaluate a ray-tracing formula for intraocular lens (IOL) calculation of diffractive extended depth of focus IOLs after myopic laser in situ keratomileusis (LASIK) compared to formulas from an established online calculator.
Methods:
This retrospective, consecutive case series included patients after cataract surgery with implantation of an extended depth of focus (EDOF) IOL (AT LARA, Carl Zeiss Meditec; Symfony, Johnson & Johnson) and a history of myopic LASIK. Preoperative assessments included biometry (IOLMaster; Carl Zeiss Meditec) and corneal tomography, including true net power (TNP) (Pentacam; Oculus Optikgeräte GmbH). To evaluate the measurements, the simulated keratometry values (SimK) were compared to the TNP. Regarding IOL calculation, the mean prediction error, mean and median absolute prediction error (MAE and MedAE), and number of eyes within ±0.50, ±1.00, and ±2.00 diopters (D) from the Haigis-L, Shammas, and Barrett True K No History formulas to the Potvin-Hill and Haigis with TNP (Pentacam) formulas were compared.
Results:
Thirty-six eyes matched the inclusion criteria with a mean spherical equivalent of -6.26 ± 3.25 diopters (D) preoperatively and -0.79 ± 0.75 D postoperatively. The mean difference from SimK and TNP was significantly different from zero (P < .001; -1.24 ± 0.81 D). The best performing formulas by MedAE were the Potvin-Hill and Barrett True K No History (0.39 ± 0.78 and 0.64 ± 1.00 D). The formula with the most eyes within ±0.50 D was the Potvin-Hill (64%), followed by the Barrett True K No History (44%). For MAE and percentage of eyes within ±0.50 D, the Potvin-Hill formula was significantly better than the Haigis-L, Shammas, and Haigis-TNP formulas (P < .05).
Conclusions:
Calculation of IOLs in patients who had LASIK remains less predicable than calculations for virgin eyes. Using ray-tracing to calculate diffractive EDOF IOLs after myopic LASIK, the Potvin-Hill formula outperformed established formulas in terms of the percentage within target refraction and the MAE. [J Refract Surg. 2021;37(4):231-239.].

To evaluate the accuracy of refractive prediction by the Haigis-L formula compared to four other IOL power calculation formulas in eyes with extremely long axial lengths (AL > 29.0 mm) after LASIK.
Shanghai Eye Disease and Prevention Treatment Center, Shanghai, China.
Retrospective case series.
Twenty-nine eyes from 19 patients were available for analysis. The primary outcome measure was the arithmetic refractive prediction error (RPE), defined as the difference between the actual postoperative refractive error and the intended formula-derived refractive target. The main outcome measure was the median absolute refraction prediction error (MedAE). The accuracy of the Haigis-L was compared with Barrett True K No History, Shammas-PL, SRK/Tcorrected K, and Holladay 2corrected K methods to calculate IOL power.
The Haigis-L formula had a significantly larger MedAE than Shammas-PL and SRK/Tcorrected K formulas (P = 0.005 and P = 0.015, respectively), a smaller percentage of eyes within ±1.50 diopter (D) of predicted error in refraction compared with Shammas-PL and SRK/Tcorrected K formulas (P = 0.014 and P = 0.005, respectively). The refractive prediction errors of 6 eyes with corneal keratometry of less than 35 D by Haigis-L all had more than 1.95 D of myopic overestimation, while none of the other four methods resulted in an absolute error over 1.95 D.
The Haigis-L formula was relatively accurate in predicting extreme long axis (>29.0 mm) eyes after myopic LASIK surgery but less accurate for eyes with extremely flat corneas (<35 D). SRK/Tcorrected K and Shammas-PL performed better than the other methods for refractive prediction in this type of eyes.
Haigis-L performed worse than SRK/Tcorrected K and Shammas-PL in predicting IOL power in extremely long axis (>29.0 mm) eyes after myopic LASIK, especially with extremely flat corneas (K < 35 D).

Rationale.Qualitative rehabilitation of patients with cataracts who had keratorefractive surgeries depends on phacoemulsification technology and correctly calculated optical power of the IOL. Purpose: present the author’s own approaches to the development of surgical tactics for treating patients with cataracts who underwent keratorefractive surgeries. Material and methods. The complicated character of cataract surgery performed after LASIK — deterioration of visualization due to the presence of an optical ablation zone and a transition zone (6–7 mm) — is successfully compensated by instillations of a dispersed viscoelastic (methylcellulose) onto the surface of the cornea. Another factor is the deepening of the anterior chamber in high myopia, which is uncomfortable for manipulation and may require a lowerlevel of irrigation (up to 60 mm Hg). The technology of surgery performed after radial keratotomy (RK) requires utmost attention to the prevention of surgical astigmatism that could emerge due to biomechanical instability of the cornea. To ensure such prevention, paracentesis is performed outside the zone of keratotomy scars, the main 2.2 mm incision is made after capsulorhexis in the sclerolimbal zone, and at theend of the operation, a subconjunctival injection is performed in the conjunctival zone of the knife keratom entrance for the tamponade ofthe outer part of the incision without suturing. These techniques made it possible to successfully perform more than 200 operations and achieve a favorable course of the postoperative period from the first day. Fast adaptation of the incision (1–2 days), uncomplicated course of the postoperative period and the absence of induced astigmatism are important advantages of this technology. Conclusion. The choice of surgical technology, taking into account the initial state of the eye after LASIK and RK surgeries, is an important task. Yet the main problem with which the doctor is faced after keratorefractive surgery is the difficulty of calculating the optical power of the IOL which must take into account the special needs of the patient with a particular refractive history, which will be reported in part 2 of the article.

Effective rehabilitation of patients with cataracts who underwent keratorefractive surgeries requires that the optical power of the IOL be calculated correctly to avoid hyperopic error. The purpose of the 2nd part of the research (for the 1st part, see ROJ, 2021; 14 (2): 55–58) is to present the results of cataract phacoemulsification in patients subjected to keratorefractive surgery based on the author’s algorithm for calculating the optical power of the IOL. Material and methods. The algorithm used optical biometry with an IOL-Master device. The main technique of improving the accuracy of IOL calculation after keratorefractive operations has been to introduce amendments to standard IOL calculation formulas. This work proposes an alternative, which consists in using the Hoffer Q formula, as it is more consistent with changes in the anterior segment of the myopic eye after keratorefractive surgery than other basic. The main distinguishing feature of the Hoffer Q formula is that the corneal refraction is not converted into the radius of curvature but is applied directly as the optical power of a “thin lens”. Results. The empirical customized correction was +1.0 D with regard to the estimated planned postoperative refraction (for patients with initial myopia from -3 to -9 D). The use of the “thin lens” principle made it possible to extrapolate this formula and apply it after LASIK surgery and after radial keratotomy. Conclusion . The proposed technique of IOL calculation was implemented for cataract phacoemulsification in over 200 patients who underwent keratorefractive surgeries. No cases of hyperopic shift of postoperative refraction were noted. The deviation from the planned myopic refraction did not exceed 1.0 D.

Purpose:
To evaluate the accuracy of intraocular lens (IOL) power calculation formulas from two biometers using swept-source optical coherence tomography for quadrifocal Acrysof IQ Panoptix TFNT IOL (Alcon Laboratories, Inc) implantation in patients with visually significant cataract with previous corneal refractive surgery.
Methods:
This retrospective study comprised 50 eyes from 50 patients with a history of corneal refractive surgery and TFNT IOL implantation. Candidate formulas were Shammas-PL and Barrett True-K in the Argos (Movu, Inc), Barret True-K and Haigis-L in the IOLMaster 700 (Carl Zeiss Meditec AG), and Haigis using the total keratometry (TK) mode in the IOLMaster 700. The main outcome measure was the mean absolute error (MAE) detected at postoperative 6 months. The refractive accuracy was also evaluated as number and percentage of eyes within ±0.25, ±0.50, and ±0.75 diopters (D) of the prediction error.
Results:
The uncorrected distance and near visual acuity were 0.32 ± 0.34 and 0.46 ± 0.20 logMAR at baseline, and significantly improved to 0.04 ± 0.07 and 0.03 ± 0.06 logMAR at postoperative 6 months (P < .001 for all analysis) with a mean spherical equivalent of -0.20 ± 0.39 D. The MAE was smallest for the Barrett True-K formula in the IOLMaster 700 (0.36 ± 0.26 D) and largest for the Shammas-PL formula in the Argos (0.59 ± 0.37 D). The Barrett True-K formula from both devices showed that 90% of eyes were within ±0.75 D of MAE.
Conclusions:
The visual and refractive outcomes of TFNT IOL implantation in patients with previous corneal refractive surgery were favorable. The Barrett True-K formula in the IOLMaster 700 showed the best refractive outcome for TFNT IOL implantation. [J Refract Surg. 2021;37(11):836-841.].

Objectives: To assess the impact of posterior corneal asphericity on postoperative calculation error using the Haigis-L and the Barrett formulas for eyes after laser in situ keratomileusis or photorefractive keratectomy (PRK).
Methods: We assessed the mean absolute error (MAE) of two power calculation formulas, Barrett true-K and Haigis-L formulas, in a retrospective analysis of 34 eyes of 34 patients who underwent cataract surgery. We performed a regression analysis between corneal parameters (anterior and posterior Q values, Kmax, K1, and K2) and the MAE of each formula.
Results: In the cohort, 11 eyes were of women and 23 of men.
The MAE of Haigis-L and Barrett true-K formulas were 0.72 and 0.68, respectively (P=0.54). The regression analysis showed a statistically significant relationship only between the error in refraction prediction and the posterior Q-value regardless of the formula used. The coefficient of determination was higher for the Barrett true-K formula (r=0.52; R 2 =0.28; P<0.05), compared with the Haigis-L (r=0.49; R 2 =0.25; P<0.05).
Conclusions: Posterior corneal surface asphericity influences the refractive error of calculation using both Haigis-L and Barrett true-K formulas for eyes after a myopic PRK or laser-assisted in situ keratomileusis surgery.

Modern-day cataract surgery has two goals: (1) to create a clear optical path and (2) to alter the optical properties of the eye in patients who desire to reduce or eliminate spectacle dependence. Steady improvements in technology through the years have allowed us to perform safer and less invasive cataract surgery while achieving high levels of success and refractive accuracy as well as increasing the range of spectacle independence. In this chapter, we review the key elements of the preoperative evaluation, available imaging devices, intraocular lens options, indications and contraindications for surgery, and technologies arising on the horizon.

To use optical coherence tomography (OCT) to measure corneal power and improve the selection of intraocular lens (IOL) power in cataract surgeries after laser vision correction.
Patients with previous myopic laser vision corrections were enrolled in this prospective study from two eye centers. Corneal thickness and power were measured by Fourier-domain OCT. Axial length, anterior chamber depth, and automated keratometry were measured by a partial coherence interferometer. An OCT-based IOL formula was developed. The mean absolute error of the OCT-based formula in predicting postoperative refraction was compared to two regression-based IOL formulae for eyes with previous laser vision correction.
Forty-six eyes of 46 patients all had uncomplicated cataract surgery with monofocal IOL implantation. The mean arithmetic prediction error of postoperative refraction was 0.05 ± 0.65 diopter (D) for the OCT formula, 0.14 ± 0.83 D for the Haigis-L formula, and 0.24 ± 0.82 D for the no-history Shammas-PL formula. The mean absolute error was 0.50 D for OCT compared to a mean absolute error of 0.67 D for Haigis-L and 0.67 D for Shammas-PL. The adjusted mean absolute error (average prediction error removed) was 0.49 D for OCT, 0.65 D for Haigis-L (P=.031), and 0.62 D for Shammas-PL (P=.044). For OCT, 61% of the eyes were within 0.5 D of prediction error, whereas 46% were within 0.5 D for both Haigis-L and Shammas-PL (P=.034).
The predictive accuracy of OCT-based IOL power calculation was better than Haigis-L and Shammas-PL formulas in eyes after laser vision correction.

To compare results of intraocular lens (IOL) power calculation methods after myopic excimer laser surgery.
Private practice.
In this prospective study, eyes having phacoemulsification after myopic excimer laser surgery were classified into Group 1 (preoperative corneal power available, refractive change known), Group 2 (preoperative corneal power available, refractive change uncertain), and Group 3 (preoperative corneal power unavailable, refractive change known even if uncertain). The IOL power was calculated using the following methods: clinical history, Awwad, Camellin/Calossi, Diehl, Feiz, Ferrara, Latkany, Masket, Rosa, Savini, Shammas, Seitz/Speicher, and Seitz/Speicher/Savini.
The lowest mean absolute errors (MAEs) in IOL power prediction in Group 1 (n = 12) and Group 2 (n = 11), respectively, were with the methods of Seitz/Speicher/Savini (0.51 diopter [D] +/- 0.44 [SD] and 0.55 +/- 0.50 D), Seitz/Speicher (0.58 +/- 0.47 D and 0.54 +/- 0.45 D), Savini (0.60 +/- 0.44 D and 0.65 +/- 0.63 D), Masket (0.82 +/- 0.49 D and 0.69 +/- 0.51 D), and Shammas (0.77 +/- 0.43 D and 1.11 +/- 0.50 D). In Group 3 (n = 5), the lowest MAEs were with the methods of Masket (0.23 +/- 0.27 D), Savini (0.49 +/- 0.86 D), Seitz/Speicher/Savini (0.68 +/- 0.36 D), Shammas (0.84 +/- 0.98 D), and Camellin/Calossi (0.91 +/- 0.84 D).
When corneal power is known, the Seitz/Speicher method (with or without Savini adjustment) seems the best solution to obtain an accurate IOL power prediction. Otherwise, the Masket method may be the most reliable option.

To develop a simple and accurate method for determining appropriate intraocular lens (IOL) power in cataract patients who had prior excimer laser photoablation for myopia or hyperopia, because laser vision corrective surgery interferes with traditional keratometry and corneal topography, rendering IOL power calculations inaccurate.
Private Practice in Century City (Los Angeles), California, and free-standing outpatient surgery centers with institutional review boards.
Based on the empiric experience of the senior author, an IOL power correction factor that was proportional to the prior laser photoablation was determined and applied to the IOL power calculated by the IOLMaster (Zeiss). It was necessary to add to the predicted IOL power in eyes with prior myopic laser ablation, whereas eyes having prior hyperopic laser vision correction required a reduction in the IOL power. The correction factor was applied to 30 eyes that required cataract surgery at some time after laser refractive surgery; 23 eyes had prior treatment for myopia, and the remaining 7 eyes had prior hyperopic laser ablation. A regression formula was generated from the IOL power correction factor that was used in the 30 eyes.
Using the correction factor for 30 eyes, the mean deviation from the desired postcataract refractive outcome was -0.15 diopter (D) +/- 0.29 (SD); 28 of 30 eyes were within +/-0.5 D of the intended goal; the remaining 2 eyes were both -0.75 D from the desired optical result of cataract surgery. Fourteen of the 30 eyes were emmetropic.
A simple IOL power corrective adjustment regression formula allowed accurate determination of IOL power after laser refractive photoablation surgery. The weakness of the current method is that knowledge of the amount of prior laser vision correction is necessary.

Purpose:
To compare the newer formulae, the optical coherence tomography (OCT)-based intraocular lens (IOL) power formula (OCT formula) and the Barrett True-K formula (True-K), with the methods on the American Society of Cataract and Refractive Surgery (ASCRS) calculator in eyes with previous myopic LASIK/photorefractive keratectomy (PRK).
Design:
Prospective case series.
Participants:
A total of 104 eyes of 80 patients who had previous myopic LASIK/PRK and subsequent cataract surgery and IOL implantation.
Methods:
By using the actual refraction after cataract surgery as target refraction, predicted IOL power for each method was calculated. The IOL prediction error (PE) was obtained by subtracting the predicted IOL power from the power of the IOL implanted.
Main outcome measures:
Arithmetic IOL PEs, variances of mean arithmetic IOL PE, median refractive PE, and percent of eyes within 0.5 diopters (D) and 1.0 D of refractive PE.
Results:
Optical coherence tomography produced smaller variance of IOL PE than did Wang-Koch-Maloney (WKM) and Shammas (P < 0.05). With the OCT, True-K No History, WKM, Shammas, Haigis-L, and Average of these 5 formulas, the median refractive PEs were 0.35 D, 0.42 D, 0.51 D, 0.48 D, 0.39 D, and 0.35 D, respectively, the percentage of eyes within 0.5 D of refractive PE were 68.3%, 58.7%, 50.0%, 52.9%, 55.8%, and 67.3%, respectively, and the percentage of eyes within 1.0 D of refractive PE were 92.3%, 90.4%, 86.9%, 88.5%, 90.4%, and 94.2%, respectively. The OCT formula had smaller refractive PE compared with the WKM and Shammas, and the Average approach produced significantly smaller refractive PE than all methods except OCT (all P < 0.05).
Conclusions:
The OCT and True-K No History are promising formulas. The ASCRS IOL calculator has been updated to include the OCT and Barrett True K formulas.
Trial registration:
Intraocular Lens Power Calculation After Laser Refractive Surgery Based on Optical Coherence Tomography (OCT IOL); Identifier: NCT00532051; www.ClinicalTrials.gov.

To compare the accuracy of intraoperative aberrometry technology and the Fourier-domain optical coherence tomography (OCT)-based intraocular lens (IOL) formula for IOL power calculation in eyes undergoing cataract surgery after previous laser vision correction (LVC) compared with established methods.
Retrospective consecutive case series.
Patients undergoing cataract surgery with a history of LASIK or photorefractive keratectomy.
The IOL power was estimated preoperatively using the IOLMaster 500 (Carl Zeiss Meditec, Dublin, CA) to calculate the Haigis-L and Masket regression formulae (when prior data were available), and the Optovue RTVue (Optovue Inc, Fremont, CA) spectral domain OCT was used to obtain the Fourier-domain OCT-based IOL formula. The Optiwave Refractive Analysis (ORA) System (WaveTec Vision Systems Inc, Aliso Viejo, CA) wavefront aberrometer measured aphakic refractive measurements intraoperatively and calculated the IOL power with a modified vergence formula. Comparative analysis was done for predictive accuracy of IOL power determination using 2 conventional methods and 2 new technologies: the Haigis-L formula, Masket regression formula, ORA intraoperative aberrometry, and Optovue RTVue Fourier-domain OCT-based IOL formula. Patients without historical data (N = 39) were compared using 3 methods (Haigis-L, ORA, and Optovue), and patients with historical data (N = 20) were compared using all methods (Masket regression formula, Haigis-L, ORA, and Optovue).
Median absolute error (MedAE), mean absolute error (MAE), and percentage of eyes within ±0.25, ±0.50, ±0.75, and ±1.00 diopters (D) of refractive prediction error.
A total of 39 eyes of 29 patients without historical data were analyzed separately from 20 eyes of 20 patients with historical data. In the group without historical data (N = 39), 49% of eyes were within ±0.25 D, 69% to 74% of eyes were within ±0.50 D, 87% to 97% of eyes were within ±0.75 D, and 92% to 97% of eyes were within ±1.00 D of targeted refractive IOL power prediction error. The MedAE was 0.26 D for Haigis-L, 0.29 D for ORA, and 0.28 D for Optovue. The MAE was 0.37 D for Haigis-L, 0.34 D for ORA, and 0.39 D for Optovue. In the group with historical data (N = 20), 35% to 70% of eyes were within ±0.25 D, 60% to 85% of eyes were within ±0.50 D, 80% to 95% of eyes were within ±0.75 D, and 90% to 95% of eyes were within ±1.00 D of targeted refractive IOL power prediction error. The MedAE was 0.21 D for the Masket regression formula, 0.22 D for the Haigis-L formula, 0.25 D for ORA, and 0.39 for Optovue. The MAE was 0.28 D for the Masket regression formula, 0.31 D for the Haigis-L formula, 0.37 D for ORA, and 0.44 D for Optovue. There was no statistically significant difference among the methods.
Newer technology to estimate IOL power calculations in eyes after LVC shows promising results when compared with established methods.
Copyright © 2015 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

To develop an algorithm to calculate intraocular lens (IOL) power for eyes with previous laser in situ keratomileusis (LASIK) for myopia based on data from a rotating Scheimpflug camera and to compare calculations with those of current formulas.
East Valley Ophthalmology, Mesa, Arizona, USA.
Observational case series.
Relevant IOL calculation and postoperative refractive data were obtained for eyes of patients who had previous myopic LASIK and subsequent cataract surgery. Initial screening and correlation analysis identified Pentacam Scheimpflug keratometry (K) values appropriate for use in calculating a "best K" for IOL power calculations in these eyes. Error analysis identified other eye measures to improve results. Final results were compared with results from 9 other calculation methods available on the American Society of Cataract and Refractive Surgery (ASCRS) web site.
The study obtained data from 101 eyes of 77 patients. More than 200 Scheimpflug K-formula combinations were evaluated for each eye. The true net power in the 4.0 mm zone centered on the corneal apex provided the best adjusted K reading for IOL power calculation in the Shammas no-history formula. The final formula had good outcomes, with 34%, 66%, and 91% of eyes being within ±0.25 diopter (D), ±0.50 D, and ±1.00 D of the refractive target, respectively. These results compare favorably to the best formulas on the ASCRS web site.
The no-history formula derived using the Scheimpflug device's true net power in the 4.0 mm zone centered on the corneal apex appears to be an accurate method for determining IOL power after LASIK for myopia. Corroboration with additional data sets is suggested.
Neither author has a financial or proprietary interest in any material or method mentioned.
Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

To evaluate a new method of intraoperative refractive biometry (IRB) for intraocular lens (IOL) power calculation in eyes undergoing cataract surgery after prior myopic LASIK or photorefractive keratectomy.
Retrospective consecutive cases series.
We included 215 patients undergoing cataract surgery with a history of myopic LASIK or photorefractive keratectomy.
Patients underwent IRB for IOL power estimation. The Optiwave Refractive Analysis (ORA) System wavefront aberrometer was used to obtain aphakic refractive measurements intraoperatively and then calculate the IOL power with a modified vergence formula obtained before refractive surgery. Comparative effectiveness analysis was done for IRB predictive accuracy of IOL power determination against 3 conventional clinical practice methods: surgeon best preoperative choice (determined by the surgeon using all available clinical data), the Haigis L, and the Shammas IOL formulas.
Median absolute error of prediction and percentage of eyes within ±0.50 diopters (D) and ±1.00 D of refractive prediction error.
In 246 eyes (215 first eyes and 31 second eyes) IRB using ORA achieved the greatest predictive accuracy (P < 0.0001), with a median absolute error of 0.35 D and mean absolute error of 0.42 D. Sixty-seven percent of eyes were within ±0.5 D and 94% were within ±1.0 D of the IRB's predicted outcome. This was significantly more accurate than the other preoperative methods: Median absolute error was 0.6, 0.53, and 0.51 D for surgeon best choice, Haigis L method, and Shammas method, respectively.
The IOL power estimation in challenging eyes with prior LASIK/photorefractive keratectomy was most accurately predicted by IRB/ORA.
Proprietary or commercial disclosure may be found after the references.

To investigate the refractive outcomes of intraocular lens (IOL) power calculation by ray-tracing after myopic excimer laser surgery.
Prospective, interventional case series.
setting: Multicenter study. participants: Twenty-one eyes of 21 patients undergoing phacoemulsification and IOL implantation after myopic laser in situ keratomileusis or photorefractive keratectomy were enrolled. intervention: IOL power calculation was performed using internal software of a Scheimpflug camera combined with a Placido disc corneal topographer (Sirius; CSO). Exact ray-tracing was carried out after the axial length (measured either by immersion ultrasound biometry or partial coherence interferometry), target refraction, and pupil size had been entered. main outcome measures: Median absolute error, mean absolute error, and mean arithmetic error in refraction prediction, that is, the difference between the expected refraction (as calculated by the software) and the actual refraction 1 month after surgery.
The mean postoperative refraction was -0.43 ± 1.08 diopters (D), with a range between -1.28 and 0.85 D. The mean arithmetic error was -0.13 ± 0.49 D. The median and mean absolute errors were +0.25 D and 0.36 D, respectively. Also, 71.4% of the eyes were within ± 0.50 D of the predicted refraction, 85.7% were within ± 1.00 D, and 100% within ± 1.50 D.
Ray-tracing can calculate IOL power accurately in eyes with prior myopic laser in situ keratomileusis and photorefractive keratectomy, with no need for preoperative data.

To compare the accuracy of intraocular lens (IOL) power calculation methods for post-myopic excimer laser surgery patients without previous refractive surgery data using the Holladay IOL Consultant Program and the American Society of Cataract and Refractive Surgery (ASCRS) IOL Power Calculator.
Wang Vision Cataract and LASIK Center, Nashville, Tennessee, USA.
Case series.
Eight methods were used to calculate IOL power: Holladay 2 partial coherence interferometry (PCI)-K, Holladay 2 FlatK, Wang-Koch-Maloney, Shammas No-History, Haigis-L, ASCRS-Average, ASCRS-Min, and ASCRS-Max. The optimum IOL power corresponding to the target refraction was back-calculated using the stable post-cataract surgery refraction and implanted IOL power. Using the optimum IOL power, the predicted IOL power error and the resultant refractive error with each method were calculated and compared.
The Holladay 2 FlatK method was most accurate for IOL power calculation, followed by the Holladay 2 PCI-K, ASCRS-Min, Wang-Koch-Maloney, ASCRS-Average, Shammas No-History, Haigis-L, and ASCRS-Max. Statistically significant differences were observed between Holladay 2 FlatK and Holladay 2 PCI-K (P<.05), Wang-Koch-Maloney and ASCRS-Average (P<.05), and Haigis-L and ASCRS-Max (P<.01). No statistically significant differences were observed between the Holladay 2 PCI-K, ASCRS-Min, and Wang-Koch-Maloney or between the ASCRS-Average, Shammas No-History, and Haigis-L (both P>.05).
The Holladay 2 FlatK method provided the most accurate IOL power in eyes without previous myopic laser surgery data. If the Holladay IOL Consultant Program is unavailable, the ASCRS methods can be used; the ASCRS-Min represents the most accurate method.
No author has a financial or proprietary interest in any material or method mentioned.

To assess and analyze refractive outcome after cataract surgery in Sweden from 2008 through 2010.
Swedish cataract surgery units participating in outcome registration of National Cataract Register.
Cohort study.
Planned and actual postoperative refractions were analyzed for cataract procedures and preoperative and postoperative corneal astigmatism for procedures performed in 2008 though 2010. Induced astigmatism was calculated with Naeser and Behrens polar coordinates.
Postoperative refraction was analyzed for 17,056 procedures and corneal astigmatism for 7448 procedures. Emmetropia was targeted in 78.1% of eyes and achieved in 52.7%; 43.0% had less than 1.00 diopter (D) of astigmatism. "Reading myopia" of -3.5 to -1.6 D was targeted in 7.0% of eyes and achieved in 7.8%. Planned hyperopia greater than 1.0 D or myopia greater than -3.5 D was rare. The mean absolute biometry prediction error was 0.402 D ± 0.338 (SD) in all eyes; however, astigmatic eyes and eyes planned for myopia or hyperopia had higher biometry prediction errors. Younger patients were more often astigmatic and planned for a more myopic outcome. Preoperatively, one third of eyes had more than 1.0 D of corneal astigmatism; postoperatively this figure was largely unaltered. The mean induced astigmatism was 0.525 ± 0.804 D in all eyes.
Emmetropia (spherical equivalent -0.5 to +0.5 D and <1.0 D astigmatism) is the goal in most cataract cases but was reached in only 55% of eyes planned for emmetropia. Factors precluding emmetropia included remaining corneal astigmatism and biometry prediction errors in astigmatic and ametropic eyes.
No author has a financial or proprietary interest in any material or method mentioned.

To evaluate and compare published methods of intraocular lens (IOL) power calculation after myopic laser refractive surgery in a large, multi-surgeon study.
Retrospective case series.
A total of 173 eyes of 117 patients who had uneventful LASIK (89) or photorefractive keratectomy (84) for myopia and subsequent cataract surgery.
Data were collected from primary sources in patient charts. The Clinical History Method (vertex corrected to the corneal plane), the Aramberri Double-K, the Latkany Flat-K, the Feiz and Mannis, the R-Factor, the Corneal Bypass, the Masket (2006), the Haigis-L, and the Shammas.cd postrefractive adjustment methods were evaluated in conjunction with third- and fourth-generation optical vergence formulas, as appropriate. Intraocular lens power required for emmetropia was back-calculated using stable post-cataract surgery manifest refraction and implanted IOL power, and then formula accuracy was compared.
Prediction error arithmetic mean ± standard deviation (SD), range (minimum and maximum), and percent within 0 to -1.0 diopters (D), ±0.5 D, ±1.0 D, and ±2.0 D relative to target refraction.
The top 5 corneal power adjustment techniques and formula combinations in terms of mean prediction errors, standard deviations, and minimizing hyperopic "refractive surprises" were the Masket with the Hoffer Q formula, the Shammas.cd with the Shammas-PL formula, the Haigis-L, the Clinical History Method with the Hoffer Q, and the Latkany Flat-K with the SRK/T with mean arithmetic prediction errors and standard deviations of -0.18±0.87 D, -0.10±1.02 D, -0.26±1.13 D, -0.27±1.04 D, and -0.37±0.91 D, respectively.
By using these methods, 70% to 85% of eyes could achieve visual outcomes within 1.0 D of target refraction. The Shammas and the Haigis-L methods have the advantage of not requiring potentially inaccurate historical information.

To evaluate the accuracy of methods of intraocular lens (IOL) power prediction after previous laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) using the American Society of Cataract and Refractive Surgery IOL power calculator.
Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA.
The following methods were evaluated: methods using pre-LASIK/PRK keratometry (K) and surgically induced change in refraction, methods using surgically induced change in refraction, and methods using no previous data. The predicted IOL power was calculated with each method using the actual refraction after cataract surgery as the target. The IOL prediction error was calculated as the implanted IOL power minus the predicted IOL power. Arithmetic and absolute IOL prediction errors, variances in mean arithmetic IOL prediction error, and percentage of eyes within +/-0.50 diopter (D) and +/-1.00 D of refractive prediction errors were calculated.
Methods using surgically induced change in refraction or no previous data had significantly smaller mean absolute IOL prediction errors, smaller variances, and a greater percentage of eyes within +/-0.50 D and +/-1.00 D of refractive prediction errors than methods using pre-LASIK/PRK keratometry (K) values and surgically induced change in refraction (all P<.05 with Bonferroni correction). There were no statistically significant differences between methods using surgically induced change in refraction and methods using no previous data.
Methods using surgically induced change in refraction and methods using no previous data gave better results than methods using pre-LASIK/PRK K values and surgically induced change in refraction.

Methods to attempt more accurate prediction of intraocular lens power in refractive surgery eyes are many, and none has proved to be the most accurate. Until one is identified, a spreadsheet tool is available and can be used. It automatically calculates all the methods for which data are available on a single sheet for the patient's chart. The various methods and how they work are described.

To describe the Haigis-L formula for the calculation of intraocular lenses (IOLs) after refractive laser surgery for myopia based on current biometry and keratometry and present clinical results.
University Eye Hospital, Wuerzburg, Germany, and various clinics and private practices.
The basic concepts of the new algorithm were described and summarized. The Haigis formula was analyzed with respect to its usability for eyes after laser surgery for myopia and modified accordingly. Correction curves for IOLMaster keratometry were derived from previous studies. The new formula was checked using the postoperative results of 187 cataract procedures in which 32 IOL types were implanted by 57 surgeons. Input data were current IOLMaster biometry as follows: axial length (AL), anterior chamber depth (ACD), and keratometry (corneal radii) measurements.
Before IOL surgery, the mean spherical equivalent was -7.60 diopters (D)+/-3.90 (SD) (range -20.00 to -1.25 D); the mean AL, 27.02+/-2.01 mm (range 23.09 to 35.32 mm); the mean ACD, 3.52 +/- 0.36 mm (range 2.43 to 4.39 mm); and the mean of the measured corneal radii, 8.70+/-0.60 mm (range 7.28 to 10.96 mm). The mean arithmetic refractive prediction error was -0.04+/-0.70 D (range -2.30 to +2.40 D) and the median absolute error, 0.37 D (range +0.01 to +2.40 D). The percentages of correct refraction predictions within +/-2.00, +/-1.00, and +/-0.50 D were 98.4%, 84.0%, and 61.0%, respectively.
The new formula would produce promising results in eyes without refractive history. Its refractive predictability fulfills the current criteria for normal eyes.

Although available empirically derived and theoretical formulas perform adequately for eyes of average axial length, both have been shown to be deficient for eyes that have unusually short and long axial lengths. I developed a formula based on a theoretical model eye in which anterior chamber depth is related to axial length and keratometry. A relationship between the A-constant and a "lens factor" is also used to determine anterior chamber depth. The location of the intraocular lens' principle planes of refraction is retained as a relevant variable in the formula, and the user need not know the material and construction of the lens and or its constant. I compared the new formula with the SRK II, Holladay, and SRK/T formulas in a group of 100 unselected patients and in selected subgroups of patients with average, short, and long axial lengths. The new formula was significantly more accurate than the other third-generation formulas and maintained its accuracy in the subgroups. The formula can be described as universal because it can be used for different lens styles and for eyes with short, medium, and long axial lengths.

The precision of intraocular lens (IOL) calculation is essentially determined by the accuracy of the measurement of axial length. In addition to classical ultrasound biometry, partial coherence interferometry serves as a new optical method for axial length determination. A functional prototype from Carl Zeiss Jena implementing this principle was compared with immersion ultrasound biometry in our laboratory.
In 108 patients attending the biometry laboratory for planning of cataract surgery, axial lengths were additionally measured optically. Whereas surgical decisions were based on ultrasound data, we used postoperative refraction measurements to calculate retrospectively what results would have been obtained if optical axial length data had been used for IOL calculation. For the translation of optical to geometrical lengths, five different conversion formulas were used, among them the relation which is built into the Zeiss IOL-Master. IOL calculation was carried out according to Haigis with and without optimization of constants.
On the basis of ultrasound immersion data from our Grieshaber Biometric System (GBS), postoperative refraction after implantation of a Rayner IOL type 755 U was predicted correctly within +/- 1 D in 85.7% and within +/- 2 D in 99% of all cases. An analogous result was achieved with optical axial length data after suitable transformation of optical path lengths into geometrical distances.
Partial coherence interferometry is a noncontact, user- and patient-friendly method for axial length determination and IOL planning with an accuracy comparable to that of high-precision immersion ultrasound.

To clarify the theoretical background of the rigid contact lens overrefraction (CLO) method to determine corneal power after corneal refractive surgery.
University Eye Clinic, University of Würzburg, Würzburg, Germany.
Using paraxial geometrical optics, the measurement situation for the contact lens method was analyzed and the definitions of corneal refractive power were reviewed. Based on the theoretical Gullstrand eye, model eyes were constructed, representing 1 emmetropic and 2 myopic eyes (primary refraction -5.21 diopters [D] and -10.25 D, respectively) before and after photorefractive keratectomy and laser in situ keratomileusis. In these eyes, the application of the CLO was mathematically simulated using Gaussian thick-lens optics and commercial ray-tracing software.
The CLO method measured neither the equivalent (total) power nor the vertex (back) power of the cornea but rather the quantity 336/R(1C) (R(1C) = anterior corneal radius). Based on these results and the Gullstrand eye, new formulas are proposed to derive the equivalent power and vertex power of the cornea by the CLO method.
Depending on whether intraocular lens calculation formulas are based on equivalent (total) corneal power or vertex corneal power, the respective new formulas for the CLO method should be applied in patients after corneal refractive surgery. An increase in prediction accuracy of the refractive outcome is expected.

To describe and evaluate a refraction-derived method and a clinically derived method to calculate the correct corneal power for intraocular lens (IOL) power calculations after laser in situ keratomileusis (LASIK) and to compare the results to the commonly used history-derived method.
Interventional case series.
Retrospective analysis of consecutive cases from clinical practice. Two hundred randomly selected eyes from 200 patients were evaluated before and after LASIK surgery. For each patient, we established the pre-LASIK and post-LASIK spectacle refraction, the pre-LASIK (Kpre) and post-LASIK K readings (Kpost). We then calculated for each case the pre- and post-LASIK refraction at the corneal plane and the amount of correction obtained by the refractive surgery (CRc). The cases were divided into two groups. Group I was used to derive the two formulas. The K values were calculated using the history-derived method (Kc.hd) in which Kc.hd = Kpre - CRc. Kc.hd was compared with Kpost. The average difference was 0.23 diopters for every diopter of myopia corrected. This value was used to calculate the corneal power using the refraction-derived method (Kc.rd) where Kc.rd = Kpost -0.23CRc. A regression equation was used to develop a clinically derived method (Kc.cd) where Kc.cd = 1.14Kpost -6.8. The values obtained with the two methods were compared with the Kc.hd values in group II to validate the results.
Both Kc.rd and Kc.cd values correlated highly with Kc.hd when plotted on a scattergram (P <.001), and there was no statistically significant difference between the mean keratometric values (P >.5).
The corneal power measurements for intraocular lens power calculations after LASIK need to be corrected to avoid hypermetropia after cataract surgery by either the history-derived method, the refraction-derived method, or the clinically derived method.

To determine the accuracy of a method of calculating intraocular lens (IOL) power after corneal refractive surgery.
Department of Ophthalmology, Hospital de Gipuzkoa, San Sebastián, Spain.
The SRK/T formula was modified to use the pre refractive surgery K-value (Kpre) for the effective lens position (ELP) calculation and the post refractive surgery K-value (Kpost) for IOL power calculation by the vergence formula. The Kpre value was obtained by keratometry or topography and the Kpost, by the clinical history method. The formula was assessed in 9 cases of cataract surgery after laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) in which all relevant data were available. Refractive results of the standard SRK/T and the double-K SRK/T were compared statistically.
The mean IOL power for emmetropia and the achieved refraction (mean spherical equivalent [SE]), respectively, were +17.85 diopters (D) +/- 3.43 (SD) and +1.82 +/- 0.73 with the standard SRK/T and +20.25 +/- 3.55 D and +0.13 +/- 0.62 D with the double-K SRK/T. No case in the standard SRK/T group and 6 cases (66.66%) in the double-K group achieved a +/-0.5 D SE.
Double-K modification of the SRK/T formula improved the accuracy of IOL power calculation after LASIK and PRK.

To evaluate the effect of refractive surgery on intraocular lens (IOL) power calculation, compare methods of IOL power calculation after refractive surgery, evaluate the effect of pre-refractive surgery refractive error on IOL deviation, review the literature on determining IOL power after refractive surgery, and introduce a formula for IOL calculation for use after refractive surgery for myopia.
Laser & Corneal Surgery Associates and Center for Ocular Tear Film Disorders, New York, New York, USA.
This retrospective noncomparative case series comprised 21 patients who had uneventful cataract extraction and IOL implantation after previous uneventful myopic refractive surgery. Six methods of IOL calculation were used: clinical history (IOL(HisK)), clinical history at the spectacle plane (IOL(HisKs)), vertex (IOL(vertex)), back-calculated (IOL(BC)), calculation based on average keratometry (IOL(avgK)), and calculation based on flattest keratometry (IOL(flatK)). Each method result was compared to an "exact" IOL (IOL(exact)) that would have resulted in emmetropia and then compared to the pre-refractive surgery manifest refraction using linear regression. The paired t test was used to determine statistical significance.
The IOL(HisKs) was the most accurate method for IOL calculations, with a mean deviation from emmetropia of -0.56 diopter +/-1.59 (D), followed by the IOL(BC) (+1.06 +/- 1.51 D), IOL(vertex) (+1.51 +/- 1.95 D), IOL(flatK) (-1.72 +/- 2.19 D), IOL(HisK) (-1.76 +/- 1.76 D), and IOL(avgK) (-2.32 +/- 2.36 D). There was no statistical difference between IOL(HisKs) and IOL(exact) in myopic eyes. The power of IOL(flatK) would be inaccurate by -(0.47x+0.85), where x is the pre-refractive surgery myopic SE (SEQ(m)). Thus, without adjusting IOL(flatK), most patients would be left hyperopic. However, when IOL(flatK) is adjusted with this formula, it would not be statistically different from IOL(exact).
For IOL power selection in previously myopic patients, a predictive formula to calculate IOL power based only on the pre-refractive surgery SEQ(m) and current flattest keratometry readings was not statistically different from IOL(exact). The IOL(HisKs), which was also not statistically different from IOL(exact), requires pre-refractive surgery keratometry readings that are often not available to the cataract surgeon.

To prospectively evaluate the no-history method for intraocular lens (IOL) power calculation in 15 cataractous eyes that had previous myopic laser in situ keratomileusis (LASIK) and for which the pre-LASIK K-readings were not available.
Private practice, Lynwood, California, USA.
The predicted IOL power was calculated in each case. Also calculated were the mean arithmetic and absolute IOL predictor errors, range of the prediction errors, and number of eyes in which the error was within +/-1.00 diopter (D).
The mean arithmetic IOL prediction error was -0.003 D +/- 0.63 (SD), and the mean absolute IOL prediction error was 0.55 +/- 0.31 D (range -0.89 to +1.05 D). Fourteen eyes (93.3%) were within +/-1.00 D. The results of the Shammas post-LASIK formula compared favorably to the results obtained with the optimized Holladay 1 (P = .42), Hoffer Q (P = .25), Haigis (P = .30), and Holladay 2 (P = .19) formulas and were better than the results obtained with the optimized SRK/T formula (P = .0005).
The no-history method is a viable alternative for IOL power calculation after myopic LASIK when the refractive surgery data are not available.