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Accuracy of the Barrett True-K formula for intraocular lens power prediction after laser in situ keratomileusis or photorefractive keratectomy for myopia
Abstract
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.
... Laser vision correction alters the curvature of the cornea in the area of the ablation zone, as well as the anterior/posterior curvature ratio, making conventional lens power calculations less accurate. 2 Current methods that have been proposed to improve the accuracy of IOL power calculation in post-refractive eyes include no clinical history post-laser refractive surgery formulas, such as the Haigis-L, 3 Masket, 4 Shammas, 5 and Barrett True-K (BTK) [6][7][8] formulas, and combinations of conventional formulas, such as the traditional Haigis 9 and Emmetropia Verifying Optical (EVO) 10 formulas, with total keratometry results obtained with the optical biometer IOLMaster 700 (Carl Zeiss Meditec). ...
... Not only can this formula incorporate measurements of keratometry and refraction before and after laser correction, 3,4,20 but also calculate the required power of the IOL in the absence of pre-refractive surgery measurements (no-history formula). 6 BTK has been shown to achieve equal or better refractive predictability than other formulas including the Shammas and Haigis-L formulas. 6 The ORA SYSTEM was found to provide refractive outcomes in postrefractive eyes that were equal to or better than outcomes obtained with the Haigis-L, Shammas, and Masket formulas. ...
... 6 BTK has been shown to achieve equal or better refractive predictability than other formulas including the Shammas and Haigis-L formulas. 6 The ORA SYSTEM was found to provide refractive outcomes in postrefractive eyes that were equal to or better than outcomes obtained with the Haigis-L, Shammas, and Masket formulas. 1,16 For example, a study of 116 eyes from 79 patients reported that a higher proportion of post-myopic eyes achieved refractive outcomes with an APE ≤0.50 D following keratorefractive surgery using the ORA SYSTEM (73%) than using the BTK formula (69%), although the difference was not statistically significant. ...
Purpose
To compare the refractive prediction accuracy of the Optiwave Refractive Analysis (ORA) SYSTEM with the Barrett True-K (BTK) formula in calculating intraocular lens (IOL) power in eyes that underwent cataract surgery after previous myopic photorefractive keratectomy (PRK) or laser-assisted in situ keratomileusis (LASIK).
Methods
This retrospective study evaluated patients aged ≥22 years with prior myopic PRK or LASIK who underwent unilateral or bilateral cataract removal and monofocal IOL implantation using the ORA SYSTEM at 177 sites in the United States. Two datasets were analyzed: All Eyes (ie, all eligible eyes) and First Surgery Eyes (ie, each patient’s first implanted eye). All Eyes were subgrouped by axial length (AL) and further analyzed. The main outcomes included paired differences in absolute prediction errors (APEs) between the ORA SYSTEM and BTK and differences in the proportion of eyes with APEs of ≤0.25 diopter (D) and ≤0.50 D.
Results
1067 eyes were analyzed, including 897 First Surgery Eyes. Significantly higher proportions of All Eyes had APEs of ≤0.25 D (P = 0.0128) and ≤0.50 D (P < 0.0001) using the ORA SYSTEM than the BTK formula. Similarly, significantly higher proportions of First Surgery Eyes had APEs of ≤0.25 D (P = 0.0037) and ≤0.50 D (P = 0.0004) using the ORA SYSTEM than the BTK formula. In both datasets, mean (P < 0.0001) and median (P ≤0.0005) APEs were significantly lower with the ORA SYSTEM than with the BTK formula. AL did not affect the differences in prediction accuracy between these IOL power calculations.
Conclusion
In post-myopic PRK or LASIK eyes undergoing cataract surgery, the ORA SYSTEM provided significantly more accurate refractive predictability than the BTK formula, as determined by mean and median APE.
... [1][2][3] As many of the traditional calculation formulas were based on assumptions of unmodi ed corneal measurements and structural properties, using these formulas on patients who have had LASIK can lead to "refractive surprise" after cataract surgery, resulting in unsatisfactory refractive error following lens implantation. 2 A recent report released by the American Academy of Ophthalmology found when using automated keratometry and IOL power theoretical formulas developed for eyes without previous corneal refractive surgeries, the mean predicted error in post-LASIK eyes trended hyperopic, with a large proportion falling outside 0.50 D of the target refractive power. 1 Attempts have been made to establish more reliable IOL power calculation formulas for post-refractive surgery eyes, with some success, [4][5][6][7][8][9][10][11] but the accuracy of refractive prediction in post-refractive surgery eyes has not yet reached that in normal eyes. Accurate IOL power prediction also relies upon precise measurement of the corneal curvature. ...
... 7,25,26 The Barrett True-K formula's notable prediction accuracy has been demonstrated in several previous studies. 4,27 In a study by Ferguson et al., the Barrett True-K alone was shown to be as accurate as the American Society of Cataract and Refractive Surgery (ASCRS) average, a multi-formula average approach for post-refractive surgery eyes, and it was signi cantly more accurate when compared to the Haigis-L formula, which was the second-most accurate formula of those studied. 7 Similarly, the Barrett True-K performed well in our study, but the Haigis TK was more accurate than the Haigis-L. ...
... 30 It is a theoretical model that adjusts keratometry measurements for patients who have received LASIK or PRK and can be used even when no pre-operative refractive history is available to the surgeon. 4 The Haigis-L formula is another commonly used no-history formula for IOL power calculation. 31 The EVO (Emmetropia Verifying Optical) formula utilizes thick lens modelling to generate an "emmetropia factor" ...
This retrospective study compared postoperative prediction errors of recent formulas using standard- or total keratometry (K or TK) for intraocular lens (IOL) power calculation in post-myopic LASIK patients. It included 56 eyes of 56 patients who underwent uncomplicated cataract surgery, with at least 1-month follow-up at Keio University Hospital in Tokyo or Hayashi Eye Hospital in Yokohama, Japan. Prediction errors, absolute errors, and percentage of eyes with prediction errors within ± 0.25 D, ± 0.50 D, and ± 1.00 D were calculated using nine formulas: Barrett True-K, Barrett True-K TK, Haigis-L, Haigis TK, Pearl-DGS, Hoffer QST, Hoffer QST PK, EVO K, and EVO PK. Statistical comparisons utilized Friedman test, Conover’s all-pairs post-hoc, Cochran’s Q, and McNemar post-hoc testing. Root-Mean-Square Error (RMSE) was compared with Welch’s test and paired t-test post-hoc testing.
Barrett True-K TK had the lowest median predicted refractive error (-0.01). EVO PK had the smallest median absolute error (0.20). EVO PK had the highest percentage of eyes within ± 0.25 D of the predicted value (58.9%), significantly better than Haigis-L (p = 0.047). EVO PK had the lowest mean RMSE value (0.499).
The EVO PK formula yielded the most accurate IOL power calculation in post-myopic LASIK eyes, with TK/PK values enhancing accuracy.
... The Maloney method became popular later with a posterior value of 6.1 D [19]; empirical adjustment with a linear regression function by Shammas [20]; radius of curvature correction as a function of the CRS dioptric correction and AL [21]. Two methods that correct the anterior radius of curvature empirically still in use by many surgeons are the Haigis-L and the Barrett True K formulas [22,23]. ...
... This unpublished formula is a modification of the Barrett Universal II where the ELP estimation error is avoided using the Double K method and, on the other hand, the keratometric error is fixed using an internal regression formula that modifies the prediction in a different way for myopic laser, hyperopic laser, and radial keratotomy. The "history" version of the Barrett True-K formula requires the surgically induced refractive change (SIRC) and has been found to be an accurate option for IOL power calculation, as the prediction error (PE) is within ±0.50 D in 64-67% of eyes [23,31,32]. Its results are further improved by adding the posterior corneal curvature data measured by Scheimpflug or OCT. ...
... It can be accessed in the previously reported websites. The results are good (56-63% of eyes with a PE within ±0.50 D) [23,31,32] and can be improved by adding the posterior corneal curvature (up to 70% of eyes with a PE within ±0.50 D) [31,45]. Compared to other No-History formulas, it appears to be the most accurate choice in eyes with axial length (AL) <28 mm [46]. ...
Intraocular lens (IOL) power calculation is affected by the effect of any previous corneal refractive surgery. In this chapter, an extensive analysis of the different sources of error and the correspondent solutions is performed. Corneal shape change and keratometric error are the main contributors to the final refractive error. Incorrect IOL position estimation is another potential cause of error in determined formulas. New corneal tomographers and the use of a correct calculation method will improve the outcomes avoiding the commission of significant errors. A classification of the published methods to be used in these cases with their performance data will allow the surgeon to select the best option in each particular case.
... Among the methods that do not require the use of preoperative parameters or amount of treatment to calculate the IOL power [11,24,26,[28][29][30][31][32][33][34][35][36][37][38][39][40][41], it was possible to evaluate the methods described by Rosa (ALMA) [24], Barrett (True-K) [30], Ferrara [31], Jin [34], Kim [26], Latkany (flat-K) [35], and Shammas [39]. ...
... Among the methods that do not require the use of preoperative parameters or amount of treatment to calculate the IOL power [11,24,26,[28][29][30][31][32][33][34][35][36][37][38][39][40][41], it was possible to evaluate the methods described by Rosa (ALMA) [24], Barrett (True-K) [30], Ferrara [31], Jin [34], Kim [26], Latkany (flat-K) [35], and Shammas [39]. ...
... When limited data are available, analyzing more than one IOL model is appropriate [21]. In addition, multiple IOL models were analyzed in other recent studies regarding IOL power calculation accuracy after myopic-LRS [16][17][18]24,30]. In fact, multicenter nature of the study was justified by the extreme difficulty to obtain a large and reliable database of post-refractive surgery eyes that underwent cataract surgery. ...
This retrospective comparative study proposes a multi-formula approach by comparing no-history IOL power calculation methods after myopic laser-refractive-surgery (LRS). One-hundred-thirty-two eyes of 132 patients who had myopic-LRS and cataract surgery were examined. ALMA, Barrett True-K (TK), Ferrara, Jin, Kim, Latkany and Shammas methods were evaluated in order to back-calculate refractive prediction error (PE). To eliminate any systematic error, constant optimization through zeroing-out the mean error (ME) was performed for each formula. Median absolute error (MedAE) and percentage of eyes within ±0.50 and ±1.00 diopters (D) of PE were analyzed. PEs were plotted with corresponding mean keratometry (K), axial length (AL), and AL/K ratio; then, different ranges were evaluated. With optimized constants through zeroing-out ME (90 eyes), ALMA was better when K ≤ 38.00 D-AL > 28.00 mm and when 38.00 D < K ≤ 40.00 D-26.50 mm < AL ≤ 29.50 mm; Barrett-TK was better when K ≤ 38.00 D-AL ≤ 26.50 mm and when K > 40.00 D-AL ≤ 28.00 mm or AL > 29.50 mm; and both ALMA and Barrett-TK were better in other ranges. (p < 0.05) Without modified constants (132 eyes), ALMA was better when K > 38.00 D-AL ≤ 29.50 mm and when 36.00 < K ≤ 38.00 D-AL ≤ 26.50 mm; Barrett-TK was better when K ≤ 36.00 D and when K ≤ 38.00 D with AL > 29.50 mm; and both ALMA and Barrett-TK were better in other ranges (p < 0.05). A multi-formula approach, according to different ranges of K and AL, could improve refractive outcomes in post-myopic-LRS eyes.
... [2] Even with historical data and various post-LASIK IOL calculation methods, postoperative refractive surprises can still occur due to alteration of the natural corneal curvature. [2][3][4][5][6][7] Monofocal lenses can offer great refractive results in patients with no previous keratorefractive surgeries, and most patients achieve excellent uncorrected distance visual acuity (UCDVA) with predictable results. In contrast, multifocal IOLs (MFIOLs) are sensitive to corneal irregularities, and therefore, most surgeons are hesitant to place MFIOL in patients with previous keratorefractive surgery. ...
... [1] Various formulas have been used for patients with previous keratorefractive surgeries to improve postoperative predictability. [1,[4][5][6] In our study of post-LASIK patients, we used the Barrett True-K Formula through the American Society of Cataract and Refractive Surgery (ASCRS) website and IOL power was selected by choosing the negative SE closest to zero. The Barrett True-K formula has been shown to be equal to or better than the alternative methods available on the ASCRS website for predicting IOL power in eyes with previous LASIK or Photorefractive keratectomy (PRK). ...
... The Barrett True-K formula has been shown to be equal to or better than the alternative methods available on the ASCRS website for predicting IOL power in eyes with previous LASIK or Photorefractive keratectomy (PRK). [5] In addition, we further showed that our patients with diffractive MFIOL had very good near vision in post-LASIK cataract surgery, a finding that is comparable to previous studies. [11][12][13][14][15][16]20,21,24,25] The promising results may be attributed to diffractive design or continuous power change of the MFIOL. ...
Purpose:
To compare the clinical outcomes of diffractive multifocal and monofocal lenses in post-laser in situ keratomileusis (LASIK) patients who underwent cataract surgery.
Methods:
This was a retrospective, comparative study of clinical outcomes that was conducted at a referral medical center. Post-LASIK patients who underwent uncomplicated cataract surgery and received either diffractive multifocal or monofocal lens were studied. Visual acuities were compared at baseline and postoperatively. The intraocular lens (IOL) power was calculated with Barrett True-K Formula only.
Results:
At baseline, both groups had comparable age, gender, and an equal distribution hyperopic and myopic LASIK. A significantly higher percentage of patients receiving diffractive lenses achieved uncorrected distance visual acuity (UCDVA) of 20/25 or better (80 of 93 eyes, 86% vs. 36 of 82 eyes, 43.9%, P = 1.0 x 105) and uncorrected near vision of J1 or better (63% vs. 0) compared to the monofocal group. The residual refractive error had no significant difference (0.37 ± 0.39 vs. 0.44 ± 0.39, respectively, P = 0.16) in these two groups. However, more eyes in the diffractive group achieved UCDVA of 20/25 or better with residual refractive error of 0.25-0.5 D (36 of 42 eyes, 86% vs. 15 of 24 eyes, 63%, P = 0.032) or 0.75-1.5 D (15 of 21 eyes, 23% vs. 0 of 22 eyes, P = 1.0 x 10-5) compared to the monofocal group.
Conclusion:
This pilot study shows that patients with a history of LASIK who undergo cataract surgery with a diffractive multifocal lens are not inferior to those who receive monofocal lens. Post-LASIK patients with diffractive lens are more likely to achieve not only excellent near vision, but also potentially better UCDVA, regardless of the residual refractive error.
... The difficulty lies in the calculation of accurate corneal refractive power because of the altered anterior to posterior corneal power ratio, and unreliable prediction of the effective lens position (ELP) due to the inclusion of the inaccurate corneal curvature [4,5]. Methods and formulas have been proposed to improve the accuracy of IOL calculation in these eyes and many studies have been published focusing mainly on the eyes, which have undergone prior myopic refractive surgery [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Although many formulas have been proposed to improve IOL calculation accuracy, in eyes that have undergone hyperopic refractive surgery as well, there is a lack of studies focusing on the comparison of the results obtained using these formulas [21][22][23]. ...
... Many methods have been proposed in an attempt to avoid these difficulties, and many studies have been published, although tending to focus more on myopic rather than hyperopic surgery [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Very few studies compare the results of different IOL power calculation formulas in previously hyperopic eyes [21][22][23]. ...
Background: We evaluate the accuracy of intraocular lens (IOL) power calculation in the following formulas—Barrett True-K No History (BTKNH), EVO 2.0 Post-Hyperopic LASIK/PRK (EVO 2.0), Haigis-L, Pearl-DGS, and Shammas (SF)—with patients who have undergone cataract surgery at the Eye Unit of University of Campania Luigi Vanvitelli, Naples, Italy, and had prior hyperopic laser refractive surgery. Methods: A monocentric, retrospective, comparative study, including the charts of patients who had undergone cataract surgery and previous hyperopic laser refractive surgery, was retrospectively reviewed. Patients with no other ocular or systemic disease which might interfere with visual acuity results and no operative complications or combined surgery were enrolled. The mean absolute prediction error (MAE) was calculated for each formula and compared. Subgroup analysis based on the axial length and mean keratometry was performed. Results: A total of 107 patients (107 eyes) were included. The MAE calculated with SF provided less accurate (p < 0.05) results when compared to both BTKNH and EVO 2.0 formulas. The MAE obtained using Haigis-L, EVO 2.0, Pearl-DGS, and BTKNH showed no significant differences. Conclusions: The analysis of the accuracy of the selected formulas shows no clear advantage in using one specific formula in standard cases, but in eyes where it is mandatory to reach the target refraction, SF should be avoided.
... The choice of presbyopia-correcting intraocular lenses (IOLs) for patients undergoing post-LASIK cataract surgery is a signi cant consideration. Previous studies have suggested that multifocal IOLs may be suitable for eyes with a history of LASIK under speci c conditions, such as regular corneal astigmatism and the application of an appropriate IOL calculation formula [3,4]. However, direct comparison studies between cataract eyes with and without a history of LASIK are limited. ...
... Among these, the Haigis L formula has gained popularity because it does not require previous refractive surgery data [14]. In the study by Abula a et al., which examined patients with a history of LASIK or photorefractive keratectomy, the mean absolute prediction error was 0.68 ± 0.45 D by the Haigis-L method, 0.63 ± 0.48 D by the Shammas method, and 0.52 ± 0.43 D using the Barrett true-K formula [4]. These values were similar to the 0.65 ± 0.26 D observed in our study. ...
Background
Laser-assisted in situ keratomileusis (LASIK) is widely used to correct refractive errors in myopia and astigmatism. The choice of presbyopia-correcting intraocular lenses (IOLs) for post-LASIK cataract surgery is a significant concern. However, few direct comparison studies exist between eyes with and without a history of LASIK. We analyzed the performance of extended depth of focus (EDOF) IOL implantation in these two groups.
Methods
This retrospective single-center study included patients with or without previous LASIK who underwent cataract surgery and EDOF Symfony IOL implantation, with follow up. All patients underwent optical biometry using the IOLMaster (IOLMaster 500, Carl Zeiss). IOL power was calculated using the SRK/T formula for non-LASIK patients and the Haigis-L formula for LASIK patients. Uncorrected distance visual acuity (UDVA), uncorrected near visual acuity (UNVA), refraction, and corneal tomography were recorded. The prediction error was the absolute difference between the postoperative sphere and the target refraction. The right eyes of patients who met the inclusion criteria were selected for analysis.
Results
Among the 331 recruited eyes, 18 underwent previous LASIK. After 1:3 age/sex matching, 17 LASIK and 49 non-LASIK eyes from 66 patients were analyzed. No significant preoperative differences existed in target refraction, spherical equivalent, or best-corrected visual acuity. All surgical procedures were uneventful. Non-inferiority tests showed that LASIK exhibited non-inferiority to non-LASIK for predictive refraction error and UNVA. Age/sex matched regression analysis results suggested that there was no UDVA superiority between the two groups.
Conclusion
Previous LASIK had no discernible effect on the visual performance of presbyopia-correcting EDOF IOLs with respect to the absolute refractive error, UNVA, and UDVA. For further validation, larger-scale or multicenter studies are required to ensure the robustness and generalizability of our results in diverse clinical settings.
Trial registration
ClinicalTrials.gov, NCT06165796. Registered 4 December 2023 - Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT06165796
... The ASCRS calculation and the Barrett True K and Double K modified-Holladay 1 formulas were accessed from the ASCRS post-RK IOL online calculator (https://ascrs.org/tools/post-refractiveiol-calculator). This online calculator has the option to include pre-and post-RK refractive data, keratometry, axial length, anterior chamber depth (ACD), lens thickness, and white-towhite [13][14][15]. The Double K modified-Holladay 1 formula was also used in conjunction with the Holladay EKR65 values to yield an additional formula variation [16]. ...
... The Kane and PEARL-DGS formulas also showed promising results in post-RK IOL calculation, indicating the potential of these AIbased formulas [15]. An analysis of MAE did not differ significantly for either formula; however, an analysis of AME revealed that there was a statistically significant difference between the Kane and Potvin Hill (P = 0.042), DK-Holladay (P = 0.021), EKR65 (P = 0.018), Haigis (P = 0.025), and Panacea (P = 0.016) calculators. ...
This study aims to evaluate the accuracy of 12 different intraocular lens (IOL) power calculation formulas for post-radial keratotomy (RK) eyes. The investigation utilizes recent advances in topography/tomography devices and artificial intelligence (AI)-based calculators, comparing the results to those reported in current literature to assess the efficacy and predictability of IOL calculations for this patient group.
In this retrospective study, 37 eyes from 24 individuals with a history of RK who underwent cataract surgery at Hoopes Vision Center were analyzed. Biometry and corneal topography measurements were taken preoperatively. Subjective refraction was obtained 6 months postoperatively. Twelve different IOL power calculations were used, including the American Society of Cataract and Refractive Surgery (ASCRS) post-RK online formula, and the Barrett True K, Double K modified-Holladay 1, Haigis-L, Panacea, Camellin-Calossi, Emmetropia Verifying Optical (EVO) 2.0, Kane, and Prediction Enhanced by Artificial Intelligence and output Linearization-Debellemanière, Gatinel, and Saad (PEARL-DGS) formulas. Outcome measures included median absolute error (MedAE), mean absolute error (MAE), arithmetic mean error (AME), and percentage of eyes achieving refractive prediction errors (RPE) within ± 0.50 D, ± 0.75 D, and ± 1 D for each formula. A search of the literature was also performed by two independent reviewers based on relevant formulas.
Overall, the best performing IOL power calculations were the Camellin-Calossi (MedAE = 0.515 D), the ASCRS average (MedAE = 0.535 D), and the EVO (MedAE = 0.545 D) and Kane (MedAE = 0.555 D) AI-based formulas. The EVO and Kane formulas along with the ASCRS calculation performed similarly, with 48.65% of eyes scoring within ± 0.50 D of the target range, while the Equivalent Keratometry Reading (EKR) 65 Holladay formula achieved the greatest percentage of eyes scoring within ± 0.25 D of the target range (35.14%). Additionally, the EVO 2.0 formula achieved 64.86% of eyes scoring within the ± 0.75 D RPE category, while the Kane formula achieved 75.68% of eyes scoring within the ± 1 D RPE category. There was no significant difference in MAE between the established and newer generation formulas (P > 0.05). The Panacea formula consistently underperformed when compared to the ASCRS average and other high-performing formulas (P < 0.05).
This study demonstrates the potential of AI-based IOL calculation formulas, such as EVO 2.0 and Kane, for improving the accuracy of IOL power calculation in post-RK eyes undergoing cataract surgery. Established calculations, such as the ASCRS and Barrett True K formula, remain effective options, while under-utilized formulas, like the EKR65 and Camellin-Calossi formulas, show promise, emphasizing the need for further research and larger studies to validate and enhance IOL power calculation for this patient group.
... The formulae with historical data would require knowledge of pre-operative data and stable post-operative refractions [3]. For example, surgically induced refractive change at the corneal plane is needed in Barrett True K, Masket or Modified Masket methods [5,6]. And pre-refractive surgery keratometry is required in Double-K or clinical history method (CHM) [7][8][9]. ...
... However, as the historical data are not available or not credible, the formulae with historical data were proved to be not as accurate as it was thought to be. Since then, several formulae that do not rely on historical data have been proposed, including Barrett True-K no history, Hill Potvin Shammas PM, Haigis-L, Shammas-PL and others [5,[10][11][12][13][14]. However, most of them are derived based on empirical regression analysis, resulting in the accuracy of IOL power calculation for patients after excimer surgery has been lower than that of the virgin eyes [15][16][17]. ...
Aim To evaluate the accuracy of the raytracing method for the calculation of intraocular lens (IOL) power in myopic eyes after small incision extraction of the lenticule (SMILE).
Methods Retrospective study. All patients undergoing surgery for myopic SMILE between May 1, 2020, and December 31, 2020, with Scheimpflug tomography optical biometry were eligible for inclusion. Manifest refraction was performed before and 6 months after refractive surgery. One eye from each patient was included in the final analysis. A theoretical model was invited to predict the accuracy of multiple methods of lens power calculation by comparing the IOL-induced refractive error at the corneal plane (IOL-Dif) and the SMILE-induced change of spherical equivalent (SMILE-Dif) before and after SMILE surgery. The prediction error (PE) was calculated as the difference between SMILE-Dif–IOL-Dif. IOL power calculations were performed using raytracing (Olsen Raytracing, Pentacam AXL, software version 1.22r05, Wetzlar, Germany) and other formulae with historical data (Barrett True-K, Double-K SRK/T, Masket, Modified Masket) and without historical data (Barrett True-K no history, Haigis-L, Hill Potvin Shammas PM, Shammas-PL) for the same IOL power and model. In addition, subgroup analysis was performed in different anterior chamber depths, axial lengths, back-to-front corneal radius ratio, keratometry, lens thickness, and preoperative spherical equivalents.
Results A total of 70 eyes of 70 patients were analyzed. The raytracing method had the smallest mean absolute PE (0.26 ± 0.24 D) and median absolute PE (0.16 D), and also had the largest percentage of eyes within a PE of ± 0.25 D (64.3%), ± 0.50 D (81.4%), ± 0.75 D (95.7%), and ± 1.00 D (100.0%). The raytracing method was significantly better than Double-K SRK/T, Haigis, Haigis-L, and Shammas-PL formulae in postoperative refraction prediction (all p < 0.001), but not better than the following formulae: Barrett True-K (p = 0.314), Barrett True-K no history (p = 0.163), Masket (p = 1.0), Modified Masket (p = 0.806), and Hill Potvin Shammas PM (p = 0.286). Subgroup analysis showed that refractive outcomes exhibited no statistically significant differences in the raytracing method (all p < 0.05).
Conclusion Raytracing was the most accurate method in predicting target refraction and had a good consistency in calculating IOL power for myopic eyes after SMILE.
... The Haigis-L formula is a modified form of the regular Haigis formula utilizing a regression-based algorithm, which generates a corrected central corneal power based on the corneal radius, thereby relatively accurately predicting the myopic LASIK eyes for extremely long eyes 37 . The Barrett True-K formula is based on the Barrett Universal II formula and calculates the modified K value and applies the double K method 38 . We hypothesized that for the Haigis-L and Barrett True-K formulas, which do not consider posterior corneal radii curvature, the AP ratio and APE may have statistically significant correlation on simple linear regression analysis. ...
... In 2022, Fang et al. 39 found that Haigis-L was relatively accurate in predicting extreme long axis (> 29.0 mm) eyes after M-LVC but less accurate for eyes with extremely flat corneas (< 35 D). In our study, the percentage of APE within 1.0 D was significantly lower in Haigis-L than in Barrett True-K and Barrett True-TK in eyes with 26.0 mm ≤ AL < 28.0 mm, which is consistent with the previous results 38,[40][41][42] . Although there was no statistical significance, the Barrett True-TK showed higher prediction accuracy than Barrett True-K, which need to be confirmed in further studies. ...
We retrospectively evaluate the actual anterior–posterior (AP) corneal radius ratio in eyes with previous laser correction for myopia (M-LVC) according to axial length (AL) using biometry data exported from swept-source optical coherence tomography between January 2018 and October 2021 in a tertiary hospital (1018 eyes with a history of M-LVC and 19,841 control eyes). The AP ratio was significantly higher in the LVC group than in the control group. Further, it was significantly positively correlated with AL in the LVC group. We also investigated the impact of the AP ratio, AL and keratometry (K) on the absolute prediction error (APE) in 39 eyes that underwent cataract surgery after M-LVC. In linear regression analyses, there were significant correlations between APE and AL/TK, while APE and AP ratio had no correlation. The APE was significantly lower in the Barrett True-K with total keratometry (Barrett True-TK) than in the Haigis-L formula on eyes with AL above 26 mm and K between 38 and 40 D. In conclusion, in eyes with previous M-LVC, AP ratio increases with AL. The Barrett True-K or Barrett True-TK formulas are recommended rather than Haigis-L formula in M-LVC eyes with AL above 26 mm and K between 38 and 40D.
... The Barrett True-K formula represents an advancement over the Barrett Universal II formula, specifically designed to address corneal power estimation in post-refractive surgery eyes while providing reliable IOL power predictions across varying axial lengths [13,[17][18][19][20][21][22][23]. Nevertheless, cataract surgery in post-refractive [24][25][26][27]. ...
Background
Anterior subcapsular cataract (ASC) is a leading complication of implantable collamer lens (ICL) implantation and a common indication for secondary ICL removal. However, the visual outcomes of combined ICL explantation, cataract extraction, and implantation of a TECNIS Symfony ZXR00 IOL with a targeted myopic shift (-0.50D to -0.75D) remain uncertain in highly myopic patients with prior ICL and photorefractive keratectomy (PRK) surgeries.
Case presentation
A 39-year-old male highly myopic patient who underwent concurrent ICL removal, phacoemulsification, and TECNIS Symfony ZXR00 IOL implantation in both eyes, spaced two weeks apart, is reported in this case. Surgical planning prioritized spectacle independence, occupational visual needs, and the IOL’s optical properties, with a deliberate residual myopic refraction (-0.50D to -0.75D). At the 3-month follow-up, comprehensive evaluation was conducted, included manifest refraction, anterior segment OCT (Casia2), defocus curves, OPD-Scan III, and the NEI-VFQ-14 questionnaire. The patient achieved excellent near and intermediate vision, high overall optical quality, and reported exceptional satisfaction.
Conclusion
For patients developing ASC post-ICL implantation, particularly those with strong preferences for spectacle independence and specific visual demands, the TECNIS Symfony ZXR00 IOL, combined with optimized residual myopia, may provide outstanding visual performance and patient satisfaction.
... Therefore, it must be stated that each formula that is not designed for post refractive surgery eyes lacks of accuracy despite its generation, Only specific post refractive surgery formulas should be employed for these eyes. Abulafia et al. [65] reported that the Barrett True-K formula gives small postoperative refractive error for cataract patients with a history of LASIK or PRK refractive surgery. For patients with a history of corneal refractive surgery lacking accurate corneal curvature measurement and complete preoperative case data, the Barrett True-K formula is generally considered the best choice in clinical practice. ...
Modern cataract surgery has entered the era of precision refractive surgery and is no longer only about the restoration of vision, and the factors affecting the refractive error after cataract surgery are gaining increasing attention with the patients’ growing expectation of postoperative visual quality. The refractive error after cataract surgery is related to the accurate measurement of ocular biological parameters, the optimization of the intraocular lens calculation formula, and the prediction of the effective lens position. Clinicians must consider multiple factors to reduce the postoperative refractive error and improve the postoperative satisfaction of cataract patients. In this work, we review factors that affect the refractive error after cataract surgery.
... Several studies have reported favorable outcomes after using ASCRS post-refractive surgery calculator in eyes with prior laser refractive surgery. [12][13][14][15][16] IOLMaster 700 (Carl Zeiss Meditec AG, Jena, Germany), is an optical biometer based on swept-source OCT. A unique parameter it measures is the total keratometry (TK) -TK1 and TK2 -using telecentric three-zone keratometry along with swept-source OCT, and it has provisions for calculation of IOL powers in eyes subjected to refractive surgery -the LASIK/PRK and RK modes. ...
Purpose
To evaluate the prediction accuracy of various intraocular lens (IOL) power calculation formulas on American Society of Cataract and Refractive Surgery (ASCRS) calculator and Barrett True-K total keratometry (TK) in eyes with previous laser refractive surgery for myopia.
Methods
This retrospective study included eyes with history of myopic laser refractive surgery, which have undergone clear or cataractous lens extraction by phacoemulsification followed by IOL implantation. Those who underwent uneventful crystalline lens extraction were included. Eyes with any complication of refractive surgery or those with eventful lens extraction procedure and those who were lost to follow-up were excluded. Formulas compared were Wang–Koch–Maloney, Shammas, Haigis-L, Barrett True-K no-history formula, ASCRS average power, ASCRS maximum power on the ASCRS post-refractive calculator and the IOLMaster 700 Barrett True-K TK. Prediction error was calculated as the difference between the implanted IOL power and the predicted power by various formulae available on ASCRS online calculator.
Results
Forty post-myopic laser-refractive surgery eyes of 26 patients were included. Friedman’s test revealed that Shammas formula, Barrett True-K, and ASCRS maximum power were significantly different from all other formulas ( P < 0.00001 for each). Median absolute error (MedAE) was the least for Shammas and Barrett True-K TK formulas (0.28 [0.14, 0.36] and 0.28 [0.21, 0.39], respectively) and the highest for Wang–Koch–Maloney (1.29 [0.97, 1.61]). Shammas formula had the least variance (0.14), while Wang–Koch–Maloney formula had the maximum variance (2.66).
Conclusion
In post-myopic laser refractive surgery eyes, Shammas formula and Barrett True-K TK no-history formula on ASCRS calculator are more accurate in predicting IOL powers.
... Similarly, the Barrett True K is based on the BUII with an additional theoretical model to account for the disrupted relationship of the anterior and posterior cornea in eyes that had undergone myopic [35] or hyperopic [36] refractive surgery including RK [37]. Keratoconus is another example where the relationship of the posterior and anterior radii is altered, and more recently, a solution for this condition has been added to the online True K available at apacrs.org ...
The Barrett Universal II Formula has become a popular and well-documented formula as regards its accuracy compared to third-generation formulas. The author lays out the history of IOL power calculation, the groundwork and framework for the development of his formula, as well as his related formulas to deal with special problem eyes. There is a description of his method to predict the final lens position. There is the Barrett toric calculator for toric calculations and the Barrett True K Formula for post-corneal surgery eyes. There is a careful analysis of the issue of optical biometer use of a group refractive index for axial length measurement versus the use of individual indices for each segment of the eye measured. There is a full discussion of the new Barrett True AL formula which deals with this issue. There is a full analysis of this formula compared to the Haigis, Hoffer Q, Holladay 1, and SRK/T formulas. There is also a discussion of the causes that lead to IOL power errors.
... Although previous studies have demonstrated the superiority of the Barrett True-K formulas over other formulas, 16 the performance of other new online formulas with post-LRS versions is rarely compared with that of other formulas for eyes that have undergone corneal refractive surgery. The EVO 2.0 is a thick-lens formula based on the emmetropization theory. ...
Purpose
To assess the predictive accuracy of new-generation online intraocular lens (IOL) power formulas in eyes with previous myopic laser refractive surgery (LRS) and to evaluate the influence of corneal asphericity on the predictive accuracy.
Methods
The authors retrospectively evaluated 52 patients (78 eyes) with a history of laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) who subsequently underwent cataract surgery. Refractive prediction errors were calculated for 12 no-history new online formulas: 8 formulas with post-LRS versions (Barrett True-K, EVO 2.0, Hoffer QST, and Pearl DGS) using keratometry and posterior/total keratometry measured by IOLMaster 700 and 4 formulas without post-LRS versions (Cooke K6 and Kane) using keratometry and total keratometry. The refractive prediction error, mean absolute error (MAE), and percentages of eyes with prediction errors of ±0.25, ±0.50, ±0.75, ±1.00, and ±1.50 diopters (D) were compared.
Results
The MAEs of the 12 formulas were significantly different (F = 83.66, P < .001). The MAEs ranged from 0.62 to 0.94 D and from 1.07 to 1.84 D in the formulas with and without post-LRS versions, respectively. The EVO formula produced the lowest MAE (0.60) and MedAE (0.47), followed by the Barrett True-K (0.69 and 0.50, respectively). Each percentage of eyes with refractive prediction error was also significantly different among the 12 formulas ( P < .001).
Conclusions
The EVO and Barrett True-K formulas demonstrate comparable performance to the other existing formulas in eyes with a history of myopic LASIK/PRK. Surgeons should use these formulas with post-LRS versions and input keratometric values whenever possible.
[ J Refract Surg . 2024;40(6):e354–e361.]
... Clinical Ophthalmology 2024:18 power using axial length, keratometry, anterior chamber depth, lens thickness, and white-to-white distance. 7 Barrett True K could be completed with or without history. ...
Purpose
This study aimed to evaluate the accuracy of 12 intraocular lens (IOL) power calculation formulae for eyes that have undergone both radial keratotomy (RK) and laser assisted in situ keratomileusis (LASIK) surgery to determine the efficacy of various IOL calculations for this unique patient group. Currently, research on this surgical topic is limited.
Methods
In this retrospective study, 11 eyes from 7 individuals with a history of RK and LASIK who underwent cataract surgery at Hoopes Vision were analyzed. Preoperative biometric and corneal topographic measurements were performed. Subjective refraction was obtained postoperatively. Twelve different intraocular lens (IOL) power calculations were used: Barrett True K No History, Barrett True K (prior LASIK, Prior RK history), Barrett Universal 2, Camellin-Calossi-Camellin (3C), Double K-Modified Holladay, Haigis-L, Galilei, OCT, PEARL-DGS, Potvin-Hill, Panacea, and Shammas.
Results
The rankings of mean arithmetic error (MAE), from least to greatest, were as follows: 3C (0.088), Haigis-L-L (−0.508), Shammas (−0.516), OCT Average (−0.538), Barrett True K (−0.557), OCT RK (−0.563), Galilei (−0.570), IOL Master (−0.571), OCT LASIK (−0.583), Barrett True K No History (−0.597), Pearl-DGS (−0.606), Potvin-Hill SF (−0.770), Potvin-Hill TNP (−0.778), Panacea (−0.876), and Barrett Universal 2 (−1.522). The 3C formula achieved the greatest percentage of eyes within ±0.25 D of target range (91%), while Haigis-L, Shammas, Galilei, Potvin Hill, Barrett True K, IOL Master, PEARL-DGS, and OCT formulae performed similarly, achieving 45% of eyes within ±0.75D of target refraction.
Conclusion
This study demonstrates the accuracy of the lesser known 3C formula in IOL calculation, particularly for patients who have undergone both RK and LASIK. Well-known formulae, such as Haigis-L, Shammas, and Galilei, which are used by the American Society of Cataract and Refractive Surgery (ASCRS), are viable options, although 3C formulae should be considered in this patient population. Furthermore, larger studies can confirm the best IOL power formulas for post-RK and LASIK cataract patients.
... [20] . The Barrett True-K formula is an improved regression formula based on the Barrett Universal II formula, capable of correcting the K values of post-corneal refractive surgery patients and providing accurate IOL power predictions for cataract patients with long, normal, or short axial lengths [6,7,[21][22][23][24] . Thus, for this case, as a patient with an extremely long axial length and a history of ICL and PRK surgeries, the application of this formula is highly suitable. ...
Background One of the most common reasons for patients to have a second operation to remove the implantable collamer lens (ICL) is anterior subcapsular cataract (ASC), which is also one of the major problems following ICL implantation. Nonetheless, it is still unclear if patients with high myopia can benefit from contemporaneous ICL removal, cataract extraction and multifocal intraocular lens (MIOL) implantation in terms of their visual outcomes.
Case presentation A 39-year-old male highly myopic patient who underwent concurrent ICL removal, cataract extraction, and TECNIS Symfony ZXR00 IOL implantation in both eyes is reported in this case. Surgeons organize the surgery taking into account the patient's strong desire for freedom from spectacles, the needs for everyday vision, and the features of the chosen IOL. Enhanced biological measurement devices, such us Pentacam and IOL Master 700, were used to get accurate parameters. The IOL power was calculated using the Barrett True-K formula, thereby allowing a residual refraction of -0.50D to -0.75D to match patient’s demand. The surgeries were performed on the right and left eyes with a 2-week interval. A comprehensive evaluation of the patient's visual outcomes was conducted at the 3-month follow-up using manifest refraction, anterior segment OCT (Casia2), defocus curve, OPD-Scan III, and NEI-VFQ-14. The patient demonstrated excellent near and intermediate vision as well as overall visual quality, with high satisfaction.
Conclusion For patients with ASC requiring surgery after ICL implantation, and with a strong desire for spectacle independence and specific occupational demands, the use of TECNIS Symfony ZXR00 IOL, along with adjustments to the residual refractive power, may result in outstanding visual quality and patient satisfaction.
... It has long been established that intraocular lens (IOL) power calculation accuracy differs between average versus long or short eyes Hoffer, 1993;Kane & Melles, 2020;Lin et al., 2021;Röggla et al., 2021), between eyes with shallow versus deep anterior chamber depth (ACD) (Haigis et al., 2000;Hipólito-Fernandes et al., 2022;Olsen et al., 1992) and by the central corneal thickness measurements (Wei et al., 2022). Among the aforementioned anatomical features, modern IOL calculation formulas take into account various variables as accuracy predictors, including patient's post-refractive and/or corneal ectasia status (Abulafia et al., 2016; patient's gender (Hoffer & Savini, 2017;Li et al., 2022;Zhang et al., 2021) and lately age (Li et al., 2022). ...
Purpose
To assess the accuracy of intraocular lens (IOL) power calculation in different age groups using various IOL calculation formulas.
Methods
Data from 421 eyes of 421 patients ≥60 years old (ages: 60–69, n = 131; 70–74, n = 105; 75–84, n = 158 and ≥85, n = 27), who underwent uneventful cataract surgery with SN60WF IOL implantation at John A. Moran Eye Center, Salt Lake City, USA, were retrospectively obtained. The SD of the prediction error (PE), median and mean absolute PEs and the percentage of eyes within ±0.25, ±0.50, ±0.75 and ±1.00 D were calculated after constant optimizations for the following formulas: Barrett Universal II (BUII), Emmetropia Verifying Optical (EVO) 2.0, Haigis, Hoffer Q, Hoffer QST, Holladay 1, Kane, Radial Basis Function (RBF) 3.0 and SRK/T. Results were compared between the different age groups.
Results
Predictability rates within 0.25D were lower for the eldest age group compared with the other groups using the EVO 2.0 (33% vs. 37%–53%, p = 0.045), Kane (26% vs. 35%–50%, p = 0.034) and SRK/T (22% vs. 31%–49%, p = 0.002). Higher median absolute refractive errors for all formulas were observed in the oldest group [range: 0.39 D (Haigis, Hoffer QSR)–0.48 D (Kane)], followed by the youngest group [range: 0.30 D (RBF 3.0)–0.39 D (Holladay 1, SRK/T)] but did not reach statistical significance. No significant differences between the groups in the distribution parameter were seen.
Conclusion
Current IOL power calculation formulas may have variable accuracy for different age groups. This should be taken into account when planning cataract surgery to improve refractive outcomes.
... More recent studies have focused on comparing IWA to newer formulas tailored toward predicting IOL outcomes in post-LVC eyes, such as Barrett True K (BTK). Some have demonstrated IWA to be superior to BTK [7], but the difference is small and other studies suggest the results are similar between the two [8][9][10][11]. Although previous studies have evaluated other next generation formulas such as Haigis and AL-adjusted Holladay 1 compared to IWA in normal eyes [12,13], few have compared these additional formulas in the setting of post LVC eyes [14], and none have included Hill-Radial Basis Function Version 3.0 (Hill-RBF v3.0) in their analysis. ...
Purpose
To assess the accuracy of intraoperative wavefront aberrometry (IWA) versus modern intraocular lens formulas in post-myopic laser vision correction (LVC) patients undergoing cataract surgery with capsular tension ring placement.
Methods
This is a retrospective chart review conducted at an academic outpatient center. All post-myopic LVC eyes undergoing cataract surgery with IWA from a single surgeon from 05/2017 to 12/2019 were included. All patients received a capsular tension ring (CTR). Mean numerical error (MNE), median numerical error (MedNE), and percentages of prediction error within 0.50D, 0.75D, and 1.00D were calculated for the above formulas.
Results
Twenty-seven post-myopic LVC eyes from 18 patients were included. In post-myopic LVC, MNE with Optiwave Refractive Analysis (ORA), Barrett True K (BTK), Haigis, Haigis-L, Shammas, SRK/T, Hill-RBF v3.0, and W-K AL-adjusted Holladay 1 were + 0.224, − 0.094, + 0.193, − 0.231, − 0.372, + 1.013, + 0.860, and + 0.630 (F = 8.49, p < 0.001). MedNE were + 0.125, − 0.145, + 0.175, + 0.333, + 0.333, + 1.100, + 0.880, and + 0.765 (F = 7.89, p < 0.001), respectively. BTK provided improved accuracy in both MNE (p < 0.001) and MedNE (p = .033) when compared to ORA in pairwise analysis. If the ORA vs. BTK-suggested IOL power were routinely selected, 30% and 15% of eyes would have projected hyperopic outcomes, respectively (p = 0.09).
Conclusions
Our study suggests that in post-myopic LVC eyes undergoing cataract surgery with CTRs, BTK performed more accurately than ORA with regard to accuracy and yielded a lower percentage of eyes with hyperopic outcomes. Haigis, Haigis-L, and Shammas yielded similar results to ORA with regard to accuracy and percentage of eyes with hyperopic outcomes. On average, Shammas and Haigis-L suggested IOLs that would yield outcomes more myopic than expected when compared to BTK.
... In both postmyopic and posthyperopic patients, the BTK formula had the highest percentage of errors within ± 0.25 D (44.8% and 42.6%, respectively), and the average error was less than 0.5 D (0.41 D). Abulafia et al. 19 found that the BTK had significantly smaller prediction errors and a higher percentage of eyes within ± 0.50 D than the Shammas and Haigis-L formulas in postmyopic LASIK cases (88 postmyopic eyes). Notably, Savini et al. 20 found that when combined with measured posterior corneal power (PK, obtained with a Pentacam) in cases with available historical data, the BTK yielded the best results (lowest prediction error of 0.52 D and the highest percentage of eyes with a prediction error within ± 0.25 D [54%]). ...
As of 2021, over 2.8 million small-incision lenticule extraction (SMILE) procedures have been performed in China. However, knowledge regarding the selection of intraocular lens (IOL) power calculation formula for post-SMILE cataract patients remains limited. This study included 52 eyes of 26 myopic patients from northern China who underwent SMILE at Tianjin Eye Hospital from September 2022 to February 2023 to investigate the suitability of multiple IOL calculation formulas in post-SMILE patients using a theoretical surgical model. We compared the postoperative results obtained from three artificial intelligence (AI)-based formulas and six conventional formulas provided by the American Society of Cataract and Refractive Surgery (ASCRS). These formulas were applied to calculate IOL power using both total keratometry (TK) and keratometry (K) values, and the results were compared to the preoperative results obtained from the Barrett Universal II (BUII) formula for the SMILE patients. Among the evaluated formulas, the results obtained from the Emmetropia Verifying Optical 2.0 Formula with TK (EVO-TK) (0.40 ± 0.29 D, range 0–1.23 D), Barrett True K with K formula (BTK-K, 0.41 ± 0.26 D, range 0.01–1.19 D), and Masket with K formula (Masket-K, 0.44 ± 0.33 D, range 0.02–1.39 D) demonstrated the closest proximity to BUII. Notably, the highest proportion of prediction errors within 0.5 D was observed with the BTK-K (71.15%), EVO-TK (69.23%), and Masket-K (67.31%), with the BTK-K showing a significantly higher proportion than the Masket-K ( p < 0.001). Our research indicates that in post-SMILE patients, the EVO-TK, BTK-K, and Masket-K may yield more accurate calculation results. At their current stage in development, AI-based formulas do not demonstrate significant advantages over conventional formulas. However, the application of historical data can enhance the performance of these formulas.
... Ferguson and colleagues Table 5 The percentage of eyes with absolute refractive prediction errors falling within various ranges was analyzed for the formulas used in the SMILE group recently conducted a study involving postmyopic and post hyperopic eyes (FS-LASIK or PRK) and found that the BTKNH formula performed equivalently to a multiple formula approach on the ASCRS online calculator in both types of eyes [18]. Similarly, Abulafia and colleagues reached a consistent conclusion in their study involving 88 eyes (FS-LASIK or PRK) [25]. Another study by Lawless, which included 50 patients (72 eyes, FS-LASIK or PRK), not only found that the BTK formula performed better than other formulas but also discussed whether Total K or Sim K should be chosen in the formula [26]. ...
Background
As the two most prevalent refractive surgeries in China, there is a substantial number of patients who have undergone Femtosecond Laser-assisted In Situ Keratomileusis (FS-LASIK) and Small Incision Lenticule Extraction (SMILE) procedures. However, there is still limited knowledge regarding the selection of intraocular lens (IOL) power calculation formulas for these patients with a history of FS-LASIK or SMILE.
Methods
A total of 100 eyes from 50 postoperative refractive surgery patients were included in this prospective cohort study, with 25 individuals (50 eyes) having undergone FS-LASIK and 25 individuals (50 eyes) having undergone SMILE. We utilized a theoretical surgical model to simulate the IOL implantation process in postoperative FS-LASIK and SMILE patients. Subsequently, we performed comprehensive biological measurements both before and after the surgeries, encompassing demographic information, corneal biometric parameters, and axial length. Various formulas, including the Barrett Universal II (BUII) formula, as a baseline, were employed to calculate IOL power for the patients.
Results
The Barrett True K (BTK) formula, demonstrated an mean absolute error (AE) within 0.5 D for both FS-LASIK and SMILE groups (0.28 ± 0.25 D and 0.36 ± 0.24 D, respectively). Notably, the FS-LASIK group showed 82% of results differing by less than 0.25 D compared to preoperative BUII results. The Barrett True K No History (BTKNH) formula, which also incorporates measured posterior corneal curvature, performed similarly to BTK in both groups. Additionally, the Masket formula, relying on refractive changes based on empirical experience, displayed promising potential for IOL calculations in SMILE patients compared with BTK ( p = 0.411).
Conclusion
The study reveals the accuracy and stability of the BTK and BTKNH formulas for IOL power calculations in myopic FS-LASIK/SMILE patients. Moreover, the Masket formula shows encouraging results in SMILE patients. These findings contribute to enhancing the predictability and success of IOL power calculations in patients with a history of refractive surgery, providing valuable insights for clinical practice. Further research and larger sample sizes are warranted to validate and optimize the identified formulas for better patient outcomes.
... which incorporates different formulas for the calculation of IOL powers in eyes with prior RK and is shown to provide favorable results as reported by many studies. [10][11][12][13][14] Optical coherence tomography (OCT)-based IOL calculation formula and Barrett True-K formula are the most recent additions in the updated version 4.7, 2015 of the ASCRS calculator. In eyes with prior RK, though the existing formulas on the ASCRS calculator can predict IOL powers for emmetropia, further improvements in the methods of corneal power measurement and IOL power calculation are required for these eyes as reported by several studies. ...
Purpose
To evaluate the accuracy of intraocular lens (IOL) power prediction of the formulas available on the American Society of Cataract and Refractive Surgery (ASCRS) post-refractive calculator in eyes with prior radial keratotomy (RK) for myopia.
Methods
This retrospective study included 25 eyes of 18 patients whose status was post-RK for treatment of myopia, which had undergone cataract extraction with IOL implantation. Prediction error was calculated as the difference between implanted IOL power and predicted power by various formulae available on ASCRS post-refractive calculator. The formulas compared were Humphrey Atlas method, IOLMaster/Lenstar method, Barrett True-K no-history formula, ASCRS Average power, and ASCRS Maximum power on ASCRS post-refractive calculator.
Results
Median absolute errors were the least for Barrett True-K and ASCRS Maximum power, that is, 0.56 (0.25, 1.04) and 0.56 (0.25, 1.06) D, respectively, and that of Atlas method was 1.60 (0.85, 2.28) D. Median arithmetic errors were positive for Atlas, Barrett True-K, ASCRS Average (0.86 [−0.17, 1.61], 0.14 [−0.22 to 0.54], and 0.23 [−0.054, 0.76] D, respectively) and negative for IOLMaster/Lenstar method and ASCRS Maximum power (−0.02 [−0.46 to 0.38] and − 0.48 [−1.06 to − 0.22] D, respectively). Multiple comparison analysis of Friedman’s test revealed that Atlas formula was significantly different from IOLMaster/Lenstar, Barrett True-K, and ASCRS Maximum power; ASCRS Maximum power was significantly different from all others ( P < 0.00001).
Conclusion
In post-RK eyes, Barrett True-K no-history formula and ASCRS Maximum power given by the ASCRS calculator were more accurate than other available formulas, with ASCRS Maximum leading to more myopic outcomes when compared to others.
... Ferguson and colleagues recently conducted a study involving postmyopic and post hyperopic eyes (FS-LASIK or PRK) and found that the BTKNH formula performed equivalently to a multiple formula approach on the ASCRS online calculator in both types of eyes [30]. Similarly, Abula a and colleagues reached a consistent conclusion in their study involving 88 eyes (FS-LASIK or PRK) [31]. Another study by Lawless, which included 50 patients (72 eyes, FS-LASIK or PRK), not only found that the BTK formula performed better than other formulas but also discussed whether Total K or Sim K should be chosen in the formula [32]. ...
Background
As the two most prevalent refractive surgeries in China, there is a substantial number of patients who have undergone Femtosecond Laser-assisted In Situ Keratomileusis (FS-LASIK) and Small Incision Lenticule Extraction (SMILE) procedures. However, there is still limited knowledge regarding the selection of intraocular lens (IOL) power calculation formulas for these patients with a history of FS-LASIK or SMILE.
Methods
A total of 100 eyes from 50 postoperative refractive surgery patients were included in the study, with 25 individuals (50 eyes) having undergone FS-LASIK and 25 individuals (50 eyes) having undergone SMILE. By using a theoretical surgical model, we conducted extensive preoperative and postoperative measurements, including demographic data, corneal biometric parameters, and axial length. Various formulas, including the Barrett Universal II (BUII) formula, as a baseline, were employed to calculate IOL power for the patients.
Results
The Barrett True K (BTK) formula, demonstrated an mean absolute error (AE) within 0.5 D for both FS-LASIK and SMILE groups (0.28 ± 0.25 D and 0.36 ± 0.24 D, respectively). Notably, the FS-LASIK group showed 82% of results differing by less than 0.25 D compared to preoperative BUII results. The Barrett True K No History (BTKNH) formula, which also incorporates measured posterior corneal curvature, performed similarly to BTK in both groups. Additionally, the Masket formula, relying on refractive changes based on empirical experience, displayed promising potential for IOL calculations in SMILE patients compared with BTK (p = 0.411).
Conclusion
The study reveals the accuracy and stability of the BTK and BTKNH formulas for IOL power calculations in myopic FS-LASIK/SMILE patients. Moreover, the Masket formula shows encouraging results in SMILE patients. These findings contribute to enhancing the predictability and success of IOL power calculations in patients with a history of refractive surgery, providing valuable insights for clinical practice. Further research and larger sample sizes are warranted to validate and optimize the identified formulas for better patient outcomes.
... A multi-formula average method was utilized for lens power calculation, including three formulas using no previous data from the Hagis-L [10], Barrett True K no-history [11], Shammas no-history [12]. The target refraction was set to postoperative emmetropia. ...
PURPOSE. To evaluate the tolerance for refractive errors and visual outcomes of extended depth of focus intraocular lens (EDOF IOLs) in patients with previous corneal refractive surgery for myopia.
METHODS. Patients from Aier Eye Hospital of Wuhan University with previous myopia excimer laser. correction underwent cataract surgery and implan- tation of an EDOF IOL. The follow-up period was three months. The uncorrected distance, intermedi- ate, and near visual acuities (UDVA, UIVA, UNVA), corrected distance visual acuity (CDVA), spheri- cal equivalent (SE), defocus curve, optical quality, including modulation transfer functions (MTF) and Strehl ratio (SR), National Eye Institute Visual Func- tioning Questionnaire-14 for Chinese people (VF- 14-CN), spectacle independence, and dysphotopsia were assessed.
RESULTS. At the final visit, UDVA, CDVA, UIVA, and UNVA (LogMAR) were 0.06±0.09, 0.01±0.06, 0.11 ± 0.08, 0.20 ± 0.10, respectively. The mean spherical equivalent (SE) was − 0.57 ± 0.58D, sphere and cylinder were−0.24±0.60D,−0.70±0. 58D respectively. No statistical difference in UDVA between eyes with SE in±0.50 D and in±1.0 D (p > 0.05). Corneal astigmatism > 1.00D has no signif- icant effect on postoperative visual acuity (p>0.05). The defocus curve showed that visual acuity could reach 0.2 in the refractive range of + 0.50D ~ − 1.50D. SR and MTF values were all higher than before the surgery. In bilateral implantation patients, the VF- 14-CN questionnaire score and visual quality were quite excellent.
CONCLUSIONS. The EDOF IOL have a certain toler- ance for refractive errors and corneal astigmatism, and it’s recommended for patients with prior myopia excimer laser surgery to achieve satisfactory visual performance.
... Ferguson et al. reported that BTK outperformed other ASCRS formulas in both myopic and hyperopic post laser refractive surgery patients (96 post myopic eyes and 47 post hyperopic eyes)23 . Abula a et al. found that BTK had signi cantly smaller prediction errors and a higher percentage of eyes within ± 0.50 D than the Shammas and Haigis-L formulas in postmyopic LASIK cases (80 postmyopic eyes)24 . Notably, Savini et al. found that BTK yielded the best results when combined with measured posterior corneal power (PK, obtained with Pentacam) in cases with available historical data, while using PK without historical data led to larger errors (50 postmyopic eyes)25 . ...
As of 2021, over 2.8 million cases of small incision lenticule extraction (SMILE) procedures had been performed in China. However, there remains limited knowledge regarding the selection of intraocular lens (IOL) power calculation formulas for post-SMILE cataract patients. This study included 52 eyes of 26 myopic patients from northern China who underwent SMILE at Tianjin Eye Hospital from September 2022 to February 2023 and was designed to investigate the performance of multiple IOL calculation formulas in post-SMILE patients using a theoretical surgical model. We compared the postoperative results obtained from three artificial intelligence (AI)-based formulas and six conventional formulas provided by the American Society of Cataract and Refractive Surgery (ASCRS). These formulas were applied to calculate IOL power using both total keratometry (TK) and keratometry (K) values, and the results were compared to the preoperative results obtained from the Barrett Universal II (BUII) formula in SMILE cases. Among the evaluated formulas, the results obtained from Emmetropia Verifying Optical 2.0 Formula with TK (EVO-TK) (0.40 ± 0.29 D, range 0 to 1.23 D), Barrett True K with K (BTK-K, 0.41 ± 0.26 D, range 0.01 to 1.19 D), and Masket with K (Masket-K, 0.44 ± 0.33 D, range 0.02 to 1.39 D) demonstrated the closest proximity to BUII. Notably, the highest proportion of prediction errors within 0.5 D was observed with BTK-K (71.15%), EVO-TK (69.23%), and Masket-K (67.31%), with BTK-K showing a significantly higher proportion compared to Masket-K (p < 0.001). Our research indicates that in post-SMILE patients, EVO-TK, BTK-K, and Masket-K may yield more accurate calculation results. At the current stage, AI-based formulas do not demonstrate significant advantages over conventional formulas. However, the application of historical data can enhance the performance of these formulas.
... Among various parameters affecting cataract surgery outcome, the selected IOL power is a quantitative and traceable factor [8] . Numerous studies have emphasized that accurate measurement of ocular biometric indices and selection of the appropriate IOL power calculation formula are key factors in reducing residual refractive error after cataract surgery [8][9][10] . Erroneous axial length (AL) and corneal power measurements, errors in predicting the anterior chamber depth (ACD) after surgery or the IOL location, and fluctuation in pupil size have been suggested as the associated factors of a refractive surprise after cataract surgery among various studies [11][12] . ...
Aim:
To determine residual refractive error after cataract surgery in pseudophakic eyes and its relationship with age, sex, and axial length (AL).
Methods:
In this population-based cross-sectional study, the sampling was performed on individuals aged 60y and above in Tehran, Iran using a multi-stage stratified random cluster sampling method. Pseudophakic eyes with a best-corrected visual acuity of 20/32 or better were analyzed and their refractive results were reported.
Results:
The mean spherical equivalent (SE) refraction was -0.34±0.97 diopters (D) and the mean absolute SE was 0.72±0.74 D with a median of 0.5 D. Moreover, 32.68% (n=546, 95%CI: 30.27%-35.08%), 53.67% (n=900, 95%CI: 51.23%-56.1%), 68.99% (n=1157, 95%CI: 66.96%-71.02%), and 79.73% (n=1337, 95%CI: 77.69%-81.76%) of the eyes had a residual SE within ±0.25, ±0.50, ±0.75, and ±1.00 D of emmetropia, respectively. According to the multiple logistic regression model, increasing age was associated with a statistically significant decrease in predictability for all cut points. Moreover, the predictability based on all cut points was significantly lower in individuals with an AL longer than 24.5 mm than in those with an AL between 22 to 24.5 mm.
Conclusion:
Based on the results, the accuracy of intraocular lens (IOL) power calculation is lower for those who underwent cataract surgery during the last 5y in Tehran, Iran. Among the most important influential factors, the choice of IOL or it's power disproportionate to eye conditions and age can be mentioned.
Purpose: To evaluate the accuracy of modern intraocular lens (IOL) power calculation formulas in eyes with previous myopic laser vision correction (LVC), and to assess the impact of axial length (AL) on the formula performance.
Methods: A total of 108 eyes were included, with 52 eyes in the AL less than 28 mm group and 56 eyes in the AL 28 mm or greater group. Refractive prediction errors (RPEs) were compared among nine post-LVC formulas: Haigis-TK, Haigis-TKCMAL (incorporating Cooke-modified axial length [CMAL]), PEARL-DGS, Hoffer-QST TK, LISA TK, Barrett True-K TK, EVO TK, Haigis-L, and Shammas. Pearson correlation analysis was employed to evaluate the influence of AL and other biometric parameters on RPEs.
Results: In the AL less than 28 mm group, no significant differences were observed between all formulas (all adjusted P > .05). However, in the AL 28 mm or greater group, Haigis-TKCMAL demonstrated significantly lower root mean square absolute error (RMSAE) and mean absolute error (MAE) compared to the Hoffer-QST, Barrett True-K TK, Shammas, and Haigis-L (all adjusted P < .001). Similarly, the PEARL-DGS showed significantly lower RMSAE than the Barrett True-K TK, Shammas, and Haigis-L (both adjusted P < .001), and significantly lower MAE compared to the Barrett True-K TK and Haigis-L (both adjusted P < .001). The Haigis-TKCMAL had the highest percentage of eyes with RPEs within ±0.50 diopters (D) (73.21%), whereas the PEARL-DGS had the highest percentage of eyes with RPEs within ±1.00 D (94.64%). A significant negative correlation between AL and RPE was found in most formulas, leading to a myopic shift in eyes with extremely long AL.
Conclusions: The performance of current post-LVC formulas was comparable in eyes with AL less than 28 mm, whereas the Haigis-TKCMAL and PEARL-DGS demonstrated superior accuracy in eyes with AL 28 mm or greater. A notable myopic shift occurred in post-LVC eyes with extremely long AL, highlighting the need for careful formula selection in such cases.
This retrospective study compared postoperative prediction errors of recent formulas using standard- or total keratometry (K or TK) for intraocular lens (IOL) power calculation in post-myopic LASIK patients. It included 56 eyes of 56 patients who underwent uncomplicated cataract surgery, with at least 1-month follow-up at Keio University Hospital in Tokyo or Hayashi Eye Hospital in Yokohama, Japan. Prediction errors, absolute errors, and percentage of eyes with prediction errors within ± 0.25 D, ± 0.50 D, and ± 1.00 D were calculated using nine formulas: Barrett True-K, Barrett True-K TK, Haigis-L, Haigis TK, Pearl-DGS, Hoffer QST, Hoffer QST PK, EVO K, and EVO PK. Statistical comparisons utilized Friedman test, Conover’s all-pairs post-hoc, Cochran’s Q, and McNemar post-hoc testing. Root-Mean-Square Error (RMSE) was compared with heteroscedastic testing. Barrett True-K TK had the lowest median predicted refractive error (-0.01). EVO PK had the smallest median absolute error (0.20). EVO PK had the highest percentage of eyes within ± 0.25 D of the predicted value (58.9%), significantly better than Haigis-L (p = 0.047). EVO PK had the lowest mean RMSE value (0.499). The EVO PK formula yielded the most accurate IOL power calculation in post-myopic LASIK eyes, with TK/PK values enhancing accuracy.
Purpose
To evaluate the accuracy of current intraocular lens (IOL) formulas and identify factors influencing mean error in eyes undergoing Descemet membrane endothelial keratoplasty (DMEK) triple procedure, that is, DMEK combined with cataract extraction and IOL placement for concurrent Fuchs endothelial corneal dystrophy (FECD) and cataracts.
Design
Retrospective cohort study.
Subjects
90 eyes with FECD undergoing uncomplicated DMEK triple procedure at Wilmer Eye Institute.
Methods
We analysed tomographic features of oedema, including loss of regular isopachs, displacement of the thinnest point of the cornea and the presence of posterior surface depression, and assessed the correlation with the prediction error.
Main outcome measures
We compared the mean error (±SD) for the Barrett Universal II (BU2), Hoffer QST, Haigis-L (HL) and Barrett True K (BTK) formulas and the percentage of eyes within 0.25, 0.5 and 1 diopter (D) of error.
Results
All formulas resulted in a mean hyperopic error, with the HL having the lowest mean error of 0.24 D (±0.97 D) and BU2 having the highest ME of 0.94 D (±0.97 D). For each additional tomographic feature of corneal oedema in the BU2 and Hoffer QST formulas, the mean hyperopic error increased by 0.38 D. For the BTK and HL formulas, the mean error increased by 0.35 D (p<0.001).
Conclusion
The number of tomographic features of oedema can be useful in identifying eyes with higher errors in IOL calculation when performing the DMEK triple procedure for FECD.
Intraocular lens (IOL) power calculation is normally performed using theoretical Gaussian formulas. Paraxial calculation renders clinically acceptable outcomes in normal eyes with regular corneal shape and optics but leads to refractive error whenever the cornea is irregular in terms of anterior surface shape or anterior to posterior curvature proportions. The most prevalent conditions are keratoconus, keratoplasty, or corneas that have undergone refractive surgery, especially with old techniques. In this chapter, a more robust calculation methodology is proposed based on a three-dimensional model of the cornea constructed from tomographic data. Optical calculations are done by exact ray tracing, overcoming the limitations of the paraxial constraints and managing adequately the effect of higher-order aberrations. Image quality metrics that correlates with subjective vision will be used as a target to determine the best IOL sphere and cylinder power.
PURPOSE:
To describe the Shammas-Cooke formula, an updated no-history (NH) formula for IOL calculation in eyes with prior myopic laser vision correction (M-LVC), and to compare the results to the Shammas PL, Haigis-L and Barrett True-K NH formulas.
SETTING:
Bascom Palmer Eye Institute (BPEI), The Lennar Foundation Medical Center, University of Miami, Miami, Florida, USA; Dean A. McGee Eye Institute (DMEI), University of Oklahoma, Oklahoma City, Oklahoma, USA; and private practice, Lynwood, California, USA and St Joseph, Michigan, USA.
DESIGN:
Retrospective observational study.
METHODS:
We analyzed two large series of cataractous eyes with prior M-LVC. The training set (BPEI series of 330 eyes) was used to derive the new corneal power conversion equation to be used in the novel Shammas-Cooke formula, and the testing set (165 eyes of 165 patients in the DMEI series) to compare the updated formula to three other M-LVC NH formulas on the ASCRS calculator: Shammas PL, Haigis-L and Barrett True-K NH.
RESULTS:
Mean prediction error was 0.09±0.56, -0.44±0.61, -0.47±0.59 and -0.18±0.56 D, and the mean absolute error was 0.43, 0.60, 0.61 and 0.45 D for the Shammas-Cooke, Shammas PL, Haigis-L and Barrett True-K NH. The percentage of eyes within ± 0.50 D was 66.7% versus 47.9%, 48.5% and 65.5%, respectively.
CONCLUSION:
The Shammas-Cooke formula performed better than the Shammas PL and Haigis-L (P<0.001 for both) and as well as the Barrett True-K NH formula (P=0.923).
Purpose
To report a combined Descemet stripping automated endothelial keratoplasty (DSAEK) with cataract surgery in a case of Fuchs endothelial corneal dystrophy (FECD) and keratoconus after corneal crosslinking combined with photorefractive keratectomy.
Methods
We report a case of a 56-year-old woman with a history of subclinical keratoconus who underwent corneal crosslinking (CXL) plus 7 years ago. At presentation, the patient complained of blurry vision, which was more prominent in the morning over the past few years, and frequent changes of spectacle prescription ever since the initial treatment with CXL plus. Post-CXL plus corneal tomographies revealed progressive corneal flattening of 6.20 diopters (D) and 6.50 D in the right (OD) and left (OS) eye, respectively, in terms of mean keratometry values over a period of 7 years, which resulted in significant hyperopia. Corrected distance visual acuity (CDVA) at presentation was 20/50 in the OD and 20/200 in the OS. Slit-lamp examination revealed guttae (diagnosis of FECD) with associated posterior corneal edema and advanced nuclear sclerotic cataracts in both eyes. Combined DSAEK with cataract surgery was performed on the left eye.
Results
One year after the combined procedure, CDVA improved to 20/25, with the correction of (−0.25, −4.25 × 25). Slit-lamp examination revealed a clear cornea without evidence of corneal edema or scarring. Corneal tomography indicated discontinuation of the corneal flattening in the left eye while the fellow eye continued to flatten.
Conclusions
Combined DSAEK with cataract surgery provides an effective surgical option for patients with FECD after CXL plus procedures for keratoconus, offering fast visual rehabilitation and functional visual outcomes.
In this article, we reviewed recently published papers of intraocular lens (IOL) power calculation in special eyes. In short eyes, accurate estimation of effective lens position is critical, and the ZEISS artificial intelligence IOL calculator produces the best outcomes. In long eyes, accuracy has been improved with axial length (AL) adjusted formulas such as the Wang–Koch AL adjustment and newer IOL formulas. In keratoconic eyes, hyperopic refractive outcomes increase with steeper keratometric values, and accuracy is poor in eyes with keratometric values ≥50.0 D. Two keratoconus-specific formulas (Barrett True K for keratoconus and Kane keratoconus) have been introduced. In eyes undergoing combined Descemet membrane endothelial keratoplasty and cataract surgery, steeper corneas and corneas with a lower anterior/posterior ratio may have higher degrees of corneal flattening, and more myopia ranging from −0.75 to −1.0 D should be targeted. The postrefractive IOL power calculator from the American Society of Cataract and Refractive Surgery website has been a useful tool for postrefractive IOL power calculation. Recently, newer IOL formulas incorporating both anterior and posterior corneal measurements were introduced for eyes with previous corneal refractive surgery: Barrett True-K TK, Pearl-DGS, EVO 2.0, and Hoffer QST. It is recommended to obtain IOL calculations using as many formulas as possible and select the IOL power based on the consensus of multiple methods, with more weight given to the newer IOL power calculation formulas.
Purpose
This study aimed to evaluate the visual and refractive outcomes in eyes with a history of laser corneal refractive surgery implanted with the second-generation light-adjustable lens (LAL).
Setting
Private Practice, Sioux Falls, South Dakota, US.
Design
Retrospective, consecutive case series.
Methods
Eyes with a history of prior corneal refractive surgery that underwent cataract surgery with implantation of the LAL and were targeted for plano were included. Data on the type and number of prior refractive surgeries were collected, in addition to the timing and number of postoperative adjustments. The primary outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and the percentage (%) of eyes within ±0.25 diopter (D), ±0.50D, and ±1.00 D of their refractive target.
Results
76 eyes from 70 patients were included. A total of 45 eyes with a history of one prior refractive surgery and 31 eyes with a history of ≥2 refractive surgeries were included. 74% (n=56) of all eyes achieved UDVA of 20/20 or better, 88% (n=67) achieved 20/25 UDVA or better and 93% (n=71) were correctable to 20/20 or better postoperatively. For refractive outcomes, 66% of eyes (n=50) were within ±0.25 D and 86% (n=65) were within ±0.50 D of refractive target.
Conclusions
Patients with a history of laser corneal refractive surgery achieved favorable visual and refractive outcomes with the LAL. This intraocular lens (IOL), which affords postoperative adjustability, is a promising option for patients with a history of corneal refractive surgery who maintain high expectations for functional uncorrected acuity following cataract surgery.
Purpose
To assess the performance of the Camellin-Calossi formula in eyes with prior myopic laser vision correction.
Methods
This was a retrospective case series. Patients included had a history of uncomplicated myopic laser vision correction and cataract surgery. The primary outcome measures were cumulative distribution of absolute refractive prediction error, absolute refractive prediction error, and refractive prediction error. These parameters were estimated post-hoc using the Camellin-Calossi, Shammas, Haigis-L, Barrett True-K with or without history, Masket, and Modified Masket formulas and their averages starting from biometric data, clinical records, postoperative refraction, and intraocular lens power implanted.
Results
Seventy-seven eyes from 77 patients were included. The Camellin-Calossi, Shammas, Haigis-L, Barrett True-K No History, Masket, Modified Masket, and Barrett True-K formulas showed a median absolute refractive error (interquartile range) of 0.25 (0.53), 0.51 (0.56), 0.44 (0.65), 0.45 (0.59), 0.40 (0.61), 0.60 (0.70), and 0.55 (0.76), respectively. The proportion of eyes with an absolute refractive error of ±0.25, 0.50, 0.75, 1.00, 1.50, and 2.00 diopters (D) for the Camellin-Calossi formula was 54.5%, 72.7%, 85.7%, 92.2%, 98.7%, and 100%, respectively. The cumulative distribution of the Camellin-Calossi formula showed the best qualitative performances when compared to the others. A statistically significant difference was identified with all of the others except the Haigis-L using a threshold of 0.25, with the Shammas, Modified Masket, and Barrett True-K at a threshold of 0.50 D and the Barrett True-K and Modified Masket at a threshold of 1.00 D.
Conclusions
The Camellin-Calossi formula is a valid option for intraocular lens power calculation in eyes with prior myopic laser vision correction.
[ J Refract Surg . 2024;40(3):e156–e163.]
Purpose of review
There is an ever-growing body of research regarding intraocular lens (IOL) power calculations following photorefractive keratectomy (PRK), laser-assisted in-situ keratomileusis (LASIK), and small-incision lenticule extraction (SMILE). This review intends to summarize recent data and offer updated recommendations.
Recent findings
Postmyopic LASIK/PRK eyes have the best refractive outcomes when multiple methods are averaged, or when Barrett True-K is used. Posthyperopic LASIK/PRK eyes also seem to do best when Barrett True-K is used, but with more variable results. With both aforementioned methods, using measured total corneal power incrementally improves results. For post-SMILE eyes, the first nontheoretical data favors raytracing.
Summary
Refractive outcomes after cataract surgery in eyes with prior laser refractive surgery are less accurate and more variable compared to virgin eyes. Surgeons may simplify their approach to IOL power calculations in postmyopic and posthyperopic LASIK/PRK by using Barrett True-K, and employing measured total corneal power when available. For post-SMILE eyes, ray tracing seems to work well, but lack of accessibility may hamper its adoption.
A growing number of patients with prior refractive surgery are now presenting for cataract surgery. Surgeons face a number of unique challenges in a patient population that tends to be highly motivated to retain or regain functional uncorrected acuity postoperatively. Primary challenges include recognition of the specific type of prior surgery, use of appropriate intraocular lens (IOL) power calculation formulas, matching IOL style with spherical aberration profile, the recognition of corneal imaging patterns that are and are not compatible with toric and/or presbyopia-correcting lens implantation, and surgical technique modifications, which are particularly relevant in eyes with prior radial keratotomy or phakic IOL implantation. Despite advancements in IOL power formulae, corneal imaging, and IOL options that have improved our ability to achieve targeted postoperative refractive outcomes, refractive outcome accuracy remains inferior to eyes that undergo cataract surgery without a history of corneal refractive surgery. Thus, preoperative evaluation of patients who will and will not be candidates for postoperative refractive surgical enhancements is also paramount. We provide an overview of the specific challenges in this population and offer evidence-based strategies and considerations for optimizing surgical outcomes.
The calculation of intraocular lens (IOL) power in eyes with prior corneal refractive surgery has remarkably improved over the last decade and is now approaching the accuracy of unoperated eyes, with about 70% of eyes showing a prediction error (PE) within ±0.50 diopters (D) [1-8]. These results can be obtained using a combination of the latest generation technologies and the best formulae.KeywordsRefractive surgeryIol power calculation
To develop a novel algorithm based on ray tracing, simulated visual performance and through-focus optimization for an accurate intraocular lens (IOL) power calculation. Custom-developed algorithms for ray tracing optimization (RTO) were used to combine the natural corneal higher-order aberrations (HOAs) with multiple sphero-cylindrical corrections in 210 higher order statistical eye models for developing keratoconus. The magnitude of defocus and astigmatism producing the maximum Visual Strehl was considered as the optimal sphero-cylindrical target for IOL power calculation. Corneal astigmatism and the RMS HOAs ranged from − 0.64 ± 0.35D and 0.10 ± 0.04 μm (0-months) to − 3.15 ± 1.38D and 0.82 ± 0.47 μm (120-months). Defocus and astigmatism target was close to neutral for eyes with low amount of HOAs (0 and 12-months), where 91.66% of eyes agreed within ± 0.50D in IOL power calculation (RTO vs. SRK/T). However, corneas with higher amounts of HOAs presented greater visual improvement with an optimized target. In these eyes (24- to 120-months), only 18.05% of eyes agreed within ± 0.50D (RTO vs. SRK/T). The power difference exceeded 3D in 42.2% while the cylinder required adjustments larger than 3D in 18.4% of the cases. Certain amounts of lower and HOAs may interact favourably to improve visual performance, shifting therefore the refractive target for IOL power calculation.
【PURPOSE】The usefulness of Total Keratometry (TK) was evaluated by comparing the IOL power calculation formula for laser in situ keratomileusis (LASIK) using the Total Keratometry and the predicted refraction error by the conventional formula for the post-LASIK eyes.
【SUBJECTS AND METHODS】The subjects were 18 patients (mean age, 60.4±9.7 years) who underwent cataract surgery after myopic LASIK surgery. The mean±standard deviation (SD) of axial length, corneal anterior refractive power (K value), and TK value were 26.9±1.5mm, 39.7±1.8D, 39.2±2.0D, respectively. Barrett TK True-K (B-TK), EVO TK (E-TK), Haigis TK (H-TK), Barrett True-K (B), EVO (E), Haigis-L (H), Shammas-PL (S), and Camellin-Calossi (C) were used for comparison expressions. We compared the average absolute value (MAE)± SD of the predicted refraction error and the percentage within±0.5D.
【RESULTS】MAE±SD and the ratio within±0.5D was for B-TK formula: 0.18±0.16D (96%), E-TK formula: 0.20±0.16D (93%), H-TK formula: 0.46±0.39D (52%), B formula: 0.18±0.35D (85%), E formula: 0.21±0.32D (89%), H formula: 0.35±0.25D (78%), S formula: 0.29±0.27D (78%), and C formula: 0.37±0.33D (56%).
【CONCLUSION】The usefulness of the B-TK and E-TK formulas using TK values are useful because they have similar or smaller prediction refraction errors than the other equations.
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.