Article

Comparing surgically induced astigmatism calculated by means of simulated keratometry versus total corneal refractive power

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Abstract

Purpose: To evaluate surgically induced astigmatism as computed by means of either simulated keratometry (KSIM) or total corneal refractive power (TCRP) after temporal incisions. Methods: Prospective observational study including 36 right eyes undergoing cataract surgery. Astigmatism was measured preoperatively during the 3-month follow-up period using Pentacam. Surgically induced astigmatism was computed considering anterior corneal surface astigmatism at 3 mm with KSIM and considering both corneal surfaces with TCRP from 1 to 8 mm (TCRP3 for 3 mm). The eyes under study were divided into two balanced groups: LOW with KSIM astigmatism <0.90 D and HIGH with KSIM astigmatism ≥0.90 D. Resulting surgically induced astigmatism values were compared across groups and measuring techniques by means of flattening, steepening, and torque analysis. Results: Mean surgically induced astigmatism was higher in the HIGH group (0.31 D @ 102°) than in the LOW group (0.04 D @ 16°). The temporal incision resulted in a steepening in the HIGH group of 0.15 D @ 90°, as estimated with KSIM, versus 0.28 D @ 90° with TCRP3, but no significant differences were found for the steepening in the LOW group or for the torque in either group. Differences between KSIM- and TCRP3-based surgically induced astigmatism values were negligible in LOW group. Conclusion: Surgically induced astigmatism was considerably higher in the high-astigmatism group and its value was underestimated with the KSIM approach. Eyes having low astigmatism should not be included for computing the surgically induced astigmatism because steepening would be underestimated.

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... Right eyes of 91 men and 113 women of 66 ± 9 years old were included in the first stage. The arithmetic median [interquartile range] of preoperative corneal astigmatism was 1. 22 preoperative anterior corneal astigmatism in the femtosecond eyes. An underestimation of SIA Cornea in ATR and overestimation in WTR cases, especially in femtosecond cases, was obtained for the C-model. ...
... In this regard, some authors report an underestimation of SIA Cornea or a flattening effect when only the anterior corneal surface was considered. 22,23 However, the effect on PE of combining old approaches for SIA Cornea calculation, considering the anterior corneal surface, with PCA estimation has not been previously assessed to this date. ...
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... In our study, considering the magnitude of the low non-significant prediction errors in Phaco (0.07@127 • ) and Femto (0.07@19 • ) after the application of the AK formula with vector addition to the previously reported anterior corneal SIA of 0.14 D@65 • and 0.24 D@92 • , respectively, it would have resulted in an increase of the PE to 0.11@80 • and 0.19@86 • , respectively. The combination of SIA derived from total cornea and these algorithms should be also evaluated in future studies because latest research suggests that corneal SIA differs between the derived from anterior cornea and total cornea [27,28]. Kohnen et al. [29] reported differences in the percentage of eyes with anterior corneal SIA < 0.25 D in WTR and ATR cases but these differences were completely reduced when total cornea was considered suggesting that these incisions can be considered as neutral due to the minimal induced astigmatism. ...
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Modern cataract and refractive surgery aims not only to improve vision but to provide a good unaided visual acuity. Correcting astigmatic errors and control of surgically induced astigmatism are now an integral part of such operative procedures. Technological innovations and surgical developments in recent times have provided new methods for correction of astigmatism. However, evaluating the outcome of surgery for astigmatism presents particular difficulties, especially with the statistical comparison of different treatment groups. In this review we will discuss the nature of astigmatism and its various refractive effects and how this relates to cataract and refractive surgical outcomes. The use and limitations of vectors and other methods for the analysis of change in astigmatism after surgery will be discussed along with appropriate statistical methods and suggestions for data presentation. Astigmatism occurs when toricity of any of the refractive surfaces of the optical system produces two principal foci delimiting an area of intermediate focus called the conoid of Sturm. Thomas Young in 1801 was the first to describe ocular astigmatism, discovering that his own astigmatism was predominantly lenticular.1 However, it was some years later before Airy (1827) corrected astigmatism with a cylindrical lens.2 Corneal astigmatism was characterised by Knapp and also Donders in 1862 after the invention of the ophthalmometer by Helmholtz.34 In the same year Donders5 also described the astigmatism due to cataract surgery and soon after Snellen (1869) suggested that placing the incision on the steep axis would reduce the corneal astigmatism.6 Surgery to specifically treat astigmatism was suggested by Bates7 who described corneal wedge resection in 1894, but it was the work of Lans8 that provided most of the early theoretical basis for refractive corneal surgery. Little further work was published until that of Sato in the 1940s and 1950s. …
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Although there are inherent differences between corneal and IOL-based refractive surgery procedures, the aim of the procedure is the same in each case, so it makes sense that the 9 standard graphs be applied unaltered to corneal laser refractive surgery, phakic IOL implantation, and RLE. Cataract surgery is a different scenario that warrants a simplified version of the standard graphs. By considering these issues, we hope to standardize the quality of reporting for lens-based procedures from its current level and strive to encourage authors to go beyond these basic graphs to match the standard of studies reporting outcomes of corneal refractive surgery that now have good adherence to the standard graphs. Only by homogenizing the reporting of outcomes as a first step can we hope to glean comparative information among published studies.
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Purpose: To investigate the value of posterior keratometry in the assessment of surgically induced astigmatic change (AC) in cataract surgery, with particular emphasis on the influence of test-retest variability. Methods: Seventy-seven eyes of 77 cataract patients scheduled for routine cataract surgery were enrolled. All patients received a 2.2-mm self-sealing scleral incision (n = 24), single-plane clear corneal incision (SPCCI; n = 29) or biplanar clear corneal incision (BPCCI; n = 24). Measurements of anterior and posterior corneal astigmatism were performed with a rotating Scheimpflug camera (Pentacam HR) preoperatively and postoperatively. Two repeated readings were taken preoperatively to assess the role of the test-retest effect. Astigmatic change (AC) was analysed according to the polar value method. Results: On the anterior corneal surface, SPCCIs and BPCCIs caused a statistically significant mean flattening of the incisional meridian of 0.37 and 0.27 dioptres (D), respectively. Scleral incisions on average did not cause AC, although steepening, flattening or torque beyond the test-retest effect was observed in individual cases. On the posterior surface, mean power changes in the incisional meridian were below 0.1 D for all incisions, and these changes were of the same order of magnitude as the test-retest effect. Conclusion: Surgically induced AC of the posterior corneal surface after cataract surgery is of negligible clinical relevance. Moreover, it is of the same order of magnitude as the test-retest variability of the measurement device and therefore cannot (yet) be reliably assessed.
Article
To identify factors associated with surgically induced astigmatism (SIA) following phacoemulsification. Six hundred five eyes underwent phacoemulsification with a 2.2-mm (the 2.2-mm group, n = 248) or 2.75-mm (the 2.75-mm group, n = 357) superior limbal incision. Preoperative axial length, anterior chamber depth, corneal curvature, and intra-ocular pressure were measured. Corneal curvature and intraocular pressure were measured at 1 day, 1 week, and 1, 2, and 3 months postoperatively. SIA, corneal flattening, and torque were calculated using the Alpins method. The effect of preoperative corneal astigmatism meridian on SIA was also examined. Differences in SIA between the 2.2- and 2.75-mm groups were explored, and correlations between SIA and preoperative corneal astigmatism, anterior chamber depth, axial length, age, and intraocular pressure were analyzed. SIA, corneal flattening, and torque were smaller in the 2.2-mm group than in the 2.75-mm group at 1 week (P = .003, .006, and .014, respectively), but not statistically different thereafter. Higher preoperative corneal astigmatism, older age, and shallower anterior chamber depth were associated with greater SIA in both groups. The effect of astigmatism meridian on SIA was more noticeable in the 2.75-mm group. Shorter axial length and lower intraocular pressures were associated with greater SIA in the 2.75-mm group but not in the 2.2-mm group. Reducing limbal incision width and considering patient age, the meridian and magnitude of corneal astigmatism, anterior chamber depth, axial length, and intraocular pressure, and adjusting the flattening component of SIA input for toric intraocular lens power calculation could potentially improve the astigmatism control in refractive lens surgery. [J Refract Surg. 2015;31(2):82-88.]. Copyright 2015, SLACK Incorporated.
Article
• Objective. —No previous study documents improvement in visual acuity and subjective visual function associated with cataract surgery in the first eye, second eye, and both eyes. Measurement of subjective aspects of visual function and quality of life provides information that cannot be obtained with simple measurement of Snellen visual acuity.Methods. —From 76 ophthalmology practices in three cities, patients undergoing cataract extraction with intraocular lens implantation (n=613) and comparison patients (n=408) were enrolled in a prospective study. Questionnaires elicited visual function information before and after surgery, and visual acuity was obtained from the ophthalmologic record.Results. —Among patients with cataract and no other eye disease, baseline subjective visual function before surgery in the second eye was better than that before surgery in the first eye. Improvement in subjective visual function was approximately equal postoperatively in first and second eyes. Improvement in subjective function in both eyes postoperatively was significantly greater than that after surgery in the first eye or second eye alone. No statistically significant difference across surgical groups in the proportion of patients demonstrating improvement in visual acuity was observed.Conclusion. —Patients who underwent surgery in both eyes reported greater improvement in subjective visual function than did those who underwent surgery in one eye. Thus, there seems to be a benefit associated with restoring binocular vision in this population. These findings support the policy recommendation that cataract surgery in both eyes remains the appropriate treatment for patients with bilateral, cataract-induced visual impairment.
Article
To evaluate the impact of posterior corneal astigmatism on outcomes with toric intraocular lenses (IOLs). Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Case series. Corneal astigmatism was measured using 5 devices before and 3 weeks after cataract surgery. Toric IOL alignment was recorded at surgery and at the slitlamp 3 weeks postoperatively. The actual corneal astigmatism was calculated based on refractive astigmatism 3 weeks postoperatively and the effective toric power calculated with the Holladay 2 formula. The prediction error was calculated as the difference between the astigmatism measured by each device and the actual corneal astigmatism. Vector analysis was used in all calculations. With the IOLMaster, Lenstar, Atlas, manual keratometer, and Galilei (combined Placido-dual Scheimpflug analyzer), the mean prediction errors (D) were, respectively, 0.59 @ 89.7, 0.48 @ 91.2, 0.51 @ 78.7, 0.62 @ 97.2, and 0.57 @ 93.9 for with-the-rule (WTR) astigmatism (60 to 120 degrees), and 0.17 @ 86.2, 0.23 @ 77.7, 0.23 @ 91.4, 0.41 @ 58.4, and 0.12 @ 7.3 for against-the-rule (ATR) astigmatism (0 to 30 degrees and 150 to 180 degrees). In the WTR eyes, there were significant WTR prediction errors (0.5 to 0.6 diopters [D]) by all devices. In ATR eyes, WTR prediction errors were 0.2 to 0.3 D by all devices except the Placido-dual Scheimpflug analyzer (all P<.05 with Bonferroni correction). Corneal astigmatism was overestimated in WTR by all devices and underestimated in ATR by all except the Placido-dual Scheimpflug analyzer. A new toric IOL nomogram is proposed. Drs. Koch, Weikert, and Wang received research support from Ziemer USA, Inc. Dr. Koch has a financial interest with Alcon Laboratories, Inc., Abbott Medical Optics, Inc., Optimedica Corp., and Ziemer USA, Inc. No other author has a financial or proprietary interest in any material or method mentioned.
Article
A problem in cataract surgery consists in the preoperative identification of the appropriate intraocular lens (IOL) power. Different calculation approaches have been developed for this purpose; raytracing methods represent one of the most exact but also mathematically more challenging methods. This article gives a systematic overview of the different raytracing calculations available and described in the literature and compares their results. It has been shown that raytracing includes physical measurements and IOL manufacturing data but no approximations. The prediction error is close to zero and an essential advantage is the applicability to different conditions without the need of modifications. Compared to the classical formulae the raytracing methods are more precise overall, but due to the various data and property situations they are hardly comparable yet. The raytracing calculations represent a good alternative to the 3rd generation formulae. They minimize refractive errors, are wider applicable and provide better results overall, particularly in eyes with preconditions. Georg Thieme Verlag KG Stuttgart · New York.
Article
Purpose: To assess the accuracy of corneal power measurements provided by a Scheimpflug camera (Pentacam HR) for intraocular lens (IOL) power calculation in unoperated eyes and compare the results with those of simulated keratometry (SimK) performed with a Placido-disk corneal topographer (Keratron). Setting: Private practice. Design: Evaluation of diagnostic test. Methods: Eight Scheimpflug camera corneal power measurements were analyzed: (1) average K, (2) true net power calculated using the Gaussian optics formula, (3) total corneal refractive power at 2.0 mm calculated by ray tracing on a ring and (4) as the average of the zone inside the ring, (5) total corneal refractive power at 3.0 mm on a ring and (6) as the average of the zone inside the ring, (7) the equivalent K reading at 3.0 mm and (8) at 4.5 mm. The IOL power was calculated using the Hoffer Q, Holladay 1, and SRK/T formulas. Results: No statistically significant differences were observed between any corneal power measurements, including simulated K, in 41 consecutive patients. The latter showed slightly lower mean absolute errors with all 3 formulas (range 0.26 to 0.27 diopter [D]). The Scheimpflug camera gave the lowest median absolute errors with all formulas; that is, the 3.0 mm equivalent K reading with the Hoffer Q formula (0.18 D) and Holladay 1 formula (0.17 D) and the 2.0 mm total corneal refractive power ring with the SRK/T formula (0.18 D). Conclusion: Corneal power measurements provided by the Scheimpflug camera and Placido disk corneal topographer displayed comparable accuracy in IOL power calculation.
Article
Purpose: To determine the contribution of posterior corneal astigmatism to total corneal astigmatism and the error in estimating total corneal astigmatism from anterior corneal measurements only using a dual-Scheimpflug analyzer. Setting: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Design: Case series. Methods: Total corneal astigmatism was calculated using ray tracing, corneal astigmatism from simulated keratometry, anterior corneal astigmatism, and posterior corneal astigmatism, and the changes with age were analyzed. Vector analysis was used to assess the error produced by estimating total corneal astigmatism from anterior corneal measurements only. Results: The study analyzed 715 corneas of 435 consecutive patients. The mean magnitude of posterior corneal astigmatism was -0.30 diopter (D). The steep corneal meridian was aligned vertically (60 to 120 degrees) in 51.9% of eyes for the anterior surface and in 86.6% for the posterior surface. With increasing age, the steep anterior corneal meridian tended to change from vertical to horizontal, while the steep posterior corneal meridian did not change. The magnitudes of anterior and posterior corneal astigmatism were correlated when the steeper anterior meridian was aligned vertically but not when it was aligned horizontally. Anterior corneal measurements underestimated total corneal astigmatism by 0.22 @ 180 and exceeded 0.50 D in 5% of eyes. Conclusions: Ignoring posterior corneal astigmatism may yield incorrect estimation of total corneal astigmatism. Selecting toric intraocular lenses based on anterior corneal measurements could lead to overcorrection in eyes that have with-the-rule astigmatism and undercorrection in eyes that have against-the-rule astigmatism. Financial disclosure: The authors received research support from Ziemer Group. In addition, Dr. Koch has a financial interest with Alcon Laboratories, Inc., Abbott Medical Optics, Inc., Calhoun Vision, Inc., NuLens, and Optimedica Corp.
Article
To evaluate the visual and refractive outcomes after toric intraocular lens (IOL) implantation in patients with high amounts of corneal astigmatism. University Eye Clinic, Maastricht, The Netherlands; Oftalvist Centro Integral Ocular and Fundación Oftalmológica del Mediterráneo, Valencia, Spain. Cohort study. This study comprised eyes with cataract and more than 2.25 diopters (D) of corneal astigmatism who had toric Acrysof SN60T6, SN60T7, SN60T8, or SN60T9 IOL implantation. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, visual potential index (ratio of postoperative UDVA to postoperative CDVA), residual refractive cylinder, IOL misalignment, and surgically induced astigmatism (SIA) were evaluated. The mean follow-up in this study of 67 eyes (45 patients) was 6.3 months. Postoperatively, the mean UDVA was 0.61 ± 0.26 (SD) and the mean CDVA, 0.81 ± 0.21. The UDVA of 20/40 was better in 83% of eyes and 20/30 or better in 50% of eyes. The mean visual potential index was 0.78. The residual refractive cylinder was less than 0.75 D in 62% of eyes and less than 1.00 D in 81% of eyes. The mean IOL misalignment was 3.2 ± 2.8 degrees. The mean SIA was -0.40 ± 0.60 D with a superior incision and -0.19 ± 0.78 D with a temporal incision (P=.034). Implantation of the toric IOL during cataract surgery was effective and safe in correcting high amounts of corneal astigmatism.
Article
To determine the accuracy of the keratometric index of 1.3315 based on the Gullstrand model eye in predicting the power of the posterior cornea, Gullstrand's model was compared to a calculated keratometric index derived from actual measurements of the cornea. Eye Institute, Tan Tock Seng Hospital, Singapore. One eye of 2429 subjects with a mean spherical equivalent of -5.32 diopters (D) +/- 2.88 (SD) was measured with the Orbscan II (Bausch & Lomb). The following variables were analyzed: anterior radius of curvature (r(anterior)), posterior radius of curvature (r(posterior)), radius of keratometry (r(simK)), and central pachymetry. The r(anterior), r(posterior), and r(simK) were normally distributed, with a mean of 7.87 +/- 0.25 mm (95% confidence interval [CI], 7.38-8.36), 6.46 +/- 0.26 mm (95% CI, 5.95-6.97), and 7.71 +/- 0.27 mm (95% CI, 7.18-8.24), respectively. The mean ratio between the anterior corneal curvature and posterior corneal curvature was 1.22 +/- 0.03 (95% CI, 1.16-1.28). Based on the measurements of each eye, the mean calculated keratometric index, N(calc), was 1.3273 +/- 0.0013 (95% CI, 1.3248-1.3298). Using N(calc), the posterior corneal power was predicted to within +/-0.50 D of the actual posterior power in 98.3% of eyes. The mean absolute error between the actual and calculated posterior power was 0.157 +/- 0.123 D using N(calc) and 0.326 +/- 0.133 D using the Gullstrand model. Modifying the keratometric index increased the accuracy of predicting the posterior corneal power.
Article
To analyze the symptoms, etiology, and treatment of patient dissatisfaction after multifocal intraocular lens (IOL) implantation. Department of Ophthalmology, Maastricht University Medical Center, The Netherlands. Case series. In this retrospective chart review, the main outcome measures were type of complaints, uncorrected and corrected distance visual acuities, uncorrected and distance-corrected near visual acuities, refractive state, pupil diameter and wavefront aberrometry measurements, and type of treatment. Seventy-six eyes of 49 patients were included. Blurred vision (with or without photic phenomenon) was reported in 72 eyes (94.7%) and photic phenomena (with or without blurred vision) in 29 eyes (38.2%). Both symptoms were present in 25 eyes (32.9%). Residual ametropia and astigmatism, posterior capsule opacification, and a large pupil were the 3 most significant etiologies. Sixty-four eyes (84.2%) were amenable to therapy, with refractive surgery, spectacles, and laser capsulotomy the most frequent treatment modalities. Intraocular lens exchange was performed in 3 cases (4.0%). The cause of dissatisfaction after implantation of a multifocal IOL can be identified and effective treatment measures taken in most cases.
Article
To evaluate with the use of corneal topographic data the differences between total corneal power calculated using ray tracing (TCP) and the Gaussian formula (GEP) in normal eyes, eyes that previously underwent laser in situ keratomileusis/photorefractive keratectomy (LASIK/PRK), and theoretical models. TCP and GEP using mean instantaneous curvature were calculated over the central 4-mm zone in 94 normal eyes, 61 myopic-LASIK/PRK eyes, and 9 hyperopic-LASIK/PRK eyes. A corneal model was constructed to assess the incident angles at the posterior corneal surface for both refracted rays and parallel rays. Corneal models with varying parameters were also constructed to investigate the differences between mean TCP and GEP (4-mm zone), and an optical design software validation was performed. The TCP values tended to be less than GEP in normal and myopic-LASIK/PRK eyes, with the opposite relationship in some hyperopic-LASIK/PRK eyes having the highest anterior surface curvature. The difference between TCP and GEP was a function of anterior surface instantaneous radii of curvature and posterior/anterior ratio in postrefractive surgery eyes but not in normal eyes. In model corneas, posterior incident angles with parallel rays were greater than those with refracted rays, producing an overestimation of negative effective posterior corneal power; differences in magnitude between TCP and GEP increased with decreasing ratio of posterior/anterior radii of curvature, consistent with clinical results. In eyes after refractive surgery, calculating posterior corneal power using the Gaussian formula and its paraxial assumptions introduces errors in the calculation of total corneal power. This may generate errors in intraocular lens power calculation when using the Gaussian formula after refractive surgery.
Article
To evaluate the difference between 2.2-mm incision micro-coaxial phacoemulsification and traditional 3.0-mm coaxial phacoemulsification with respect to surgically induced astigmatism after temporally oriented clear corneal incision cataract surgery. This prospective, randomized, intra-patient controlled study comprised 22 patients who underwent clear corneal cataract surgery in both eyes. One eye received 2.2-mm incision micro-coaxial phacoemulsification with intraocular lens (IOL) implantation and the fellow eye received traditional 3.0-mm coaxial incision phacoemulsification with IOL implantation. The 2.2-mm incisions were created with a diamond keratome after a 200-microm groove was constructed in clear cornea at the temporal limbus. The 3.0-mm incisions were created without a pre-cut groove, using a metal keratome. All cases were uncomplicated. Pre- and postoperative keratometric astigmatism at 6 weeks was measured using a hand held Nikon Retinomax K-plus 2 Autorefractor. Three methods were used to analyze the surgically induced astigmatism (SIA) data: 1) algebraic analysis of the magnitude of keratometric astigmatism induced by the surgery, 2) magnitude of SIA by vector analysis, and 3) aggregate analysis of astigmatism using vector analysis. The mean change in the magnitude of keratometric astigmatism was 0.10+/-0.08 diopters (D) with the 2.2-mm micro-coaxial incisions and 0.32+/-0.20 D with the 3.0-mm traditional incisions (P=.0002). Usingvector analysis, the mean magnitude of SIA was 0.35+/-0.21 D with the 2.2-mm incisions and 0.67+/-0.48 D (P=.006) with the 3.0-mm incisions. Surgically induced astigmatism with 2.2-mm micro-coaxial incisions and traditional 3.0-mm clear corneal incisions with intra-patient control resulted in statistically and clinically significant reduction in surgically induced astigmatism with the smaller incision size.
Article
To evaluate the accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement. Prospective, observational study. The right eyes of 493 subjects were measured with a rotating Scheimpflug camera (Pentacam; Oculus, Wetzlar, Germany). The keratometric corneal astigmatism (KA) was obtained by using the anterior corneal surface measurement and the keratometric index (1.3375) while neglecting the posterior corneal surface measurement. The Pentacam-derived total corneal astigmatism (PA) was derived by doubled-angle vector analysis of the astigmatisms on both corneal surfaces. The mean arithmetic and absolute estimation errors of the KA magnitude for the PA magnitude were -0.06 +/- 0.28 diopters (D) (range, -0.59 to 0.91 D) and 0.24 +/- 0.16 D (range, 0 to 0.91 D), respectively. The mean arithmetic and absolute estimation errors of the KA angle for the PA angle were -0.6 degrees +/- 12.7 degrees (range, -69.9 degrees to 83.4 degrees) and 7.4 degrees +/- 10.3 degrees (range, 0 degrees to 83.4 degrees), respectively. Among all eyes, 142 eyes (28.8%) had either a KA magnitude that differed by > 0.50 D from the PA magnitude or a KA angle that differed by > 10 degrees from the PA angle. For the 282 eyes with a KA magnitude exceeding 1.0 D (that are candidates for intraoperative correction of a preexisting astigmatism during cataract surgery), 29 eyes (10.3%) had either a KA magnitude that differed by > 0.50 D from the PA magnitude or a KA angle that differed by > 10 degrees from the PA angle. Neglecting the posterior corneal surface measurement may lead to significant deviation in the corneal astigmatism estimation in a proportion of eyes.
Article
To analyze the prevalence and presentation patterns of corneal astigmatism in cataract surgery candidates. University of Valencia, Valencia, Spain. Refractive and keratometric values were measured before surgery in patients having cataract extraction. Descriptive statistics of refractive and keratometric cylinder data were analyzed and correlated by age ranges. Refractive and keratometric data from 4,540 eyes of 2,415 patients (mean age 60.59 years +/- 9.87 [SD]; range 32 to 87 years) differed significantly when the patients were divided into 10-year subsets. There was a trend toward less negative corneal astigmatism values, except the steepest corneal radius and the J(45) vector component, in older groups (Kruskal-Wallis, P<.01). In 13.2% of eyes, no corneal astigmatism was present; in 64.4%, corneal astigmatism was between 0.25 and 1.25 diopters (D) and in 22.2%, it was 1.50 D or higher. Corneal astigmatism less than 1.25 D was present in most cataract surgery candidates; it was higher in about 22%, with slight differences between the various age ranges. This information is useful for intraocular lens (IOL) manufacturers to evaluate which age ranges concentrate the parameters most frequently needed in sphere and cylinder powers and for surgeons to evaluate which IOLs provide the most effective power range.
Article
This paper presents a general statistical methodology for the analysis of multivariate categorical data arising from observer reliability studies. The procedure essentially involves the construction of functions of the observed proportions which are directed at the extent to which the observers agree among themselves and the construction of test statistics for hypotheses involving these functions. Tests for interobserver bias are presented in terms of first-order marginal homogeneity and measures of interobserver agreement are developed as generalized kappa-type statistics. These procedures are illustrated with a clinical diagnosis example from the epidemiological literature.
Article
No previous study documents improvement in visual acuity and subjective visual function associated with cataract surgery in the first eye, second eye, and both eyes. Measurement of subjective aspects of visual function and quality of life provides information that cannot be obtained with simple measurement of Snellen visual acuity. From 76 ophthalmology practices in three cities, patients undergoing cataract extraction with intraocular lens implantation (n = 613) and comparison patients (n = 408) were enrolled in a prospective study. Questionnaires elicited visual function information before and after surgery, and visual acuity was obtained from the ophthalmologic record. Among patients with cataract and no other eye disease, baseline subjective visual function before surgery in the second eye was better than that before surgery in the first eye. Improvement in subjective visual function was approximately equal postoperatively in first and second eyes. Improvement in subjective function in both eyes postoperatively was significantly greater than that after surgery in the first eye or second eye alone. No statistically significant difference across surgical groups in the proportion of patients demonstrating improvement in visual acuity was observed. Patients who underwent surgery in both eyes reported greater improvement in subjective visual function than did those who underwent surgery in one eye. Thus, there seems to be a benefit associated with restoring binocular vision in this population. These findings support the policy recommendation that cataract surgery in both eyes remains the appropriate treatment for patients with bilateral, cataract-induced visual impairment.
Article
A prospective, randomized study compared the surgically induced astigmatism after 3.5 mm, 4.0 mm, and 5.0 mm temporal corneal tunnel incisions over six months. We studied 60 eyes of 60 patients who had phacoemulsification through a two-step clear corneal tunnel incision and implantation of one of three posterior chamber intraocular lenses (IOLs). Patients were divided into three groups of 20 each: Group A, cartridge injection of a foldable plate-haptic silicone IOL through a 3.5 mm self-sealing incision; Group B, cartridge injection of a disc silicone IOL through a 4.0 mm self-sealing incision; Group C, 5.0 mm optic poly(methyl methacrylate) IOL through a 5.0 mm incision with one radial suture. Corneal topography data were obtained using a computerized videokeratographic analysis system preoperatively and one week and six months postoperatively. Vector analysis was performed to calculate the surgically induced astigmatism. After the first postoperative week, mean induced astigmatism was 0.63 diopters (D) (+/- 0.41) in Group A, 0.64 D (+/- 0.35) in Group B, and 0.91 D (+/- 0.77) in Group C. After six months, it was 0.37 D (+/- 0.14) in Group A, 0.56 D (+/- 0.34) in Group B, and 0.70 D (+/- 0.50) in Group C. Surgically induced astigmatism was significantly lower in Group A than in Group B (P < .05) and Group C (P < .005) after six months. Vector analysis demonstrated that temporal corneal tunnel incisions induced clinically minimal astigmatism over six months postoperatively depending on incision size.
Article
To compare the torque and flattening effect induced by temporal or on-axis clear corneal incisions (CCIs) for phacoemulsification. Moorfields Eye Hospital, London, United Kingdom. Randomized controlled clinical trial on 62 eyes with cataract and mild to moderate corneal astigmatism (<2.60 diopters [D]) having phacoemulsification with a temporal CCI (temporal group) or on-axis CCI (on-axis group). Corneal astigmatism was assessed by corneal topography preoperatively and 3 weeks after surgery. The meridian of the incisions was marked on the cornea before local anesthesia was given to avoid anesthesia-related cyclotorsion. The surgically induced astigmatism (SIA) vector, torque, flattening effect, and accuracy of incision placement were analyzed in the 2 groups and compared with a paired t test. Three weeks after surgery, the on-axis CCI induced slightly more flattening of the meridian of the incision (mean -0.63 +/- 0.57 D [SD]) than the temporal CCI (mean -0.50 +/- 0.44 D); however, the differences were not statistically significant (P = .31). Simple algebraic difference showed a mean increase in astigmatism magnitude of 0.12 +/- 0.52 D in the temporal group and a mean reduction of 0.21 +/- 0.53 D in the on-axis group (P = .02). The mean absolute torque was 0.28 +/- 0.27 D and 0.53 +/- 0.37 D, respectively (P<.005). The absolute angle of error of incision placement (alpha) was greater after on-axis CCIs (mean 25.9 +/- 20.1 degrees) than after temporal CCIs (mean 14.5 +/- 14.3 degrees) (P = .01). In eyes with preoperative astigmatism less than 2.60 D, on-axis CCI phacoemulsification induced slightly more flattening along the incision meridian than temporal CCI phacoemulsification, although the differences were not significant. The on-axis CCI was associated with significantly greater absolute torque and angle of error than the temporal CCI. These factors could limit the benefit of placing the incision on axis when the aim is to reduce preoperative astigmatism in phacoemulsification.
Article
Comparison of the astigmatism induced by the operation based on the 2.8 mm incisions in the clear cornea, performed by temporal approach and superior approach. Retrospective analysis was performed on the group of 65 patients (41 women and 24 men), mean age 74.5 +/- 7.1 years old. We studied a series of 70 eyes (32 right eyes and 38 left eyes). All of the patients underwent cataract surgery by means of ultrasonic phacoemulsification conducted at the Department of Ophthalmology, Military Health Services Institute in Warsaw, Poland within 2004-2005. Follow-up examinations took place 6 months after operation. There were DBCVA. NBCVA, intraocular pressure, anterior segment of the eye and fundus examined. Curvature of the cornea was measured by means of Javal's ophthalmometry. The results were assumed as significant in view of corneal curvature stabilization. Vector analysis of astigmatism was performed on the basis of method described by Jaffe. There was preoperative astigmatism vector (K1) and post-operative astigmatism vector (K3) calculated, as well as surgically inducted astigmatism (SIA)--vector (K2). From the group of 70 eyes, 19 were excluded from the study, where vector K1 was > 1.0 D as well as four eyes, where the main opening site depended on the size and axis of K1 vector. The group of 47 eyes was divided according to the opening site into two subgroups--group I (temporal approach--2.8 mm)--25 eyes and group II (superior approach 2.8 mm)--22 eyes. Statistical analysis was performed based on Statistica package 6.0 PL., using U-Mann-Whitney's test, Chi square Yates' test, Kruskal-Wailis' variance analysis, logistic regression and W Shapiro-Wilk's test. Studied groups were homogeneous with respect to age structure, sex, number of operated eyes and pre-operative size of corneal astigmatism vector K1 (p > .05). The mean values of SIA in group I and II were respectively: 0.63 +/- 0.28 and 1.00 +/- 0.54 and were statistically significant (p < .05). The mean values of K3 post-operative vector measured 6 months following the operation was: 0.54 +/- 0.35 in the group I and 0.96 +/- 0.43 in the group II. Differences between two groups show statistical significance (p < .05). Size of SIA has crucial influence on generating post-operative astigmatism > 1.0 D (p = .03). Clear corneal temporal approach 2.8 mm is more beneficial method comparing to superior approach of the same width, because of the scale of SIA.
Article
To investigate the refractive results of clear corneal incision performed at the steepest meridian of pre-existing corneal astigmatism. One hundred eighty-two patients with astigmatism > 0.75 diopters (D) were evaluated. Superior, temporal, nasal, superotemporal, or superonasal clear corneal incisions were performed at the steep meridian. Refraction, visual acuity, and topography values were evaluated, and changes in surgically induced astigmatism were calculated by vector analysis using the Fourier formula. Paired t test was used to compare mean values. Postoperative cylinder values showed minor changes in all groups, except the nasal group. Nasal incision increased preoperative cylinder from 1.13 D to 1.83 D 6 months after surgery. Temporal and superotemporal incisions resulted only in small astigmatic changes. Conversely, superior, superonasal, and nasal incisions induced more pronounced astigmatism. Performing clear corneal incision for phacoemulsification of cataract at the steep meridian resulted in small changes with temporal incisions, whereas nasal incisions resulted in higher surgically induced astigmatism.
Article
To compare the induced astigmatism after phacoemulsification in the right vs. the left eye. An oblique clear corneal incision was made in a superotemporal location in the right (n = 344) and a superonasal location in the left (n = 292) eye. Retrospectively, patient characteristics, pre- and postoperative visual acuity, and induced astigmatism values were compared. Statistical analysis was performed with the Student t , chi2, and Mann-Whitney U tests. The proportion of against-the-rule astigmatism and surgically induced astigmatism values were significantly larger in the left-eye group (p < 0.001). Surgically induced astigmatism occurred to a greater extent in the left eyes compared with the right, possibly because of structural differences.
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Contribution of posterior corneal astigmatism to total corneal astigmatism
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Dissatisfaction after implantation of multifocal intraocular lenses
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