Cataract surgery after corneal refractive surgery: preoperative considerations and management.

PURPOSE OF REVIEW: Corneal refractive surgery (CRS) is one of the most popular eye procedures, with more than 40 million cases performed globally. As CRS-treated patients age and develop cataract, the number of cases that require additional preoperative considerations and management will increase around the world. Thus, we provide an up-to-date, concise overview of the considerations and outcomes of cataract surgery in eyes with previous CRS, including surface ablation, laser in-situ keratomileusis (LASIK), and small-incision lenticule extraction (SMILE). RECENT FINDINGS: Challenges associated with accurate biometry in eyes with CRS have been mitigated recently through total keratometry, ray tracing, intraoperative aberrometry, and machine learning assisted intraocular lens (IOL) power calculation formulas to improve prediction. Emerging studies have highlighted the superior performance of ray tracing and/or total keratometry-based formulas for IOL power calculation in eyes with previous SMILE. Dry eye remains a common side effect after cataract surgery, especially in eyes with CRS, though the risk appears to be lower after SMILE than LASIK (in the short-term). Recent presbyopia-correcting IOL designs such as extended depth of focus (EDOF) IOLs may be suitable in carefully selected eyes with previous CRS. SUMMARY: Ophthalmologists will increasingly face challenges associated with the surgical management of cataract in patients with prior CRS. Careful preoperative assessment of the ocular surface, appropriate use of IOL power calculation formulas, and strategies for presbyopia correction are key to achieve good clinical and refractive outcomes and patient satisfaction. Recent advances in CRS techniques, such as SMILE, may pose new challenges for such eyes in the future.

Artificial intelligence applications in cataract and refractive surgeries.

PURPOSE OF REVIEW: This review highlights the recent advancements in the applications of artificial intelligence within the field of cataract and refractive surgeries. Given the rapid evolution of artificial intelligence technologies, it is essential to provide an updated overview of the significant strides and emerging trends in this field. RECENT FINDINGS: Key themes include artificial intelligence-assisted diagnostics and intraoperative support, image analysis for anterior segment surgeries, development of artificial intelligence-based diagnostic scores and calculators for early disease detection and treatment planning, and integration of generative artificial intelligence for patient education and postoperative monitoring. SUMMARY: The impact of artificial intelligence on cataract and refractive surgeries is becoming increasingly evident through improved diagnostic accuracy, enhanced patient education, and streamlined clinical workflows. These advancements hold significant implications for clinical practice, promising more personalized patient care and facilitating early disease detection and intervention. Equally, the review also highlights the fact that only some of this work reaches the clinical stage, successful integration of which may benefit from our focus.

Leaving trusted paths: Estimating corneal keratometric index in cataract surgery eyes with zero-power implants.

PURPOSE: This study aimed to estimate the corneal keratometric index in the eyes of cataract surgery patients who received zero-power intraocular lenses (IOLs). METHODOLOGY: This retrospective study analyzed postoperative equivalent spherical refraction and axial length, mean anterior curvature radius and aqueous humor refractive index to calculate the theoretical corneal keratometric index value (nk). Data was collected from 2 centers located in France and Germany. RESULTS: Thirty-six eyes were analyzed. The results revealed a mean corneal keratometric index of 1.329 ± 0.005 for traditional axial length (AL) and 1.331 ± 0.005 for Cooke modified axial length (CMAL). Results ranged from minimum values of 1.318/1.320 to maximum values of 1.340/1.340. CONCLUSION: The corneal keratometric index is a crucial parameter for ophthalmic procedures and calculations, particularly for IOL power calculation. Notably, the estimated corneal keratometric index value of 1.329/1.331 in this study is lower than the commonly used 1.3375 index. These findings align with recent research demonstrating that the theoretical corneal keratometric index should be approximately 1.329 using traditional AL and 1.331 using CMAL, based on the ratio between the mean anterior and posterior corneal curvature radii (1.22).

Fourteen years follow-up of a stable unilateral Keratoconus: unique case report of clinical, tomographical and biomechanical stability.

BACKGROUND: Keratoconus (KC) is a noninflammatory corneal ectatic disorder. In 2015, the Global Consensus on Keratoconus and Ectatic Diseases agreed that the pathophysiology of KC includes environmental, biomechanical, genetic, and biochemical disorders on one hand, and that true unilateral KC does not exist on the other hand. However, with the increasingly advancements in detection methods, we report the first case of a stable unilateral keratoconus with the longest follow up period of 14 years (2006-2020). We used topographic, tomographic, and biomechanical values for both eyes over the years to confirm the diagnosis, which has never been done before. Our study focuses on a single patient therefore it illustrates the mere possibility that unilateral keratoconus exists. CASE PRESENTATION: We present the case of a 19-year-old male with no previous ocular or general health conditions who presented to our clinic in November 2006 for incidental finding of decreased vision of the right eye (OD) on a routine examination. Topographies, tomographies, and biomechanical analysis of both eyes were obtained and showed a unilateral right keratoconus at the time. Patient admitted to unilateral right eye rubbing. Although we cannot prove that previous eye rubbing alone led to these initial symptoms, he was advised to stop rubbing and was followed up without any intervention for fourteen years during which topographic, tomographic, and biomechanical values for both eyes remained stable, proving for the first time that unilateral KC could exist. CONCLUSION: We think that the data we are presenting is important because acknowledging that true unilateral keratoconus exists questions the genetic or primary biomechanical etiology of keratoconus versus the secondary biomechanical etiologies like eye rubbing. Our report also shows the importance of corneal biomechanics in detecting early changes. This is important to detect early, prevent progression, and tailor treatment.

Evaluation of a uniplanar pupil expansion ring in small-pupil cataract surgery: a feasibility study.

PURPOSE: The aim of this study was to evaluate the effectiveness of a disposable uniplanar pupil expansion device in small-pupil cataract surgery. METHODS: This is a feasibility study carried out at the Rothschild Foundation, Paris, France. Patients undergoing routine cataract surgery with a dilated pupil size < 6 mm, and who agreed to participate in the study were included. The trial enrolled 25 patients, of whom 21 proceeded to cataract surgery using the pupil expansion device to be evaluated. The pupil diameter was measured at defined stages during the cataract surgery, which was performed by a single surgeon, in a single center setting. The 1st generation Bhattacharjee pupil expansion ring was used if the preoperative pupil size was < 6 mm. Intraoperative and postoperative adverse events were recorded. RESULTS: Pupil size immediately after the Bhattacharjee ring implantation was ≥ 6 mm for 15 eyes (71.4%). The mean dilated pupil size before ring insertion was 4.5 ± 0.8 mm (range 2.5-5.8 mm), and the mean pupil size after ring insertion was 6.1 ± 0.3 mm (range 5.9-6.8 mm). Mean pupil size following removal of the ring was 4.2 ± 0.8 mm (range 2.5-5.4 mm). Two adverse events occurred during the surgeries: 1 Bhattacharjee ring broke prior to implantation, and 1 implanted Bhattacharjee ring was unstable and removed before the end of the surgery. No postoperative adverse event was recorded. CONCLUSIONS: The Bhattacharjee ring is an effective pupil expansion device, which facilitates stable pupil expansion during cataract surgery. This study was registered as a clinical trial at clinicaltrials.gov under the number NCT02434588.

Multifocal and Extended Depth-of-Focus Intraocular Lenses in 2020.

Ophthalmic surgeons have been overwhelmed by the influx of multifocal intraocular lens (IOL) options in recent years, with close to 100 IOLs on the market in 2020. This practical and technical update on a representative group of established as well as newly launched multifocal IOLs on the market focuses on multifocal IOLs, including extended depth-of-focus lenses. We also describe the optical basis of lens platforms used and thorough preoperative planning to aid decision making. This allows the surgeon the knowledge base to deliver the required relative customized spectacle independence with the least photic phenomenon and loss of contrast possible while achieving high individual patient satisfaction. Data of reviewed IOLs displayed in tabular format include mean monocular uncorrected distance, intermediate, and near visual acuities (logarithm of the minimum angle of resolution), with standard deviations and ranges where available. The range of vision targeted, pupil dependence, toric availability, as well as type of optical platform, are provided as a practical guide to demystify existing terminology on the market that may create interest around a seemingly new design that is actually not novel at all. Halos and glare experienced, levels of patient satisfaction, and spectacle independence achieved also are summarized. A wide range of multifocal IOLs options are available on the market to surgeons. Comprehensive patient selection and examination, combined with knowledge of the most recent options and adequate patient counseling, including neuroadaptation, can avoid dissatisfaction. Many recently available IOLs are awaiting formal results, but the methods by which we label and compare these types of IOLs must also be standardized.

The role of environment in the pathogenesis of keratoconus.

PURPOSE OF REVIEW: This study was conducted to demonstrate the importance of the environment in keratoconus (KC) genesis. RECENT FINDINGS: Genetic-related connective tissue disorders demonstrate the inconsistency of theories regarding KC pathogenesis since no corneal steepening was observed in the majority of these patients. Despite recent advances and decades of research into the genetics of KC, the identification of disease-causing KC genes has been frustrating. Variants found based on genome-wide and next-generation sequencing only seem to account for a small number of cases or play a limited role in KC pathogenesis. SUMMARY: The literature shows that mechanical manipulation may be the common underlying factor or the indispensable act precipitating the cascade of events leading to permanent corneal deformation. Hence, ophthalmologists have the opportunity to increase patient awareness about eye manipulation repercussions and treatment for ocular surface disorders. VIDEO ABSTRACT: http://links.lww.com/COOP/A42.

Incorrect sleeping position and eye rubbing in patients with unilateral or highly asymmetric keratoconus: a case-control study.

PURPOSE: To evaluate eye rubbing and sleeping position in patients with Unilateral or Highly Asymmetric Keratoconus (UHAKC). METHODS: Case-control study of consecutive UHAKC patients diagnosed at the Rothschild Foundation. Controls were age- and sex-matched, randomly selected refractive surgery clinic patients. Patients self-administered questionnaires regarding their family history of keratoconus, eye rubbing, and sleeping habits. All the eyes underwent a comprehensive ocular examination. Logistic regression was used to analyze univariate and multivariate data to identify risk factors for keratoconus. RESULTS: Thirty-three UHAKC patients and 64 controls were included. Univariate analyses showed that daytime eye rubbing [OR = 172.78], in the morning [OR = 24.3], or in eyes with the steepest keratometry [OR = 21.7] were significantly different between groups. Allergy [OR = 2.94], red eyes in the morning [OR = 6.36], and sleeping on stomach/sides [OR = 14.31] or on the same side as the steepest keratometry [OR = 94.72] were also significantly different. The multivariate model also showed statistical significance for most factors including daytime eye rubbing [OR = 134.96], in the morning [OR = 24.86], in the steepest eye [OR = 27.56], and sleeping on stomach/sides [OR = 65.02] or on the steepest side [OR = 144.02]. A univariate analysis in UHAKC group, comparing the worse and better eye, showed that eye rubbing [OR = 162.14] and sleeping position [OR = 99.74] were significantly (p < 0.001) associated with the worse eye. CONCLUSION: Our data suggests that vigorous eye rubbing and incorrect sleeping position are associated with UHAKC. This is especially true in rubbing the most afflicted eye, and contributory sleep position, including positions placing pressure on the eye with the steepest keratometry.

Polynomial decomposition method for ocular wavefront analysis.

Zernike circle polynomials are in widespread use for wavefront analysis because of their orthogonality over a circular pupil and their representation of balanced classical aberrations. However, some of the higher-order modes contain linear and quadratic terms. A new aberration series is proposed to better separate the low- versus higher-order aberration components. Because its higher-order modes are devoid of linear and quadratic terms, our new basis can be used to better fit the low- and higher-order components of the wavefront. This new basis may quantify the aberrations more accurately and provide clinicians with coefficient magnitudes which better underline the impact of clinically significant aberration modes.

Simultaneous Correction of Unilateral Rainbow Glare and Residual Astigmatism by Undersurface Flap Photoablation After Femtosecond Laser-Assisted LASIK.

PURPOSE: To report and document a case of successful rainbow glare correction using undersurface ablation of the LASIK flap. METHODS: A 33-year-old woman was treated bilaterally for myopia using femtosecond laser-assisted LASIK with the FS200 femtosecond laser (Alcon Laboratories, Inc., Fort Worth, TX). Postoperatively, she complained of rainbow glare in her right eye, and presented some residual myopic astigmatism. Six months after the initial LASIK procedure, the right eye flap was lifted and a toric excimer correction was delivered on its stromal side. RESULTS: Visual symptoms related to the rainbow glare disappeared immediately after the completion of the procedure and did not reoccur. Uncorrected visual acuity improved by two lines. CONCLUSIONS: Rainbow glare following femtosecond laser-assisted LASIK can be successfully corrected by undersurface ablation of the flap.

Astigmatic equivalence of 2.2-mm and 1.8-mm superior clear corneal cataract incision.

PURPOSE: To evaluate the astigmatic effects of 2.2-mm and 1.8-mm cataract incisions. METHODS: A randomized prospective study of 190 eyes of 151 patients undergoing superior clear corneal incision (SCCI) was divided into three groups: 61 eyes with a control 3.2-mm SCCI; 66 eyes with a 2.2-mm SCCI; and 63 eyes with a 1.8-mm SCCI. The corneal astigmatism was measured with an autokeratometer preoperatively and 1 month after surgery. The with-the-wound (WTW), against the-wound (ATW), and WTW-ATW changes were calculated using the Holladay-Cravy-Koch formula. RESULTS: The WTW, ATW, and WTW-ATW changes were significantly higher for the control 3.2-mm SCCI than for the 2.2- and 1.8-mm SCCI (all p < 0.001), and no difference was found between the 2.2- and 1.8-mm SCCI incision groups. CONCLUSION: In our study, the astigmatic effects were the same for the 2.2 mm and 1.8 mm incisions and as expected, were significantly lower than the control 3.2 mm incision group.

AcuTarget measurements: repeatability and comparison to OPD-Scan III.

PURPOSE: To evaluate repeatability of the AcuTarget (SensoMotoric Instruments, Teltow, Germany) measurements and compare them to those obtained with the OPD-Scan III (NIDEK, Inc., Fremont, CA). METHODS: Measurements were taken with the AcuTarget and OPD-Scan III in 62 eyes of 31 patients. Results were compared using paired Student's t tests, Pearson correlation coefficients, and 95% limits of agreement. RESULTS: Repeatability of the AcuTarget was good with intraclass correlation coefficients of 0.773, 0.777, and 0.780 for Purkinje-versus-pupil along the x-axis, y-axis, and chord length measurements, respectively. No statistically significant difference was observed between the AcuTarget and OPD-Scan III for Purkinje-versus-pupil measurement along the x-axis (P = .061) and chord length (P = .950). Conversely, a statistically significant difference was observed between the two systems for measurements along the y-axis (P < .001). No statistical difference was found between the mean of the first three acquisitions and the best acquisition obtained with the AcuTarget. CONCLUSIONS: Measurements provided by the AcuTarget have good repeatability and are close to those obtained with the OPD-Scan III. Although controversies remain on where to best center refractive procedures, this may help in analyzing the importance of refractive surgery centration in relation to visual acuity and visual symptoms.

Corneal enantiomorphism in normal and keratoconic eyes.

PURPOSE: To evaluate the ability to discriminate between normal and keratoconic corneas by analyzing intereye corneal asymmetry parameters and defining a score of similarity that outlines the normal range of asymmetry between right and left eyes. METHODS: This prospective, non-randomized study included 102 normal corneas of 51 patients and 64 keratoconic corneas of 32 patients. Topographic and tomographic parameters of the right and left eyes were extracted from an elevation and Placido-based corneal topography. Asymmetry was determined by subtracting the right eye value from the left eye value for each variable and by considering the absolute value of the result. A discriminant function was constructed to separate the normal and keratoconic groups. RESULTS: The mean intereye asymmetry differences were statistically significant for all variables except the vertical and horizontal decentration of the thinnest point, the corneal thickness at 2.5, 3, 3.5, and 4 mm from the thinnest point, and the posterior keratometry at 4.5 mm from the thinnest point. The discriminant function was composed of three variables (the difference between flat and steep keratometry, the 3-mm irregularity, and the anterior elevation of the thinnest point) and reached an area under the receiver operator characteristic curve of 0.992, a sensitivity of 94%, and a specificity of 100%. CONCLUSIONS: A discriminant function constructed from the intereye difference of three corneal indices may be accurate and useful for the topography-based detection of advanced keratoconus. In the future, incorporating such data in automated artificial intelligence software may improve the detection ability of earlier forms of keratoconus.

Measurement of pupil center shift in refractive surgery candidates with caucasian eyes using infrared pupillometry.

PURPOSE: To evaluate the effectiveness of the pupil center shift with changes in the state of pupil size and with other ocular variables. METHODS: Dynamic pupillometry with the Topolyzer Vario (Alcon Laboratories, Inc., Fort Worth, TX) was performed in 248 eyes of 124 patients scheduled for corneal laser refractive surgery. High-resolution images were obtained using the infrared-sensitive camera (incorporated in the videokeratoscope) under mesopic and photopic conditions. Measurements of pupil diameters, distance between the pupil center and keratoscopic axis, and spatial shift of the pupil center were obtained after analysis. RESULTS: The mean distance between the pupil center and the corneal vertex in mesopic and photopic conditions of illumination in myopic eyes was 0.27 ± 0.14 (range: 0.02 to 0.70 mm) and 0.24 ± 0.12 mm (range: 0.06 to 0.65 mm), respectively, whereas it was 0.36 ± 0.15 (range: 0.03 to 0.70 mm) and 0.31 ± 0.16 mm (range: 0.03 to 0.77 mm) in hyperopic eyes, respectively. The mean spatial pupil center shift was significant: 0.11 ± 0.07 mm (range: 0.02 to 0.57 mm) in myopic eyes and 0.12 ± 0.09 mm (range: 0.02 to 0.47 mm) in hyperopic eyes. The pupil center shifted consistently temporally as the pupil dilated. The pupil center shift was not significantly related to sex, age, eye (right or left), or refractive error. CONCLUSIONS: The mean distance between the pupil center and the corneal vertex is greater in hyperopic eyes than in myopic eyes, whereas the spatial shift of this pupil center has a temporal direction as the pupil dilates and is constantly small in all groups. However, pupil center shift can be important in a few patients.

Effect of anterior corneal surface asphericity modification on fourth-order zernike spherical aberrations.

PURPOSE: To evaluate the theoretical influence of the change in corneal asphericity (ΔQ) on the change in fourth-order Zernike spherical aberration coefficient (ΔC(4)0) with customized aspheric refractive correction of myopia and hyperopia. METHODS: The initial anterior corneal surface profile was modeled as a conic section of apical radius of curvature R0 and asphericity Q0. The postoperative corneal profile was modeled as a conic section of apical curvature R1 and asphericity Q1, where R1 was computed from defocus D, and Q1 selected for controlling the postoperative asphericity. The corresponding change in fourth-order spherical aberration (ΔC(0)4) was computed within a 6-mm optical zone using inner products applied to the incurred optical path changes. These calculations were repeated for different values of D, R0, Q0, and various intended ΔC(4)0 values. RESULTS: Increasing negative spherical aberration (ΔC(4)(0) < 0) requires a change toward more negative values of asphericity (increased prolateness; ΔQ < 0) for hyperopic and low myopic corrections, but more positive values (ΔQ < 0) for high myopic correction. The larger the intended change in corneal spherical aberration (ΔC(4)(0)), the more myopic the threshold value for which the required change in asphericity, ΔQ, becomes positive. The influence of the magnitude of paraxial defocus correction is less pronounced when larger changes in C(4)(0) are intended. CONCLUSIONS: These results provide a basis for controlling the direction (sign) and the magnitude of spherical aberration changes when using customized aspheric profiles of ablation.

Clinical outcomes with a trifocal intraocular lens: a multicenter study.

PURPOSE: To evaluate the clinical results and safety obtained with a new type of multifocal intraocular lens (IOL) using a trifocal design to achieve pseudoaccommodation. METHODS: A pilot observational study of patients with a trifocal IOL (FineVision; PhysIOL, Liege, Belgium) implanted by 1 of 12 surgeons between March and December 2010. Visual outcomes that were assessed postoperatively included uncorrected and corrected distance, intermediate, and near visual acuity. RESULTS: One hundred ninety-eight eyes of 99 patients were analyzed. Patients were observed for an average of 6.44 ± 4.67 months (range: 0.2 to 17 months). Preoperative corrected distance visual acuity was 0.22 ± 0.26 logMAR. At the final follow-up visit, corrected distance visual acuity was 0.01 ± 0.10 logMAR, uncorrected distance visual acuity was 0.01 ± 0.06 logMAR, uncorrected intermediate visual acuity was 0.08 ± 0.10 logMAR, and mean uncorrected near visual acuity was 0.00 ± 0.04 logMAR. Postoperative binocular uncorrected distance visual acuity was 0.01 ± 0.07 logMAR, uncorrected intermediate visual acuity was 0.06 ± 0.08 logMAR, and uncorrected near visual acuity was -0.03 ± 0.04 logMAR. Postopeative mean residual sphere was 0.21 ± 0.48 diopters (D), with a residual cylinder of -0.24 ± 0.31 D. Postoperative spherical equivalent was 0.11 ± 0.36 D. CONCLUSIONS: The results demonstrated that the trifocal FineVision IOL is able to restore near, intermediate, and distance visual function.

A Technique of Multiple Corneal Allogeneic Ring Segments Prepared from a Single Corneal Graft: A Case Series.

PURPOSE: To describe a novel technique for preparing multiple corneal allogeneic ring segments (CAIRS) from a single corneal graft using femtosecond laser technology. METHODS: This is a case series of 10 eyes from 10 patients with keratoconus who underwent FS-assisted CAIRS implantation using corneas from 4 donors at the Hospital Foundation Adolphe de Rothschild-Noémie de Rothschild institute. A preoperative and postoperative examination was performed at 1 day, 1 week, and 1 month. Anterior segment OCT and corneal tomography with aberrometric and pachymetric analyses were performed at each visit. Visual, refractive, and topographic parameters were extracted. The thickness and width of implanted CAIRS were analyzed. RESULTS: Patients were classified according to keratoconus severity: group A (maximal keratometry Kmax <75D) and group B (Kmax >75D). At 1 month postoperatively, both groups A and B showed a significant decrease in mean keratometry by 4.78 ± 1.57D and 12.87 ± 4.62D, respectively. Total and higher order aberrations decreased by 5.66 ± 4.55 and 0.65 ± 1.54 in group A and by 9.45 ± 9.15 and 0.49 ± 1.39 in group B, respectively. The corrected distance visual acuity improved by 4.8 ± 1.7 lines in group A. Visual improvement was not significant in group B. One eye in group B exhibited acute rejection and required explantation. CONCLUSIONS: FS-assisted multiple CAIRS implantation using a single corneal graft maximizes the utilization of viable corneal tissue. CAIRS implantation is an effective and biocompatible therapeutic alternative, particularly in cases of moderate to advanced keratoconus with Kmax <75D.

Paper waste from instructions for use brochures in cataract surgery implant packaging in Europe and the United States.

PURPOSE: To assess the extent of paper waste generated per year by instructions for use (IFUs) brochures included in intraocular lens (IOL) packaging in Europe and the U.S. SETTING: Rothschild Foundation Hospital, Paris, France; Royal Free London NHS Foundation Trust; Center for Sight, London, United Kingdom. DESIGN: Experimental study. METHODS: A sample of IOLs were collected and each IFU was weighed. In addition, the cumulative weight of these brochures used in cataract surgeries performed annually in Europe and the U.S. was estimated, and the potential annual paper conservation that could be achieved if all manufacturers adopted electronic IFUs (e-IFUs) in Europe and the U.S. was determined. RESULTS: The mean and standard deviation of the weight for overall IFUs, classic IFUs, and e-IFUs were 17.6 ± 13.8 g, 23.5 ± 13.2 g, and 2.9 ± 1.9 g, respectively. The estimated cumulative weight of paper generated from the IFUs accompanying implants used in European and U.S. cataract surgeries is 153 tons. If all manufacturers transition to e-IFUs, the cumulative weight saved would be 128 tons (-84%), equivalent to 120 tons of carbon dioxide equivalent and the preservation of more than 2000 trees annually. CONCLUSIONS: The classic IFUs in IOL packaging result in a significant amount of paper waste annually. Therefore, there is an urgent need for a rapid transition to e-IFU technology. The adoption of e-IFUs has already been authorized in Europe and the U.S., and it is crucial to expedite this process.

Investigating the topographic effect of epithelium in myopic eyes with subtle topographic preoperative abnormalities.

PURPOSE: To explore the topographic effect of the epithelium in keratoconus suspected (KCS) and in normal Placido classified corneas. SETTING: Rothschild Foundation, Paris, France. DESIGN: Prospective interventional case series. METHODS: Anterior corneal specular Placido topography using OPD-Scan II was performed in 97 eyes of 67 patients undergoing photorefractive keratectomy for myopia, before and after epithelium removal. The differences in axial keratometry, asphericity, and astigmatism were computed. RESULTS: After epithelial peeling, some Placido-normal classified corneas became KCS. Therefore, we have subdivided this group into 2 groups: one of normal classified corneas which stayed normal after epithelium removal (Group NN) and another of corneas that became KCS classified (Group NK). The mean difference in axial mean keratometry in the third central millimeter rings was +0.50 ± 0.24 diopters (D), 0.69 ± 0.31 D, and 0.49 ± 0.35 D and the mean difference in the magnitude of epithelial-induced astigmatism in the first central millimeter ring was 0.37 D × 89 degrees (positive cylinder), 0.54 D 86 degrees, and 0.52 D 86 degrees, respectively, in Group NN, NK, and KK (KCS corneas that stayed KCS). These differences were significant ( P < .0001). Preoperative keratometry was the only predictive factor differentiating Group NN from NK ( P < .001). CONCLUSIONS: The epithelial layer tended to reduce the magnitude of the Bowman layer's astigmatism, prolateness, and keratometry, more importantly in Group NK. In the KK group, we found a similar trend as in normal eyes (Group NN). The epithelium would be able to mask Bowman layer's irregularities until a certain degree of severity.

Performance evaluation of a simple strategy to optimize formula constants for zero mean or minimal standard deviation or RMS prediction error in intraocular lens power calculation.

PURPOSE: To investigate the performance of a simple prediction scheme for the formula constants optimized for a mean (MPE), standard deviation (SDPE) or root-mean-squared refractive prediction error (RMSPE). DESIGN: Retrospective cross-sectional study. METHODS: Using IOLMaster 700 biometric data from 888 eyes treated with the Hoya Vivinex lens and 821 eyes treated with the Alcon SA60AT lens, plus the power of the implanted lens and postoperative spherical equivalent refraction, optimized constants for SRKT, Hoffer Q, Holladay 1, Haigis, and K6 formulae were calculated using an iterative nonlinear optimization for zero MPE and minimal SDPE and RMSPE. Start values were detuned by ±1.5 from the MPE optimized constants and formula constants generated using the simple prediction scheme were compared to the corresponding directly optimized constants. RESULTS: For all 5 formulae under test and with both datasets, constants optimized using the simple scheme showed excellent agreement with those from the iterative method with either MPE or RMSPE used as the optimization metric, and good agreement with SDPE as the metric. Constants optimized for zero MPE or minimal RMSPE agreed within 0.05, whereas constants for minimal SDPE could be systematically off by up to 0.6 from the MPE values, making SDPE unsuitable as an optimization metric. CONCLUSIONS: This simple formula constant optimization scheme performs excellently for 4 disclosed formulae and one nondisclosed formula in our 2 monocentric datasets with zero MPE or minimal RMSPE as metrics. Multicentric studies with other study populations and biometers are required to further investigate the clinical applicability.