Samir Jacob Bechara

An independent evaluation of second generation suction microkeratomes.

BACKGROUND Microkeratome designs for lamellar refractive surgery have changed significantly in recent years. Three microkeratome systems (Automatic Corneal Shaper (Steinway Instrument Company, Inc, San Diego, Calif), Draeger Lamellar Keratome (Storz Instrument GmbH, Heidelberg, Germany), and Microprecision test model (Microprecision Instrument Company, Inc, Phoenix, Ariz) were subjected to a concurrent and independent evaluation. METHODS Three types of keratectomies (primary superficial stromal, secondary intrastromal, and primary deep stromal) were performed under identical conditions in human cadaver eyes. The resected discs and the beds were observed for uniformity, accuracy, centering, and smoothness. Scanning electron microscopy of the corneal beds and cutting blades was done. RESULTS The three systems produced irregular surfaces with chatter lines that appeared least rough with the Draeger rotating machine. The average primary and secondary section diameters were undersized by 10% in all three systems. The average primary keratectomy thickness was more accurate with Steinway, but the variability was over 20 microns in all three systems. Regarding the average secondary keratectomy thickness, Steinway tended to cut thicker, whereas Draeger and Microprecision tended to cut thinner than attempted. The Draeger blade presented the smoothest edge. CONCLUSIONS All three systems need substantial improvements to produce more accurate, reproducible, and smooth resections. More reliable methods to accurately measure the thickness of the resected cornea should be developed.

Corneal topography in asymptomatic family members of a patient with pellucid marginal degeneration.

PURPOSE To report corneal topographic patterns in asymptomatic family members of a patient with pellucid marginal degeneration. METHODS Computer-assisted corneal topography was used to study the corneas of five family members of a patient with pellucid marginal degeneration. RESULTS In all five asymptomatic family members, corneal biomicroscopy was normal. Corneal topography, however, showed various abnormalities in different members of this family, particularly a topographic pattern suggesting keratoconus in one family member and a topographic pattern suggesting pellucid marginal degeneration in another family member. CONCLUSION This study reinforces the hypothesis that corneal ectatic disorders may represent different manifestations of a clinical spectrum.

Visual performance of an apodized diffractive multifocal intraocular lens with +3.00-d addition: 1-year follow-up.

PURPOSE To determine whether implantation of a multifocal intraocular lens (IOL) with a lower addition (+3.00 diopters [D]) at the lens plane results in better intermediate visual acuity 1 year after surgery compared with a multifocal IOL with higher addition (+4.00 D). METHODS This prospective, randomized, double-masked study included 80 eyes from 40 patients. Twenty patients were implanted bilaterally with the ReSTOR +3.00-D add IOL and 20 patients were implanted bilaterally with the ReSTOR +4.00-D add IOL. Primary outcome measures were distance, intermediate, and near visual acuity. Secondary outcomes were defocus curves, best reading distance, mesopic and photopic contrast sensitivity, quality of life, and spectacle independence. Monocular and binocular visual acuity were measured as uncorrected and corrected distance visual acuity at 4 m, uncorrected near and distance-corrected near visual acuity at 40 cm, and uncorrected intermediate visual acuity and distance-corrected intermediate visual acuity at 50, 60, and 70 cm. RESULTS Twelve months postoperatively, no statistically significant difference between groups in distance and near visual acuity was noted. The ReSTOR +3.00-D add group performed better than the ReSTOR +4.00-D add group at all intermediate distances studied. The ReSTOR +4.00-D group chose a reading distance 8 cm closer than the +3.00-D group. Both groups performed similarly with respect to contrast sensitivity, quality of life, and spectacle independence rates. CONCLUSIONS Patients implanted with a multifocal IOL with lower addition (ReSTOR +3.00 D) had better performance at intermediate distances compared with the ReSTOR +4.00-D add IOL with similar performance for distance and near visual acuity, contrast sensitivity, and quality of life.

Modulation transfer function and optical quality after bilateral implantation of a +3.00 D versus a +4.00 D multifocal intraocular lens

PURPOSE: To determine whether the improvement in intermediate vision after bilateral implantation of an aspheric multifocal intraocular lens (IOL) with a +3.00 diopter (D) addition (add) occurs at the expense of optical quality compared with the previous model with a +4.00 D add. SETTING: Department of Ophthalmology, University of São Paulo, São Paulo, Brazil. DESIGN: Prospective randomized double‐masked comparative clinical trial. METHODS: One year after bilateral implantation of Acrysof Restor SN6AD1 +3.00 D IOLs or Acrysof Restor SN6AD3 +4.00 D IOLs, optical quality was evaluated by analyzing the in vivo modulation transfer function (MTF) and point‐spread function (expressed as Strehl ratio). The Strehl ratio and MTF curve with a 4.0 pupil and a 6.0 mm pupil were measured by dynamic retinoscopy aberrometry. The uncorrected and corrected distance visual acuities at 4 m, uncorrected and distance‐corrected near visual acuities at 40 cm, and uncorrected and distance‐corrected intermediate visual acuities at 50 cm, 60 cm, and 70 cm were measured. RESULTS: Both IOL groups comprised 40 eyes of 20 patients. One year postoperatively, there were no statistically significant between‐group differences in the MTF or Strehl ratio with either pupil size. There were no statistically significant between‐group differences in distance or near visual acuity. Intermediate visual acuity was significantly better in the +3.00 D IOL group. CONCLUSION: Results indicate that the improvement in intermediate vision in eyes with the aspheric multifocal + 3.00 D add IOL occurred without decreasing optical quality over that with the previous version IOL with a +4.00 D add. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Screening of refractive surgery candidates for LASIK and PRK.

Purpose: The aim of this study was to evaluate exclusion criteria in screening patients for refractive surgery. Methods: Patients screened for initial refractive surgery by a single surgeon at the Cole Eye Institute (Cleveland Clinic) between 2007 and 2012 were reviewed. Exclusion criteria for patients who were not offered refractive surgery based on history and/or examination parameters were analyzed. Results: A total of 1067 refractive candidates were enrolled in the study. Five hundred nineteen (48.6%) were male and 548 (51.4%) were female with a mean age of 39 ± 12 (range, 17–78) years. Refractive surgery was performed in 657 (61.6%) patients, and photorefractive keratectomy was considered the best option for 106 (9.9%) patients. Four hundred ten (38.4%) of all screened patients did not have refractive surgery, and 134 of these patients (12.6%) were considered to have contraindications for laser in situ keratomileusis and photorefractive keratectomy. Among the excluded patients, 69 (51.5%) were male and 65 (48.5%) were female with a mean age of 40 ± 14 (range, 18–78) years. Abnormal corneal topography (34.3%) and low or insufficient corneal thickness (23.1%) were the most common reasons for exclusion. High myopia (10.5%) and (insipient or definite) cataract (9.7%) were also common reasons for exclusion. Other common factors for exclusion were high hyperopia (3.7%), need to wear reading glasses after surgery (3.7%), and severe dry eye unresponsive to treatment (3.7%). Conclusions: Abnormal corneal topography and low, or insufficient, corneal thickness remain the most common exclusion factors for corneal refractive surgery. Factors such as cataract, too high of correction, and severe dry eye are also common reasons for exclusion of patients.

Surgical management of presbyopia.

Presbyopia, the gradual loss of accommodation that becomes clinically significant during the fifth decade of life, is a physiologic inevitability. Different technologies are being pursued to achieve surgical correction of this disability; however, a number of limitations have prevented widespread acceptance of surgical presbyopia correction, such as optical and visual distortion, induced corneal ectasia, haze, anisometropy with monovision, regression of effect, decline in uncorrected distance vision, and the inherent risks with invasive techniques, limiting the development of an ideal solution. The correction of the presbyopia and the restoration of accommodation are considered the final frontier of refractive surgery. The purpose of this paper is to provide an update about current procedures available for presbyopia correction, their advantages, and disadvantages.

Intraocular Straylight and Contrast Sensitivity After Contralateral Wavefront-Guided LASIK and Wavefront-Guided PRK for Myopia

PURPOSE To compare intraocular straylight measurements and contrast sensitivity after wavefront-guided LASIK (WFG LASIK) in one eye and wavefront-guided photorefractive keratectomy (WFG PRK) in the fellow eye for myopia and myopic astigmatism correction. METHODS A prospective, randomized study of 22 eyes of 11 patients who underwent simultaneous WFG LASIK and WFG PRK (contralateral eye). Both groups were treated with the NIDEK Advanced Vision Excimer Laser System, and a microkeratome was used for flap creation in the WFG LASIK group. High and low contrast visual acuity, wavefront analysis, contrast sensitivity, and retinal straylight measurements were performed preoperatively and at 3, 6, and 12 months postoperatively. A third-generation straylight meter, C-Quant (Oculus Optikgeräte GmbH), was used for measuring intraocular straylight. RESULTS Twelve months postoperatively, mean uncorrected distance visual acuity was -0.06 +/- 0.07 logMAR in the WFG LASIK group and -0.10 +/- 0.10 logMAR in the WFG PRK group. Mean preoperative intraocular straylight was 0.94 +/- 0.12 logs for the WFG LASIK group and 0.96 +/- 0.11 logs for the WFG PRK group. After 12 months, the mean straylight value was 1.01 +/- 0.1 log s for the WFG LASIK group and 0.97 +/- 0.12 log s for the WFG PRK group. No difference was found between techniques after 12 months (P = .306). No significant difference in photopic and mesopic contrast sensitivity between groups was noted. CONCLUSIONS Intraocular straylight showed no statistically significant increase 1 year after WFG LASIK and WFG PRK. Higher order aberrations increased significantly after surgery for both groups. Nevertheless, WFG LASIK and WFG PRK yielded excellent visual acuity and contrast sensitivity performance without significant differences between techniques.

Ectasia risk factors in refractive surgery

This review outlines risk factors of post-laser in situ keratomileusis (LASIK) ectasia that can be detected preoperatively and presents a new metric to be considered in the detection of ectasia risk. Relevant factors in refractive surgery screening include the analysis of intrinsic biomechanical properties (information obtained from corneal topography/tomography and patient’s age), as well as the analysis of alterable biomechanical properties (information obtained from the amount of tissue altered by surgery and the remaining load-bearing tissue). Corneal topography patterns of placido disk seem to play a pivotal role as a surrogate of corneal strength, and abnormal corneal topography remains to be the most important identifiable risk factor for ectasia. Information derived from tomography, such as pachymetric and epithelial maps as well as computational strategies, to help in the detection of keratoconus is additional and relevant. High percentage of tissue altered (PTA) is the most robust risk factor for ectasia after LASIK in patients with normal preoperative corneal topography. Compared to specific residual stromal bed (RSB) or central corneal thickness values, percentage of tissue altered likely provides a more individualized measure of biomechanical alteration because it considers the relationship between thickness, tissue altered through ablation and flap creation, and ultimate RSB thickness. Other recognized risk factors include low RSB, thin cornea, and high myopia. Age is also a very important risk factor and still remains as one of the most overlooked ones. A comprehensive screening approach with the Ectasia Risk Score System, which evaluates multiple risk factors simultaneously, is also a helpful tool in the screening strategy.

Intense Early Flattening After Corneal Collagen Cross-linking

PURPOSE To report two cases of significant flattening after corneal cross-linking (CXL) for keratoconus and discuss its potential explanations and implications. METHODS Observational case report. RESULTS One year after standard CXL protocol (3 mW/cm(2) for 30 minutes and total energy of 5.4 J/cm(2)), a 28-year-old woman presented a flattening of greater than 14 diopters and a 14-year-old boy presented a flattening of 7 diopters. CONCLUSIONS Although rare, a significant flattening effect may occur during the first year after CXL, probably related to intense wound healing, increase in corneal elasticity, CXL effective depth, and central cone location. These cases suggest the necessity of a patient-specific approach and a better understanding regarding the actual mechanism behind its potent effect.

Precision of Higher Order Aberration Repeatability With NIDEK OPD-Scan Retinoscopic Aberrometry

PURPOSE To evaluate repeatability of the total high order aberrations with a retinoscopic wavefront sensor. METHODS This prospective case series analyzed 12 eyes from 6 patients who underwent wavefront measurement using retinoscopic aberrometry with the NIDEK Optical Path Difference Scan (OPD-Scan). Four consecutive wavefront measurements of each eye were taken by two trained examiners for 5.8+/-0.8-mm and 8.2+/-0.6-mm pupils (P=.002, Wilcoxon test). Total high order aberrations out to the eighth order were assessed including third order coma, third order trefoil, fourth order quadrafoil, fourth order secondary astigmatism, and fourth order spherical aberrations. Differences between measurements of all of the variables were analyzed. A P value <.05 was considered statistically significant. RESULTS Repeatability analysis of the root-mean-square of total higher order aberrations, coma, trefoil, quadrafoil, secondary astigmatism, and spherical aberrations for both dilated and nondilated pupils did not show a statistically significant difference among all repeated measurements, except for trefoil and secondary astigmatism (analysis of variance and the Friedman test). The repeatability of total higher order aberrations was 0.15 microm for nondilated pupils and 0.18 microm for dilated pupils. Except for trefoil measurements, all high order aberrations showed reproducibility >0.15 microm when Zernike coefficients were analyzed individually. CONCLUSIONS The NIDEK OPD-Scan aberrometer measures total higher order astigmatism and most individual aberrations with acceptable repeatability. However, measurement of trefoil with this instrument is less repeatable.