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Purpose: To investigate the impact of corneal higher-order aberrations (HOAs) on predicted corrected distance visual acuity (CDVA) in patients with keratoconus at varying simulated pupil apertures., Setting: Ophthalmology Clinics, Medical University of South Carolina, Charleston, South Carolina., Design: Retrospective chart review study., Methods: 56 eyes with keratoconus were examined using Scheimpflug tomography during routine examinations before medical intervention. The severity of keratoconus was graded using the Amsler-Krumeich classification. Zernike analysis was used to obtain corneal aberrations using simulated pupil diameters of 6 mm, 4 mm, and 2 mm. These data were extrapolated to obtain the total root mean square HOAs for a 1.6 mm simulated pupil to evaluate the potential effect of a small aperture intraocular lens (IOL). Correlation analysis was used to study the impact and relative contributions of HOAs on CDVA. Convolution of HOAs from OPD-Scan III provided a clinical method to predict CDVA with different simulated pupil sizes in corneas with irregular astigmatism., Results: There were statistically significant positive correlations between photopic CDVA and the magnitude of total and individual (coma, spherical aberration, and trefoil) HOAs in this cohort of keratoconus participants. A keratoconus case with the small aperture IOL confirms the improvement in vision due to the pinhole effect., Conclusions: The small aperture IOL is expected to markedly reduce aberrations in patients with keratoconus up to Amsler-Krumeich class 4 severity to levels consistent with the levels seen in healthy patients. Convolution of corneal HOAs with the Early Treatment Diabetic Retinopathy Study chart provides a useful simulation of the impact of pinhole optics in aberrated eyes., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of ASCRS and ESCRS.)

The purpose of this article is to review the current status of presbyopia amelioration with surgical and pharmacologic procedures that partially compensate for loss of accommodation in advance of cataract surgery and lens replacement. Over the last few years, several corneal surgical and topical pharmacological approaches for the treatment of presbyopia have been introduced to the marketplace or are in the developmental pipeline. The approaches vary in invasiveness, duration of effect, reversibility, risk/benefit ratio, and clinical results. The advantages and disadvantages for each are discussed. Corneal surgical interventions aim to provide improved near and intermediate vision in patients with presbyopia through refractive means that extend ocular depth of focus through shape modification. The use of miotic drops or corneal lamellar implants extend depth of focus with the "pinhole" aperture size reduction effect. Unlike in adults younger than 40 years, the refractive status of the patient with presbyopia is not stable. Hence, procedures that provide a permanent refractive change may not provide long-term full correction; eye drops or other treatments that are self-reversing in time or are easily reversible may be used as needed. On the horizon, procedures are being explored that may add years of functional lens accommodation by preserving the deformable gel properties of the lens. [ J Refract Surg . 2021;37(6 Suppl):S20-S27.] .

The mammalian cornea maintains its thickness and transparency primarily by the activity of a fluid pump located in the endothelial cell layer. The accepted concept, the "pump-leak" theory, holds that the active transport of solute from the stroma to the aqueous humor leads to a steady state osmotic pressure gradient across the endothelium that balances the imbibition pressure created by the hydrophilic proteoglycans in the stromal ground substance. The details of this process are controversial and some of the classical in vitro studies aimed to explore the fluid pump using low temperature to challenge the regulatory behavior cannot be duplicated in vivo. The activity of sensory or sympathetic innervation may play a role in this low temperature tolerance. Asymmetry in endothelial cell volume regulation could be the basis for the fluid pump., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Objectives: To evaluate corneal irregular astigmatism due to the anterior corneal surface using Fourier harmonic analysis with a Placido ring-based corneal topographer (Placido-based topographer) and three-dimensional anterior segment optical coherence tomography (OCT) in dry eyes., Methods: Forty-four eyes of 44 subjects with dry eye and 20 eyes of 20 normal control subjects were enrolled. Corneal topographic data were obtained using a Placido-based topographer and OCT. Dioptric data from the central 3-mm zone of the anterior corneal surface were decomposed using Fourier harmonic analysis. Spherical, regular astigmatism, and irregular astigmatism (asymmetry and higher-order irregularity) refractive error components of the cornea from the two imaging modalities were compared., Results: Both asymmetry and higher-order irregularity values were significantly greater in dry eyes than in control eyes for both the Placido-based topographer and OCT measurements (all P<0.05). In dry eyes, measured values of asymmetry and higher-order irregularities were significantly smaller when obtained with OCT than with the Placido-based topographer (both P<0.001). By contrast, these parameters were not significantly different between the two devices in control eyes. In dry eyes, severity of superficial punctate keratopathy in the central corneal region was correlated with irregular astigmatism., Conclusions: The amount of corneal irregular astigmatism, quantified using Fourier harmonic analysis, was significantly higher in dry eyes than in normal eyes. Measurements obtained with OCT and the Placido-based topographer differed in subjects with dry eyes. Therefore, caution should be practiced when trying to use these measurements interchangeably.

Purpose: To investigate chronological changes in patients with very asymmetric keratoconus (KC) by Scheimpflug-based corneal tomographic evaluation., Methods: We retrospectively reviewed the clinical records of 382 patients with KC attending a university hospital. Patients who were diagnosed with KC in one eye and forme fruste keratoconus in the other eye at the last visit and followed up with Scheimpflug-based tomographic corneal imaging were included. The anterior radius of curvature (ARC) and posterior radius of curvature (PRC) obtained at a 3.0-mm optical zone and the thinnest pachymetry reading of corneal thickness (Tmin), were used to investigate the chronological changes in tomographic parameters., Results: Twenty-six patients aged 16 to 66 years met the inclusion criteria. The mean observation period was 6 years and 4 months. There was a significant increase in annual change in PRC with a longer follow-up period after initial examination (P = 0.011). Moreover, a greater increase in annual change in ARC was observed in patients in whom the initial examination was performed at a younger age than in those in whom it was performed at an older age (P < 0.001)., Conclusions: On the basis of tomographic evaluation, even if the measured values are almost stable and within normal limits, a long-term clinical follow-up is warranted in forme fruste keratoconus eyes. Younger patients with very asymmetric keratoconus should be monitored carefully.

Purpose: To explore the use of microperimetry in the evaluation of macular dysfunction in patients with cataract, to aid in proper intraocular lens selection (multifocal vs monofocal), and to set expectations for postoperative visual function., Methods: One randomly chosen eye of 10 patients diagnosed as having mild (1+) to moderate (3+) cataract was evaluated before and 1 week after cataract surgery with the MAIA microperimeter (Centervue S.p.A, Padova, Italy). Corrected distance visual acuity, dilated and undilated biomicroscopy and indirect fundus examinations, intraocular pressure measurement, and a MAIA microperimeter test to measure macular sensitivity and fixation pattern were also performed., Results: Two patients showed macular abnormalities before and after surgery that were noted on MAIA testing: one patient showed reduced average threshold sensitivity and abnormal percent reduced threshold, whereas the other patient showed fixation drift demonstrating eccentric fixation. Both eyes had reduced postoperative visual performance after uneventful cataract surgeries., Conclusions: Because not every macular lesion noted on fundus examination or optical coherence tomography may be clinically significant, microperimetry can be useful to detect clinically significant retinal dysfunction prior to cataract surgery. The outcome may aid in the selection of intraocular lens type and may yield a better documented surgical prognosis. Further studies are necessary to confirm these findings., (Copyright 2015, SLACK Incorporated.)

Purpose: To compare objective and subjective metrics from regular and high-resolution Scheimpflug devices (Pentacam) to determine their equivalence and interchangeability for refractive surgery screening., Setting: Emory Vision at Emory University, Atlanta, Georgia, USA., Design: Retrospective comparative case series., Methods: Eyes of consecutive screened refractive surgery patients were evaluated with high-resolution and regular Scheimpflug devices. Objective parameters evaluated included keratometry (K) values, central corneal thickness (CCT), and device-generated keratoconus screening indices. Masked expert reviewers subjectively graded images as normal, suspicious, or abnormal., Results: One hundred eyes of 50 patients were evaluated. The mean K values were not significantly different (anterior K: high resolution 1.21 diopters [D] ± 1.13 (SD) versus regular 1.15 ± 1.16 D, P = 0.73; posterior K: 0.34 ± 0.23 D versus regular 0.35 ± 0.23 D, P = .67). The mean CCT was significantly thinner in the high-resolution group (514.7 ± 26.6 μm versus 527.6 ± 27.6 μm (P < .0001) with limits of agreement of -12.9 to +17.5 μm. Most keratoconus screening indices were more suspicious with the high-resolution device than with the regular device except the indices of height asymmetry and height deviation. Subjectively, 60% of cases received the same score, high resolution was more suspicious in 28% of cases, and regular was more suspicious in 12% of cases; there was only slight subjective agreement between technologies (κ = 0.26 to 0.31)., Conclusions: Regular and high-resolution Scheimpflug imaging devices generated different objective values and significantly different subjective interpretations with poor inter-reviewer agreement. The high-resolution device provided a more conservative overall output. For refractive surgical screening, the 2 devices are not interchangeable., Financial Disclosure: Proprietary or commercial disclosures are listed after the references., (Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.)

Purpose: To evaluate the variability of subjective corneal topography map classification between different experienced examiners and the impact of changing from an absolute to a normative scale on the classifications., Methods: Preoperative axial curvature maps using Scheimpflug imaging obtained with the Pentacam HR (Oculus Optikgeräte, Wetzlar, Germany) and clinical parameters were sent to 11 corneal topography specialists for subjective classification according to the Ectasia Risk Scoring System. The study population included two groups: 11 eyes that developed ectasia after LASIK and 14 eyes that had successful and stable LASIK outcomes. Each case was first reviewed using the absolute scale masked to the patient group. After 3 months, the same cases were represented using a normative scale and reviewed again by the same examiners for new classifications masked to the patient group., Results: Using the absolute scale, 17 of 25 (68%) cases had variations on the classifications from 0 to 4 for the same eye across examiners, and the overall agreement with the mode was 60%. Using the normative scale, the classifications from 11 of 25 (44%) cases varied from 0 to 4 for the same eye across examiners, and the overall agreement with the mode was 61%. Eight examiners (73%) reported statistically higher scores (P < .05) when using the normative scale. Considering all 550 topographic analyses (25 cases, 11 examiners, and two scales), the same classification from the two scales was reported for 121 case pairs (44%)., Conclusion: There was significant inter-observer variability in the subjective classifications using the same scale, and significant intra-observer variability between scales. Changing from an absolute to a normative scale increased the scores on the classifications by the same examiner, but significant inter-observer variability in the subjective interpretation of the maps still persisted., (Copyright 2013, SLACK Incorporated.)

Purpose: Wavefront data are expressed in micrometers and referenced to the pupil plane, but current methods to map wavefront error lack standardization. Many use normalized or floating scales that may confuse the user by generating ambiguous, noisy, or varying information. An absolute scale that combines consistent clinical information with statistical relevance is needed for wavefront error mapping. The color contours should correspond better to current corneal topography standards to improve clinical interpretation., Design: Retrospective analysis of wavefront error data., Participants: Historic ophthalmic medical records., Methods: Topographic modeling system topographical examinations of 120 corneas across 12 categories were used. Corneal wavefront error data in micrometers from each topography map were extracted at 8 Zernike polynomial orders and for 3 pupil diameters expressed in millimeters (3, 5, and 7 mm). Both total aberrations (orders 2 through 8) and higher-order aberrations (orders 3 through 8) were expressed in the form of frequency histograms to determine the working range of the scale across all categories. The standard deviation of the mean error of normal corneas determined the map contour resolution. Map colors were based on corneal topography color standards and on the ability to distinguish adjacent color contours through contrast., Main Outcome Measures: Higher-order and total wavefront error contour maps for different corneal conditions., Results: An absolute color scale was produced that encompassed a range of +/-6.5 microm and a contour interval of 0.5 microm. All aberrations in the categorical database were plotted with no loss of clinical information necessary for classification. In the few instances where mapped information was beyond the range of the scale, the type and severity of aberration remained legible., Conclusions: When wavefront data are expressed in micrometers, this absolute scale facilitates the determination of the severity of aberrations present compared with a floating scale, particularly for distinguishing normal from abnormal levels of wavefront error. The new color palette makes it easier to identify disorders. The corneal mapping method can be extended to mapping whole eye wavefront errors. When refraction data are expressed in diopters, the previously published corneal topography scale is suggested.

Purpose: When keratorefractive surgery is used to treat a central corneal diameter smaller than the resting pupil, visual symptoms of polyopia, ghosting, blur, haloes, and glare can be experienced. Progress has been made to enlarge the area of surgical treatment to extend beyond the photopic pupil; however, geometric limitations can pose restrictions to extend the treatment beyond the mesopic pupil diameter and can lead to impediments in night vision. The size of the treated area that has achieved good optical performance has been defined as the functional optical zone (FOZ). In this study the authors developed three objective methods to measure the FOZ., Methods: Corneal topography examination results from 1 eye of 34 unoperated normal eyes and 32 myopic eyes corrected by laser in situ keratomileusis (LASIK) were evaluated in three ways. First, a uniform axial power method (FOZ(A)) assessed the area of the postoperative cornea that was within a +/-0.5-D window centered on the mathematical mode. Second, FOZ was determined based on the corneal wavefront true RMS error as a function of the simulated pupil size (FOZ(R)). Third, FOZ was determined from the radial MTF, established at the retinal plane as a function of pupil size (FOZ(M))., Results: Means for each of the FOZ methods (FOZ(A), FOZ(R), and FOZ(M)) were 7.6, 9.1, and 7.7 mm, respectively, for normal eyes. For LASIK-corrected eyes, these means were 6.0, 6.9, and 6.0 mm. Overall, an average decrease of 1.8 mm in the functional optical zone was found after the LASIK procedure. Correlations between the FOZ methods after LASIK showed acceptable and statistically significant values (R = 0.71, 0.70, and 0.61; P < 0.01)., Conclusions: These methods will be useful to more fully characterize corneal treatment profiles after keratorefractive surgery. Because of its ease of implementation, direct spatial correspondence to corneal topography, and good correlation to the other more computationally intensive methods, the semiempiric uniform axial power method (FOZ(A)) appears to be most practical in use. The ability to measure the size of the FOZ should permit further evolution of keratorefractive surgical lasers and their algorithms to reduce the night vision impediments that can arise from functional optical zones that do not encompass the entire mesopic pupil.

Purpose: To determine the goodness-of-prediction of the fitting routine by measuring the difference between topographic corneal surfaces and their Zernike reconstructions as a function of polynomial order and optical zone size for various corneal conditions., Setting: Corneal research laboratory in a university eye center., Methods: Corneal topography maps (N = 253) were obtained from the Louisiana State University Eye Center. A variety of corneal conditions were used: normals; astigmatism; laser in situ keratomileusis, photorefractive keratoplasty (PRK), and radial keratotomy (RK) postoperative cases (myopic spherical corrections); keratoconus suspect; mild, moderate, and severe keratoconus; pellucid marginal degeneration; contact lens-induced corneal warpage; and penetrating keratoplasty. The root-mean-square (RMS) error of the goodness-of-prediction of the Zernike representation of corneal surface elevation was extracted for 4, 6, and 10 mm optical zones, whereas Zernike radial orders were varied from 3 to 14 in 1-order steps. The mean +/- SEM of the RMS error was plotted as a function of Zernike order and compared with criteria for normal surface fits., Results: Fitting accuracy improved as more Zernike terms were included, but some conditions showed significant errors (when compared with normal surfaces), even with many added terms. For a 6 mm optical zone, the normal cornea group had the lowest RMS error and did not require terms above the 4th order to achieve <0.25 microm RMS error. Astigmatism met the 0.25 microm threshold at the 5th order, whereas keratoconus suspect required 7 orders. Laser in situ keratomileusis and PRK met the 0.25 microm threshold at the 8th order, whereas RK required 10 orders. Contact lens-induced corneal warpage and mild keratoconus needed 12 orders to meet the 0.25 microm threshold, whereas pellucid marginal degeneration, moderate and severe keratoconus, and keratoplasty categories were not well fitted even at 14 orders., Conclusions: A 4th-order Zernike polynomial appeared reliable for modeling the normal cornea, but using a 4th-order fitting routine with an abnormal corneal surface caused a loss of fine-detail shape information. As more Zernike terms were added, the accuracy of the fit improved, and the result approached the minimum error found with normal corneas. Unless sufficient higher-order Zernike terms are included when analyzing irregular surfaces, some diagnostic applications of Zernike coefficients may not be rigorous. This conclusion also suggests that wavefront shape analysis is similarly dependent on the number of orders used. Current surgical corrections based on normal-eye wavefronts may fail to capture all visually relevant aberrations in abnormal eyes, such as those having laser retreatments or experiencing corneal warpage from contact lens wear. A clinical goodness-of-fit or goodness-of-prediction index would indicate whether the number of terms in use has fully accounted for all of the visually significant aberrations present in the eye.

Purpose: To present a corneal topography screening device for the detection of corneal ectasias and various refractive procedures based on corneal topography patterns., Methods: A database of corneal topography patterns were analyzed and used to "train" a neural network on nine different corneal topography patterns using nineteen corneal topography indices of corneal shape and power., Results: Sample normal and corneal topographies were recognized correctly., Conclusions: The use of the corneal navigator to screen various corneal topographies aids clinical diagnosis.

Purpose: Zernike expansion has been selected for use in describing wavefront aberrations in the human eye. The advantages and limitations of this approach are assessed for eyes with varying degrees of aberration., Methods: Corneal topography examinations were taken with the Nidek OPD-Scan topographer/aberrometer. These higher data density corneal topography examinations were converted to height data and subsequently to wavefront representations. System noise was evaluated with a 2D frequency analysis of 43-D test balls. Both Zernike polynomials and 2D Fourier transforms were used to evaluate fidelity in the presentation of the point spread function. A display format for potential clinical use was developed based upon Zernike decomposition., Results: Systematic noise from the corneal topographer was found to be minimal and, when eliminated, produced small changes in the point spread function. Using Zernike decomposition up to the 30th order failed to preserve the higher frequency aberrations present in aberrated eyes. Use of a Zernike decomposition display with a fixed micron scale presented only clinically significant details of spherical aberration, coma, trefoil, irregular components above third order and total higher-order aberrations (above second order)., Conclusions: Zernike polynomials excel in extracting the low-order optical characteristics of visual optics. Zernikes accurately represent both low- and high-order aberrations in normal eyes where high-order aberrations are clinically insignificant. For eyes after corneal surgery or eyes with corneal pathology such as keratoconus that have significant higher-order aberrations, the Zernike method fails to capture all clinically significant higher-order aberrations.

The air/tear interface contributes 70% of the vergence in the eye and, because of this, even minor variations in its shape can produce significant visual deficit. Placido disc-based corneal topographers measure the precise characteristics of the corneal surface, transforming shape into color-coded dioptric power maps and topography indexes related to optical quality and specific patterns associated with pathology. Artificial intelligence-based methods are used to classify corneal topography and these are used as screening tools. Coupling corneal topography measurements with aberrometry measurements permits the display of the internal aberrations of the eye. Together, these data provide the opportunity to extend refractive correction beyond sphere and cylinder to the higher order aberrations as well.

Purpose: To evaluate the tear film stability of patients before and after laser in situ keratomileusis (LASIK) using the tear film stability analysis system (TSAS)., Design: Prospective observational case series., Methods: New videokeratography software for a topographic modeling system (TMS-2N) was developed that can automatically capture consecutive corneal surface images every second for 10 seconds. Thirty-four subjects (64 eyes) who underwent myopia LASIK were enrolled in this study. All subjects were examined with the new system before LASIK and at 1 week, 1 month, 3 months, and 6 months after the surgery. Corneal topographs were analyzed for tear breakup time (TMS breakup time) and breakup area (TMS breakup area). Based on pre-LASIK TSAS analysis, subjects were separated into normal and abnormal TSAS value groups. The criteria for the normal group were either TMS breakup time more than 5 seconds or TMS breakup area less than 0.2. The percentage of the occurrence of superficial punctuate keratitis was compared between the two groups with regard to subject's dry eye signs and symptoms., Results: Tear film stability decreased significantly during the early period after LASIK, as indexed by decreased TMS breakup time and increased TMS breakup area. Tear film instability resolved at 6 months after surgery. Before LASIK, 22 subjects (43 eyes) had normal TSAS evaluation and 12 subjects (21 eyes) were abnormal. After LASIK, among normal TSAS value eyes, 8 of 43 (18.6%) eyes developed superficial punctuate keratitis. In sharp contrast, 14 of 21 (66.7%) eyes in the abnormal group displayed superficial punctuate keratitis, correlating well with the patients' dry eye symptoms. The difference in the presence of superficial punctuate keratitis after LASIK between normal and abnormal TSAS value groups was statistically significant (P <.001). Subjects with abnormal TSAS evaluation also displayed resistance to dry eye treatment and had extended period of recovery., Conclusions: Tear film stability analysis can be a useful means for screening LASIK candidates before surgery and for prognosticating dry eye symptoms thereafter.

Purpose: It is assumed that wavefront error data arising from aberrometry are adequately described by a Zernike polynomial function, although this assumption has not been extensively tested. Inaccuracies in wavefront error may compromise clinical testing and refractive correction procedures. The current retrospective study correlates visual acuity with corneal wavefront error and with the residual surface elevation error after fitting with the Zernike method., Methods: Corneal topography maps were obtained from 32 keratoconus cases, 27 postoperative penetrating keratoplasty cases, and 29 postoperative conductive keratoplasty cases (88 total). The best spectacle-corrected visual acuity (BSCVA) for each case ranged from -0.2 to 1.3 logarithm of the minimum angle of resolution (logMAR) units (20/12.5-20/400). Topography was analyzed to determine wavefront error and the elevation fit error for a 4-mm optical zone. The 4th and 10th expansion series were analyzed with the 0th-order (piston) and 1st order (tip and tilt) removed. Linear regression analysis was performed. The difference in root mean square (RMS) error between the 4th- and 10th-order analyses was assessed for both wavefront and elevation fit error., Results: The correlation of BSCVA to wavefront error for 4th-order terms was moderately strong and significant (R2=0.581; P<0.001). The 10th-order correlation for wavefront error had a similar result (R2=0.565; P<0.001), but the regression was not significantly different from the 4th-order result. The correlation of BSCVA to the elevation fit error was strong and significant for the 4th order (R2=0.658; P<0.001). The 10th-order data had a similar result (R2=0.509; P<0.001), and there was no significant difference between the two regressions. Only 72% of the cases showed a shift toward increased wavefront error with the 10th-order series, whereas 18% lost wavefront error. All cases showed a shift toward improved elevation fit with the 10th-order expansion., Conclusions: The wavefront error correlation to acuity was moderately strong, but the corneal elevation fit error also strongly correlated with visual acuity, indicating that Zernike polynomials do not fully characterize the surface shape features that influence vision and that exist in postsurgical or pathologic eyes. In addition, the change in wavefront error when using a larger expansion series was found to increase or diminish somewhat unpredictably. The authors conclude that Zernike polynomials fail to model all the information that influences visual acuity, which may confound clinical diagnosis and treatment.

Purpose: To determine the specific biochemical pathways involved in the initial-phase inflammatory response that causes stromal edema after epithelial debridement of the rabbit cornea., Methods: Adult New Zealand White rabbit corneas were treated with 2 mM synthetic inhibitor of metalloproteinase (SIMP)-1, 1 mM DFU (a specific cyclooxygenase [COX]-2 inhibitor) in 50/50 dimethyl sulfoxide (DMSO)/Ringer's solution, 300 KIU aprotinin (a serine protease inhibitor), 0.05% or 0.10% IL-1 receptor type II solution, 1 mM gliotoxin (a Ras farnesyltransferase inhibitor), or vehicle alone (the control). These were applied topically in vivo in five doses over a 3-hour period except IL-1 receptor type II, which was applied in vitro. After rabbits were killed, the corneas were mounted in perfusion chambers with the endothelium bathed in a modified Ringer's solution and the epithelium bathed with silicone oil. Corneal thickness was measured with an automatic specular microscope. The corneal thickness typically stabilized 1 hour after mounting. After stabilization, the corneal epithelium was removed with a rotating bristle brush and stromal thickness monitored for 1 hour. Paired control corneas were treated similarly. RESULTS. Stromal swelling after epithelial debridement was significantly less in most treated corneas, compared with untreated controls: 18.4 +/- 5.3 microm vs. 28.6 +/- 7.7 microm (n = 6, P = 0.004); SIMP-1, 18.7 +/- 10.2 microm vs. 34.3 +/- 10.2 microm (n = 7, P = 0.02); DFU, 19.3 +/- 10.2 microm vs. 23.5 +/- 8.4 microm (n = 6, P = 0.01); and IL-1 receptor type II (0.05%), 26.2 +/- 5.6 microm vs. 30.4 +/- 5.6 microm (n = 5, P = 0.03) and (0.10%), 26.6 +/- 5.6 microm vs. 32.1 +/- 7.4 microm (n = 8, P = 0.03). Gliotoxin was not effective (21.5 +/- 8.0 microm vs. 21.9 +/- 6.2 microm; n = 5, P = 0.94)., Conclusions: The reduction of stromal edema after topical administration of the inhibitors demonstrates the involvement of the COX-2 enzyme, the matrix metalloproteinase family, plasminogens, and the IL-1 system in the trauma-induced inflammatory response of the rabbit cornea. The inflammatory process in the cornea associated with trauma can proceed along multiple redundant parallel pathways.

Purpose: To report a new tear film stability analysis system using videokeratography., Design: Observational case series., Methods: New videokeratography software for TMS-2N (topographic modeling system; TOMEY Corporation, Nagoya, Japan) was developed that can automatically capture consecutive corneal surface images every second for 10 seconds. Forty-eight adult volunteers (80 eyes) were recruited for this study, and all subjects were examined with the new system. Corneal topographs were analyzed for tear breakup time (TMS-BUT) and the ratio of breakup area to entire color-code area (TMS-BUA) was calculated. Routine methods for tear film breakup time evaluation using slit-lamp microscope and fluorescence staining (SLE-BUT) were performed for comparison purposes. Regressive correlations of TMS-BUT or TMS-BUA with SLE-BUT were analyzed. Based on SLE results, subjects were separated into two groups with normal and short BUT, respectively. TMS-BUT and TMS-BUA were compared with SLE-BUT data with regard to the sensitivity and specificity of evaluation of dry eye symptoms., Results: Topographic modeling system-tear breakup time (TMS-BUT) had a positive correlation with SLE-BUT (R = 0.7219, P <.0001), whereas TMS-BUA showed a negative correlation (R = 0.6317, P <.0001). Among 34 eyes with normal SLE-BUT, 11 eyes (32.35%) displayed abnormal TMS-BUT, 9 (81.82%) of which were associated with dry eye symptoms. The sensitivities of TMS-BUT and TMS-BUA were 97.5% and 95%, respectively, significantly higher than that of SLE-BUT (75%), with P =.008 and 0.01, respectively. Topographic modeling system-BUT and TMS-BUA displayed a similar rate of specificity in comparison with SLE-BUT., Conclusions: This new videokeratography system is a noninvasive and objective method with increased sensitivity for tear film stability analysis.

The corneal endothelium transports solute from the stroma to the aqueous humor, maintaining corneal hydration. Currently, little is known about how this active transport system is controlled. The purpose of this study is to investigate in greater detail the corneal response to small NaCl osmotic perturbations using a more refined automatic thickness measurement system in a search for response signatures of transport control. Adult New Zealand White rabbit corneas were debrided of their epithelium, excised and mounted in perfusion chambers. The endothelium, thus isolated, was bathed in isotonic Glutathione Bicarbonate Ringer's (GBR) solution and the bare anterior stroma was covered with silicone oil. Following stabilization in isotonic GBR, the endothelial perfusate was altered by +/-15 mOsm or+/-45 mOsm for 1 hr and 45 min by addition or removal of NaCl and returned (reversal) to GBR for 1 hr and 45 min. An enhanced, automatic scanning specular microscope monitored stromal thickness. The effective membrane transport coefficients were determined from the stromal thickness vs. time curves using an established numerical model of corneal hydration dynamics. It was found that the small (+/-15 mOsm) NaCl perturbations of the rabbit corneal endothelium resulted in a rapid trans-endothelial stromal volume control response that was not reversible after return to GBR. Long after the expected dissipation of the induced transients, this thickness 'controlling' response ultimately resulted in a sustained net thinning of 14 microm following the hypotonic perturbation and reversal, and a net swelling of 16 microm following the hypertonic perturbation and reversal. Model calculations indicated that the change induced by the perturbation could be explained by an immediate and persistent reduction of the passive endothelial NaCl permeability by 26% for the -15 mOsm perturbation compared to the +15 mOsm perturbation. This change persisted even after return to GBR. In contrast, the larger (+/-45 mOsm) perturbations did not elicit a similar response consistently. Our data suggest that trans-endothelial fluid transport can be rapidly modulated to control stromal hydration in response to small NaCl osmotic stresses in a way that cushions the shock and reduces the change in corneal thickness. Moreover, this behavior is not reversible in the short term, and may assist the regulation of corneal hydration homeostatically.

Purpose: To review the incidence of corneal abnormalities detected in the preoperative examination, using videokeratography and pachymetry that excluded patients from laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK)., Methods: We conducted a chart review of consecutive patients who had a preoperative examination and were excluded from refractive surgery., Results: Eighteen patients from 1,392 refractive candidates (1.3%) were designated as poor candidates for LASIK or PRK based on corneal topography and/or pachymetry. Thirteen patients (0.9%) were identified as having keratoconus suspect, keratoconus, or pellucid marginal degeneration. Five patients (0.4%) were excluded due to thin corneas (<490 microm) despite normal corneal topography., Conclusions: Corneal topography and pachymetry are indispensable tools in the preoperative screening of refractive surgery candidates.

Background: The nonsuperimposable mirror-image symmetry of the body (enantiomorphism) is reflected in the wavefront error maps of eyes. Averaging the wavefront errors of right and left eyes has the potential to adversely affect correlations made between wavefront error and visual acuity or other factors. Not only are the results of past studies using Zernike terms suspected of being invalid, there is concern about possible errors in the algorithms used to create customized corneal ablations., Objective: To compare the results of analysis with and without correction for enantiomorphism., Methods: Fourteen TMS-1 corneal topographic maps from 7 patients having with-the-rule astigmatism in both corneas were selected for Zernike decomposition to 45 terms. The maps were distributed among 3 groups: 7 right eye maps, 7 left eye maps, and 7 left eye maps in which the topography was transposed about the vertical axial to correct for enantiomorphism (left eye-corrected). The wavefront error difference between the right and left eyes was compared with the difference between the right eyes and the left eyes in which enantiomorphism was corrected (right eye vs left eye-corrected). The left eye wavefront error was then compared with the left eye wavefront error after correction (left eye vs left eye-corrected)., Results: Correcting for enantiomorphism produced a statisticially significant difference in the first 5 radial orders of Zernike terms (P=.02). Of the 45 Zernike terms analyzed, 7 terms were significantly different at the P<.05 level in the right eye vs left eye category, compared with 4 terms in the right eye vs left eye-corrected category. Eleven terms were significantly different at the P<.05 level in the left eye vs left eye-corrected category., Conclusions: Correcting for enantiomorphism makes the Zernike terms in right and left eyes appear more similar. Failure to correct for enantiomorphism causes certain terms to cancel each other when averaged across right and left eyes. Wavefront error studies that do not consider enantiomorphism, including those used to adjust laser surgical nomograms, will introduce significant errors to certain Zernike terms.

Purpose: To evaluate the American National Standards Institute (ANSI) corneal topography scale (ANSI Z-80.23-1999) and to develop a Universal Standard Scale (USS) based on scientific principles and clinical usefulness., Design: Retrospective data analysis and computer modeling of frequency of corneal power distributions., Methods: Four variations of corneal topography color scales were constructed using the ANSI standard description. The scales used 21 contour intervals with step sizes of 0.5, 1.0, or 1.5 diopters (D). In example 1, hue was varied, whereas saturation and brightness were held constant. In example 2, hue was varied systematically, whereas luminance was varied to compensate for spectral sensitivity. In example 3, hue was varied, whereas luminance was adjusted to improve color contrast at the center of the scale. In example 4, the palette was generated by varying the red, green, and blue color intensity levels. In the USS, colors were defined by hue, brightness, and saturation, and appearance was optimized by using contrast. The contour interval was determined from the standard deviation of keratometry for 27 normal corneas. The scale range was based on corneal powers found in 388 topography maps of 12 different corneal conditions., Results: ANSI-derived maps were difficult to interpret because of poor color contrast and the inability to associate contours with specific colors in the scale. The 0.5 D interval slightly improved the appearance of some patterns but reduced the useful clinical range of the scale. ANSI colors did not match the user's expectations; abnormal patterns appeared in shades of green, which is associated with normality. The standard deviation of keratometry readings for the normal population was 1.59 D. Hence, the contour interval for the USS was set to 1.5 D. More than 99.9% of the corneal powers in 388 clinical maps were within the range of 30 to 67.5 D, which was chosen as the range for the USS., Conclusions: The ANSI scale for corneal topography is a series of scales that lead to clinical misinterpretations. The alternative USS would provide uniform presentation, unambiguous interpretation, and greater ease of comparison among maps produced by different topographers.

Purpose: To demonstrate an objective method of screening for previous refractive surgery using corneal topography., Setting: Corneal topography research laboratories, LSU Eye Center, New Orleans, Louisiana, USA., Methods: Videokeratography (TMS-1, Tomey) examinations from the LSU Eye Center were randomly divided into training and test sets that each included 32 normal corneas and 106 corneas with previous radial keratotomy or photorefractive keratectomy from 1 month up to 10 years after surgery. A set of 1024 axial curvature values were extracted from mires 1 to 25 from each cornea to form a 1-dimensional waveform. Multiresolution wavelet decomposition was performed on this waveform using the s8 Symmlet wavelet. A portion of the resulting wavelet coefficients was input into a backpropagation neural network that was trained to 5% error. After training, the independent test set was passed though the neural net and scored., Results: The trained network correctly recognized 32 of 32 normal corneas and 105 of 106 refractive surgery corneas for a 99.3% accuracy, 99.1% sensitivity, and 100% specificity for previous myopic refractive surgery detection., Conclusions: The 1-dimensional wavelet-based neural network approach was an effective and accurate method of distinguishing eyes that had had myopic refractive surgery from normal eyes. The single error was a result of having too few examples of grossly decentered procedures in the training set.

Objective: To evaluate the effects of photorefractive keratectomy on corneal optical aberrations using a 5.5-mm optical zone and a 7.0-mm transition zone., Methods: Videokeratographs of 72 eyes from 47 patients treated for low to moderate (1-9 diopters) myopia were obtained at the preoperative and 1-, 3-, 6-, 12-, and 18-month postoperative examinations. The videokeratoscopy data files were used to calculate the wavefront variance of the corneas for small (3-mm) and large (7-mm) pupils using a previously described method., Results: In general, all optical aberrations decreased postoperatively for 3-mm pupils and increased for 7-mm pupils compared with preoperative values. For 3-mm pupils, the 2 common optical aberrations (comalike [S(3)] and spherical-like [S(4)]) decreased postoperatively and never returned to preoperative values. For 7-mm pupils, however, comalike aberrations increased slightly and spherical-like aberrations increased by nearly an order of magnitude during the postoperative period. Similarly, for 3-mm pupils, the higher order S(5) and S(6) aberrations decreased throughout the postoperative period, with S(6) values showing an approximately 23-fold reduction at 12 and 18 months. For 7-mm pupils, S(5) and S(6) aberrations increased slightly, more so for S(5) (approximately 3-fold) than for S(6). Total wavefront aberrations decreased an average of 2.3 times postoperatively for 3-mm pupils, and increased significantly (P<.05) at all postoperative examinations for 7-mm pupils. Opening the pupil from 3 mm to 7 mm before surgery produced a 14-fold increase in total aberrations, whereas this same change produced an average 113-fold increase after photorefractive keratectomy., Conclusions: Corneal optical aberrations after photorefractive keratectomy with a larger ablation zone and a transition zone are less pronounced and more physiologic than those associated with first-generation (5-mm) ablations with no transition zone., Clinical Relevance: Evaluating the postoperative corneal aberration structure will help us devise ways to minimize the wavefront aberrations of the eye through the creation of an ideal corneal first surface, thereby improving visual results for patients undergoing excimer laser ablations for refractive correction.

Purpose: To investigate gender- and age-related differences in the corneal topography of a normal population., Methods: One hundred thirty-two topographic examinations were collected from 100 patients ranging in age from 23 to 83 years (average, 57.35+/-17.38 years). Data were segregated by gender and further divided into younger (less than 50 years) and older (50 years or more) age groups. The topographic indices of Surface Regularity Index, Surface Asymmetry Index, Irregular Astigmatism Index, Standard Deviation of Corneal Power, Corneal Eccentricity Index, Coefficient of Variation of Corneal Power, Simulated Keratometry 1 and 2, and Average Corneal Power were examined. The astigmatism pattern and corneal irregularity were determined and compared with respect to gender and age., Results: The corneas of older men were flatter than those of older women (p < 0.001). The vertical corneal meridian, but not the horizontal meridian, showed statistically significant gender-related changes with aging (p < 0.001). Older men had a significantly higher potential for against-the-rule astigmatism than women (p < 0.001). Corneal irregularity (measured in terms of the Surface Regularity Index and Irregular Astigmatism Index) increased with age (p < 0.001 and p < 0.001, respectively), although there was no gender-related difference. In the younger group, no gender-related differences in corneal curvature or astigmatism pattern were found., Conclusion: Aging influences changes in patterns of astigmatism differently in men and women. Decreases in levels of sex hormones may play a role in gender-related changes in corneal structure with age.

There is now a wide range of devices available for corneal topographic analysis. Although most devices use the Placido disk approach, fluorescein profilometry, laser holography and scanning slit technology have also been employed. The colour-coded topographical maps have been designed for ease of clinical interpretation. The application of this technology to further our understanding of the effects of contact lens wear and various forms of refractive surgery is demonstrated. Current developments include the merging of corneal topographic analysis and ocular wavefront sensing technology to create the capability of etching sophisticated corneal shapes in the course of refractive surgery so as to provide optimal aberration control.

Background: Keratoconus has long been considered to be an ectasia produced by stromal stretching. Although stretching should result in increased corneal surface area, previous observations of topography during progression of keratoconus have suggested that surface area may actually be conserved. A novel objective surface area measurement based on corneal topography was tested and applied to data from actual corneas under various conditions for comparative analysis., Setting: The LSU Eye Center clinic videokeratography archives., Methods: TMS-1 videokeratography files (Tomey Corp, Cambridge, Mass) were obtained from 6 groups of corneas: normal (n = 29), keratoconus from mild to severe states (n = 51), topographically judged keratoconus-suspect conditions (n = 10), postoperative photorefractive keratectomy for myopia (n = 39), with-the-rule corneal astigmatism (n = 17), and keratoglobus (n = 1). Additionally, 3 different spherical test surfaces were analyzed to verify the accuracy of the process. Only maps with no missing data out to ring 29 were used. The cumulative surface area from center to periphery was determined by calculating and summing the area of individual patches along consecutive annular rings. Mean surface area with respect to mean chord radius was plotted for each corneal condition, and curve fitting was used to extend each result to a 5. 85-mm limbus. Means, SEs, and 95% confidence intervals were calculated at intervals for statistical comparisons among all groups. Computer-generated surfaces helped to evaluate the relationship between shape and surface area., Results: When videokeratographic test targets were used, surface area error was less than 2%, which was deemed acceptable. Normal corneas had a mean +/- SE surface area of 120.3 +/- 2.2 mm(2), whereas all keratoconus corneas combined had a mean +/- SE surface area of 116.2 +/- 3.4 mm(2). The difference was not significant at any chord radius (analysis of variance, P<. 05). The keratoglobus cornea was found to have a surface area of 129. 9 mm(2), which was 7.98% greater than normal. An individual with progressive keratoconus exhibited no appreciable trend toward increasing surface area during a 76-month period. The corneas in the other groups resembled normal corneas in their total surface area., Conclusions: With the exception of the single case of keratoglobus, corneal surface area tended to be conserved near a value of 120 mm(2) for all groups in the study, including corneas with keratoconus. Surface area is remarkably insensitive to curvature change near the vertex. Flattening seen in the periphery of corneas with keratoconus suggests that biomechanical coupling compensates for any increase in curvature occurring in the region of the cone itself. Thus, it seems that keratoconus is not a true ectasia as is keratoglobus, but rather a specialized type of warpage, at least in mild to moderate forms of the disease. Arch Ophthalmol. 2000;118:1179-1186

Purpose: To investigate the nature and cause of an acute, anomalous stromal edema after epithelial debridement in the rabbit cornea., Methods: Series I: Adult New Zealand White rabbit corneas were mounted in perfusion chambers. The endothelium was bathed with Ringer's fluid, and the outer surface was covered with silicone oil. The epithelium of one eye was débrided with a scalpel before mounting, and the cornea of the fellow eye was débrided with a rotating brush after stabilization in the perfusion chamber. Using specular microscope tracking software, it was possible to measure total swelling and local swelling within the cornea. Series II: Diclofenac sodium ophthalmic solution 0.1% or a placebo was applied topically, 1 drop per 45 minutes for 3 hours before animals were euthanatized., Results: Series I: Corneas with their epithelium scraped with a scalpel before mounting were 37.5 +/- 17.5 microm (n = 6; P < 0.001) thicker in vitro than the stromas of perfused, intact fellow corneas. Epithelial débridement with a rotating brush after mounting resulted in an immediate (within 8 minutes) stromal swelling that plateaued in 1 hour at 31.0 +/- 5.3 microm (n = 6; P < 0.001). Curiously, in six of six corneas, the anterior stroma swelled more than the posterior stroma. In four of six corneas, the posterior stroma thinned. Analysis showed this pattern to be consistent with a sudden increase in anterior swelling pressure or osmotic pressure and to be inconsistent with a change in endothelial transport properties. Series II: Placebo-treated corneas swelled 30.6 +/- 7.7 microm (n = 5) 1 hour after débridement, whereas corneas pretreated with diclofenac sodium swelled only 19.2 +/- 3.1 microm (n = 6; P < 0.008)., Conclusions: The anterior stromal swelling occurs rapidly and near the site of epithelial injury suggesting messenger and/or enzymatic involvement with an effect parallel to apoptosis. Reduction of the swelling response with nonsteroidal anti-inflammatory drugs (NSAIDs) implicates the cyclooxygenase pathway. The swelling is similar to the unexplained acute edema that occurs during inflammation in the rat paw edema model, and may represent a general mechanism for mobilization of inflammatory cells.

Purpose: To correlate clinically observed fluctuations in manifest refraction, visual acuity, keratometry, and intraocular pressure (IOP) with changes in the anterior corneal surface as measured by videokeratography in patients 10 years after radial keratotomy (RK)., Setting: Four clinical centers in the United States that participated in the Prospective Evaluation of Radial Keratotomy (PERK) study., Methods: Thirty-two eyes of 20 PERK patients who noted diurnal fluctuations in vision had clinical examination and videokeratography (TMS-1, Computed Anatomy Inc.) in the morning and evening of the same day a mean of 10.3 years (range 7.8 to 11.7 years) after RK. The videokeratographs were analyzed in terms of various indexes generated by custom-designed software. Morning-to-evening changes in the means of the various clinical and videokeratographic values were assessed using pairwise methods., Results: The mean increase in myopia was 0.36 diopters (D) +/- 0.58 (SD) from morning to evening (P < .01). Analysis of the videokeratographs showed a corresponding increase in average corneal power (ACP), reflecting a steepening of 0.52 +/- 0.45 D (P < .001). The change in ACP was correlated with a change in the manifest spherical equivalent refraction (R = 0.39, P = .03) and a change in best spectacle-corrected visual acuity (R = 0.38, P = .03) over the same period. Similarly, simulated keratometry (SimK) readings correlated with the change in the manifest spherical equivalent refraction (R = 0.38, P = .03 for SimK1; R = 0.37, P = .35 for SimK2; R = 0.4, P = .02 for average SimK), although the standard clinical keratometric data did not (P = .26 for K1, P = .11 for K2, and P = .09 for the mean K). The elevation depression magnitude, a measure of the low-frequency irregularities of the cornea, showed a decrease of 0.32 +/- 1.59, which also correlated with the change in the manifest spherical equivalent refraction (R = 0.37, P = .04). Intraocular pressure tended to decrease from morning to evening (mean change of -0.97 +/- 3.29 mm Hg), but the difference was not significant. Variations in IOP in individual patients, however, were correlated with changes in the manifest spherical equivalent refraction (R = 0.37, P = .04)., Conclusions: Diurnal fluctuations in corneal topographic indexes can be used to evaluate the diurnal fluctuations in refraction and visual acuity after RK. The study findings provide statistical support for the idea that IOP contributes to the diurnal fluctuation in visual acuity after RK.

Purpose: To investigate whether corneal wavefront aberrations vary with aging., Methods: One hundred two eyes of 102 normal subjects were evaluated with videokeratography. The data were decomposed using Taylor and Zernike polynomials to calculate the monochromatic aberrations of the cornea for both small (3-mm) and large (7-mm) pupils., Results: For a 3-mm pupil, the amount of total aberrations (Spearman rank correlation coefficient r(s) = 0.145; P = 0.103) and spherical-like aberrations (r(s) = -0.068; P = 0.448) did not change with aging, whereas comalike aberrations exhibited a weak but statistically significant correlation with age (r(s) = 0.256; P = 0.004). For a 7-mm pupil, total aberrations (r(s) = 0.552; P < 0.001) and comalike aberrations (r(s) = 0.561; P < 0.001) significantly increased with aging, but spherical-like aberrations showed no age-related changes (r(s) = 0.124; P = 0.166). Simulated pupillary dilation from 3 mm to 7 mm caused a 38.0+/-28.5-fold increase in the total aberrations, and the extent of increases significantly correlated with age (r(s) = 0.354; P < 0.001). Pupillary dilation influenced the comalike aberrations more in the older subjects than in the younger subjects (r(s) = 0.243; P = 0.006), but such age dependence was not found for spherical-like aberrations (r(s) = 0.141; P = 0.115)., Conclusions: Comalike aberrations of the cornea correlate with age, implying that the corneas become less symmetrical along with aging. Spherical-like aberrations do not vary significantly with aging. Pupillary dilation markedly increases wavefront aberrations, and those effects are more prominent in older subjects than in younger subjects.

Purpose: To evaluate the topographic characteristic of photorefractive keratectomy (PRK) for low myopia performed with a small-beam (0.9 mm) tracking excimer laser., Setting: Department of Ophthalmology, LSU Eye Center, Louisiana State University Medical Center School of Medicine in New Orleans, and the Refractive Surgery Center of the South at the Eye, Ear, Nose, & Throat Hospital, New Orleans, Louisiana, USA., Methods: Sixty-seven eyes of 47 patients had PRK with a small-beam tracking laser. Of these, 49 eyes had data permitting evaluation of ablation centration; usable data for topographic analysis were available for 59 eyes preoperatively, 54 eyes at 1 month, 42 eyes at 3 months, and 25 eyes at 6 months, permitting measurement of various topographic parameters, including the cylinder (CYL), average corneal power (ACP), surface regularity index (SRI), surface asymmetry index (SAI), corneal eccentricity index (CEI), and coefficient of variation of corneal power (CVP)., Results: Preoperatively, all eyes were topographically normal. Postoperatively, no eye exhibited a "central island" by even the least-restrictive definition, and all eyes had best spectacle-corrected visual acuities (BSCVAs) of 20/20 or better at all follow-ups. Mean decentration of the ablations from the pupil centers was 0.42 mm +/- 0.28 (SD) (n = 49). There was no correlation between measured decentration and BSCVA (P = .46). The central cornea was flattened (decreased ACP; P < .001) and made oblate (decreased CEI; P < .001) as expected. There was no increase in SRI or SAI (irregular astigmatism) at 6 months compared with preoperative values (P = .91); however, CYL and CVP (varifocality) increased slightly (P = .04 and .02, respectively)., Conclusion: The absence of significant regular or irregular astigmatism 6 months after PRK with the small-beam laser is an improvement over published results achieved with wide-beam lasers and is consistent with the excellent visual acuity results in this cohort.

Objective: To compare laser in situ keratomileusis (LASIK) with photorefractive keratectomy (PRK) in the correction of myopia from -2.00 to -5.50 diopters., Design: Prospective, randomized, paired clinical trial., Participants: Fifty-two eyes of 26 myopic patients were enrolled in the study., Intervention: Each patient received PRK on one eye (PRK eye) and LASIK on the other (LASIK eye); the procedure assigned to each eye, and the sequence of surgeries for each patient was randomized., Main Outcome Measures: Slit-lamp microscopy, manifest refraction, uncorrected and spectacle-corrected visual acuity, and videokeratography were done before operation, and 2 weeks, 6 weeks, 3 months, 6 months, and 12 months after operation. Patient satisfaction and preference were assessed by a subjective questionnaire., Results: All LASIK eyes had fast, painless recovery. At 1 year, 24 patients (92.3%) were examined, the mean spherical equivalent refraction was -0.08 +/- 0.38 diopter in the PRK eyes and -0.14 +/- 0.31 diopter in the LASIK eyes, and the uncorrected visual acuity was 20/20 or better in 15 PRK eyes (62.5%) and 19 LASIK eyes (79.2%); no eye lost 2 or more Snellen lines of spectacle-corrected visual acuity. Both procedures were stable throughout the first year. One PRK eye developed dense subepithelial corneal haze. The strongest correlate to spectacle-corrected visual acuity after the two procedures was the coefficient of variation of corneal power over the pupil. Nineteen patients (79.2%) preferred the LASIK procedure because of the fast, painless recovery., Conclusions: In the current study, PRK and LASIK were found to be similarly effective, predictable, stable, and reasonably safe for the correction of myopia between -2.00 and -5.50 diopters. Laser in situ keratomileusis has the advantage of fast, painless recovery. Patients prefer LASIK.