Influence of pterygium size on corneal higher-order aberration evaluated using anterior-segment optical coherence tomography.

BACKGROUND: The prospective observation study aimed to evaluate changes in corneal higher-order aberrations induced by advancement of pterygium using an anterior-segment optical coherence tomography (AS-OCT) and Zernike aberration analysis. METHODS: The corneal topography of 284 eyes with primary pterygia originating from the nasal region was measured using an AS-OCT (SS-1000, Tomey). With anterior corneal elevation data, Zernike polynomial coefficients were calculated in diameters of 1.0, 3.0, and 5.0 mm, and the coma, spherical, coma-like, spherical-like, and total higher-order aberrations were obtained. Pterygium size was also measured as a ratio of positions of the pterygium end with respect to the corneal diameter and categorized in eight classes: less than 15%, 15-20%, 20-25%, 25-30%, 30-35%, 35-40%, 40-45, and 45% or larger. Increases in the aberrations were analyzed with reference to those in eyes with pterygium size < 15%. RESULTS: The mean age of the participants was 69.3 years, and the pterygium size ranged from 2 to 57% (mean: 28.8%). The coma aberration significantly increased when the pterygium size was 45% or larger in 1.0 and 3.0 mm diameters and over 25-30% in 5.0 mm diameter. Similar increases were found in the pterygium sizes exceeding 45, 40, and 25%, respectively, in the coma-like, spherical-like, and total higher-order aberrations. On contrast, there was no increase in the spherical aberration. CONCLUSION: Increases in higher-order aberrations reflected the pterygium size, and significant aberrations were induced in 5.0 mm diameter when the end exceeded 25% of corneal diameter. The use of AS-OCT and Zernike analysis could enable objective grading of pterygium advancement based on changes in corneal optics.

Long-term follow-up of transplantation of preserved limbal allograft and amniotic membrane for recurrent pterygium.

PURPOSE: To conduct a long-term follow-up study evaluating the efficacy and safety of transplantation of preserved limbal allograft and amniotic membrane for recurrent pterygium. METHODS: This was a retrospective, non-comparative, interventional case series conducted at a private eye hospital. Eighty-four eyes of 80 patients with recurrent pterygium were included in the study. The mean number of previous surgeries for pterygium was 1.36 ± 0.98 (range, 1-8). All subjects received transplantation of preserved limbal allograft and amniotic membrane. RESULTS: The mean follow-up period was 73.0 ± 38.1 months (range, 12-154 months). Pterygium recurred in 10 eyes (11.9 %). The mean period to recurrence was 16.3 ± 11.3 months (range, 5-33 months). Symblepharon was cured in 21 eyes, persisted in 2 eyes, and newly occurred in 3 eyes. Diplopia was cured in eight eyes, persisted in five eyes, and newly occurred in one eye. As for complications, intraocular pressure elevations over 21 mmHg were recognized in ten eyes of nine cases, in which the intraocular pressure was controlled by reduction of topical steroid in four eyes and by addition of topical prostaglandin derivatives in six eyes. Twenty-four eyes (28.6 %) gained two lines or more of Landolt best spectacle-corrected visual acuity (BSCVA), 56 eyes (66.7 %) stayed within one line from preoperation, and four eyes (4.8 %) lost two lines or more. There were no major complications and no graft rejection. CONCLUSIONS: Transplantation of preserved limbal allograft and amniotic membrane is a safe and effective procedure for recurrent pterygium.

Prevalence of Accommodative Microfluctuations in Eyes after Cataract Surgery.

BACKGROUND: We aimed to evaluate the existence of accommodative microfluctuations in eyes after cataract surgery. METHODS: This retrospective observational cohort study included 1160 eyes of 713 patients (mean age: 72.5 ± 8.3 years) who underwent phacoemulsification, intraocular lens insertion, and an evaluation of accommodative microfluctuations with an autorefractometer. Patients with posterior segment disorders resulting in visual acuity impairment and those with unavailable medical information were excluded. High-frequency components (HFCs), between 1.0-2.3 Hz, based on fast Fourier transform analysis of the accommodative microfluctuation data were examined at postoperative 2-3 (2 M) and 6 months (6 M). The relationships between the HFCs and patient age, manifest refraction, and axial length were analyzed. RESULTS: Increased HFC values (>65) were observed at a constant rate after cataract surgery, with prevalence rates of 33.4% at 2 M and 34.7% at 6 M. Postoperatively, at 2 M, increased HFC values were significantly more common for eyes with axial length ≥26 mm than for those with axial length <26 mm (p = 0.0056). However, they were not significantly correlated to age or postoperative manifest refraction. CONCLUSIONS: At 2 M postoperatively, increased HFC values presented more frequently in eyes with a greater axial length; hence, the precise detection and understanding of postoperative accommodative spasms in high myopia patients is important.

Effect of topical steroid instillation on central corneal thickness in eyes with bullous keratopathy.

PURPOSE: To examine the effects of topical steroid instillation on central corneal thickness in eyes with bullous keratopathy (BK). STUDY DESIGN: Retrospective case series METHODS: Consecutive patients with BK who did not wish to receive corneal transplantation and were treated with 0.1% betamethasone eyedrops were included. Patients with BK treated with 5% sodium chloride (hypertonic saline) eyedrops served as controls. Central corneal thickness (CCT), best-corrected visual acuity (BCVA), intraocular pressure (IOP), BK etiology, and clinical courses from medical records were retrospectively reviewed. We compared the two groups for differences in CCT, BCVA and IOP before treatment and 2 weeks, 1 month, and 3 months after treatment. RESULTS: Eighteen eyes of 18 patients who were treated with betamethasone and 18 eyes of 18 patients who were treated with hypertonic saline were included. There was no significant difference in CCT between the two groups before treatment. The reduction of CCT in the betamethasone group was significantly larger than in the hypertonic saline group at 2 weeks (p = 0.002), 1 month (p = 0.02), and 3 months (p = 0.001) after treatment. Complications such as infectious keratitis and IOP rise did not occur during the observation period. CONCLUSIONS: Topical steroid instillation reduced central corneal thickness in eyes with BK.

Detection of increase in corneal irregularity due to pterygium using Fourier series harmonic analyses with multiple diameters.

PURPOSE: To determine steep increase of corneal irregularity induced by advancement of pterygium. METHODS: A total of 456 eyes from 456 consecutive patients with primary pterygia were examined for corneal topography and advancement of pterygium with respect to the corneal diameter. Corneal irregularity induced by the pterygium advancement was evaluated by Fourier harmonic analyses of the topographic data that were modified for a series of analysis diameters from 1 mm to 6 mm. Incidences of steep increases in the asymmetry or higher-order irregularity components (inflection points) were determined by using segmented regression analysis for each analysis diameter. RESULTS: The pterygium advancement ranged from 2% to 57%, with a mean of 22.0%. Both components showed steep increases from the inflection points. The inflection points in the higher-order irregularity component altered with the analysis diameter (14.0%-30.6%), while there was no alternation in the asymmetry components (35.5%-36.8%). For the former component, the values at the inflection points were obtained in a range of 0.16 to 0.25 D. CONCLUSION: The Fourier harmonic analyses for a series of analysis diameters revealed that the higher-order irregularity component increased with the pterygium advancement. The analysis results confirmed the precedence of corneal irregularity due to pterygium advancement.

Changes in contrast sensitivity function and ocular higher order aberration by conventional myopic photorefractive keratectomy.

PURPOSE: To evaluate the relation between induced changes in ocular higher order aberrations and changes in the contrast sensitivity function in patients undergoing excimer laser photorefractive keratectomy (PRK). METHODS: Myopic PRK using excimer laser was performed in 31 patients (56 eyes). The preoperative refractive error was -6.2 +/- 2.9 diopters. Before and 1 month after surgery, we measured the ocular higher order aberrations for a 4-mm pupil, and three indices of contrast sensitivity function. From the data collected, the area under the log contrast sensitivity function (AULCSF) was calculated. RESULTS: PRK significantly reduced AULCSF (P = 0.004), low-contrast visual acuity (P = 0.004), and letter-contrast sensitivity (P = 0.013). Coma-like (P < 0.001) and spherical-like (P < 0.001) aberrations were significantly increased by surgery. The change in AULCSF by surgery significantly correlated with the change in coma-like (r = -0.468, P < 0.001) and spherical-like (r = -0.291, P = 0.033) aberrations. The change in low-contrast visual acuity by PRK significantly correlated with the change in coma-like aberration (r = 0.599, P < 0.007), but not with change in spherical-like aberrations (r = 0.136, P = 0.326). There were significant correlations between changes in letter-contrast sensitivity and changes in coma-like (r = -0.450, P < 0.001) and spherical-like (r = -0.255, P = 0.048) aberrations. CONCLUSIONS: PRK significantly increases ocular higher order aberrations, which compromise contrast sensitivity function after surgery.

Proposal for a Novel Severity Grading System for Pterygia Based on Corneal Topographic Data.

PURPOSE: To propose a grading system of pterygium severity based on corneal higher-order irregularity (HOI) and to evaluate postoperative changes in corneal irregularity of the graded pterygia. METHODS: In 268 eyes of 226 patients undergoing excision surgery of primary nasal pterygium, Placido corneal topography images were taken before and until 6 months after surgery. The best-corrected visual acuity (BCVA) and pterygium size with respect to the corneal diameter were also measured. HOI components within 1.0-, 3.0-, and 5.0-mm diameters were obtained using Fourier harmonic analysis of corneal topography data. With threshold levels when the HOIs for 3 diameters steeply increased, 4 levels of grading from 0 (mild) to 3 (severe) were determined. Associations of the grades with the preoperative surface regularity index (SRI), irregular components (IRRs) obtained from the 3.0-mm diameter Fourier analysis, and BCVA were examined. Time-course changes in the indexes after surgery were evaluated for each grade. RESULTS: There were 62, 65, 41, and 100 eyes in grades 0 to 3, respectively. Preoperatively, the SRI in grade 3 was significantly higher than in the other grades (P < 0.001), and the IRR and BCVA varied with the grade (P < 0.001). Between 1 and 6 months postoperatively, grade 3 pterygia showed significant changes in the SRI and IRR (P = 0.013 and 0.017, respectively), whereas there was no change after 3 months postoperatively in the SRI, IRR, and BCVA for all other grades. CONCLUSIONS: The proposed grading effectively classified the severity of pterygia and evaluated postoperative restoration of corneal irregularity. Using corneal topographic data allowed for objective evaluation of pterygium severity.

Influence of pupil diameter on the relation between ocular higher-order aberration and contrast sensitivity after laser in situ keratomileusis.

PURPOSE: To investigate the influence of pupil diameter on the relation between induced changes in ocular higher-order wavefront aberrations and changes in contrast sensitivity by conventional laser in situ keratomileusis (LASIK) for myopia. METHODS: In 215 eyes of 117 patients (age, 33.2 +/- 8.3 years) undergoing LASIK for myopia of -1.25 to -13.5 D (-5.28 +/- 2.55 D), ocular wavefront aberrations and contrast sensitivity function were determined before and 1 month after surgery. Preoperative photopic pupil diameter was measured with a digital camera. Ocular higher-order aberrations were measured for a 4-mm pupil with a Hartmann-Shack wavefront analyzer. The root-mean-square (RMS) of the third- and fourth-order Zernike coefficients was used to represent coma- and spherical-like aberration, respectively. From the contrast-sensitivity data, the area under the log contrast sensitivity function (AULCSF) was calculated. RESULTS: One hundred five eyes had a photopic pupil diameter of 4 mm or larger, and the remaining 110 had a photopic pupil diameter smaller than 4 mm. There were no statistically significant differences in the background clinical data between these two groups. In the eyes with a photopic pupil diameter of 4 mm or larger, the changes in third-order comalike aberrations did not correlate with the changes in AULCSF (Pearson correlation coefficient, r = -0.037, P = 0.723) and 10% low-contrast visual acuity (r = 0.125, P = 0.224), but fourth-order spherical-like aberrations correlated significantly with the changes in AULCSF (r = -0.229, P = 0.024) and 10% low-contrast visual acuity (r = 0.221, P = 0.038). In the eyes with photopic pupil size smaller than 4 mm, there were significant correlations between the changes in comalike aberrations and the changes in AULCSF (r = -0.487, P < 0.001) and 10% low-contrast visual acuity (r = 0.310, P = 0.003), but spherical-like aberrations showed no correlation with the changes in AULCSF (r = -0.078, P = 0.485) and 10% low-contrast visual acuity (r = 0.208, P = 0.158). CONCLUSIONS: In eyes with larger photopic pupil diameter, increases in spherical-like aberration dominantly affect contrast sensitivity, whereas in eyes with smaller pupil size, changes in coma-like aberration exert greater influence on visual performance.

Contrast sensitivity function and ocular higher-order wavefront aberrations in normal human eyes.

PURPOSE: To investigate the relation between contrast sensitivity function and ocular higher-order wavefront aberrations in normal human eyes. STUDY DESIGN: Prospective observational case series. PARTICIPANTS: Three hundred seven eyes of 161 normal subjects, ranging in age from 15 to 60 years (30.9+/-8.0 [mean +/- standard deviation]). METHODS: Ocular higher-order aberrations were measured for a 4-mm pupil using the Hartmann-Shack wavefront analyzer. The root-mean-square of the third- and fourth-order Zernike coefficients was used to represent comalike and spherical-like aberrations, respectively. We measured contrast sensitivity, low-contrast visual acuity (VA), and letter contrast sensitivity. From the contrast sensitivity data, the area under the log contrast sensitivity function (AULCSF) was calculated. Pupil diameter in a photopic condition was recorded using a digital camera. RESULTS: Multiple linear regression analysis revealed that comalike aberration (P = 0.002) was significantly associated with AULCSF, but spherical-like aberration (P = 0.200), age (P = 0.185), and photopic pupil diameter (P=0.252) were not. Comalike aberration showed a significant correlation with low-contrast VA (P<0.001), but spherical-like aberration (P = 0.293), age (P = 0.266), and pupil diameter (P = 0.756) did not. Comalike aberration was found to be significantly associated with letter contrast sensitivity (P<0.001), but spherical-like aberration (P=0.082), age (P = 0.370), and pupil diameter (P = 0.160) were not. CONCLUSIONS: In normal human eyes, comalike aberration of the eye significantly influences contrast sensitivity function.

Prospective intrapatient comparison of 6.0-millimeter optic single-piece and 3-piece hydrophobic acrylic foldable intraocular lenses.

PURPOSE: To compare postoperative performance and stability of 6.0-mm optic single- and 3-piece acrylic foldable intraocular lenses (IOLs). DESIGN: Prospective, randomized, self-controlled trial. PARTICIPANTS: Eighty eyes of 40 patients with bilateral senile cataracts. INTERVENTION: Phacoemulsification and IOL implantation were performed. One eye of a patient was randomly assigned to the SA60AT single-piece IOL, and the contralateral eye was allocated to the MA60AC 3-piece IOL. MAIN OUTCOME MEASURES: Best-corrected visual acuity (BCVA), spherical equivalent, aqueous flare intensity, anterior chamber depth, amount of IOL decentration and tilt, area of anterior capsule opening, and degree of posterior capsule opacification (PCO) were measured 2 days, 1 week, and 1, 3, 6, and 12 months after surgery. Specular microscopy was performed at 12 months postoperatively. RESULTS: In the SA60AT group, the anterior chamber depth did not show significant changes after surgery (P>0.05; paired t test), and the refraction remained highly stable throughout the 1-year study period. The MA60AC group showed significant shallowing of the anterior chamber (P<0.05) and a myopic shift (P<0.05) up to 1 month after surgery. There were no significant differences between the 2 groups (P>0.05) in BCVA, aqueous flare intensity, the amount of IOL decentration, IOL tilt, area of anterior capsule opening, and degree of PCO throughout the 12-month follow-up period. CONCLUSIONS: Both the SA60AT single-piece and MA60AC 3-piece lenses showed a minimum amount of decentration, tilt, anterior capsule contraction, and PCO. Although the MA60AC showed significant forward shift and myopic refractive changes after surgery, the SA60AT displayed little axial movement associated with highly stable refraction after surgery. This feature of the SA60AT should facilitate earlier spectacle prescription and quicker visual/social rehabilitation of patients after cataract surgery.

Central corneal thickness measurements using Orbscan II scanning slit topography, noncontact specular microscopy, and ultrasonic pachymetry in eyes with keratoconus.

PURPOSE: To compare corneal thickness measurements using Orbscan II scanning slit topography, Topcon SP-2000P noncontact specular microscopy, and ultrasonic pachymetry in eyes with keratoconus. METHODS: Central corneal thickness was measured in 22 eyes with keratoconus. Eyes with apparent corneal opacity were excluded. Scanning slit topography, noncontact specular microscopy, and ultrasonic pachymetry were used in this sequence. The acoustic equivalent correlation factor (0.92) was used for Orbscan readings. RESULTS: Three devices gave significantly different corneal thickness readings (P < 0.001, repeated-measure analysis of variance). Measurements with Orbscan scanning slit topography (449.5 +/- 43.2 [SD] mum) were significantly smaller than those of ultrasonic pachymetry (485.0 +/- 29.3 microm; P < 0.001, Tukey multiple comparison) and SP-2000P noncontact specular microscopy (476.7 +/- 28.3 microm; P = 0.002). There were significant linear correlations between ultrasonic pachymetry and scanning slit topography (Pearson correlation coefficient r = 0.741, P < 0.001), between scanning slit topography and noncontact specular microscopy (r = 0.880, P < 0.001), and between noncontact specular microscopy and ultrasonic pachymetry (r = 0.811, P < 0.001). CONCLUSION: In eyes with keratoconus, Orbscan II scanning slit topography system gave significantly smaller corneal thickness readings than the other 2 devices. Measurements taken by noncontact specular microscopy and ultrasonic pachymetry were comparable. Three devices showed significant linear correlations with one another.

Time course of changes in corneal forward shift after excimer laser photorefractive keratectomy.

BACKGROUND: Excimer laser refractive surgery has been reported to induce forward shift of the cornea, but its long-term sequelae remain unknown. OBJECTIVES: To prospectively investigate the time course of changes in corneal elevation after excimer laser photorefractive keratectomy (PRK). METHODS: We performed PRK on 65 eyes of 34 patients with refractive errors of -1.25 to -10.0 diopters. The anterior/posterior corneal elevation and corneal thickness were measured with a scanning-slit corneal topography system before and 1 week and 1, 3, 6, and 12 months after surgery. Twenty eyes of 10 healthy control subjects underwent similar measurements at 3-month intervals. RESULTS: The posterior corneal surface displayed a mean +/- SD forward shift of 36.6 +/- 25.3 microm 1 week after PRK, which gradually increased to 55.1 +/- 46.1 microm at 1 year. All postoperative values were significantly larger than those of healthy controls (2.4 +/- 8.9 microm; P<.001, Mann-Whitney test). The largest forward shift occurred within the first postoperative week. The progression thereafter was most pronounced from 1 to 6 months, and nearly stabilized at 6 months. The variance of postoperative data was statistically significant (P<.001, repeated-measures analysis of variance). Multiple postoperative comparisons demonstrated significant differences between measurements at 1 week and 6 months (P =.002, Tukey Honestly Significant Difference), at 1 week and 1 year (P<.001), at 1 and 6 months (P<.001), and at 1 month and 1 year (P<.001). Progression of forward shift was more prominent in eyes with less preoperative corneal thickness and greater myopia that required larger laser ablation. We observed no progressive thinning and expansion of the cornea during the 1-year follow-up, which refuted the occurrence of true ectasia. A statistically significant correlation was found between the amount of myopic regression and the forward shift of the cornea (Pearson correlation coefficient, r = -0.37; P =.005). CONCLUSIONS: Photorefreactive keratectomy induced forward shift of the cornea, which is not true corneal ectasia. The largest forward shift occurred within the first postoperative week. Changes were progressive up to 6 months postoperatively, but became almost stable thereafter. Eyes with thinner cornea and higher myopia, requiring greater photoablation, are more predisposed to progression. Forward shift of both corneal surfaces added to the tendency toward myopic regression after PRK.

Residual bed thickness and corneal forward shift after laser in situ keratomileusis.

PURPOSE: To prospectively assess the forward shift of the cornea after laser in situ keratomileusis (LASIK) in relation to the residual corneal bed thickness. SETTING: Miyata Eye Hospital, Miyazaki, Japan. METHODS: Laser in situ keratomileusis was performed in 164 eyes of 85 patients with a mean myopic refractive error of -5.6 diopters (D) +/- 2.8 (SD) (range -1.25 to -14.5 D). Corneal topography of the posterior corneal surface was obtained using a scanning-slit topography system before and 1 month after surgery. Similar measurements were performed in 20 eyes of 10 normal subjects at an interval of 1 month. The amount of anteroposterior movement of the posterior corneal surface was determined. Multiple regression analysis was used to assess the factors that affected the forward shift of the corneal back surface. RESULTS: The mean residual corneal bed thickness after laser ablation was 388.0 +/- 35.9 microm (range 308 to 489 microm). After surgery, the posterior corneal surface showed a mean forward shift of 46.4 +/- 27.9 microm, which was significantly larger than the absolute difference of 2 measurements obtained in normal subjects, 2.6 +/- 5.7 microm (P<.0001, Student t test). Variables relevant to the forward shift of the corneal posterior surface were, in order of magnitude of influence, the amount of laser ablation (partial regression coefficient B = 0.736, P<.0001) and the preoperative corneal thickness (B = -0.198, P<.0001). The residual corneal bed thickness was not relevant to the forward shift of the cornea. CONCLUSIONS: Even if a residual corneal bed of 300 microm or thicker is preserved, anterior bulging of the cornea after LASIK can occur. Eyes with thin corneas and high myopia requiring greater laser ablation are more predisposed to an anterior shift of the cornea.

Structural analysis of the cornea using scanning-slit corneal topography in eyes undergoing excimer laser refractive surgery.

PURPOSE: To review the time course of corneal anteroposterior shift and refractive stability after myopic excimer laser keratorefractive surgery. METHODS: We examined 65 eyes undergoing photorefractive keratectomy (PRK) and 45 eyes undergoing laser in situ keratomileusis (LASIK). Corneal elevation maps and pachymetry were obtained by scanning-slit corneal topography before; 1 week; and 1, 3, 6, and 12 months after surgery. RESULTS: Both PRK and LASIK induced significant forward shifts of the cornea. Corneal forward shift was progressive up to 6 months after PRK, but no progression was seen after LASIK. Progressive thinning and expansion of the cornea were not observed after either procedure. The amount of corneal forward shift showed a significant negative correlation with preoperative corneal thickness (r = -0.586; P < 0.01) and a significant positive correlation with the amount of myopic correction (r = 0.504; P < 0.01). A significant correlation was found between the amount of forward shift and the degree of myopic regression after surgery (r = -0.347; P < 0.05). CONCLUSION: Myopic PRK and LASIK induce significant forward shifts of the cornea, which are not true corneal ectasia. Eyes with thinner corneas and higher myopia requiring greater ablation are more predisposed to anterior protrusion of the cornea. Corneal forward shift was progressive up to 6 months after PRK but not progressive after LASIK. Forward shift of the cornea can be one of the factors responsible for myopic regression after surgery.

Difference map or single elevation map in the evaluation of corneal forward shift after LASIK.

PURPOSE: Forward shift of the cornea after excimer laser refractive surgery has been assessed on a difference map generated from two elevation maps of the scanning-slit corneal topography. The current study was conducted to test whether similar evaluation is possible on a postoperative color-coded elevation map alone. DESIGN: Prospective, noncomparative case series. PARTICIPANTS: One hundred sixty-three eyes of 86 patients with myopic refractive errors of -1 to -13.50 diopters. INTERVENTION: LASIK was performed. Corneal topography of the posterior corneal surface was obtained with the scanning-slit topography system before and 1 month after surgery. MAIN OUTCOME MEASURES: The amount of forward shift of the posterior corneal surface was determined at the center of the difference map generated from preoperative and postoperative elevation maps. For surface alignment in the difference map, the 3-mm wide peripheral annular fit-zone was used. The eyes were classified into two groups depending on the amount of forward shift, using 50 micro m as the threshold. Next, on the single postoperative color-coded elevation map, which is drawn relative to the individual best-fit sphere, the eye was judged to be abnormal (with significant forward shift) when more than three colors (discriminant number) were found within the central 3-mm area, and sensitivity and specificity were calculated. By varying the discriminant number from 3 to 9, receiver operator characteristic (ROC) curves were created. RESULTS: The ROC curve analyses demonstrated that sufficient true positive ratio (sensitivity) and false-positive ratio (100-specificity [%]) could not be obtained with any discriminant color number when judgments were made on a single color-coded map. There was a weak, but significant, correlation between the amount of corneal forward shift and the radius of curvature of the posterior best-fit sphere (Pearson r = -0.170; P = 0.030), indicating that a cornea with greater forward shift tended to be drawn on a steeper best-fit sphere, and thus the forward protrusion of the posterior surface failed to be depicted. CONCLUSIONS: Forward shift of the cornea after excimer laser surgery should be evaluated on the difference map generated from two elevation maps, such as preoperative and postoperative maps.

Standardized color-coded scales for anterior and posterior elevation maps of scanning slit corneal topography.

PURPOSE: To find the most appropriate color-coded scales for the anterior and posterior elevation maps of scanning slit topography in the screening of abnormal corneas such as keratoconus. DESIGN: Retrospective case-control study. PARTICIPANTS: Eighty eyes of 40 normal subjects and 175 eyes of 95 patients with keratoconus. INTERVENTION: Anterior and posterior corneal elevations were assessed using Orbscan 2. Best-fit sphere maps were drawn with several color-coded scales: 2-, 5-, 10-, and 20-microm height per each color interval. MAIN OUTCOME MEASURES: The maps were judged to be abnormal when more than three colors (discriminant number) were found within the central 3-mm area. For each color-coded scale, sensitivity, specificity, positive predictive value, negative predictive value, and sensitivity + specificity were calculated. After determining the most appropriate color-coded scales for the anterior and posterior elevation maps, validity of the discriminant number was assessed. By varying the discriminant number from two to eight, receiver operator characteristic (ROC) curves were created using the sensitivity and specificity for each threshold number. RESULTS: The highest sensitivity + specificity values and highly balanced predictive values were obtained with the 10- and 20-microm scales for the anterior and posterior elevation maps, respectively. The ROC curve analyses showed that the best discriminant color number is three, indicating that maps with four or more colors within the central 3-mm area are judged abnormal in screening. CONCLUSIONS: The 10- and 20-microm interval color scales are most appropriate for the anterior and posterior elevation maps of the scanning slit topography, respectively.

Higher order wavefront aberrations of cornea and magnitude of refractive correction in laser in situ keratomileusis.

OBJECTIVE: To assess the relation between magnitude of refractive correction and changes in higher order wavefront aberrations of the cornea after laser in situ keratomileusis. DESIGN: Prospective, consecutive, nonrandomized comparative trial (self-controlled). PARTICIPANTS: One hundred eyes of 53 patients with myopia (-2.0 to -13.0 diopters) were included. INTERVENTION: Laser in situ keratomileusis was performed. Videokeratography measurements were conducted before and 1 month after surgery. MAIN OUTCOME MEASURES: The videokeratography data were used to calculate the higher order wavefront aberrations of the cornea for both small (3 mm) and large (6 mm) pupils. RESULTS: For a 3-mm pupil, the surgery significantly increased coma-like (2.4 +/- 1.3-fold, P < 0.001, paired t test) and spherical-like (1.8 +/- 0.9-fold, P < 0.001) aberrations. For a 6-mm pupil, both coma-like (4.4 +/- 3.3-fold, P < 0.001) and spherical-like (9.4 +/- 5.2-fold, P < 0.001) aberrations were significantly increased by surgery. The amount of achieved correction showed significant correlations with the changes in coma-like (Pearson correlation coefficient r = 0.446, P < 0.001) and spherical-like (r = 0.348, P < 0.001) aberrations for a 3-mm pupil, and coma-like (r = 0.566, P < 0.001) and spherical-like (r = 0.693, P < 0.001) aberrations for a 6-mm pupil. The eyes that lost 2 or more lines of baseline spectacle-corrected visual acuity showed significantly larger induced increases in coma-like (P = 0.003, Mann-Whitney U test) and spherical-like (P = 0.009) aberrations for a 3-mm pupil than those that either improved or remained within 1 line of spectacle-corrected visual acuity CONCLUSIONS: Laser in situ keratomileusis, performed using the current algorithms, increases higher order wavefront aberrations of the cornea, dependent on the amount of refractive correction.