Faculty Bibliography

PURPOSE: To analyze cellular populations in healthy human corneas. METHODS: The study group consisted of 58 eyes of 45 patients with normal corneas. The age distribution was 45 +/- 17 years (mean +/- SD; range, 20-84). Scanning slit confocal microscopy of the central corneas was performed. The images were analyzed visually for cell morphology, and the densities and areas of cells were measured. RESULTS: No statistically significant differences were measured in cell densities or cell areas of any corneal layer between female and male patients (p = 0.22-0.50) nor between right and left eyes (p = 0.16-0.45). The area of superficial epithelial cells was 913 +/- 326 microm2 (mean +/- SD; range, 518-2,112), and the superficial epithelial cell density was 1,213 +/- 370 cells/mm2 (mean +/- SD; range, 473-1,929). The area of basal epithelial cells was 177 +/- 19 microm2 (mean +/- SD; range, 138-242), and the basal epithelial cell density was 5,699 +/- 604 cells/mm2 (mean +/- SD; range, 4,135-7,267). The average apparent keratocyte density was 1,058 +/- 217 cells/mm2 (mean +/- SD; range, 604-1,599) in the anterior stroma, and 771 +/- 135 cells/mm2 (mean +/- SD; range, 493-1,145) in the posterior stroma. The difference in apparent keratocyte densities between the anterior and posterior stroma was statistically significant (p < 0.001). The average endothelial cell area was 334 +/- 51 microm2 (range, 273-553), and the cell density was 3,055 +/- 386 cells/mm2 (mean +/- SD; range, 1,809-3,668). The endothelial cell density had a negative, statistically significant correlation with age (r = -0.68, p < 0.001). The densities of the other corneal cell layers did not have a statistically significant correlation with age. CONCLUSION: In vivo scanning slit confocal microscopy is a useful tool for studying corneal cell populations. Central corneal cell densities were found to decrease significantly with age only in the endothelium. For the first time in human corneas using in vivo confocal microscopy, this study statistically confirms a higher apparent number of keratocytes in the anterior stroma than in the posterior stroma

PURPOSE: The purpose of this study is to analyze in vivo confocal microscopic findings of corneas with Fuchs' endothelial dystrophy. METHODS: Central corneas of 17 eyes of 11 patients aged 41-86 years were examined using in vivo scanning slit confocal microscopy after being diagnosed with Fuchs' endothelial dystrophy. The cellular structure of the corneas was analyzed morphologically and quantitatively and compared to control results from 22 healthy corneas. RESULTS: Bullae were detected in the basal epithelial layer of one eye. Eight of 17 eyes (47%) exhibited an abnormal Bowman's layer: diffuse bright reflection and absence of nerves. Eleven eyes (65%) exhibited abnormal anterior stroma: lacunae and diffuse increased light reflection due to edema. In 12 eyes (71%), lacunae or dark bands 5-20 microm wide against increased background reflection were noted in the posterior stroma. Descemet's membrane was thickened in all eyes. Dark bands were detected in six eyes (35%). Guttae (137-1,231/mm2) 20-40 microm in diameter were found in every endothelial cell layer. The mean endothelial cell count was 1,202 +/- 850 (cells/mm2 +/- SD; range, 0-2,735). There was a positive correlation between endothelial cell counts obtained by specular microscopy and those obtained by confocal microscopy (r = 0.95). CONCLUSION: In vivo confocal microscopic findings of Fuchs' endothelial dystrophy are described for the first time in a series of cases. Pathological changes in Fuchs' dystrophy were detected in all corneal layers, more frequently in the posterior layers. Endothelial cell counts obtained with confocal microscopy were statistically similar to those obtained with standard specular microscopy

BACKGROUND: Complaints of glare, halos, and disturbances of night vision after photorefractive keratectomy (PRK) probably result from changes in the corneal aberration structure induced by the laser ablation procedure. The purpose of this article is to characterize changes in the corneal aberration structure after PRK and to demonstrate the effect of pupil dilation on these changes. METHODS: Videokeratographs obtained preoperatively (n = 112) and at 1 (n = 94), 3 (n = 103), 6 (n = 91), 12 (n = 60), 18 (n = 53), and 24 (n = 44) months postoperatively from 112 eyes of 89 patients who had undergone PRK for myopia were analyzed. The data were used to calculate the wavefront variance of the cornea for both small (3-mm) and large (7-mm) pupils. RESULTS: For both the 3- and 7-mm pupil, coma-like aberrations increased significantly from preoperative values to 1-month postoperative values (P < .05 and P < .001, respectively); for 7-mm pupils, the postoperative values never returned to preoperative values (P < .001, 24 months). For the 3-mm pupil, spherical-like aberrations decreased significantly 1 month after surgery (P < .001), and never returned to preoperative values. For the 7-mm pupil, spherical-like aberrations increased significantly 1 month after surgery (P < .001) and did not return to preoperative values. Opening the pupil from 3 to 7 mm increased spherical-like aberrations only 7-fold before PRK. After PRK, however, pupillary dilation caused a 300-fold increase in this type of aberration. For both pupil sizes at all times after PRK, the magnitude of the surgically induced aberration correlated with the amount of the attempted correction (P < .001, r2 = 0.6 at 1 month for a 7-mm pupil). CONCLUSIONS: Photorefractive keratectomy increases the wavefront variance of the cornea; PRK changes the relative contribution of coma-like and spherical-like aberrations; after PRK, the diameter of the entrance pupil greatly affects the amount and character of the aberrations; and the magnitude of the aberration increases with the attempted correction. CLINICAL RELEVANCE: Quantitative characterization of irregular astigmatism with the measurement of aberration structures following corneal surgery and the correlation of these data with visual performance in clinical trials provide the basis for understanding patient complaints and for improving surgical approaches. Our analysis shows that, whereas induced aberrations are minimal for simulated day-time vision (3-mm pupil), the increase in aberrations measured for simulated night vision (7-mm pupil) supports the use of large treatment zones to reduce visual disturbances such as glare and halos

OBJECTIVE: To correlate new quantitative topographic indexes of corneal irregular astigmatism to best spectacle-corrected visual acuity (BSCVA) following excimer laser photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, LSU Eye Center, and Refractive Surgery Center of the South, Ear, Nose & Throat Hospital, New Orleans, Louisiana; Manhattan Eye, Ear and Throat Hospital, New York, New York, USA. METHODS: Videokeratography data (TMS-1) were obtained preoperatively and 1, 3, 6, 12, 18, and 24 months postoperatively from 100 eyes having PRK for low to mild myopia. Algorithms measured fine local irregularity with the surface regularity index (SRIp), varifocality with the coefficient of variation of corneal power (CVPp), and central islands with the elevation/depression magnitude (EDM). RESULTS: The SRIp and CVPp increased after surgery and remained significantly higher than the preoperative levels throughout the 24 month follow-up (P < .05). The increase in EDM was significant from 1 to 6 months (P < .05) but not thereafter. Multiple regression analysis revealed that variables having a statistically significant relationship with postoperative BSCVA were CVPp and EDM at 1 month, CVPp at 3 months, and CVPp, haze, and age at 6 months. No statistically significant correlation between any measures of irregular astigmatism and BSCVA was found after 1 year of follow-up. CONCLUSION: The quantitative measures used in this study are sensitive methods by which irregular astigmatism after keratorefractive procedures can be classified, evaluated, and compared

PURPOSE: Because keratometry readings may no accurately reflect the refractive changes after keratorefractive surgery for myopia, better methods for the assessment of corneal curvature in the postsurgical cornea are needed. METHODS: We developed a procedure to calculate the average central power (ACP) of the cornea within the entrance pupil from videokeratography. Videokeratograph-derived keratometry-style readings (average K; K) and calculated ACPs, as well as the differences between the two values, were compared in four groups: normal corneas (n = 30), corneas with regular astigmatism (n = 30); post-radial keratotomy corneas (RK, n = 85), and post-excimer laser photorefractive keratectomy corneas (PRK, n = 63). Intraocular lens (IOL) powers calculated by using K or ACP in the Sanders-Retzlaff-Kraff formula were compared. RESULTS: In the groups with normal corneas or regular astigmatism, none of the eyes showed a difference between K and ACP > 0.25 D. However, six (7%) of the RK eyes and 16 (25%) of the PRK eyes had differences > 0.55 D; in these eyes, the disparity between IOL powers calculated by using K and IOL powers calculated by using ACP was > 0.5 D. CONCLUSION: These results suggest that basing the calculation of IOL powers on keratometry readings in patients who have undergone RK. PRK, or possibly other refractive procedures may result in a residual refractive error in some eyes. In particular, patients undergoing surgery involving a small optical zone or large attempted correction or both, as well as those with low postoperative keratometry readings, may be at risk for this problem if IOL placement becomes necessary in later years

BACKGROUND: To evaluate near vision contrast sensitivity as a measure of visual performance after photorefractive keratectomy (PRK). SETTING: LSU Eye Center, New Orleans, Louisiana. METHODS: Using Holladay Contrast Acuity Test cards, near (reading) vision for five levels of contrast sensitivity was evaluated in a cross section of 53 eyes of 31 patients 25 to 732 days after PRK. Twenty-four normal eyes of 22 myopic patients served as controls. RESULTS: Near contrast sensitivity decreased at all tested contrast levels for approximately 7 months after PRK and then returned to baseline. This phenomenon paralleled the fluctuation in best corrected distance Snellen acuity. CONCLUSIONS: These preliminary results indicate that Snellen visual acuity and near contrast sensitivity returned to baseline within 1 year after PRK