DIRECT OBJECTIVE QUANTIFICATION OF CORNEAL HAZE AFTER EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY FOR HIGH MYOPIA

Purpose: The purpose of the study is to measure regional distribution differences in corneal haze after excimer laser photorefractive kerate ctomy for high myopia. Methods: The authors developed computerized gra dient edge detectors with which were analyzed digitized anterior slit- lamp photographs of 40 eyes, an average of 21.0 plus or minus 14.5 wee ks after photorefractive keratectomy for high myopia (-6 to -22 diopte rs). A treated area and an adjacent untreated area on the anterior cor neal surface, each containing six regions, were quantified, and the di fference was correlated with various parameters. Results: Mean differe nces between scarred and clear areas for haze grade 0.5, 1.0, 2.0, 3.0 , and 4.0 were 16.9, 26.6, 42.6, 60.4, and 76.4 gray levels, respectiv ely (r(s) = 0.96; P = 0.0001). A low but statistically significant cor relation between the intended correction and postoperative corneal haz e was found (r = 0.33; P = 0.037). The mean coefficient of variation o f the amount of opacification within each treated area was 9.4%. This coefficient of variation increased with a longer follow-up time (r = 0 .88; P = 0.0001). The difference in the intensity of haze between the center and more peripheral regions over the entrance pupil did not cor relate with the attempted correction. However, a strong association be tween a relatively less severe central corneal haze with respect to mo re peripheral haze and longer follow-up time was found (r = -0.96; P = 0.0001). Conclusion: The amount of corneal haze showed a weak positiv e association with the attempted correction in excimer laser photorefr active keratectomy for high myopia. Corneal haze appeared fairly unifo rmly distributed within the ablation zone, but a more heterogeneous di stribution was found with a longer follow-up time. Furthermore, later postoperative examinations disclosed a clear trend toward diminishing central opacification relative to peripheral regions over the entrance pupil.