6533b7d0fe1ef96bd125aed9

RESEARCH PRODUCT

Direct Objective Quantification of Corneal Haze after Excimer Laser Photorefractive Keratectomy for High Myopia

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Purpose: The purpose of the study is to measure regional distribution differences in corneal haze after excimer laser photorefractive keratectomy for high myopia. Methods: The authors developed computerized gradient edge detectors with which were analyzed digitized anterior slit-lamp photographs of 40 eyes, an average of 21.0 plus or minus 14.5 weeks after photorefractive keratectomy for high myopia (−6 to −22 diopters). A treated area and an adjacent untreated area on the anterior corneal surface, each containing six regions, were quantified, and the difference was correlated with various parameters. Results: Mean differences 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, respectively ( r s = 0.96; P = 0.0001). A low but statistically significant correlation between the intended correction and postoperative corneal haze was found ( r = 0.33; P = 0.037). The mean coefficient of variation of 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 correlate with the attempted correction. However, a strong association between a relatively less severe central corneal haze with respect to more peripheral haze and longer follow-up time was found ( r = −0.96; P = 0.0001). Conclusion: The amount of corneal haze showed a weak positive association with the attempted correction in excimer laser photorefractive keratectomy for high myopia. Corneal haze appeared fairly uniformly distributed within the ablation zone, but a more heterogeneous distribution 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.