Backscattered light from the cornea before and after laser-assisted subepithelial keratectomy for myopia

Abstract

PURPOSE: To study corneal backscatter changes after laser-assisted subepithelial keratectomy (LASEK) and to search for correlations between the changes in forward and backward corneal light scatter. SETTING: Antwerp University Hospital, Edegem, Belgium. DESIGN: Prospective interventional case series. METHOD: Corneal backscatter was determined with a commercial Scheimpflug device and purpose-written image-analysis software. The mean backscatter profile and gray value distributions of the images for a 1.0 mm zone around the corneal apex were obtained preoperatively and 6 months after LASEK for myopia. This was compared with forward light scatter (or straylight) using measurements obtained with the compensation comparison method. RESULTS: The study enrolled 80 eyes (40 patients; mean age 34.2 years ± 10.4 [SD]). Very strong correlations were found between the backscatter profiles of right eyes and left eyes preoperatively. Hence, only right eyes were used for further calculations. The epithelial-Bowman peak of the backscatter profile decreased significantly after LASEK (mean decrease -2.2 ± 4.7 grayscale units) (P=.002, paired t test), which corresponded to the ablation of Bowman layer. Significant changes in the gray-value distribution were observed postoperatively, corresponding to the decreases in the epithelium-Bowman peak. Forward light scatter decreased significantly after LASEK (mean decrease -0.10 ± 0.13) (P<.001); however, no significant correlation with corneal backscatter was observed. CONCLUSIONS: The anterior part of the corneal backscatter profile decreased significantly after LASEK. A significant reduction in forward light scatter was also seen, although it was not correlated to backward light scatter.