PURPOSE To measure the corneal epithelium with high revolution OCT and determine the relation between corneal epithelium thickness and refraction power, corneal thickness, corneal curvature, age. To evaluate corneal epithelium before and after Epi-Lasik surgery.
METHODS 60 subjects (Age between 18~40yrs，39 male, 21 female，sphere equivalent(SE)（0~-10.00D）), were classified into three groups by their refraction. Low myopia group, SE (0~-3.00D), has 20 subjects. Moderate myopia group, SE (-3.25~-6.00D), has 20 subjects. High myopia group, SE (-6.25~-10.00D),
has 20 subjects. We all measured and analyzed right eyes. We used Pentacam HR for corneal curvature measurement, and RTVue OCT for corneal epithelial and corneal thickness measurement. Another 20 eyes of 20 subjects, who chose Epi-Lasik for myopia correction, were enrolled for epithelium study. Uncorrected VA, refraction, corneal epithelium change were assessed before and after Epi-Lasik in 3-day, 1 week, 1 month. The corneal epithelium was evaluated by RTVue OCT and confocal microscope.
RESULTS 1.Corneal epithelial thickness: the mean corneal epithelial thickness at corneal vertex High myopia group was51.03±4    .74µm; Moderatemyopia group was 50.45±3.92µm; Low myopia group50.98±3.89µm. Near peripheral corneal epithelial thickness (2.5mm horizontally and vertically from corneal vertex) is statistically thicker than the vertex (P<0.05). There were statistically correlation between near-peripheral and central area (1.0mm horizontally and vertically from corneal vertex and corneal vertex) corneal epithelial thickness and corneal thickness, correlation between corneal epithelial thickness and age, but no significant correlation between corneal epithelial thickness and gender, corneal curvature, spherical equivalent refraction (P>0.05) in all groups. More locations were found statistically relevant in near peripheral than corneal central area in all three groups. 2. After Epi-LASIK，the whole corneal epithelium had high reflectivity since postoperative 3 days. And the reflectivity gradually decreased until postoperative 1 month. The vivo confocal microscopy showed that corneal epithelium basal cell nucleus changed from without visualized in pre-operation into prominent status and the epithelium superficial cells were gradually found during postoperative 3 days and 1week.At postoperative 1 month, the corneal epithelium structure almost became normal.
CONCLUSIONS 1. The corneal epithelial thickness measurement by the fourth generation OCT was feasible.The distribution of corneal epithelium between central area and near peripheral was different. There were correlation between corneal epithelial thickness and age. 2. The high reflectivity in corneal epithelium found by OCT may related to wound heal reaction in epithelium, and the change in basal cell nucleus status. This may partly affected the refractive status a few weeks after operation.