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Thickening of epithelial lenticule following corneal refractive surgery as an OCT quantifiable source of error

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First Author: R.Wiener ISRAEL

Co Author(s):    D. Smadja   A. Shoshani   D. Zadok              

Abstract Details

Purpose:

To measure changes to epithelial lenticule thickness and power before and after corneal refractive surgery using OCT.

Setting:

Academic medical center

Methods:

Five eyes of patients having undergone corneal laser refractive surgery with residual refractive error >2D were evaluated. Patient had manifest refraction, anterior-segment OCT, and Placido-ring performed preoperatively and 3-months post-surgery. OCT images were segmented using Canny method of edge detection of Bowman’s layer to epithelial and stromal lenticules. Central 3mm of each surface was fitted to a sphere using direct least-square fitting, yielding lenticule radius and thickness. Power of epithelial and stromal lenticules were calculated by summation of anterior and posterior surface powers. Total corneal power was calculated as sum of lenticule powers and was compared with simulated keratometry.

Results:

Following refractive surgery, anterior radius of epithelial lenticule increased by 6.5%, decreasing power by 2.80 D. Epithelial lenticule thickness increased by 47%, and stromal thickness decreased by 26%. Bowman's layer radius increased by 16.3%, increasing power by 0.36 D. Posterior radius was unchanged.

Conclusions:

The corneal epithelium and stroma are distinct anatomical layers, possessing different refractive indices. Myopic laser refractive surgery acts by decreasing stromal thickness, however, may be accompanied by thickening of the higher refractive index epithelium. This results in underestimated refractive-surgery induced refractive change. OCT-based segmentation of the cornea to two physical layers explains this prediction error and holds promise for improved refractive surgery planning.

Financial Disclosure:

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