Corneal Epithelial Thickness in Normal Corneas with Low and High Toricity

Purpose: To compare the corneal epithelial thickness along the flat and steep meridians of corneas with low and high toricity.

Methods: This was a prospective observational comparative study on healthy subjects with normal corneas seeking preoperative evaluation for refractive surgery at a university-based hospital. Subjects with up to 2 diopters (D) of corneal with-the-rule astigmatism were defined as low corneal toricity (CT), whereas cylinder > two-dimensional was considered as high CT. The anterior segment optical coherence tomography was conducted to measure the epithelial thickness along the principle meridians of CT over a diameter of 9 mm. At the eye level, outcome variables (corneal and epithelial thicknesses in low- and high-astigmatism groups) were assessed using generalized estimating equation models.

Results: Included were 98 eyes (49 subjects): 46 eyes (23 subjects) with low CT and 52 eyes (26 subjects) with high CT. Two groups were similar with respect to the age (P = 0.82), sex (P = 0.49), and spherical equivalent (P = 0.11). Although the corneal thickness at steep and flat meridians was not different between two groups, high-CT group had significantly thinner epithelium at inferior 2.5-3.5 and 3.5-4.5 mm zones (P = 0.01 and 0.04) as well as superior 2.5-3.5 mm zone (P = 0.03) along the steep meridian. Two groups were similar with respect to epithelial thickness of flat meridian (all P > 0.05).

Conclusion: The epithelium of steep meridian was thinner in the high-CT group compared to the low-CT group.