Corneal Epithelial Thickness in Normal Corneas with Low and High Toricity

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

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.

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).

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