Effects of Bowman Layer Integrity Impairment on the Central Epithelial Corneal Thickness in Patients with Keratoconus

Abstract

Purpose : To investigate the pathophysiological mechanisms and effects of impairment in the Bowman layer integrity on the central epithelial corneal thickness in patients with keratoconus.

Methods : Penetrating keratoplasty histopathology specimens from 43 patients with advanced keratoconus were evaluated using bright field microscopy. Total central corneal thickness, epithelial central corneal thickness, and number of Bowman layer breaks were compared between the groups with hypertrophic and atrophic/average central epithelial thickness. Results were analyzed using t-test assuming unequal variance, and Fisher’s exact test.

Results : There were no statistically significant differences in the overall reduced total central corneal thickness between the group with hypertrophic central epithelium (n=19, 308±23 μm) and the group with atrophic or average thickness central epithelium (n=23; 278±15 μm). However, the central epithelial thickness differed significantly from 28.7±2 μm in the atrophic group to 70±6 μm in the hypertrophic epithelium group (p<0.05). There was a statistically significant difference in the proportion of patients who had no Bowman layer breaks in the two groups (Fisher exact test, p<0.05). In the atrophic and average thickness epithelium group, a significant proportion of patients (8 /24) had no frank Bowman layer breaks. In contrast, there were no patients with intact Bowman layer in the hypertrophic epithelium group.

Conclusions : Majority of keratoconic corneas with atrophic central epithelial pattern tend to show Bowman layer with preserved integrity in contrast to those with hypertrophic central epithelia who have abundant Bowman layer breaks. This fact suggests that the striking central epithelial hypertrophy present in some advanced keratoconic patients might represent a compensatory mechanism to increase the epithelial cushioning in the settings of severely impaired Bowman layer integrity.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.