Large Field of View Corneal Epithelium and Bowman's Layer Thickness Maps in Keratoconic and Healthy Eyes

Abstract

Purpose: To assess differences between epithelium thickness (ET) and Bowman's layer thickness (BLT) maps in keratoconic eyes and healthy eyes.

Design: Cross-sectional study.

Methods: Setting: institutional.

Study population: 47 patients (1 eye) with keratoconus (KC) and 20 healthy subjects (1 eye).

Observation procedure: epithelium and Bowman's layer measurements were performed by using custom-designed polarization-sensitive optical coherence tomography (PS-OCT) with a conical scanning optics design. En face corneal ET and BLT maps with a diameter of 11 mm were computed. Main outcome measurements were mean ET and BLT of 25 sectors; the thinnest (minET, minBLT) and thickest sectors (maxET, maxBLT) were assessed. Ratios between thinnest/thickest sectors (R1) and between mean ET and BLT of the inferior temporal quadrant/superior nasal quadrant (R2) were calculated (R1ET, R1BLT; R2ET, R2BLT). Receiver operator characteristic (ROC) curve analysis was used to assess the diagnostic power of statistically different parameters.

Results: In healthy eyes, smooth ET maps were observed. KC eyes showed a "doughnut pattern." The BLT maps of healthy eyes had a smooth appearance, but highly irregular "moth"-like damage pattern could be observed in keratoconic eyes. Highest area under the curve values were found for the thinnest sector of the BLT map, the R1ET, and the thinnest sector of the ET map.

Conclusions: PS-OCT imaging enables the visualization of significant differences of the corneal epithelium and the Bowman's layer in en face maps covering almost the entire cornea. ET and BLT profiles could clearly show their diagnostic importance for the distinguishing of keratoconic eyes and healthy eyes.