# Bowman’s layer and corneal thickness in health and disease

## TL;DR

This study measures the thickness of Bowman’s layer in healthy and diseased corneas, finding it is consistently related to overall corneal thickness but not influenced by age, sex, or other factors.

## Contribution

The study introduces a novel automated segmentation method to measure central Bowman’s layer thickness in corneal diseases.

## Key findings

- Central Bowman’s layer thickness is on average 3% of central corneal thickness.
- Bowman’s layer thickness is independent of age, sex, corneal curvature, and epithelial thickness.
- Keratoconus patients have thinner central Bowman’s layer than those with corneal dystrophies.

## Abstract

To investigate central Bowman’s layer thickness (BT) in relation to central corneal thickness (CCT) and curvature, and epithelial thickness in healthy and disease corneas.

Patients with keratoconus (KC), corneal dystrophies (CD) and healthy controls (HC) were included. Linnik and Mirau versions of an ultra-high axial resolution line field spectral domain optical coherence tomography device were used to image the cornea, in addition to commercially available devices. A supervised automated segmentation process was used to extract the quasi-point thickness of Bowman’s layer.

62 participants: 24 with KC, 20 with CD and 18 HC were included. Mean central BT was 15.41 µm (SD 0.49; min-max: 12.28–19.54) in HC, 14.27 µm (SD:0.43; min-max: 11.22–18.25) in KC and 15.65 µm (SD 0.64; min-max: 12.42–20.06) in CD (mainly Fuchs CD). Patients with KC had thinner central BT than those with CD (p=0.03), but not compared with HC (p=0.13). Central BT was significantly associated with CCT (p<0.01), being on average 3% of CCT. The ratio of BT to CCT was independent of diagnosis (CD 0.028, HC 0.030, KC 0.028, p=0.88), age (p=0.23), sex (p=0.67), Kmax (p=0.77) or epithelial thickness (p=0.72).

Over sample populations of healthy, keratoconic and dystrophic corneas, central BT was consistently associated with corneal thickness and was independent of age, sex, Kmax, and epithelial thickness.

ISRCTN40558.