Bowman’s layer and corneal thickness in health and disease

PURPOSE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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. TRIAL REGISTRATION NUMBER: ISRCTN40558.