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 mu m (SD 0.49; min-max: 12.28-19.54) in HC, 14.27 mu m (SD:0.43; min-max: 11.22-18.25) in KC and 15.65 mu m (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.