*Correspondence, Stephen Kaye: s.b.kaye@liverpool.ac.uk

Purpose To assess the accuracy, repeatability, and performance limits of in vivo Mirau ultrahigh axial resolution (UHR) line field spectral domain (LF-SD) optical coherence tomography (OCT) for the clinical in vivo measurement of Bowman’s layer thickness in subjects with and without keratoconus.

Methods Patients with keratoconus and volunteers with no corneal disease were included. The thickness of Bowman’s layer was measured in the clinic. An in vivo graph search image segmentation of the central cornea was obtained at the normal interface vector orientation. The Mirau-UHR-LF-SD-OCT system used has an axial resolution down to 2.4 µm in air (1.7 µm in tissue), with an A-scan speed of 204.8 kHz and a signal to noise ratio (sensitivity) of 69 (83) dB.

Results 40 patients with keratoconus and 20 healthy volunteers were included. The repeatability of mean Bowman’s and epithelial thicknesses were 0.3 and 1.0 µm, respectively. The measured 95% population range for Bowman’s layer thickness was 13.7 to 19.6 µm for healthy (mean 16.65, SD 1.48) and 10.94 to 16.99 for 23 of the keratoconics (mean 13.96 SD 1.51) (p<0.05).

Conclusions The measured thicknesses of Bowman’s layer using the Mirau-UHR-LF-SD-OCT were both accurate, with the range for healthy in vivo thicknesses matching prior confocal and OCT systems of varying axial resolutions and repeatable. Bowman’s layer was significantly thinner in patients with keratoconus. Bowman’s layer can be accurately measured in the clinical setting using a Mirau-UHR-LF-SD-OCT and can be useful for disease monitoring.