Corneal epithelial thickness mapping precision in keratoconic eyes with two different optical coherence tomographers

Aims/Purpose: Corneal epithelial thickness measurement precision was evaluated with an anterior segment optical coherence tomography (AS‐OCT) and a posterior segment OCT adapted with an anterior module in subjects with keratoconus and healthy controls. Methods: The MS‐39 (spectral domain AS‐OCT) and the HS‐100 (posterior segment OCT with ASA‐1 adaptor) were used to measure the corneal epithelium. On each participant, three consecutive measurements were taken. The metrics used to describe the repeatability of each OCT were the within‐subject standard deviation (S w ) and repeatability limit (Rlim). Results: 81 controls (81 eyes) and 52 keratoconus subjects (80 eyes) were measured. The best repeatability was obtained in the central sector for both control and keratoconus groups with both MS‐39 and HS‐100. The Rlim never exceeded 5μm in any of the sectors for both groups with MS‐39. With the HS‐100, the Rlim never exceeded 7μm in any of the sectors for the control group and in all but one sector in the keratoconus group. In the keratoconus group, there was a weak negative correlation ( p < 0.05) between the thinnest corneal thickness and their respective Sw for both instruments. For the control group, the correlations between the three different metrics (the thinnest epithelial thickness measured with the MS‐39, the thinnest corneal thickness measured with the MS‐39, and the thinnest corneal thickness measured with the Canon OCT) and their respective Sws were not statistically significant ( p > 0.05). Conclusions: Both OCTs showed good repeatability to measure corneal epithelial thickness in both healthy and keratoconus eyes, independent on the history of corneal crosslinking or contact lens use.