Evaluation of the repeatability of corneal epithelial thickness mapping in healthy and keratoconic eyes with two spectral domain optical coherence tomography

Abstract

Purpose: To evaluate the repeatability of corneal epithelial thickness measurements using 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: A spectral domain AS-OCT (MS-39) and a posterior segment OCT (HS-100) with ASA-1 adaptor were used to measure the corneal epithelial thickness in healthy and keratoconic eyes. Three measurements per participant were taken, and the repeatability was described using the repeatability limit (Rlim), calculated from the within-subject standard deviation.

Results: 81 eyes of 81 controls and 80 eyes of 52 keratoconus subjects (43 % cross-linking, and 13 % contact lens users) were included. For the MS-39, the central sector showed the best repeatability for both groups, with Rlim never exceeding 5 μm in any sector. For the HS-100, the best repeatability was obtained for the central sector, with the Rlim never exceeding 7 μm in any of the sectors for the control group and all but one (outer-inferior) in the keratoconus group. The Rlim for the keratoconus group varied <1 μm between contact users/non-users or between eyes with/without a history of CXL. Differences in Rlim were larger than 2 μm in the peripheral horizontal sectors between each sub-group with the HS-100.

Conclusions: Both OCTs showed good epithelial thickness measurement repeatability in all groups, though the repeatability of the HS-100 was mildly lower for keratoconic eyes. Contact lens use and crosslinking history did not affect repeatability. These OCTs effectively measure epithelial thickness in keratoconus patients, which could be helpful in monitoring keratoconus progression.

Keywords: Anterior segment optical coherence tomography oct; Epithelial thickness; Keratoconus; precision; repeatability.