Manual corneal thickness measurements of healthy equine eyes using a portable spectral-domain optical coherence tomography device

Abstract

Reasons for performing study: Corneal thickness measurements of the equine globe using spectral-domain optical coherence tomography (SD-OCT) have not been reported.

Objectives: To determine corneal thickness measurements and the intra- and interoperator reliability of a portable SD-OCT device in equine eyes.

Study design: Prospective observational study.

Methods: Horses free of ocular disease were used for this study. Gentle manual restraint, in combination with detomidine hydrochloride and a head stand, were employed to ensure proper animal positioning. Corneal pachymetry measurements were obtained from both eyes of each animal 3 times by 2 operators in succession. A 6 mm corneal pachymetry protocol was performed using a portable SD-OCT device. All measurements were obtained manually by one operator (C.G.P.) using the integrated calliper function. Measurements included epithelial thickness, stromal thickness, Descemet's membrane thickness and total corneal thickness. All recorded measurements were analysed to determine both intra- and interoperator reliability.

Results: Thirty horses with a mean age of 10.6 ± 6.4 years were examined. Mean epithelial, stromal, Descemet's membrane and total corneal thickness values obtained were, respectively, 174.7 ± 13.6, 599.2 ± 45.4, 38.4 ± 15.3 and 812.0 ± 44.1 μm for operator A and 175.9 ± 12.9, 599.2 ± 44.9, 38.4 ± 15.0 and 812.9 ± 42.9 μm for operator B. A positive correlation was found between Descemet's membrane thickness and age, whereby Descemet's membrane thickness increased by 2 μm/year (P<0.0001). The coefficients of variation for both operators were <4% for all measurements. Intraclass correlations ranged from 0.92 to 0.98.

Conclusions: Manual corneal thickness measurement using a portable SD-OCT device provides epithelial, stromal, Descemet's membrane and total corneal thickness measurements with clinically acceptable intra- and interoperator reliability in healthy equine eyes.

Keywords: cornea; horse; optical coherence tomography; pachymetry; thickness.