Manual corneal thickness measurements of healthy equine eyes using a portable spectral-domain optical coherence tomography device.
Authors: Pirie C G, Alario A F, Barysauskas C M, Gradil C, Uricchio C K
Journal: Equine veterinary journal
Summary
# Editorial Summary: Corneal Thickness Measurement in Horses Using Portable SD-OCT Establishing normative corneal dimensions and reliable measurement techniques is essential for equine ophthalmologists managing conditions affecting corneal integrity, yet portable spectral-domain optical coherence tomography (SD-OCT)—a non-invasive imaging tool already established in human and small animal practice—had not been systematically validated for equine corneal pachymetry. Pirie and colleagues examined 30 healthy horses using a portable SD-OCT device to generate baseline corneal measurements and assess both intra- and interoperator reliability, employing gentle restraint with detomidine sedation and manual calliper measurements to quantify epithelial, stromal, Descemet's membrane, and total corneal thickness across three repeat measurements per eye. The team established normative values of approximately 175 µm (epithelium), 599 µm (stroma), 38 µm (Descemet's membrane), and 812 µm (total corneal thickness), with coefficients of variation below 4% and intraclass correlations between 0.92–0.98, indicating excellent repeatability between operators; notably, they identified a significant age-related thickening of Descemet's membrane at approximately 2 µm per year. These findings provide equine practitioners with clinically reliable baseline data and validate portable SD-OCT as a practical tool for monitoring corneal changes in cases of ulceration, dystrophy, oedema, or scarring, though users should account for age-related membrane changes when interpreting measurements in older horses.
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Practical Takeaways
- •Portable SD-OCT is a reliable tool for measuring corneal thickness in horses without requiring specialized training or sedation beyond routine handling protocols
- •Reference values for healthy equine corneal structure can now inform detection of corneal disease, thinning, or edema in clinical cases
- •Age-related thickening of Descemet's membrane should be considered when interpreting corneal measurements in older horses
Key Findings
- •Mean total corneal thickness in healthy horses is 812.0–812.9 μm with excellent intra- and interoperator reliability (intraclass correlations 0.92–0.98)
- •Epithelial thickness averaged 174.7–175.9 μm, stromal thickness 599.2 μm, and Descemet's membrane thickness 38.4 μm across operators
- •Descemet's membrane thickness increases with age at a rate of 2 μm per year (P<0.0001)
- •Portable SD-OCT device provides clinically acceptable manual corneal pachymetry measurements in equine eyes with coefficients of variation <4% for all measurements