Canine central corneal thickness measurements via Pentacam-HR , optical coherence tomography (Optovue iVue ), and high-resolution ultrasound biomicroscopy.

Objective: To compare central corneal thickness (CCT) values in canine eyes using Pentacam-HR Scheimpflug imaging (Pentacam), Optovue iVue spectral-domain optical coherence tomography (SD-OCT), and high-resolution ultrasound biomicroscopy (UBM) and generate normative canine Pentacam CCT values.

Animals Studied: Twenty-four client-owned dogs (37 eyes) with nondiseased cornea(s) presenting to the Colorado State University Veterinary Teaching Hospital.

Procedures: Corneal images were acquired via Pentacam, SD-OCT, and UBM in the listed order. Machine-calculated values of CCT from Pentacam and SD-OCT were compared to operator-measured values from UBM. Bland-Altman analysis was performed to evaluate agreement between instruments.

Results: Mean CCT ± SD measured by Pentacam was 629.73 ± 64.57 μm, by SD-OCT was 610.56 ± 57.48 μm, and by UBM was 689.77 ± 55.93 μm. On average, Pentacam CCT was 19.17 ± 32.90 μm (3%) thicker than SD-OCT and 65.12 ± 44.52 μm (10.3%) thinner than UBM. SD-OCT was on average 82.47 μm (13.5% ) thinner than UBM. The 95% limits of agreement were (-45.31, 83.65), (-152.38, 22.13), and (-126.674, -38.270) for Pentacam vs. SD-OCT, Pentacam vs. UBM, and SD-OCT vs. UBM respectively. All differences were statistically significant (P < 0.01).

Conclusions: Considering there is an average of 7.5% normal diurnal variation in canine CCT, a 3.0% difference between Pentacam and SD-OCT values is likely not clinically relevant. However, Pentacam measurements were both statistically and clinically significantly different from UBM and SD-OCT measurements.