Tear clearance rate in dogs: Measurement using anterior segment optical coherence tomography

Objective: The tear clearance rate (TCR), determined using anterior segment optical coherence tomography (AS-OCT) images, and its correlation with ocular surface parameters, including blink rate, Schirmer tear test-1 (STT-1) and tear film breakup time (TFBUT), were evaluated. Animals studied: Left eyes of 20 client-owned dogs with no ocular disease symptoms. Procedures: The tear meniscus height (TMH) was evaluated using AS-OCT images before the instillation of 5 μL saline (TMH_base), immediately post-instillation (TMH₀), 30-s post-instillation (TMH_0.5) and at 1 min intervals for 5 min post-instillation (TMH₁, TMH₂, TMH₃, TMH₄ and TMH₅). The TCR was calculated using the formula [(TMH₀ − TMH_0.5)/TMH₀]×100 (%). The eyes were classified into two groups with the median: ‘High TMH_base’ (n = 10) and ‘Low TMH_base’ (n = 10). Eyes with STT-1 values ≥15 mm/min and TFBUT ≥ 12 s were assigned to the ‘Satisfied’ subgroup, whereas eyes not satisfying these criteria were assigned to the ‘Not satisfied’ subgroup. Results: TMH₀ was higher than TMH_0.5 (p = 0.02), wherein TMH_0.5 to TMH₅ did not differ significantly. The TCR and blink rate were negatively correlated (p = 0.02). The ‘Not satisfied’ subgroup in the low TMH_base group had a lower TCR (p = 0.02) and higher blink rate (p = 0.04) than the ‘Satisfied’ subgroup. Conclusions: TCR can be evaluated using AS-OCT in dogs. Eyes with a lower TCR blink more frequently. TMH merits studying to understand ocular surface health.