Normative values of tear film parameters in brachycephalic dogs using OSA-Vet®: meniscometry and TBUTNI

The precorneal tear film is critical for ocular surface health, and brachycephalic dogs are particularly predisposed to tear film instability due to their unique conformation. This study aimed to establish normative values for tear film parameters in healthy brachycephalic dogs using the OSA-Vet®, including Schirmer tear test-1 (STT-1), tear meniscus height (TMH), and non-invasive tear breakup time (TBUTNI). Forty brachycephalic dogs (66 eyes) with STT-1 values between 15 and 25 mm/min underwent complete ophthalmological examination and OSA-Vet® evaluation. Data were analyzed for distribution, descriptive statistics, and correlations. Median values were 20 mm/min [19–22] for STT-1, 0.45 mm [0.36–0.62] for TMH, and 1.25 s [0.70–4.00] for TBUTNI. Spearman’s analysis revealed no significant association between STT-1 and TMH (ρ = 0.136, p = 0.277) or between TMH and TBUTNI (ρ = 0.046, p = 0.716). A weak positive correlation was observed between STT-1 and TBUTNI (ρ = 0.256, p = 0.038). These results demonstrate that even in dogs with preserved aqueous tear production, TBUTNI values remain low and variable, highlighting the predisposition of brachycephalic breeds to evaporative instability. TMH showed limited diagnostic value, underscoring the importance of multimodal tear film assessment. Previous studies have used OSA-Vet® to evaluate ocular surface parameters across cephalic conformations. The present study focuses specifically on establishing clinically applicable reference values in phenotypically brachycephalic dogs screened for normal aqueous tear production.