Tear film breakup time and Schirmer tear test in normal dogs: Effects of age, sex, reproductive status, skull type, and nasolacrimal duct patency

Objective The present study aimed to determine the effects of age, sex, reproductive status, skull type, and nasolacrimal duct (NLD) patency on tear production and tear film breakup time (TBUT) in normal dogs. Animals studied The ophthalmic data of 82 healthy adult dogs were evaluated in this study. Procedures Age, sex, breed, and reproductive status were recorded. Schirmer tear test (STT) and TBUT were assessed in all dogs, and interferometry was available for the selected dogs. The Jones test was used to evaluate NLD patency. The cephalic index (CI) was calculated for each dog (skull width/skull length x100). Results Mean (SD) values for the STT results for the right (OD) and left (OS) eyes were 20.6 (2.7) and 20.2 (2.7) mm/min, respectively. Mean (SD) TBUT values for OD and OS were 6.5 (2.5) and 6.1 (2.3) mm/min in all dogs, respectively. Sex and reproductive status had no significant effect on STT and TBUT (P-[OU] > 0.05). Skull type significantly affected TBUT in both eyes (P-(OD) = 0.01, P-(OS) = 0.003), but had no effect on STT (P-[OU] > 0.3). Age had no correlation with STT and TBUT in either eye (P-[OU] > 0.05). STT and TBUT had no correlation in either eye (P-[OU] > 0.2). NLD patency had no significant effect on STT or TBUT (P-[OU] > 0.1). Conclusions The results of this study showed lower TBUT values in brachycephalic breeds than in non-brachycephalic breeds. A compensatory increase in STT values was observed in dogs with low TBUT values.