Objective: To investigate the effects of age, weight, gender, and of time of day on tear production in normal dogs.
Animals: studied One hundred ophthalmoscopically and systemically unremarkable dogs.
Procedure: Schirmer tear tests (STT) were performed every 2 h during the day on one randomly chosen eye of each of 100 dogs.
Results: There was a statistically significant effect of time of day and age on the STT measurement. The mean STT decreased by 0.4 mm for every 1 year that age increased (P=0.007). Mean STT values taken at 10:00 am were 0.7 mm lower than values taken at 4:00 pm (P=0.04).
Conclusions: Tear production decreases with age in the normal dog. In this population of dogs the largest difference was between the 10:00 am and the 4:00 pm STT measurements, but this still only amounted to 0.7 mm. This value is unlikely to be of clinical significance in the diagnosis of keratoconjunctivitis sicca (KCS).