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).