Pilot evaluation of the circadian rhythm of tear production in a population of healthy adult cats.

Objectives The purpose of this study was to determine if a circadian rhythm exists in Schirmer's tear test (STT-1) values in a group of healthy adult cats. Animals studied Twenty adult neutered Domestic Short-haired cats (DSH) were used in the study. Procedures Tear production was measured with the Schirmer tear test (STT-1) at 12 different time points over a 48-hour period. Results A significant difference (approximately 4.3 mm/min) was noted between STT-1 values measured between 4 pm (lowest) and 12 am (highest) on both day 1 (P = 0.02) and day 2 (P = 0.01), and substantial variation in STT-1 values was observed at different times during the 48-hour period. Conclusions Significant variation in mean STT-1 values demonstrates that there is a circadian rhythm in tear production in cats and thus shows the importance of taking the time of day into account when measuring STT-1 in cats.