Daily rhythm of tear production in normal horse.

OBJECTIVE This study was designed to assess the daily rhythm of tear production in clinically healthy horses, to compare left eye and right eye, and to evaluate the influence of time and gender. ANIMAL STUDIED For our study 18 horses (nine female and nine male) were subjected to three different light/dark (L/D) schedules: 12/12 L/D cycles, constant light (24/0 L/D) and constant darkness (0/24 L/D). PROCEDURES In all subjects Schirmer tear tests were performed at 4-h intervals over a 24-h period. RESULTS A circadian rhythm of tear production was found during the 12/12 L/D period and during constant darkness. Also our results showed a statistical significant difference comparing left eye and right eye, and between gender. CONCLUSIONS Our findings would suggest that the time of tear evaluation is significant in the diagnosis of tear film disorders, and that the difference between the two eyes and the two genders should be taken into consideration during the ophthalmic exam.