Daytime profile of the intraocular pressure and tear production in normal dog

Abstract

Objective To evaluate the circadian rhythms of intraocular pressure (IOP) and tear production in dog exposed to a natural photoperiod. Animals studied We used 12 clinically healthy Beagles dog housed under natural photoperiod at indoor temperature and humidity. Procedure Intraocular pressure and Schirmer tear test (STT) I were measured every 4 h over a 48‐h period in both eyes in each animal. Statistical analysis of the data was performed by one‐way repeated‐measures anova, Student’s t‐test, and single cosinor method. Results On each day, there was a highly significant effect of time on both parameters. A statistically significant difference of STT I values was observed comparing left and right eyes (P < 0.0001). Robust daily rhythms were observed for both parameters, IOP values showed diurnal acrophase (left eye: 09:33 ± 00:50 h; right eye: 09:25 ± 00:22 h), while STT I values showed nocturnal acrophase (left eye: 20:27 ± 00:46 h; right eye: 20:00 ± 00:05 h). Conclusion This study has demonstrated circadian rhythms in both IOP and STT I.