Circadian rhythm of intraocular pressure in clinically normal donkeys (Equus asinus)

Abstract

ABSTRACT The present study aimed to report the circadian rhythm of intraocular pressure (IOP) in clinically normal donkeys. A prospective study was conducted on 30 adult donkeys. Measurement of the IOP was made at 2-hr interval starting at 6:00 hr till the next day at 4:00 using applanation tonometry. Measurements were recorded for both eyes and compared for male and female differences. The overall mean (± SEM) IOP measurement was 24.99 ± 0.14 mmHg. The mean (± SEM) IOP of the right and left eyes was 25.59 ± 0.19 and 24.27 ± 0.19 mmHg, respectively. The IOP values of the right and left eyes as well as of male and female values did not change significantly (P > 0.05) at all times. IOP measurements demonstrated diurnal fluctuation during the light phase of the day. The IOP significantly (P < 0.001) increased (27.07 ± 0.42) in the early morning (peak daytime at 8:00 hr) and was significantly (P < 0.001) lower (20.68 ± 0.34) at the mid-light phase (12:00 hr) compared to all evaluation times. The study documented the daily rhythm of IOP in donkeys. The 24-hr variation of IOP measurement should be considered when evaluating IOP in donkeys.