Factors influencing intraocular pressure in cynomolgus monkeys

Abstract

Intraocular pressure (IOP) is widely measured for evaluating physiology, diseases and toxic changes of the eye. IOP was reported to be influenced by various factors in many species including humans, rhesus monkeys and dogs.^1-10) In the present study, we evaluated the effects of anesthesia, body positioning, time of measurement during the day and mydriasis on the IOP in cynomolgus monkeys.
When ketamine HCl was intramuscularly administered at 10 mg/kg as an anesthesia, the IOP level was highest at 5 minutes after the anesthesia and thereafter it decreased. It was stable between 15 and 30 minutes after the administration of ketamine HCl and the variations of 5 minutes interval were within 3 mmHg during this period after the administration. Measurement at the prone position showed significantly higher IOP values (p<0.05) when compared to those at the sitting position. As for difference in the measurement time during a day, tendency towards higher values of IOP was seen in the morning measurement when compared to those in the afternoon measurement. To examine the effect of mydriasis on IOP, the left eye was treated with tropicamide and phenylephrine HCl and the right eye was dropped physiological saline in the same individual animals, and IOP was measured. There were no significant differences in IOP values between the left and right eye.
It is concluded that IOP values of the monkeys were apparently influenced by body positioning and might be influenced by the time of measurement during the day but not by mydriasis. It is also suggested that measurement of IOP should be conducted at earliest, 15 minutes after administration of ketamine HCl, to obtain reliable and less variable results in cynomolgus monkeys.