Abstract
Purpose :
Measurement of intraocular pressure (IOP) in young Rhesus monkeys is important for the study of numerous ocular conditions, including eye growth and myopia. Recent studies show that select ocular hypotensive agents may protect against experimental myopia. In young monkeys, IOP is traditionally measured under anesthesia, which may confound the findings. This study aimed to establish a method for awake IOP measurement in young monkeys, assess the effects of dilation and sedation, and determine diurnal variation.
Methods :
Subjects were infant Rhesus monkeys (Macaca mulatta, n = 11) undergoing lens-treatment for a refractive study. IOP was measured with a rebound tonometer (iCare TonoVet). At three weeks of age, awake IOP was measured every two hours from 7:30 am to 5:30 pm to determine potential diurnal variations. Beginning the following day, awake IOP, awake and dilated IOP (tropicamide 0.05%), and sedated (ketamine 20 mg/kg + acepromazine 0.2 mg/kg) and dilated IOP was measured biweekly from ages 3-15 weeks. Intraclass correlation coefficient (ICC) was used to determine intersession repeatability for IOP measurement on 2 consecutive days at 3 weeks of age.
Results :
At age 3 weeks, mean (±SEM) awake IOP was 15.4±0.6 and 15.2±0.7 mmHg for right and left eyes, respectively (P=.59). The ICC between sessions was .63[-.5 to .9], with a mean difference of 2.2±0.3 mmHg between days. Diurnal IOP measurement from 7:30 am to 5:30 pm showed no significant variation (P=.67). For all ages, IOP while awake and undilated was 17.2±0.5 mmHg, awake and dilated was 18.5±0.5 mmHg, and sedated and dilated was 11.1±0.9 mmHg. There was a significant effect of age (P=.01) and condition (P<.001), with no interaction between age and condition (P=.46).
Conclusions :
Awake IOP measurement is feasible in young Rhesus monkeys with moderate repeatability. There was no significant diurnal fluctuation in IOP between 7:30 am and 5:30 pm. IOP measured under sedation was significantly lower than IOP measured in awake monkeys, while topical administration of tropicamide did not affect IOP. Findings show that ketamine/acepromazine anesthesia affects IOP in young Rhesus monkeys, suggesting that measurement should be performed before sedation.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.