Evaluation of Monkey Intraocular Pressure by a Rebound Tonometer

Abstract

Purpose: : To evaluate the usefulness of a rebound tonometer in measuring intraocular pressure (IOP) in the monkey.

Methods: : The accuracy of the TonoVet^TM rebound tonometer was determined in cannulated eyes of anesthetized rhesus monkeys, where IOP was controlled by adjusting the height of a connected perfusate reservoir. To assess the applicability of the equipment in in vivo studies, the circadian fluctuation of IOP and effect of a known IOP-lowering medication, the Travatan® ophthalmic solution, were evaluated in monkeys in a seated posture under light anesthesia.

Results: : IOP readings generated by the TonoVet tonometer correlated very well with the actual pressure in the cannulated monkey eye. The linear correlation had a slope of 0.922 ± 0.014 (mean ± SEM, n = 4), a Y-intercept of 3.04 ± 0.61, and a correlation coefficient r² = 0.97. Using this method, a trend of diurnal IOP fluctuation of the rhesus monkey was demonstrated. The highest IOP was observed at 15:00 (16.7 ± 0.6 mmHg; mean ± SEM, n = 16), the lowest at 9:00 (15.1 ± 0.7 mmHg). The tonometer was also able to detect the IOP change induced by Travatan. A single topical ocular instillation (30 µL) of Travatan induced a small transient IOP increase (1.1 mmHg versus vehicle control; p = 0.26) at 2 h after treatment, followed by a pressure reduction at 23 h (-2.4 mmHg; p < 0.05). Multiple daily dosing with the drug produced persistent IOP-lowering effect. Three consecutive daily Travatan treatment produced ocular hypotension of -2.0 to -2.2 mmHg (p < 0.05) on the following day.

Conclusions: : The rebound tonometer was easy to use and accurately measured IOP in the rhesus monkey eye.

Keywords: intraocular pressure • anterior chamber