Intraocular pressure distribution in old and young cynomolgus monkeys following general anesthesia and mydriasis

To investigate the intraocular pressure (IOP) distribution of cynomolgus monkeys in different age groups after anesthesia and mydriasis.

A total of 158 young and 252 old cynomolgus monkeys, aged 3.95 (1.61; range, 1.38 to 5.97) and 18.80 (1.67; range, 15.21 to 24.69) years, respectively, were subjected to general anesthesia (intramuscular injection of Zoletil 4 mg/kg mixed with xylazine/ketamine 0.2 mg/kg). IOP was measured using an Icare tonometer at three time points: immediately following the onset of anesthesia, after stabilization but before mydriasis, and after mydriasis (induced by 1% tropicamide eye drops).

No significant differences were observed between sexes or between eyes within the Macaca fascicularis colony. After anesthesia stabilization but before mydriasis, the IOP of the old M. fascicularis colony was 22.33 mm Hg (4.12; range, 12.33 to 37.33), whereas the IOP of the young M. fascicularis colony was 16.67 mm Hg (4.00; range, 10.67 to 25.67). After mydriasis, the IOP of the old M. fascicularis colony was 19.33 mm Hg (5.00; range 11.33 to 33.00), while the IOP of the young M. fascicularis colony was 15.67 mm Hg (4.50; range, 9.67 to 24.00). All measurements were conducted with the monkeys in a prone position. Notably, both the young and old colonies experienced a significant decrease in IOP after mydriasis (p < 0.001). Moreover, the reduction observed in the young colony was significantly greater than that in the old colony (p < 0.001).

The IOP levels of the old M. fascicularis colony were higher than those of the young one, regardless of whether it was after anesthesia, before mydriasis, or after mydriasis. Furthermore, monkeys of different age groups had different reductions in IOP under different interventions (anesthesia, mydriasis). Additionally, within the M. fascicularis colony, IOP was equivalent between males and females, as well as between the right and left eyes.