Effects of three mydriatic drug regimens on pupil size in rhesus (Macaca mulatta) and African green monkeys (Chlorocebus aethiops)

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Human mydriatric drug use in non-human primates (NHPs) has been documented but not quantified and compared for effectiveness. The objective of this study was to determine which drug regimen provided the most effective and consistent mydriatic effect for ophthalmologic examinations and other procedures. Secondary objectives were to determine average time to maximum dilation and whether species differences existed.


Twelve rhesus and 12 African green monkeys were randomly assigned to one of six treatment combinations to test the mydriatic effects of three drug regimens: (1) tropicamide 1% (T); (2) tropicamide 1% and phenylephrine hydrochloride 2.5% (TP); and (3) tropicamide 1%, phenylephrine HCL 2.5% and cyclopentolate 1% (TPC). Left and right eyes of each monkey received a different drug regimen, depending on random assignment.


TPC showed a significantly larger mydriatic response in both species than T alone. Average time to maximum dilation with all three drug regimens was 50–60 minutes. Rhesus had a larger response to the mydriatic drug regimens than the African green monkeys.


The TPC regimen had the largest and longest lasting mydriatic effect in both species.

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