Effect of Topical Carbachol on the Pupil and Refraction in Young and Presbyopic Monkeys

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Abstract

Pupil diameter and refractive state were measured after carbachol was applied onto the cornea or injected into the anterior chamber of cynomolgus monkeys (Macaca irus) and vervets (Cercopithecus aethiops). The results are presented as dose-response curves. The refraction dose-response curves are expressed in both diopters and per cent of maximal accommodation. No important species differences were observed. ED₅₀ for refractive change after carbachol was placed onto the cornea was approximately 30 mcg., and after injection into the anterior chamber it was 0.12 to 0.18 meg. ED₅₀ for pupil contraction after carbachol was applied onto the cornea was 0.3 to 0.5 meg., and after carbachol was injected into the anterior chamber it tuas 0.005 to 0.006 meg. An accommodation amplitude (determined after drug stimulation) of 15 to 20 D. is common among young monkeys. Two of the monkeys in the present series were presbyopic. They had flat dose-response curves, i.e., needed a stronger pharmacologic stimulus per diopter of accommodation