Comparative Studies of the Effect of Pilocarpine on the Pupil and on the Refraction in two Species of Monkey (Cercopithecus Ethiops and Macaca Irus)

¹ Department of Pharmacology, University of Uppsala, Sweden

It is known that pilocarpine injected into the anterior chamber affects outflow facility in much smaller doses in the vervet (Cercopithecus ethiops) than in the cynomolgus (Macaca irus). The present experiments toere performed in order to determine whether a similar species difference, with respect to pilocarpine sensitivity, is present in the sphincter pupillae and the muscle of accommodation. In order to make possible the study of pilocarpine-induced refraction changes, the pupil of one eye was immobilized by a partial excision of the sphincter region of the iris. The other eye was used for studies of the pupil. Pilocarpine was applied to the cornea (in 10 µl), injected into the anterior chamber (in 1 µl), and injected intramuscularly. Dose-response curves were determined for pupillary size and changes in refraction. No important species difference in the sensitivity to pilocarpine of the pupil or of refraction was observed. This was true for all modes of administration. When pilocarpine teas applied to the cornea, the dose necessary to effect a half-maximal change in refraction tvas about 100 times that necessary to cause half-maximal pupillary constriction. This applied to both species of monkey. The ratio betioeen the doses was approximately of the same order when pilocarpine toas injected into the anterior chamber. With systemic administration of pilocarpine, no difference could be detected for the effective doses on the pupil and on refraction in either species. If the pilocarpine was injected into the anterior chamber, only about one tenth of the corneal dose was required to obtain the same change in refraction. This applied to both species of monkey.