Effects of pilocarpine, timolol, epifrin and thymoxamine on iris vessels in rhesus monkeys

In 24 normal eyes of healthy adult rhesus monkeys, the effects of 1% Pilocarpine, 0.5% Timolol, 0.5% levo-epinephrine (Epifrin) and 0.5% Thymoxamine were tested on the iris vessels, intraocular pressure and pupil size. Fluorescein iris angiography and applanation tonometry were performed on the eyes before the use of any drug, and then 2-4 h after topical instillation of each drug; all drugs were used in all the eyes, an interval of one week being left after the use of each drug. The findings of this study suggest that Pilocarpine and Timolol produced vasodilation. Epifrin and Thymoxamine seemed to have no appreciable effect. Pilocarpine produced miosis while other drugs had no significant effect on pupil size. Pilocarpine, Timolol and Epifrin each produced a significant fall in the intraocular pressure. The mechanisms of vascular changes are discussed. The various limitations of fluorescein iris angiography in such a study are stressed.