Factors determining the potency of cholinomimetic miotic drugs and their effect upon the light reflex in man

1. Television pupillometry was used to measure the effect of six topically applied cholinomimetic drugs on the resting diameter and light reflex amplitude of the human pupil. Drug potency was obtained from dose response curves. 2. The tertiary amines arecoline, aceclidine and pilocarpine were considerably more effective miotics than the choline esters carbachol, methacholine and acetylcholine. 3. All the drugs which caused miosis also reduced light reflex amplitude proportionally. 4. The in vitro potency of these drugs was also measured on preparations of rabbit iris sphincter and guinea pig ileum. 5. Dose response relationships for pilocarpine in man and in vitro showed evidence of partial agonist activity on the rabbit iris only. 6. A comparison of the in vivo and in vitro results showed that three factors influenced the potency of topically applied miotics: accessibility to the iris; sensitivity to cholinesterase; and cholinoceptor agonist potency.