SUBSENSITIVITY TO CHOLINOCEPTOR STIMULATION OF THE HUMAN IRIS SPHINCTER in situ FOLLOWING ACUTE AND CHRONIC ADMINISTRATION OF CHOLINOMIMETIC MIOTIC DRUGS

Abstract

Maximal pupillary miosis was obtained with single topical applications of 4 cholinomimetic drugs in therapeutic concentrations to normal human subjects. When the pupil had recovered from the miosis, there remained a reduced light reflex response of 22.7% at 24 h after aceclidine, 18.0% at 31 h after pilocarpine, 10.3% at 48 h after physostigmine and 4.9% at 7 h after arecoline. This reduced sensitivity to light was accompanied by an overshoot of the resting pupil diameter and, after aceclidine miosis, a reduced response to a second application of miotic. Similar findings were observed in glaucoma patients following withdrawal of chronic pilocarpine therapy. It is suggested that the slowly reversible after‐effects of acute and chronic administration of cholinomimetic miotics can be explained by desensitization of iris sphincter cholinoceptors. 1980 British Pharmacological Society