Anticholinesterase-induced cholinergic subsensitivity in primate accommodative mechanism.

I treated cynomolgus monkeys with topical echothiophate iodide twice daily for several months. Accommodative responses to topical or intramuscular pilocarpine were determined after ciliary ganglion or cholinergic nerve blockade. During echothiophate treatment, there was little or no accommodative response to intramuscular pilocarpine doses which were near maximal in nonechothiophate-treated eyes. Similarly, echothiophate-treated eyes demonstrated little or no response to topical pilocarpine doses that were more than 50 times supramaximal in nontreated eye. Within two weeks after stopping echothiophate, accommodative responses to intramuscular pilocarpine had returned noticeably, and by seven weeks after stopping echothiophate, sensitivity to intramuscular pilocarpine had increased to 30 to 50% of control levels. The findings are compatible with acetylcholine-induced cholinergic subsensitivity of the ciliary muscle.