Early lens changes in Macaca fascicularis monkeys under topical treatment with echothiophate or carbachol studied by slit-image photography.

Cynomolgus monkeys were given topical treatment with echothiophate or carbachol, and the lens changes were followed by slit-image photography. Both drugs caused an early retrodisplacement of the anterior zone of disjunction due to swelling of the most superficial lens cortex. Deeper layers of the cortex did not swell. The exact cause of the swelling is not known, but there must be a true cholinergic link. Accommodation as such is not the cause, since (1) the effect was seen also in a monkey eye which had its ciliary muscle disinserted from the scleral spur and therefore had little accommodation left and (2) acute accommodation produced by systemic pilocarpine did not cause the effect. Anterior subcapsular opacities were quantified and appeared very early in the echothiophate-treated eyes but were not seen with the doses of carbachol used.