Purpose: To study a potential role for muscarinic receptors in the inhibition of deprivation-induced excessive axial elongation and myopia in a monkey model.
Methods: The right eyes of 20 newborn rhesus monkeys were occluded with a black contact lens. In seven monkeys each, either atropine or pirenzepine was topically applied daily to the occluded eyes. The nonoccluded fellow eyes and both the occluded and nonoccluded fellow eyes of another six monkeys were treated with vehicle solution.
Results: After 33 to 39 weeks, in 5 monkeys of the vehicle group, occluded eyes were longer and the myopic shift significantly greater than in the nonoccluded fellow eyes. In six atropine-treated monkeys, axial length and reduction of the initial hyperopia of occluded and nonoccluded fellow eyes were not different statistically. The myopic shift of the occluded eyes was significantly smaller than in the vehicle-treated occluded eyes. In the pirenzepine-treated group, axial length of the occluded eyes was similar to the nonoccluded eyes of controls and the occluded eyes of atropine-treated monkeys. There was a trend of pirenzepine to reduce the myopic shift of the occluded eye. No effect of atropine or pirenzepine was noted on muscarinic receptor density in retina, brain, or heart, but a small increase was observed in iris + ciliary body.
Conclusions: The drug treatment results implicate muscarinic receptors in postnatal eye growth regulation. Because of interanimal differences our data do not indicate whether nonselective or selective muscarinic blockade is more effective in reducing deprivation-induced myopia.