The Mx Muscarinic Antagonist Pirenzepine Reduces Myopia and Eye Enlargement in the Tree Shrew

Results. In sham-injected and saline-injected MD tree shrews, 12 days of MD produced —13.2 D ± 0.8 D and —14.1 D ± 0.5 D of axial myopia, respectively. In pirenzepine-injected MD tree shrews, 12 days of MD induced an axial myopia of only —2.1 D ± 1.4 D. The significant reduction in myopia in pirenzepine-injected MD tree shrews was caused by significantly less vitreous chamber elongation of the deprived eye (0.05 mm ± 0.04 mm) relative to the contralateral control eye when compared to sham-injected and saline-injected MD tree shrews (0.24 mm ± 0.02 mm and 0.29 mm ± 0.01 mm). Mean equatorial enlargement and increased eye weight were prevented in pirenzepine-injected MD tree shrews (P < 0.01). Pirenzepine also was found to reduce myopia and ocular enlargement in lens defocus-induced myopia. Control experiments demonstrated that pirenzepine did not cause a significant reduction in amplitude of carbachol-induced accommodation.