Atropine reduces experimental myopia and eye enlargement via a nonaccommodative mechanism.

To determine whether the muscarinic antagonist atropine effectively reduces or prevents experimentally induced myopia via a nonaccommodative mechanism.Chicks were monocularly deprived (MD) of pattern vision by placement of a translucent occluder over the left eye. In two of the three MD groups, chicks received a series of intravitreal injections of atropine (n = 8) or saline vehicle (n = 8) with MD. Control groups (n = 8) of chicks were employed to assess the effects of MD, intravitreal injections, and drug effects.In sham-injected or saline-injected MD chicks, 8 days of MD produced -18.5 D and -20.9 D of experimental myopia, respectively. In atropine-injected MD chicks, 8 days of MD produced only -2.8 D of experimental myopia. This significant reduction in experimentally induced myopia in atropine-injected MD chicks was associated with a marked reduction in the relative axial elongation of the deprived eye (0.21 mm) when compared to saline-injected or sham-injected MD chicks (1.04 mm and 1.00 mm). This reduction in axial length in atropine-injected MD chicks was predominantly the result of a reduction in vitreous chamber elongation, although a reduction in anterior segment depth also was observed. Mean equatorial diameter was significantly reduced in atropine-injected MD chicks compared to saline-injected and sham-injected MD chicks, although to a lesser extent. Control experiments demonstrated that intravitreally injected atropine did not reduce carbachol-induced accommodation or light-induced pupil constriction in the skeletal intraocular muscles of the chick eye.These findings demonstrate that chronic administration of the muscarinic antagonist atropine prevents experimentally induced myopia in chick via a nonaccommodative mechanism.