Cholinergic vasoconstriction in the eye.

Data is presented to support a physiologic vasoconstrictor function of the parasympathetic nervous system in the anterior uvea of the eye. Studies in rabbits, cats and monkeys demonstrate that stimulation of the parasympathetic nerve fibers running with the oculomotor nerve to the eye induces a reduction in blood flow of the iris and in rabbits in the ciliary processes in addition. Pharmacologic blocking experiments indicate that most of this phenomenon is based on a cholinergic component. Since at least in rabbits mechanical factors such as stretching of the iridial tissue, a steeling phenomenon to nearby tissues of blood as well as secondary effects caused by changes in the intraocular pressure can be excluded, the reduction in blood flow in all likelihood reflects a true vasoconstriction. Experiments in unanesthetized rabbits indicate that there is a continuous physiologic cholinergic vasoconstrictor tone in the iris and ciliary processes normally. Thus, the anterior uvea in mammals may be one of the tissues exhibiting a cholinergic vasoconstriction phenomenon, found more commonly in lower vertebrates.