REFLEX CONTROL OF THE CILIARY MUSCLE

Abstract

In expts. on cats under nembutal anesthesia, faradic stimulation of a peripheral nerve or of the skin of the snout resulted in a dioptric change in the direction of hypermetropia both before and after sympathetic denervation of the eye. Depression of the cholinergic fibers through complete atropiniza-tion of the eye did not abolish this response. It was abolished by intracranial section of the oculomotor nerve and by depression of the adrenergic nerve fibers by the intravenous administration of ergotoxine phosphate. Stimulation of the oculomotor nerve intracranially elicited a dioptric change in the direction of myopia following depression of the adrenergic nerve fibers with ergotoxine phosphate. The same stimulation following depression of the cholinergic nerve fibers by atropinization of the eye resulted in a dioptric change in the direction of hypermetropia. These results support the assumption that reflex inhibition of the ciliary muscle is an actively integrated and controlled reaction mediated through the parasympathetic nerves of the eye which involves the conduction of impulses from the ciliary ganglion to the ciliary muscle by adrenergic components of the short ciliary nerves. Mild faradic stimulation of the skin of the finger tips or of the forearm, in human subjects, elicited a small dioptric change in the direction of hypermetropia in untreated eyes as well as during cycloplegia caused by the instillation of homa-tropine into the conjunctival sac. The ciliary muscle appears to be controlled reflexly exclusively through the para-sympathetic nerves.