Accommodation in Monkeys Induced by Midbrain Stimulation

Abstract

This paper describes the graded changes in accommodation induced by electrical stimulation of the midbrain in the monkey. Objective measurements of the accommodative response were made with a Hartinger Coincidence Refractionometer. Maximum accommodative responses of about 28 diopters were obtained. Accommodation was found to increase as a function of voltage or frequency of stimulation in a linear manner at submaximal stimulus levels. The slope of this linear increase was used as an index to study the effects of drugs on accommodation. The maximal response plateau was similarly employed. Homatropine decreased the graded responses to stimulation, while echothiophate enhanced these changes. Phenylephrine, even in low dosage, depressed the accommodative response. These results were discussed with reference to their action on the peripheral accommodative mechanism.