Pupillary Effects of Levodopa Therapy

In a patient with Parkinson's disease and subclinical postganglionic Horner's syndrome anisocoria developed during chronic oral L-dopa therapy. This provided an opportunity to investigate the mechanism of action of L-dopa and dopamine on the sympathetic innervation of the eye. Five patients, one of whom had a postganglionic Horner's syndrome without Parkinson's disease, served as controls. Topical dopamine and chronic systemic L-dopa produced pupil dilatation only in eyes with intact sympathetic innervation. Single large doses of Ldopa had no effect on the pupil size. L-dopa and topical dopamine appear to produce pupillary dilatation indirectly, through a peripheral increase in activity of intact sympathetic pathways, and not through direct alpha-receptor stimulation.