Loss of visual acuity under dopamine substitution therapy

Abstract

Visual dysfunction is a well-known feature of Parkinson’s disease. Dopamine has been shown to be a functional modulator at many levels of the visual system. We report on a parkinsonian patient, suffering concurrently from various ophthalmological conditions including glaucoma and cataracts and displaying objectively measurable loss of visual acuity and blurring of vision while under medication with an MAO-B inhibitor and multiple ergolene-derived dopamine agonists. Various studies have investigated the effects of different D1- and D2-agonists and -antagonists on visual function and found that the presynaptic dopaminergic autoreceptor involved in the modulation of dopamine release in the retina displays characteristics of D2-receptors. We conclude that the observed phenomenon represents either an inhibition of dopamine release due to excessive stimulation of presynaptic D2-autoreceptors, leading to an insufficient stimulation of postsynaptic dopaminergic receptors and thus impeding retinal signal conduction, or a heretofore unclear interaction between the patient’s ophthalmological pathologies and dopaminergic therapy, possibly due to excessive stimulation of postsynaptic dopamine receptors, leading to faulty retinal information processing.