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Abstract
In recent studies disorders of chromatic and achromatic vision in Parkinsonian patients have been demonstrated, which were partially reversible after application of L-dopa. Up to now the origin of visual disorders in Parkinson's disease (PD) and the effect of further anti-Parkinsonian drugs are unclear. In this study, the authors evaluated the effect of L-dopa, apo-morphine and amantadine on color vision in PD by means of the Farns-worth-Munsell ioo hue test (FM). Nineteen patients underwent the color vision test before and after the oral administration of the morning medication with L-dopa, 24 patients before and after subcutaneous application of apomorphine, and 19 further patients were tested before and after an infusion therapy with amantadine (200 mg/d) over three days. Under those treatment conditions the motor symptoms of Parkinsonism improved significantly in all three groups as assessed by part HI of the Unified Parkinson's Disease Rating Scale (UPDRS). Before the morning medication with L-dopa the mean total error score (MTES) of the FM was 106.3 (SD 62.5). After the ingestion of the individual L-dopa medication the MTES improved to 71.9 (SD 51.0) (p<o.oo1). After subcutaneous application of apomorphine, MTES improved from 100.38 (SD 41.3) to 93.4 (SD 58.4)(not significant). In contrast, the MTES was unchanged after an infusion therapy with amantadine (MTES before amantadine-infusions: 94.5 (SD 55.2); after therapy: 99.5 (SD 55.8)). The authors conclude that the distorted color vision in Parkinson's disease is due to a dopamine deficiency involving the visual system. As far as the visual system is concerned, amantadine appears not to act via dopaminergic mechanisms. The authors suppose that antiglutamatergic properties of amantadine are a possible explanation for this phenomenon, because glutamate is regarded as the main neurotransmitter of retinal photoreceptors.