PHARMACOLOGICAL EFFECTS OF DOPAMINERGICS AND AMANTADINE ON COLOR DISCRIMINATION IN PARKINSONS-DISEASE

In recent studies disorders of chromatic and achromatic vision in Park insonian patients have been demonstrated, which were partially reversi ble after application of L-dopa. Up to now the origin of visual disord ers in Parkinson's disease (PD) and the effect of further anti-Parkins onian drugs are unclear. In this study, the authors evaluated the effe ct of L-dopa, apomorphine and amantadine on color vision in PD by mean s of the Farnsworth-Munsell 100 hue test (FM). Nineteen patients under went the color vision test before and after the oral administration of the morning medication with L-dopa, 24 patients before and after subc utaneous application of apomorphine, and Ig further patients were test ed before and after an infusion therapy with amantadine (200 mg/d) ove r three days. Under those treatment conditions the motor symptoms of P arkinsonism improved significantly in all three groups as assessed by part III of the Unified Parkinson's Disease Rating Scale (UPDRS). Befo re 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<0.001). Afte r 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 aman tadine-infusions: 94.5 (SD 55.2); after therapy: 99.5 (SD 55.8)). The authors conclude that the distorted color vision in Parkinson's diseas e is due to a dopamine deficiency involving the visual system. As far as the visual system is concerned, amantadine appears not to act via d opaminergic mechanisms. The authors suppose that antiglutamatergic pro perties of amantadine are a possible explanation for this phenomenon, because glutamate is regarded as the main neurotransmitter of retinal photoreceptors.