Visual evoked potentials in Parkinson's disease-correlation with clinical involvement

A total of 18 patients with Parkinson's disease were evaluated clinically and by transient checker-board VEP study. There were significant differences between bradykinesia (P<0.01), rigidity (P<0.02), and tremor (P<0.05) subscores of the more and less severely affected sides. There were no asymmetry of VEP latency or amplitude between the more and less severely affected sides by stimulation of the corresponding eye. There were no significant correlations between the VEP latency or amplitude and any of the clinical features except the bradykinesia scores. The bradykinesia scores on the more severely involved side (r: 0.57; P=0.014) and less severely involved side (r: 0.82; P=0.00003) showed medium to high degree positive correlations with VEP amplitudes by stimulation of the corresponding eye. By studying monocular fullfield responses our data can only suggest that there is no prechiasmal asymmetry. The positive correlation between the VEP amplitude and bradykinesia score might indicate that D2 receptors dominate in the retina.