Simultaneous VEP and PERG investigations in early Parkinson's disease.

To evaluate whether visual evoked potential (VEP) and pattern electroretinogram (PERG) abnormalities may be detectable early in the course of Parkinson's disease (PD) and to assess a possible interdependence between retinal and cortical potentials, simultaneous VEP and PERG were carried out in nine patients with early PD. The mean (SD) duration of the disease was 10 (6) months. None of the patients had been previously treated with levodopa or other anti-parkinsonian drugs. The results show VEP and PERG abnormalities that are spatial stimulus dependent, with higher frequencies being more involved and also indicate that VEP changes are not entirely dependent on alterations at the retinal level.