VISUAL ALTERATIONS IN DE-NOVO PARKINSONS-DISEASE - PATTERN ELECTRORETINOGRAM LATENCIES ARE MORE DELAYED AND MORE REVERSIBLE BY LEVODOPA THAN ARE VISUAL-EVOKED POTENTIALS

There are increased latencies of pattern-reversal visual evoked potent ials (VEPs) and electroretinograms (PERGs) in Parkinson's disease (PD) patients who have not received therapy. This study aimed to evaluate whether these delays are present in the early stage of PD and whether they are dopamine-sensitive. The results show that both PERG P50 and V EP P100 latencies are increased (p < 0.0001) in a group of patients wi th de novo PD (13 subjects; 13.3 +/- 5.6 months' mean disease duration ) before therapy in comparison with an age-matched control group (eigh t subjects). A larger latency increase (9.9% at the 47% contrast level and 7.8% at the 96% contrast level) was present in PERG recordings th an in VEPs (6.2% at the 47% contrast level and 3.9% at the 96% contras t level). Levodopa therapy produced recovery of both PERG and VEP late ncy increases at both contrast levels, but only the PERG recovery at 4 7% of contrast was statistically significant. Before therapy, five eye s from PD patients showed no reproducible PERG at the 47% contrast lev el although the simultaneously recorded VEP was present. Both potentia ls were recordable in the same eyes at the 96% contrast level. During therapy, four of those five eyes showed a clear PERG even at the 47% c ontrast level. We conclude that, using an adequate midspatial frequenc y, both VEPs and PERGs are delayed even in the early stage of PD, and that PERGs are more sensitive if low contrast (47%) is used. The large r alterations, as well as the larger recovery during levodopa therapy, seem to correlate the PERG response more than the VEP response to dop aminergic transmission.