Visual alterations in de novo Parkinson's 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 potentials (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 VEP P100 latencies are increased (p < 0.0001) in a group of patients with de novo PD (13 subjects; 13.3 +/- 5.6 months' mean disease duration) before therapy in comparison with an age-matched control group (eight 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 than in VEPs (6.2% at the 47% contrast level and 3.9% at the 96% contrast level). Levodopa therapy produced recovery of both PERG and VEP latency increases at both contrast levels, but only the PERG recovery at 47% of contrast was statistically significant. Before therapy, five eyes from PD patients showed no reproducible PERG at the 47% contrast level although the simultaneously recorded VEP was present. Both potentials 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% contrast level. We conclude that, using an adequate midspatial frequency, 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 larger alterations, as well as the larger recovery during levodopa therapy, seem to correlate the PERG response more than the VEP response to dopaminergic transmission.