Retinal electrophysiological responses to dopaminergic therapy in treatment naïve Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder in which the retina acts as a dopaminergic extension of the central nervous system. This study aimed to evaluate the effects of dopaminergic therapy on retinal electrophysiological responses in newly diagnosed, treatment-naïve PD patients and to compare these findings with those of healthy controls.

Forty eyes from 20 PD patients underwent full-field electroretinography (ffERG). Photopic a-wave, b-wave, and photopic negative response (PhNR) wave amplitudes and implicit times were recorded before and after one month of dopaminergic therapy. For comparison, one randomly selected eye from each of 20 age- and sex-matched healthy control subjects also underwent the same ffERG protocol.

Following dopaminergic treatment, a-wave (- 6.6 ± 1.4 µV, p < 0.001), b-wave (20.0 ± 4.8 µV, p = 0.001), and PhNR wave amplitudes (- 7.9 ± 1.8 µV, p < 0.001) significantly increased. Pre-treatment, a-wave (- 8.9 ± 3.5 µV, p = 0.014), b-wave (38.3 ± 9.8 µV, p < 0.001), and PhNR-wave (- 17.6 ± 2.8 µV, p < 0.001) amplitudes were significantly lower in the PD group compared with controls. Post-treatment, a- and b-wave amplitudes became comparable to those of the control group (p > 0.05), while PhNR-wave amplitude remained significantly reduced (- 9.7 ± 4.1 µV, p = 0.023).

Dopaminergic therapy significantly improved retinal electrophysiological responses in treatment-naïve PD patients. After treatment, the a- and b-wave amplitudes approached control levels, whereas the PhNR amplitude remained significantly reduced. These findings suggest that retinal dopaminergic dysfunction in PD may be partially reversible, and ffERG parameters can serve as sensitive biomarkers for monitoring treatment response.