Introduction: Parkinson's disease (PD)-associated inner retinal abnormalities, particularly the retinal ganglion cells (RGC) layer, on optical coherence tomography (OCT) have recently gained importance as a biomarker of non-motor involvement of the disease but functional RGC evaluation using photopic negative response (PhNR) has not yet been determined. This study aims to compare structural and functional findings of the retina and optic nerve in PD with healthy controls (CT) including PhNR and OCT.
Methods: Forty-one eyes of 21 PD patients and 38 eyes of 19 CT underwent ophthalmic examination including visual contrast sensitivity test (CS), OCT, light-adapted full-field electroretinography (ffERG), and PhNR. OCT was used to measure the peripapillary retinal nerve fiber layer, the segmented macular layers, and the choroid. For functional parameters, CS, ffERG (oscillatory potentials, photopic response, 30 Hz-flicker), and PhNR waves were used. Measurements were compared using generalized estimating equation and significance was set at P ≤ 0.05.
Results: The PD group presented a significantly lower mono- and binocular CS, oscillatory potentials amplitude, b-wave amplitude on ffERG (152.3[45.4] vs 187.1[32.7]μV; P = 0.002), and PhNR amplitude (135.0[35.0] vs 156.3[34.1]μV; P = 0.025). There was no statistically significant difference in OCT measurements between groups. No correlation was found between statistically significant measurements and clinical data.
Conclusions: Functional abnormalities on CS, ffERG, and PhNR can be detected in PD even when structural damages are not observed on OCT. PhNR represents a new potential biomarker in PD. Our findings indicate dysfunction of bipolar, amacrine, and retinal ganglion cells in PD, probably with a cellular dysfunction overcoming morphological damage.
Keywords: Electroretinography; Optical coherence tomography; Parkinson's disease; Retina; Retinal ganglion cells.
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