Macular Retinal Layer Thickness in Mild-to-Moderate Parkinson's Disease

Background/Objectives: Characterization of individual retinal layer thicknesses in mild-to-moderate Parkinson's disease (PD) remains limited. This study compares retinal layer thicknesses between patients with mild-to-moderate PD and controls. Methods: In this cross-sectional study, patients with PD of Hoehn and Yahr (HY) stage 1 to stage 3 and age- and sex-matched cognitively normal controls without PD underwent spectral-domain optical coherence tomography (OCT) imaging. Seven retinal layers were segmented: nerve fiber layer, ganglion cell-inner plexiform layer (GC-IPL), inner nuclear layer (INL), outer plexiform layer, outer nuclear layer (ONL), photoreceptor layer (PRL), and retinal pigment epithelium (RPE). Mean thickness for each layer and the total retina were measured within the 3 mm and 6 mm Early Treatment Diabetic Retinopathy Study rings. Results: Sixty-seven eyes from 41 patients with PD and 72 eyes from 41 controls were included. In the 6 mm ring, PD eyes had a nominally thicker GC-IPL (p = 0.01), INL (p = 0.01), RPE (p = 0.03), and total retina (p = 0.03) compared to control eyes. In the 6 mm ring, PRL was nominally thinner in HY stage 3 compared to HY stages 2-2.5 (p = 0.02). In the 6 mm ring, the ONL was nominally thinner in the eyes of PD patients in HY stage 3 compared to the eyes of PD patients in HY stages 1-1.5 (p = 0.02) and 2-2.5 (p = 0.04). However, none of these differences remained significant after False Discovery Rate adjustment (all adjusted p > 0.05). Conclusions: In this exploratory cross-sectional study, no significant differences in macular retinal layer thicknesses were found between patients with mild-to-moderate PD and controls without PD after adjusting for multiple comparisons. The nominal thickness differences observed here require larger, longitudinal cohorts to determine if true structural differences exist in mild-to-moderate PD.