Retinal Thickness Predicts the Risk of Cognitive Decline in Parkinson Disease

Objective This study was undertaken to analyze longitudinal changes of retinal thickness and their predictive value as biomarkers of disease progression in idiopathic Parkinson's disease (iPD). Methods Patients with Lewy body diseases were enrolled and prospectively evaluated at 3 years, including patients with iPD (n = 42), dementia with Lewy bodies (n = 4), E46K-SNCA mutation carriers (n = 4), and controls (n = 17). All participants underwent Spectralis retinal optical coherence tomography and Montreal Cognitive Assessment, and Unified Parkinson's Disease Rating Scale score was obtained in patients. Macular ganglion cell-inner plexiform layer complex (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thickness reduction rates were estimated with linear mixed models. Risk ratios were calculated to evaluate the association between baseline GCIPL and pRNFL thicknesses and the risk of subsequent cognitive and motor worsening, using clinically meaningful cutoffs. Results GCIPL thickness in the parafoveal region (1- to 3-mm ring) presented the largest reduction rate. The annualized atrophy rate was 0.63 mu m in iPD patients and 0.23 mu m in controls (p < 0.0001). iPD patients with lower parafoveal GCIPL and pRNFL thickness at baseline presented an increased risk of cognitive decline at 3 years (relative risk [RR] = 3.49, 95% confidence interval [CI] = 1.10-11.1, p = 0.03 and RR = 3.28, 95% CI = 1.03-10.45, p = 0.045, respectively). We did not identify significant associations between retinal thickness and motor deterioration. Interpretation Our results provide evidence of the potential use of optical coherence tomography-measured parafoveal GCIPL thickness to monitor neurodegeneration and to predict the risk of cognitive worsening over time in iPD This study was cofunded by the Michael J. Fox Foundation (RRIA [Rapid Response Innovation Awards] 2014 Program, grant ID: 10189), the Carlos III Health Institute, and the European Union (ERDF/ESF, "A Way to Make Europe"/"Investing in Your Future") through the projects PI14/00679 and PI16/00005; the Juan Rodes grant JR15/00008 (I.G.); and the Department of Health of the Basque Government through the projects 2016111009 and 2020333033. We thank all the patients and participants involved in the study.