Objective: To identify and substantiate the occurrence, extent and location of retinal degeneration in de novo Parkinson’s disease patients (PD) compared to primary open angle glaucoma patients (POAG) and healthy controls (HC).

Background: PD patients experience visual symptoms and retinal degeneration. Studies using spectral-domain optical coherence tomography (SD-OCT) have shown retinal thinning in PD, resembling the glaucoma pattern. This study investigated the retinal thinning in de novo Ldopa-naive PD patients, to analyse if the profile of retinal thinning could serve as a biomarker for PD.

Method: SD-OCT data were collected in de novo Ldopa-naive PD patients at the University Medical Center Groningen. A 5×5 mm OD macular scan was made. These scans were compared to age-matched POAG patients and HC’s. Good quality scans (≥4); segmented by Iowa Reference Algorithms [1], were divided by ETDRS 9-sector grid, and were meta-analyzed by cell-layers (Cohen’s d; 95% CI).

Results: In total 70 PD, 80 POAG patients and 61 HC were included. In PD versus HC, significant thinning was found in the inner plexiform layer (d=-0.50; 95% CI: -0.67, -0.32), outer nuclear layer (-0.18; -0.34, -0.02) and the retinal pigment epithelium (-0.12; -0.15, -0.08). Significant thickening was found in the inner nuclear layer (0.24; 0.15, 0.34), and the outer segment (0.31; 0.26, 0.35). In PD compared to glaucoma, the outer segment was thinner in PD (-0.46; -0.21, 0.10), the retinal nerve fiber layer and outer nuclear layer were not significantly different, and the ganglion cell layer (0.96; 1.96, 0.07), the inner plexiform layer (1.03; 1.60, 0.09), inner nuclear layer (0.05; 0.34, 0.10), outer plexiform layer (0.36; 0.73, 0.10), inner/outer segment junction (0.23; 0.71, 0.09), outer segment (-0.46; -0.21, 0.10) and retinal pigment epithelium (0.15; 0.23, 0.11) were significantly thinner in glaucoma.

Conclusion: De novo Ldopa-naive PD patients already show significant thinning of the inner retinal layers compared to HC. Thinning of the inner plexiform layer indicates pathology of the amacrine cells, which includes dopaminergic neurons. POAG compared to PD however showed a more severe retinal degeneration, whereas the inner plexiform layer was more severely affected in PD. Therefore, severity of amacrine cell loss possibly may serve as a potential biomarker for diagnosing PD.

References: [1] M.D. Abramoff, M.K. Garvin, M. Sonka, Retinal Imaging and Image Analysis, IEEE Rev. Biomed. Eng. 3 (2010) 169–208. doi:10.1109/RBME.2010.2084567.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/retinal-layer-thinning-in-de-novo-parkinsons-disease/