Structural and Functional Retinal and Optic Nerve Changes in Parkinson’s Disease: An OCT-Based Study

Background: Parkinson’s disease (PD) is characterized by progressive neurodegeneration involving not only motor circuits but also visual pathways, including retinal and optic nerve structures. Vision is one of the non-motor systems altered in PD, and patients often experience decreased visual acuity, contrast sensitivity, and color vision. Optical coherence tomography (OCT) is a non-invasive method for evaluating these structures and may disclose early changes. Aim: This study used OCT and visual function tests to analyze retinal and optic nerve changes in Parkinson's patients compared with controls. Methods: This comparative cross-sectional study included 16 Parkinson's patients (32 eyes) and 16 age- and sex-matched controls (32 eyes). OCT assessed the peripapillary retinal nerve fiber layer (pRNFL), macular RNFL (mRNFL), ganglion cell layer plus inner plexiform layer (GCL+), ganglion cell complex (GCL++), and optic disc characteristics. Functional tests included best-corrected visual acuity (BCVA), contrast sensitivity, and color vision. Results: Compared with controls, Parkinson’s patients showed significant thinning of the mRNFL (p = 0.012) and GCL++ (p = 0.029), along with optic disc alterations including a larger cup-to-disc ratio (p < 0.001). Inferior quadrant RNFL thinning was also observed in the PD group (p < 0.001). Patients demonstrated reduced BCVA (p < 0.001), lower contrast sensitivity (p < 0.01), and impaired color vision (p < 0.001). Conclusion: Parkinson’s disease is associated with inner-retinal thinning and visual dysfunction. OCT combined with visual testing may provide non-invasive markers of PD-related neurodegeneration. These findings highlight the potential of OCT as an adjunctive biomarker, although larger studies are needed for validation.