PurposeTo define the alterations in retinal vessel diameter in Parkinson's disease (PD) by optical coherence tomography (OCT).MethodsThis is a case-control study including 41 eyes of 41 patients with diagnosis of PD and 35 eyes of 35 age- and sex-matched control subjects. All subjects underwent complete neurological and ophthalmological examinations before measurements. Retinal vessel diameters and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were evaluated with spectral domain OCT (SD-OCT) with a circular scan centered at the optic disc. The diameters of the superior nasal and temporal arteries and veins, and inferior nasal and temporal arteries and veins were measured and then compared between the groups. Correlations with the duration of the disease, usage of levodopa, and pRNFL thicknesses between retinal vessel diameters were examined with Pearson and Spearman correlation analysis.ResultsAverage pRNFL thickness is significantly decreased in PD compared to age- and sex-matched controls (p<0.05). At all measurement points, retinal artery diameter measurements were decreased in the PD group compared to controls, but the differences did not reach statistical significance. Diameters of the retinal veins also did not show any significant difference in the PD and control groups. Superior temporal artery diameter was significantly decreased in patients using levodopa compared to nonusers (p=0.022). There were no statistically significant correlations between pRNFL thicknesses or disease duration with retinal vessel diameters in PD group.ConclusionsParkinson's disease does not seem to have an impact on the retinal vessel diameters obtained by SD-OCT.