Evaluation of the retina and optic disc in Parkinson's disease using optical coherence tomography angiography

Objective: The vascular network of the eye can serve as a mirror reflecting cerebral circulation. Therefore, investigating validated retinal biomarkers for early diagnosis may be a promising approach to better understand the pathogenesis of Parkinson's disease. The aim of our study is to investigate the alterations in retinal microcirculation within the inner retinal layers of the macular and peripapillary regions in patients diagnosed with Parkinson's disease. Methods: The study included a total of 62 healthy individuals (30 women and 32 men) who visited the Ophthalmology Department outpatient clinic at Yozgat Bozok University Research and Application Hospital, as well as 62 patients diagnosed with Parkinson's disease (32 women and 30 men) who were referred to the Ophthalmology Department by the Neurology outpatient clinic. The staging of Parkinson's disease was assessed using the Hoehn-Yahr Staging Scale (H&Y), and cognitive status was evaluated using the Mini-Mental State Examination (MMSE). All patients underwent a comprehensive ophthalmological examination. Optical Coherence Tomography Angiography (OCTA) imaging was performed to measure the superficial and deep retinal capillary plexus and the peripapillary capillary plexus. Results: When analyzing the differences in quadrants of superficial vessel densities between the groups, a statistically significant decrease was observed in patients with Parkinson's disease across the whole image, the entire parafoveal region, and in the superior and nasal quadrants of the perifoveal region (p<0.005). However, no statistically significant difference was found in the temporal and inferior quadrants of the perifoveal region (p>0.005). A statistically significant increase was noted in FAZ (foveal avascular zone) and perimetry measurements (p<0.005). In terms of deep vessel densities, a statistically significant reduction was observed across the whole image, the entire parafoveal region and its quadrants, as well as the entire perifoveal region and its quadrants (p<0.005). In the peripapillary capillary plexus, a statistically significant reduction was observed in individuals with Parkinson's disease compared to the healthy control group across whole disc, inside disc, the peripapillary region, and the quadrants of the peripapillary region: superior hemisphere, inferior hemisphere, temporal inferior, temporal superior, and superior temporal regions. However, no statistically significant difference was observed in the nasal superior, nasal inferior, inferior nasal, inferior temporal, and superior nasal quadrants of the peripapillary region (p>0.005). Conclusion: OCTA is a non-invasive imaging method that demonstrates the potential of biomarkers for the early diagnosis and monitoring of Parkinson's disease, particularly through findings related to reduced vascular density in the macular and peripapillary regions, as well as FAZ enlargement. Keywords: Parkinson's disease, retina, optic disc, microcirculation, optical coherence tomography angiography