Spectral Domain and Angiography Optical Coherence Tomography in Parkinson's Disease: Structural And Vascular Changes in the Retina Correlate with Disease Severity and Progression

Background. Parkinson's disease (PD) is a common neurodegenerative disorder characterized by bradykinesia, resting tremor, and muscle rigidity. Visual disturbances have been also described among non-motor features. Objective. We aimed to investigate the structural and vascular changes in the retinal and choroidal vascular networks, and to assess any relationship with motor and non-motor symptoms (NMS) in PD patients. Methods. Ganglion cell complex (GCC), retinal nerve fiber layer (RNFL), and subfoveal choroidal thickness (SFCT) were examined using spectral domain-optical coherence tomography (SD-OCT). The vessel density (VD) of retinal and choriocapillary vascular networks in macular area and the foveal avascular zone (FAZ) area were evaluated by OCT angiography (OCTA). All patients underwent clinical evaluation using motor section of the Unified PD Rating Scale (UPDRS-III) and the Hoehn and Yahr (HY) scale. Results. A total of 48 eyes from 24 PD patients and 50 eyes from 25 controls were assessed. At SD-OCT, GCC and RNFL were more significantly thin in patients compared to controls. At OCTA exam, PD subjects showed lower values in VD of superficial capillary plexus (SCP) and radial peripapillary capillary plexus in comparison to controls, whereas FAZ area resulted in a significant increase in the patient group. We found a negative correlation between the age at onset and VD of SCP, and between HY score and RNFL thickness and FAZ. UPDRS-III score was negatively correlated with VD of deep capillary plexus. Discussion. The impairment of retinal structure and microvasculature seems to correlate with disease severity and progression in PD. Retinal anomalies can be considered as non-motor manifestations that could occur already in the early stage of the disease.