Retinal Microvascular Impairment in the Early Stages of Parkinson's Disease.

Purpose: To detect the retinal microvascular impairment using optical coherence tomography angiography (OCT-A) in patients with Parkinson's disease (PD) and find a correlation between the microvascular impairment and the neuronal damage.
Methods: This is a prospective, observational study including 49 eyes from 38 PD patients in their early stages and 34 eyes from 28 healthy controls with comparable age range. Macula microvasculature was evaluated with the spectral-domain optical coherence tomography (SD-OCT) angiography and intraretinal layer thickness evaluated with the SD-OCT. A custom algorithm was used for custom segmentation of retinal thickness and quantification of the superficial and deep microvascular density of the macula, respectively.
Results: PD patients showed reduced microvascular density in most of the areas of the whole retina. In the superficial retinal capillary plexus, statistical difference (P < 0.01) was seen in the total annular zone (TAZ), superior, temporal, inferior, and nasal zones. In PD patients, there was a strong correlation between the average ganglion cell layer and inner plexiform (GCIP) thickness and the TAZ of the superficial microvascular density (r = 0.062, P = 0.032).
Conclusion: We demonstrated that retinal microvascular density decreased in PD patients. The correlation between microvascular impairment in the superficial retinal capillary layer and GCIP thinning also revealed that the retinal microvascular abnormality may contribute to the neurodegeneration in PD patients. OCT-A with quantitative analysis offers a new path of study and will likely be useful in the future as an objective biomarker for detecting vessel impairment in early stages of PD.