Decreased Retinal Vessel, Perfusion Densities Found in Those With Parkinson Disease

Results from a cross-sectional study show individuals with Parkinson disease (PD) exhibited decreased retinal vessel density (VD) and perfusion density (PFD), and choroidal structural changes when compared with cognitively healthy age- and sex-matched controls. Findings were published in JAMA Ophthalmology.

Between 1990 and 2016, the prevalence of PD more than doubled from 2.5 million to 6.1 million cases. The disease is a progressive neurodegenerative condition that involves both prominent motor dysfunction and nonmotor symptoms, including hallucinations and impaired circadian rhythms.

Although the underlying cause of PD is not well understood and no universally accepted biomarkers exist for an in vivo diagnosis of PD, evidence points to cerebral small vessel disease as a potential risk factor for PD. Patients with PD also have a higher prevalence of cerebral ischemic lesions.

“The diagnosis of PD is complicated by its similarity to other parkinsonian conditions, including multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration,” the researchers explained, while “noninvasive tests to improve confidence in the diagnosis of PD remain a major unmet need.”

However, additional research has suggested structural and functional changes in the retina may act as a surrogate biomarker for cerebral vascular changes and global neurodegeneration in patients with PD.

To characterize alterations in the structure and microvasculature of the retina and choroid in the eyes of individuals with PD, the researchers utilized optical coherence tomography and optical coherence tomography angiography. They then compared findings with controls’ eyes.

Participants in the study group (n = 69) were aged 50 or older, had a diagnosis of PD, and were recruited from the Duke Neurological Disorders Clinic in Durham, North Carolina. Healthy volunteers aged 50 or older without subjective cognitive dysfunction, history of tremor, or evidence of motor dysfunction made up the control group (n = 137).

Any participants with a history of diabetes, glaucoma, retinal pathology, or corrected Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity worse than 20/40 Snellen were excluded. At the time of image acquisition, participants also underwent a cognitive evaluation using the Mini-Mental State Examination, where a higher score (0-30) indicates better performance.

VD and PFD were measured in an ETDRS grid overlay. “Vessel density was defined as the total length of perfused vasculature per unit area in the region of measurement,” the authors wrote. “Perfusion density was defined as a percentage of area of perfused vasculature per unit area in a region of measurement.”

A total of 124 eyes from patients with PD and 248 eyes of controls were evaluated. The researchers found:

• In the 6 × 6-mm ETDRS circle, VD (β coefficient = 0.37; 95% CI, 0.04-0.71; P = .03) and PFD (β coefficient = 0.009; 95% CI, 0.0003-0.018; P = .04) were lower in the eyes of participants with PD
• In the inner ring of the 6 × 6-mm ETDRS circle, VD (β coefficient = 0.61; 95% CI, 0.20-1.02; P = .003) and PFD (β coefficient = 0.015; 95% CI, 0.005-0.026; P = .004) were lower in the eyes of participants with PD
• Total choroidal area (β coefficient = –1.74 pixels2; 95% CI, −3.12 to −0.37 pixels2; P = .01) and luminal area (β coefficient = –1.02 pixels2; 95% CI, −1.86 to −0.18 pixels2; P = .02) were greater in the eyes of those with PD
• Choroidal vascularity index was lower (β coefficient = 0.5%; 95% CI, 0.2%-0.8%; P < .001) in the eyes of individuals with PD

However, area under the receiver operating characteristic analyses found “individual retinal parameters may not have sufficient discriminative capacity to function as independent biomarkers of disease with prespecified cutoff values that define disease presence or absence.”

But when combined with clinical history and other existing tests, the researchers argued the choroidal and retinal microvascular imaging findings could have potential to improve clinicians’ confidence in diagnosing PD.

“Future long-term studies that characterize the natural history of microvascular and structural retinal changes in individuals across the clinical spectrum of PD is warranted,” they concluded. “Such studies may clarify whether these imaging findings may be useful as biomarkers for the onset of PD or the rapid deterioration from PD.”

Reference:

Robbins CB, Thompson AC, Bhullar PK, et al. Characterization of retinal microvascular and choroidal structural changes in Parkinson disease. JAMA Ophthalmol. Published online December 23, 2020. doi:10.1001/jamaophthalmol.2020.5730