First Alzheimer, now Parkinson: A team of researchers has identified several potential retinal and choroidal biomarkers for the diagnosis of Parkinson disease (PD).1 The team previously used optical coherence tomography (OCT) and OCT angiography (OCTA) to describe retinal changes observed in patients with Alzheimer disease.2
In Parkinson, none of the biomarkers in isolation proved useful enough to boost confidence in making the diagnosis; however, the study underscores the importance of the eye-brain connection in neurodegenerative diseases, said Dilraj S. Grewal, MD, at Duke University School of Medicine in Durham, North Carolina. “As the eye serves as the ‘window to the brain,’ noninvasive retinal imaging techniques can visualize the microvasculature in fine detail, which may help detect early neurodegenerative changes,” he said.
Imaging parameters. For this cross-sectional study, the researchers included 69 individuals with PD (124 eyes) and 137 age- and sex-matched healthy controls (248 eyes). All participants were age 50 or older; individuals were excluded if they had another dementia, glaucoma, diabetes, retinal pathology, or corrected visual acuity worse than 20/40.
All eyes underwent OCTA imaging to characterize superficial capillary plexus vessel density (VD), perfusion density (PFD), and foveal avascular zone (FAZ) area. Other OCT biomarkers included retinal nerve fiber layer (RNFL) thickness, macular ganglion cell-inner plexiform layer (GCIPL) thickness, and central subfield thickness (CST) as well as subfoveal choroidal thickness (SFCT), total choroidal area, and luminal area. A choroidal vascularity index (CVI) was calculated by dividing the luminal area by the total choroidal area.
Group differences and similarities. Retinal microvasculature alterations were seen in individuals with PD; these patients had decreased VD and PFD compared to controls. The PD cohort also had structural alterations in the choroid not observed in controls, with a decreased CVI. But both groups were similar in terms of CST, GCIPL thickness, and RNFL thickness. And neither SFCT nor the FAZ area differed between groups.
Of modest clinical value? The statistical analysis suggests that differences observed between the PD and control groups were only moderately useful as independent disease biomarkers with prescribed cutoff values that define disease presence or absence. Coauthor Sharon Fekrat, MD, said a solution more sophisticated than a simple cutoff value is needed, such as a diagnostic index incorporating multiple retinal and choroidal imaging parameters or deep learning analysis of images.
Going forward. “The greatest challenge to the broad implementation of this approach is the specificity of these findings,” Dr. Grewal said. After all, he noted, retinal microvascular changes are also seen in diseases such as diabetes, glaucoma, and hypertension, all of which tend to be more common in older adults. “We need to determine how the pattern of retinal changes in PD differs from these comorbidities,” he added. “Now that we know that retinal microvascular density and choroidal area/vascularity index are important parameters in Parkinson, there are multiple areas for future research.”
1 Robbins CB et al. JAMA Ophthalmol. Published online Dec. 23, 2020.
2 Yoon SP et al. Ophthalmol Retina. 2019;3(6):489-499.
Relevant financial disclosures—Drs. Fekrat and Grewal: None.
For full disclosures and the disclosure key, see below.
Full Financial Disclosures
Dr. Antoszyk Genentech: C,S; Jaeb Center for Health Research: C; Novartis: C; Opthea: C; Regeneron: C; Roche: C,S.
Dr. Fekrat None.
Dr. Grewal None.
Dr. Nath None.
Dr. Yiu Alimera: C; Allergan: C; Carl Zeiss: C; Clearside Biomedical: C,S; Genentech: C,S; Iridex: C,S; Intergalactic Therapeutics: C; Topcon: C; Verily: C.
||Consultant fee, paid advisory boards, or fees for attending a meeting.
||Employed by a commercial company.
||Lecture fees or honoraria, travel fees or reimbursements when speaking at the invitation of a commercial company.
||Equity ownership/stock options in publicly or privately traded firms, excluding mutual funds.
||Patents and/or royalties for intellectual property.
||Grant support or other financial support to the investigator from all sources, including research support from government agencies (e.g., NIH), foundations, device manufacturers, and/or pharmaceutical companies.
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