Eyes reveal early Alzheimer’s disease

Summary: Using OCT angiography to quantify capillary changes in the back of the eye can help in the detection, and monitor the progression, of Alzheimer’s disease.

Source: Northwestern University

Reduced blood capillaries in the back of the eye may be a new, noninvasive way to diagnose early cognitive impairment, the precursor to Alzheimer’s disease in which individuals become forgetful, reports a newly published Northwestern Medicine study.

Scientists detected these vascular changes in the human eye non-invasively, with an infrared camera and without the need for dyes or expensive MRI scanners. The back of the eye is optically accessible to a new type of technology (OCT angiography) that can quantify capillary changes in great detail and with unparalleled resolution, making the eye an ideal mirror for what is going on in the brain.

“Once our results are validated, this approach could potentially provide an additional type of biomarker to identify individuals at high risk of progressing to Alzheimer’s,” said Dr. Amani Fawzi, a professor of ophthalmology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician

“These individuals can then be followed more closely and could be prime candidates for new therapies aimed at slowing down the progression of the disease or preventing the onset of dementia associated with Alzheimer’s.”

Therapies for Alzheimer’s are more effective if they are started before extensive brain damage and cognitive decline have occurred, added Fawzi, the Cyrus Tang and Lee Jampol Professor of Ophthalmology.

The study was published on April 2 in PLOS ONE.

It’s known that patients with Alzheimer’s have decreased retinal blood flow and vessel density but it had not been known if these changes are also present in individuals with early Alzheimer’s or forgetful mild cognitive impairment who have a higher risk for progressing to dementia.

Multicenter trials could be implemented using this simple technology in Alzheimer’s clinics. Larger datasets will be important to validate the marker as well as find the best algorithm and combination of tests that will detect high-risk subjects, said Sandra Weintraub, a co-author, and professor of neurology and of psychiatry and behavioral sciences at Feinberg.

Weintraub and her team at the Northwestern Mesulam Center for Cognitive Neurology and Alzheimer’s Disease recruited 32 participants who had cognitive testing consistent with the forgetful type of cognitive impairment, and age-, gender- and race- matched them to subjects who tested as cognitively normal for their age. All individuals underwent eye imaging with OCT angiography. The data were analyzed to identify whether the vascular capillaries in the back of the eye were different between the two groups of individuals.

This shows the eyes of an older man

It’s known that patients with Alzheimer’s have decreased retinal blood flow and vessel density but it had not been known if these changes are also present in individuals with early Alzheimer’s or forgetful mild cognitive impairment who have a higher risk for progressing to dementia. The image is in the public domain.

Now the team hopes to correlate these findings with other more standard (but also more invasive) types of Alzheimer’s biomarkers as well as explore the longitudinal changes in the eye parameters in these subjects.

“Ideally the retinal findings would correlate well with other brain biomarkers,” Fawzi said. “Long-term studies are also important to see if the retinal capillaries will change more dramatically in those who progressively decline and develop Alzheimer’s dementia.”

Other Northwestern authors are first author Yi Stephanie Zhang, Nina Zhou, Brianna Marie Knoll, Sahej Samra and Mallory R. Ward.

Funding: This research was supported by the Illinois Society for the Prevention of Blindness and National Institutes of Health grants DP3DK108248 and NIA-AG13584.

About this neuroscience research article

Source:
Northwestern University
Media Contacts:
Marla Paul – Northwestern University
Image Source:
The image is in the public domain.

Original Research: Open access
“Parafoveal vessel loss and correlation between peripapillary vessel density and cognitive performance in amnestic mild cognitive impairment and early Alzheimer’s Disease on optical coherence tomography angiography”. Yi Stephanie Zhang, Nina Zhou, Brianna Marie Knoll, Sahej Samra, Mallory R. Ward, Sandra Weintraub, Amani A. Fawzi. Published 02 Apr 2019 PLOS ONE doi:10.1371/journal.pone.0214685

Abstract

Parafoveal vessel loss and correlation between peripapillary vessel density and cognitive performance in amnestic mild cognitive impairment and early Alzheimer’s Disease on optical coherence tomography angiography

Purpose
Patients with Alzheimer’s Disease (AD) exhibit decreased retinal blood flow and vessel density (VD). However, it is not known whether these changes are also present in individuals with early AD (eAD) or amnestic type mild cognitive impairment (aMCI), an enriched pre-AD population with a higher risk for progressing to dementia. We performed a prospective case-control clinical study to investigate whether optical coherence tomography angiography (OCTA) parameters in the macula and disc are altered in those with aMCI and eAD.

Methods
This is a single center study of 32 participants. Individuals with aMCI/eAD (n = 16) were 1:1 matched to cognitively normal controls (n = 16). We evaluated OCTA images of the parafoveal superficial capillary plexus (SCP) and two vascular layers in the peripapillary region, the radial peripapillary capillary (RPC) and superficial vascular complex (SVC). Outcome vascular and structural parameters included VD, vessel length density (VLD), adjusted flow index (AFI) and structural retinal nerve fiber layer (RNFL) thickness. We compared these parameters between the two groups and examined the correlation between OCTA parameters and cognitive performance on the Montreal Cognitive Assessment (MoCA).

Results
Cognitively impaired participants demonstrated statistically significant decrease in parafoveal SCP VD and AFI as compared to controls, but no statistically significant difference in peripapillary parameters. Furthermore, we found a significant positive correlation between MoCA scores for the entire study cohort and both the parafoveal SCP VD and peripapillary RPC VLD.

Conclusion
OCTA shows significant decline in parafoveal flow and VD in individuals with early cognitive impairment related to AD, suggesting that these parameters could have potential utility as early disease biomarkers. In contrast, the presence of larger vascular channels in the peripapillary region may have obscured subtle capillary changes in that region. Overall, the correlation between vascular OCTA parameters and cognitive performance supports further OCTA studies in this population.

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