BLOG: Primary eye care will screen for Alzheimer’s disease in the future
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Fifty million people worldwide and 6.7 million Americans are currently living with Alzheimer’s disease. Unfortunately, I know firsthand the suffering this disease can cause.
Both my grandmothers had late-onset AD, which increases my own genetic risk. Will I definitely develop AD? Nobody knows.
We do know that AD is a multivariate disease. While genetic factors influence risk, the relationship is not a simple one: Environmental and social factors like exercise, diet and social relationships influence risk, as do multiple comorbidities, including diabetes, hypertension and cardiovascular disease. That makes screening for AD risk a complicated proposition.
AD is currently diagnosed based on the results of cognitive testing and expensive imaging tools such as positron emission tomography, which can detect amyloid beta plaques in the brain. Diagnosis typically doesn’t happen until the patient has already developed significant memory loss and other symptoms, which experts now believe may be 20 years after the neurodegenerative changes first begin in the brain.
Simply put, we are detecting AD much too late in the course of the disease.
Investigating ocular biomarkers
In the past few years, there has been an explosion of research into methods for detecting ocular biomarkers for AD. Specific biomarkers that have been studied for a connection to AD include cone contrast functional changes, decreased retinal blood flow, structure of the retinal vasculature, thinning retinal nerve fibers, reduced ganglion cell density, retinal amyloid beta plaques and many more.
All these studies affirm the concept that the eye — and specifically the retina — is an extension of the brain that can be much more easily examined. However, no single biomarker has so far proven to have the sensitivity and specificity needed to reliably screen for AD.
My colleagues and I have been investigating whether a low-cost multimodal approach can be used to quantify retinal structural and functional changes that are sensitive to early cognitive decline. In a pilot study, we used a variety of ophthalmic techniques, full-field electroretinography (ERG) and visual performance exams to assess patients with early or mild cognitive impairment (MCI).
We found that the retinal response time to a stimulus on ERG was delayed in all patients with MCI compared with healthier patients. Additionally, measures of the vascular network were significantly altered in patients with MCI.
Advantages for primary care
A multimodal approach using a handheld ERG and retinal imaging, as in our study, has the advantage of being noninvasive, much less expensive than PET or genetic testing and more easily deployed in primary care settings, including primary eye care. Not only would such screenings add value for primary care practices, but they could help identify and treat AD earlier.
Community clinics, primary care doctors and optometrists are the first points of entry for patients within the health care system and therefore the best place to screen for diseases that take many years to develop, like AD.
Early in my research, I was focused only on structural imaging of the retina. The perspective of optometrists and neuro-optometrists has been critical in shifting my work in exciting new directions. I have learned, for example, that combining functional testing (eg, ERG, pupillometry and oculomotor function) with structural imaging holds the greatest promise for better understanding the eye-brain connectome, or the map of connections between the eye and the brain.
Unraveling the relationship between the connecting pathways of neurons in the brain and the eye will help us better understand AD and other neurodegenerative diseases — and potentially identify better treatments.
References:
- Cabrera DeBuc D, et al. Front Physiol. 2018;doi:10.3389/fphys.2018.01721.
- Cabrera DeBuc D, et al. Front Physiol. 2020;doi:10.3389/fphys.2020.570412.
For more information:
Delia Cabrera DeBuc, PhD, is a research associate professor in the department of ophthalmology at Bascom Palmer Eye Institute, part of the University of Miami Health System. She studies the link between cognitive function in Alzheimer’s disease and retinal blood flow or structure in her work. Her research has received funding from the Finker-Frenkel Family Foundation, the Alzheimer’s Association and the National Institute on Aging. She will be teaching a course, “Seeing the Brain through the Eye: What is Next for Neuro-optometry, Neuroimaging and Neurology,” at the 2023 NORA conference on Brain-Based Rehabilitation. For more information and to register, visit https://noravisionrehab.org/about-nora/annual-conferences/2023-annual-conference.
Disclaimer: The views and opinions expressed in this blog are those of the authors and do not necessarily reflect the official policy or position of the Neuro-Optometric Rehabilitation Association unless otherwise noted. This blog is for informational purposes only and is not a substitute for the professional medical advice of a physician. NORA does not recommend or endorse any specific tests, physicians, products or procedures. For more on our website and online content, click here.
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