Retinal Thickness May Mark Cognitive Decline
Thinner retinal nerve fiber layer tied to worse cognitive function
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TORONTO -- A thinning retina may be a sign of declining cognitive function, researchers reported here.
In an analysis of data from the U.K. Biobank, a thinner retinal nerve fiber layer at baseline was associated with worse performance on cognitive testing 3 years later, Fang Ko, MD, of Moorfields Eye Hospital in London, and colleagues reported at the Alzheimer's Association International Conference.
"It's amazing that we found this in such a healthy population," Ko said during a press briefing. "We wouldn't have expected in just 3 years to see any cognitive decline in this cohort, much less measurable cognitive decline with a significant association with retinal nerve fiber layer thickness."
Suzanne Craft, PhD, of Wake Forest School of Medicine in Winston-Salem, N.C., who was not involved in the study, noted that the condition of the eye is indicative of brain disease in other conditions, such as multiple sclerosis and diabetic retinopathy.
"The eye is an outpost of the brain, and the tissue in the eye is neurally derived," Craft said during the press briefing. "It may serve as an early indicator of biology going on in the brain."
The challenge, she noted, is to "find reliable and valid ways to measure ... the characteristics of the eye that we can use in yearly check-ups with your eye doctor so that we can identify Alzheimer's at its earliest stage or reliably identify people at risk for Alzheimer's."
Ko noted that the majority of ophthalmology practices have access to optical coherence tomography (OCT), which can be used to image the retinal nerve fiber layer.
To test whether the thickness of this layer was associated with dementia risk, she and colleagues looked at 32,028 people from the U.K. Biobank who also had cognitive testing, and over 3 years, a total of 1,251 patients had follow-up testing.
For cognitive assessment, they relied on four tests: the prospective memory test, the pairs matching test for episodic memory, numeric and verbal reasoning, and reaction time.
For the prospective memory test, for instance, mean thickness was 53.3 μm among those who recalled correctly on the first attempt, compared with 52.2 μm on the second attempt and 51.9 μm for those who did not recall, Ko said.
A thinner retinal nerve fiber layer was associated with poorer pairs matching, numeric and verbal reasoning, and reaction time as well, she reported.
A thinner retinal nerve fiber layer was associated with poorer pairs matching, numeric and verbal reasoning, and reaction time as well, she reported.
Ko and colleagues also found that for each additional cognitive test failed, the retinal nerve fiber layer was significantly thinner by 1 μm.
In further analyses controlling for age, sex, race, socioeconomic status, height, refraction, and intraocular pressure, performance on all tests still remained significantly associated with retinal nerve fiber layer thickness.
They also found that a thinner retinal nerve fiber layer at baseline was associated with worse future performance on the total number of cognitive tests.
Ko said they couldn't find any other variable to explain the effects, though she warned that the study was done in an older, healthier population of higher socioeconomic status; while it may not be the "most representative sample, it is a very clean sample," she said.
"This may be a biomarker [of cognitive decline] and the availability of OCT in ophthalmology offices makes this a very interesting tool for clinicians," Ko concluded.
In a second study, Melanie Campbell, PhD, of the University of Waterloo in Canada, and colleagues found that polarized light could detect amyloid deposits in the retina, which could ultimately be used as a non-invasive way to predict cognitive decline. They imaged amyloid using either polarized light, fluoroscopy, or OCT and found that all were able to detect protein accumulation.
Eliezer Masliah, MD, of the National Institute on Aging in Bethesda, Md., said that "whatever happens in the retina could be reflective of what's happening in the central nervous system," cautioning that, as with smell tests to predict dementia, "this is not unique to Alzheimer's."
"In other neurodegenerative conditions, there is thinning of the retina and accumulation of proteins," said Masliah, who was not involved in the study. "There is a lot more basic research that needs to be done to understand what is the clinical applicability of this tool."
Ko disclosed support from the Eranda Foundation, the International Glaucoma Society, and University College London (UCL). Co-authors disclosed support from the U.K. Department of Health and the UCL Institute of Ophthalmology.
Ko and co-authors disclosed no relevant relationships with industry.
The study by Campbell's group was funded by the Canadian Institutes of Health Research and Natural Sciences and Engineering Research Council of Canada.
Campbell disclosed a relevant relationship with InterVivo Solutions.
LAST UPDATED
Primary Source
Alzheimer's Association International Conference
Source Reference: Ko F, et al "Retinal nerve fiber layer associated with poor cognitive function among a large cohort, UK Biobank" AAIC 2016; Abstract O3-12-03.Secondary Source
Alzheimer's Association International Conference
Source Reference: Campbell MCW, et al "Amyloid as a biomarker of Alzheimer's Disease in post-mortem retinas in human and the dog model of the disease" AAIC 2016.
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