Aug. 4, 2016
Thinner retinal nerve fiber layer tied to worse cognitive function
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.
Overall,
they found that the retinal nerve fiber layer was thinner among those with
abnormal cognition on any one test.
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.
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.
http://www.medpagetoday.com/MeetingCoverage/AAIC/59340?xid=nl_mpt_Weekly_Education_2016-08-03&eun=g8295642d1r
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