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 Duke University reseachers found that these small retinal blood
vessels were altered in patients with Alzheimer's disease, but in
not in those with mild cognitive impairment (MCI) or those with no
signs of mental decline.
"Among the folks who had Alzheimer's there was a significant
reduction in the density of the blood vessels in the superficial
layer of the retina compared to controls and those with mild
cognitive impairment," said Dr. Dilrag Grewal, an associate
professor of ophthalmology at the Duke Eye Center. "We also found a
reduction in the thickness of (of a specific layer of the retina) in
Alzheimer's patients compared to controls and those with mild
cognitive impairment."
The findings were reported in Ophthalmology Retina, a publication of
the American Academy of Ophthalmology.
"The retina is an extension of the brain," Grewal said. "And it's
thought that changes that occur in the brain are mirrored in the
retina. With any neurodegenerative disease you lose nerve tissue.
Along with a measurable loss of brain volume, there's a loss of the
vasculature that supplies the brain. And because the retina is part
of the central nervous system, the same changes occur there."
The new findings couldn't have happened without a new scanning
technology, called optical coherence tomography angiography (OCTA),
that allows users to see in fine detail the structure of the back
part of the eye. "With previous technology you were able to measure
only the larger blood vessels in the back of the eye," Grewal said.
"Now we can look at blood vessels that are at the level of
capillaries in the different layers of the retina. Therefore we are
able to detect much smaller levels of change."
Grewal and his colleagues used OCTA to peer into the eyes of 39
Alzheimer's patients, 37 people with MCI and 133 cognitively healthy
people, the controls. Not only were the researchers able to detect
differences between the Alzheimer's patients and the other two
groups, but they were also able to see differences among the
Alzheimer's patients that appeared to be linked with the severity of
the disease.
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"The differences were proportional to the severity of the cognitive
impairment," Grewal said. "So, the folks with more severe
Alzheimer's had more severe loss of retinal blood vessels."
In the past, some small studies have suggested that there would be
differences "in both neuronal and microvascular retinal measures
between those with and those without Alzheimer's disease," said
Alison Abraham, an associate professor of ophthalmology and director
of the Wilmer Eye Institute Biostatistics Center at the Johns
Hopkins School of Medicine. "The current study gives weight to these
past findings and informs our targets for future research given the
large number of possible retinal parameters one could study."
The new research is a "small step forward," said Dr. Richard
Isaacson, director of the Alzheimer's Prevention Clinic at NewYork-Presbyterian/Weill
Cornell Medicine.
"But future studies need to focus on earlier stages of the disease,"
Isaacson said in an email. "We already have more definitive ways to
diagnose dementia due to Alzheimer's, but we need to see if OTCA can
be a useful cost-effective screening test for pre-symptomatic
Alzheimer's."
If scientists could find people who have brain changes, but no
obvious symptoms yet, there could be an opportunity to intervene,
Abraham said in an email. "But we are still a long way off," she
added.
SOURCE: http://bit.ly/2CflOBw Ophthalmology Retina, online March 11,
2019.
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