Vision impairment, cognitive decline go hand in hand

June 6, 2019
Impaired vision creates obvious functional limitations among older adults, but could it also be associated with cognitive decline? Mounting evidence suggest clues may be found in the eyes.

If memory is the first thing to go with old age, then vision might be a close second, suggests research that describes an association between cognitive decline and vision impairment among older Americans.  

Published in the Centers for Disease Control and Prevention (CDC's) May 24 Morbidity and Mortality Weekly Report (MMWR), the analysis found that among adults 45 years and older, subjective cognitive decline (SCD)-related functional limitations were 3.5 times higher among adults with vision impairment than those without. As the number of Americans with vision impairment is expected to double over the next three decades—alongside similarly alarming increases in dementia—researchers increasingly look to the eyes for early detection of cognitive decline.

Subjective cognitive decline, a self-reported experience of worsening or more frequent confusion or memory loss, affects more than 11% of American adults, ages 45 and older, the CDC notes. Cognitive decline is an expected part of the normal aging process; however, if worsening, may be indicative of mild cognitive impairment (MCI). In turn, MCI has a four-fold risk of developing dementia or Alzheimer's disease by some estimates.

Previous studies show cognitive decline and vision impairment often co-occur or might be casually related, researchers note, and the CDC's recent analysis bears a similar conclusion.

Per the analysis, researchers examined Behavioral Risk Factor Surveillance System surveys for years 2015-2017, which included data on 208,601 respondents ages 45 and older. They determined 18% of respondents with vision impairment also reported SCD-related functional limitations, while prevalence among those with no reported vision impairment was only 4%.

Vision impairment can decrease quality of life, functional limitations and an increased risk of mortality, the CDC notes. However, previous research found the relationship between cognitive decline and vision impairment may be a modifiable trait.

"Vision impairment is an important, growing public health concern in the United States," authors write. "Addressing vision impairment through prevention or corrective treatment might reduce functional SCD-associated limitations in the adult population.

"Measures to prevent vision impairment and vision loss include receiving eye care and a comprehensive eye exam."

Looking deep into dementia, Alzheimer's disease

Early detection and monitoring of preclinical cognitive decline are goals that Alzheimer's disease researchers continue to strive toward, and emerging evidence suggests that retinal microvasculature may provide that in vivo, non-invasive, neurological health proxy that could help clinicians. Promising research describes significantly reduced macular vessel density, perfusion density, macular ganglion cell-inner plexiform layer (GC-IPL) thickness in subjects with Alzheimer's disease (versus those without) using non-invasive imaging technology familiar to eye care providers: optical coherence tomography (OCT/OCT-A). Such changes may mirror minor small vessel cerebrovascular changes in Alzheimer's disease.

For as much published research touts retinal imaging as a possible means of Alzheimer's disease and neurodegeneration detection, the Alzheimer's Association is keen on continuing these investigations. And, the AOA is contributing to these efforts.

In a workshop hosted by the Alzheimer's Association, May 22-23, in Washington, D.C., the AOA joined other leading researchers to lay a groundwork for large-scale early detection and monitoring of MCI and Alzheimer's disease through retinal/ocular imaging. Michael Dueñas, O.D., AOA chief public health officer, was optometry's sole representative to the nine-member subcommittee that brought together over 90 researchers from nine different countries.

As Dr. Dueñas explains, Amyloid β plaque drives tauopathy and inflammation, which in turn leads to synaptic damage and neurologic/cell disfunction. Researchers believe it's critical to intervene in the disease process early, during the prodromal phase when damage to synapses and neuronal tissue is minimal. Therefore, researchers are striving for detection and monitoring techniques with high sensitivity. With increasing prevalence of Alzheimer's disease and current diagnostic methods often inaccessible, invasive and cost prohibitive (e.g., MRI, cerebral spinal fluid examination or PET), noninvasive and accessible OCT and OCT-A can become a mainstay toward early detection and the provision of evidence for effectiveness of potential treatment.

While results of the workshop are expected in a soon-to-be-released white paper, Dr. Dueñas says such research could be a seminal moment for Alzheimer's disease as well as optometry's retinal imaging abilities. Altogether, 276 systemic diseases have ocular findings that can be detected during a comprehensive eye exam that—combined with optometry's geographic accessibility—poise doctors of optometry to add substantially to Americans' primary care.

"Optometry is the most accessible eye care profession and that accessibility paired with technology and understanding of early cognitive decline is going to be essential in raising our patients' health outcomes and preventing or slowing neurodegenerative disease," Dr. Dueñas says.

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