The eyes aren’t just windows to the soul, they may also offer a glimpse of the future, according to a new study that links ocular issues to a rising risk of dementia.
The research, published in the British Journal of Ophthalmology, found that age-related macular degeneration, cataract and diabetes-related eye disease — impairments that reduce the stimulation of visual sensory pathways — may all expedite the advance of dementia. While previous research has hinted at a link between failing vision and the eventual loss of cognitive function, the relationship has been unclear because the prevalence of eye problems increases with age, as do most known risk factors for dementia, including diabetes, hypertension, heart disease, stroke and depression.
To investigate whether ophthalmic conditions are related to a higher risk of dementia independent of these systemic factors, researchers pored over the data of 12,364 adults, between the ages of 55 and 73, who were enrolled in the UK Biobank study. Subjects were assessed between 2006 and 2010 to establish a baseline and then followed until early last year. During the follow-up, which represented 1,263,513 person-years, 2,304 cases of dementia were discovered. Data amassed over time revealed that age-related macular degeneration, cataract and diabetes-related eye disease were all independently associated with an increased risk of dementia from any cause.
Relative to people with no eye issues at the start of the study, the risk of dementia was found to be 26 per cent greater in people with age-related macular degeneration, 11 per cent greater in those with cataracts and 61 per cent greater in people suffering from diabetes-related eye disease. Although glaucoma did not correlate with an increased risk of Alzheimer’s disease, it was tied to a higher risk of vascular dementia, the most common type of dementia after Alzheimer’s.
Alzheimer’s disease is a degenerative condition that is believed to be the result of the accumulation of certain proteins in the brain that leads to the slow death of neurons. This process eventually produces symptoms of memory loss, difficulty thinking or problem solving and changes in mood and behaviour. There are over 500,000 Canadians living with dementia today, with another 25,000 diagnosed with the progressive disease every year, according to the Alzheimer Society. Two-thirds of those diagnosed over the age of 65 are women. With the rate at which the disease is growing, it costs over $12-billion a year to care for patients.
Prior to the current study, subjects were evaluated for depression and asked about their experiences with a series of health conditions, including heart attacks, angina, hypertension, stroke or diabetes. This helped researchers conclude that having a systemic condition in addition to an ophthalmic condition further amplified the risk of dementia. The highest risk was observed in people with who had diabetes-related eye disease and a systemic condition. Relative risk for dementia increased with the number of ophthalmic conditions a person possessed.
“We found that all combinations of an ophthalmic condition and a systemic condition were associated with an increased risk of dementia,” researchers said. “This risk was greater than that associated with an ophthalmic or a systemic condition only, suggesting that there might be an additive effect of ophthalmic and systemic conditions on the development of dementia. Underlying mechanisms are unclear, but impairment of multiple organs than a single is more likely to enlarge the risk of dementia.”
The observational study had a few limitations, notably the self-reported nature of eye issues, which can result in an underestimated prevalence. It is also possible that some of the data researchers relied upon, including death records, may not have documented all cases of dementia. Also, in some instances, it is possible that the dementia discovered during follow-up appeared before any ophthalmic issues.
The findings were still significant, however, and underline the potential risks revealed by vision-related problems. “Individuals with both ophthalmic and systemic conditions are at higher risk of dementia compared with those with an ophthalmic or systemic condition only,” researchers said. “Newly developed hypertension, diabetes, stroke, heart disease and depression mediated the association between cataract/ diabetes-related eye disease and dementia.”
Dave Yasvinski is a writer with Healthing.ca