Each vision impairment was found to be "independently associated with an increased risk of dementia," Dr. Xiaohong Yang of the Guangdong Eye Institute in China, who worked on the study, told Reuters Health by email. "Major systemic diseases such as cardiovascular disease, obesity, diabetes, and depression play an important role in this association."
Dr. Cecilia S. Lee, director of clinical research at the Eye Institute at Harborview, in Seattle, who was not involved in the study, said there are "many caveats" with observational studies such as this. Still, she told Reuters Health by email, "It is exciting to see results that support previous findings in a study that evaluates such a large cohort of participants."
For their study, Dr. Yang and his colleagues identified more than 112,000 adults who had data available on eye conditions, did not have dementia at baseline and were under 55. The individuals were first assessed between 2006 and 2010 and were followed up into early 2021, for a total of more than 1.2 million person-years of follow-up.
Much of the cohort data was self-reported, including sociodemographic factors like age, sex, education and income, as well as lifestyle information on smoking, drinking, and dietary habits. The patients also self-reported walking habits and general physical activity, answering questions similar to those from the short form version of the International Physical Activity Questionnaire.
Data on incident dementia was culled from death records and hospital inpatient ICD codes, alongside other self-reported sources.
There were 2,304 cases of incident dementia during follow-up, the researchers report in the British Journal of Ophthalmology. Having AMD at baseline was linked with a 26% increase in the risk of all-cause dementia (adjusted hazard ratio, 1.26; 95% confidence interval, 1.05 to 1.52), while those with cataracts had an 11% higher risk (aHR, 1.11; 95% CI, 1.00 to 1.24)and those with DRED had a 61% higher risk (aHR, 1.61; 95% CI, 1.30 to 2.00).
Among the systemic conditions reported at baseline, diabetes, heart disease, stroke and depression all were linked to an increased risk of dementia. New cases of diabetes, hypertension, heart disease, depression and stroke identified during follow-up were found to mediate the association between cataract and incident dementia, as well as between DRED and dementia.
People suffering from both cataracts and a systemic condition were between 1.19 and 2.29 times more likely, depending on the specific comorbidity, to develop dementia than were individuals free of those ailments.
For patients with both DRED and a systemic condition, the increased risks ranged from 1.50 and 3.24.
For AMD, the combination with diabetes was associated with the highest risk for incident dementia, with an adjusted HR of 2.73 (95% CI, 1.79 to 4.17).
Although glaucoma was associated with a higher risk of vascular dementia, 1.48 (95% CI, 1.13 to 1.94), it was not linked with Alzheimer's disease (aHR, 0.89; 95% CI, 0.70 to 1.14) or all-cause dementia (aHR, 1.07; 95% CI, 0.92 to 1.25).
Dr. Fanny Elahi, a neurologist at the University of California, San Francisco, who was not involved in the research, said, "What I find most interesting in this study is that something like AMD is associated but not glaucoma."
"Over the past decade, there has been great interest in understanding the biology of brain disorders and other conditions from a different angle," Dr. Elahi, who has studied retinal markers of neurodegenerative disease, told Reuters Health by phone.
"We've turned to the eye for biomarkers of brain disorders because it's a light-penetrating organ," she said. "It's one that shares some embryological period of development with the brain."
Dr. Yang noted that previous "studies are inconsistent regarding the association between glaucoma and dementia," and that, "Given that both glaucoma and dementia are neurodegenerative diseases, they may share some pathophysiology."
He called for further study, including the generation of "genetic risk scores for ophthalmic conditions" that could then be tested for their ability to predict dementia, a proposal echoed by Dr. Elahi.
"If we combine genomic studies with these large studies, perhaps we're going to have a chance to find pathways that are shared between these conditions and that are compounded by age," she said. "I think the next step is really to take it to a precise, individualized level, use biomarkers and experimental approaches to see what are the shared molecular pathways, cellular abnormalities, etc., connecting these different disorders."
SOURCE: https://bit.ly/3ulY5tt British Journal of Ophthalmology, online September 13, 2021.
By Matthew Phelan
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