Impaired vision: A potentially modifiable risk factor for dementia
Prof. V Nagarajan, Chairman & Head Neurosciences Research & Translational Task Force, ICMR, New Delhi; Chairman, IEC, Govt. Madurai Medical College; Director, VN Neuro Care Centre, Madurai, 04 May 2022
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Vision impairment is an important potentially modifiable risk factor for dementia, finds a new study reported in JAMA Neurology.1

For this study, the researchers obtained data of 16,690 subjects, aged 50 years and older, from the 2018 US Health and Retirement Study (HRS) with an objective to calculate the population attributable fraction (PAF) taking into consideration the prevalence and risk of dementia associated with the individual risk factors. PAF is “the number of cases of dementia that would potentially be prevented if a risk factor were eliminated”. They examined the impact of 11 potentially modifiable risk factors (hypertension, obesity, depression, hearing loss, traumatic brain injury, diabetes, smoking, less education, physical inactivity, social isolation and excessive alcohol consumption) in the life-course model proposed by the Lancet Commission on Dementia prevention, intervention, and care. For the present study, the researchers replaced air pollution included in the life-course model, with vision impairment due to lack of data in the HRS study. The data was analyzed between March and September of 2021.

More than half of the study participants were women (54%); nearly 52% were aged 65 years; with regard to ethnic composition of the study group, 80.2% were White, 10.6% were Black and 9.2% belonged to other ethnic groups such as American Indian or Alaska Native, Asian, and Hawaiian Native or Pacific Islander

All the 12 potentially modifiable risk factors were associated with an estimated 62.4% of dementia cases. When individual risk factors were examined, hypertension was the most prevalent (~60%) and also had the highest weighted population attributable fraction (12.4%) followed by obesity with PAF of 9.2%, depression 9.1%, hearing loss 7%, traumatic brain injury 6.1%, diabetes 5.1%, smoking 3.2%, physical inactivity 3.1%, less education 3.1%, social isolation 1.9%, vision loss 1.8% and excessive alcohol consumption 0.3%.

The population attributable fraction of vision impairment was 1.8% almost comparable to social isolation, which had a PAF of 1.9%. Of note, vision impairment was more prevalent as a risk factor than social isolation; 8.3% vs 1.7%, respectively.

When the PAF for vision impairment was examined by race and ethnicity, the PAF was 1.8% for White non-Hispanic older adults, 2.2% among Hispanic older adults. The prevalence of vision impairment was higher in Hispanic older adults 11% compared to the overall prevalence, which was 8.3%.

The 12 risk factors are associated with about 40% of dementia cases globally, according to the 2020 report of the Lancet Commission on Dementia prevention, intervention and care, which did not include vision impairment as a risk factor, though it included hearing loss. The PAF of 1.8% for vision impairment suggests that healthy vision could have “potentially prevented more than 100,000 prevalent dementia cases in the US”.

However, the current study has demonstrated an association of vision impairment with dementia and makes a case for its inclusion in the Lancet Commission’s life-course model of potentially modifiable dementia risk factors. Given that vision impairment is often preventable and can be corrected, all older adults should be monitored and provided appropriate eye care to address the preventable and treatable causes of vision impairment. This will help them to stay independent and delay cognitive impairment and prevent dementia.

Reference

Ehrlich JR, et al. Addition of vision impairment to a Life-Course Model of Potentially Modifiable Dementia Risk Factors in the US. JAMA Neurol. 2022 Apr 25. doi: 10.1001/jamaneurol.2022.0723