​The study's main author Tham Yih Chung (left), a clinical research fellow at the Singapore Eye Research Institute's ocular epidemiology unit, with Professor Cheng Ching-Yu, the unit's head. The main causes of vision-related cognitive impairment are largely treatable or preventable, noted Prof Cheng. ST PHOTO: TIMOTHY DAVID

Women with poor vision 2.1 times more likely to develop cognitive impairment than men

Losing vision can lead to mental decline, especially among older women, a study has found.

A team of researchers led by Professor Cheng Ching-Yu, 50, head of the ocular epidemiology unit at the Singapore Eye Research Institute, found that 5.6 per cent of Singaporeans aged 60 and above who had visual impairment in at least one eye developed cognitive impairment after six years.

This is more than double the proportion of those who had no visual impairment, 2.7 per cent of whom developed cognitive impairment.

Dr Tham Yih Chung, 35, a clinical research fellow at the unit and the study's main author, said that the association was stronger for those with greater visual impairment.

Compared with those with good vision, those with any visual impairment in at least one eye were 1.63 times more likely to develop cognitive impairment, while the risk for those who were blind in at least one eye was 2.2 times.

The team took into account age and gender, various age-related chronic conditions like diabetes, hypertension and cardiovascular diseases, as well as alcohol intake and body mass index, said Dr Tham.

Overall, women with poor vision were also 2.1 times more likely to develop cognitive impairment than men with poor vision, he said.

Previous studies have shown that people with visual impairment tend to have lower mobility and less independence, and are less likely to participate in social activity, Dr Tham said, adding that these contribute to less cognitive stimulation.

The study, part of a larger Singapore Epidemiology of Eye Disease (Seed) study, was conducted in two phases.

Subjects with no cognitive impairment had their sight tested between 2004 and 2011 to establish a baseline. The team then followed up with the subjects about six years later, between 2011 and 2017, to determine whether there was an association between their visual impairment at the beginning of the study and their risk of developing cognitive impairment.

A standard questionnaire was used to assess the subjects' cognitive abilities, with scores moderated according to their education level.

The test asked simple questions, such as what the subject's age and date of birth are, and who the current prime minister is.

Previous studies done in the United States on the causal link between visual impairment and cognitive decline have shown conflicting results, Dr Tham said.

He added that the Seed study is the first of its kind to examine a multi-ethnic Asian population. Out of the 3,538 subjects without cognitive impairment at the beginning of the study, 2,195 attended a follow-up six years later. This group comprised 512 Malays, 684 Indians and 999 Chinese people.

Last October, Senior Minister of State for Health Amy Khor said that vision disorders are the fourth leading cause of disease burden in Singapore. Dr Khor said the top three causes of blindness and low vision for people over 60 years old in Singapore are cataract, glaucoma and age-related macular degeneration.

But in the Seed study, over 80 per cent of subjects with visual impairment could have easily had their vision corrected, said Prof Cheng.

Over half - 55.9 per cent - had under-corrected refractive error, which can be fixed by simply getting a new pair of glasses.

Another 26.5 per cent had cataracts, which can nowadays be quickly and safely corrected with a 20-minute operation, Prof Cheng said. Only 2.9 per cent had glaucoma and 1.5 per cent had age-related macular degeneration, which are harder to correct.

This means that the main causes of vision-related cognitive impairment are largely treatable or preventable, said Prof Cheng.

But many older people think that losing one's eyesight is a "normal" part of growing older, he said. Others do not have their vision corrected as they want to save money.

Prof Cheng said: "Community outreach vision screening will help to detect visual impairment earlier.

"There is a need to raise awareness of eye care and health among the elderly population."

For his work on the study, Dr Tham won the Young Investigator's Award in the clinical research category at the Singapore General Hospital's Annual Scientific Meeting earlier this month. The paper was submitted to a journal for publication.