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Poor eyesight could unfairly skew cognitive test results

Researchers at the University of South Australia have ascertained that millions of older people with poor vision are at risk of being misdiagnosed with mild cognitive impairments.

Their study found that cognitive tests that rely on vision-dependent tasks could be skewing results in up to a quarter of people aged over 50 who have undiagnosed visual problems such as cataracts or age-related macular degeneration (AMD).

The research team recruited 24 participants with normal vision to complete two cognitive tests – one involving vision-dependent reactive tasks and the other based on verbal fluency.

Using a set of goggles to simulate AMD, the participants scored far lower on the cognitive test involving reaction time tasks than without the goggles. There was no statistical difference with verbal fluency tests when using the goggles.

University of South Australia researchers involved in the study included PhD candidate Anne Macnamara, Dr Scott Cousens and Associate Professor Tobias Loetscher. Researchers from Bond University, Flinders Medical Centre and Singapore also took part.

Macnamara, who led the study, said the results are a stark reminder that visual impairments – which affect approximately 200 million people worldwide over the age of 50 – unfairly affect cognitive scores when tests involve visual abilities.

“A mistaken score in cognitive tests could have devastating ramifications, leading to unnecessary changes to a person’s living, working, financial or social circumstances,” she said.

“For example, if a mistaken score contributed to a diagnosis of mild cognitive impairment, it could trigger psychological problems including depression and anxiety.

“People with AMD are already experiencing multiple issues due to vision loss and an inaccurate cognitive assessment is an additional burden they don’t need.”

Visual impairments are often overlooked in research and clinical settings, the researchers said, with reduced vision underestimated in up to 50% of older adults.

With this figure expected to increase in line with an ageing population, it is critical that neuro-degenerative researchers control for vision when assessing people’s cognition.

“Mobile apps can now be used to overlay simulated visual impairments onto test materials when piloting their stimuli,” Macnamara said.

“Also, researchers can incorporate quick and simple screening tasks before getting people to do cognitive tests. Verbal tasks should always be part of the assessment, too.”

The study has been published in Scientific Reports.

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