Summary: Cognitive tests that rely on vision-dependent tasks may skew results for up to 25% of adults over 50 with undiagnosed visual problems such as AMD and cataracts. This may lead to a misdiagnosis of mild cognitive impairment in older adults.
Source: University of South Australia
Millions of older people with poor vision are at risk of being misdiagnosed with mild cognitive impairments, according to a new study by the University of South Australia.
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).
Age-related macular degeneration is a leading cause of vision loss for older people. It doesn’t cause complete vision loss, but severely impacts people’s ability to read, drive, cook, and even recognise faces. It has no bearing on cognition.
UniSA researchers 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.
The study has been published in Scientific Reports.
UniSA PhD candidate Anne Macnamara, who led the study, says 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,” Macnamara says.
“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 UniSA researchers say, with reduced vision underestimated in up to 50 percent of older adults.
And with this figure expected to increase in line with an aging 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 says.
“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.”
About this vision, cognition, and aging research news
The effect of age-related macular degeneration on cognitive test performance
The reliable assessment of cognitive functioning is critical to the study of brain-behaviour relationships. Yet conditions that are synchronous which ageing, including visual decline, are easily overlooked when interpreting cognitive test scores.
The purpose of this study was to demonstrate the negative consequences of visual impairments on cognitive tests performance.
Moderate to severe levels of age-related macular degeneration were simulated, with a set of goggles, in a sample of twenty-four normally sighted participants while they completed two cognitive tasks: a vision-dependent reaction time task and a vision-independent verbal fluency test.
Performance on the reaction time task significantly decreased (p < 0.001) in the simulated age-related macular degeneration condition, by as much as 25 percentile ranks. In contrast, performance on the verbal fluency test were not statistically different between the simulated and normal vision conditions (p = 0.78).
The findings highlight the importance of considering visual functioning when assessing cognitive function. When vision is not accounted for, low test scores may inaccurately indicate poor cognition. Such false attributions may have significant ramification for diagnosis and research on cognitive functioning.