Commonly used cognitive tests measure reaction time.

A slow response can suggest brain function isn’t as sharp as it once was, and suddenly you’re looking at a possible diagnosis for mild cognitive impairment.

But what happens when these tests are taken by people who have compromised vision, but don’t know it? Does it make a difference?

An Adelaide PhD student Anne Macnamara suspected 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 vision problems such as cataracts or age-related macular degeneration (AMD).

She led a study to find out for sure.

The study

Ms Macnamara and her study co-authors are part of the CAIN lab at the University of South Australia. CAIN stands for Cognitive Ageing and Impairment Neurosciences.

The researchers recruited 24 participants with normal vision to complete two cognitive tests – one involved vision-dependent reactive tasks and the other investigated verbal fluency.

In one round of tests, the participants were asked to wear a set of goggles that simulated the effects of age-related macular degeneration.

In a separate round, they went without the goggles and performed the tests with their regular eyesight.

Ms Macnamara told The New Daily that the study was designed so the effects of the simulated impairment and regular eyesight could be compared.

As one might expect, “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.

Millions of people could be affected

Ms Macnamara said visual impairments affect about 200 million people worldwide over the age of 50 – and “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.”

This would be particularly burdensome for people with macular degeneration whose mental health is already challenged by the realities of vision loss.

Is there misdiagnosis going on in the real word?

The answer to that question would require further study.

But the researchers say that visual impairments are “often overlooked in research and clinical settings”, given that reduced vision is underestimated in up to 50 per cent of older adults.

The numbers of people affected are bound to increase in line with an ageing population.

The key takeaway?

Ms Macnamara said “it is critical that neurodegenerative researchers control for vision when assessing people’s cognition”.