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.

University of South Australia 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 stimulate 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.

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," said Ms Macnamara.

"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 per cent of older adults.

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.

The study has been published in Scientific Reports.