Receiving a diagnosis of dementia is devastating, but what if it’s all been a terrible mistake.

A false diagnosis can and does happen, more than many doctors might like to admit.

Sometimes, a mistaken diagnosis of dementia occurs from the dementia-mimicking symptoms of prescription drug side effects, or a deficiency of vitamin B12. But there may be a much simpler explanation. And that’s faulty vision…

It’s been estimated that five out of ten older people have undetected vision impairment, most of which—thankfully—is correctable. From cataracts and dry eyes to presbyopia (being unable to see up close) and glaucoma, there are numerous vision problems that affect older folks that can be treated or stopped when caught early. Glaucoma, for instance, will cause irreversible blindness if left untreated. However, the most common reason for lost vision and blindness in people over age 65 is age-related macular degeneration (AMD).

AMD causes a loss of central vision and severely hinders peoples’ lives, and it is often undiagnosed – at least in the early stages. Vision loss from AMD can sometimes be slowed with treatment, but once the vision is gone, it doesn’t come back. And researchers believe that some of this vision loss can affect a person’s cognitive ability and can even cause symptoms that mimic dementia.

To test their theory, researchers from the University of South Australia examined the impact of visual impairment on cognitive test performance.

For their study they recruited 24 men and women between the ages of 18 and 60 – all with normal vision. Each completed two cognitive tasks twice – the first time with their usual vision and the second time with goggles that simulate the effect of having moderate to severe AMD.

Skewed Results In Up To A Quarter Of Over-50s 

On the verbal fluency test, which requires no visual input, no difference was found with or without the goggles. But on the reaction time test, which is vision-dependent, there was a significant difference. Participants wearing the goggles had much lower scores.

Based on their findings, the researchers believe cognitive tests that rely on vision-dependent tasks could be skewing results in up to a quarter of people aged 50 and over who have undiagnosed vision problems.

Anne Macnamara, who led the study, says the results are a stark reminder that visual impairment, which is very common, unfairly affects cognitive scores when tests involve visual abilities. She explains, saying, “A mistaken score in cognitive tests could have devastating ramifications, leading to unnecessary changes to a person’s living, working, financial or social circumstances.

“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.”

Vision Problems Often Overlooked When Testing For Cognitive Function 

In their paper, published in the journal Nature in March, Ms. Macnamara and her colleagues write that, unlike a language barrier which becomes quickly apparent when instructions for the test are given, there may be no clear indication of impaired visual function during cognitive testing.

“Indeed, vision impairments are often overlooked in research and clinical settings,” they write. “AMD is known to be underdiagnosed in the elderly, with an estimated 25 percent of eyes medically judged to be ‘normal’, actually having features of AMD and suboptimal vision.”

They point out that the problem is systemic across a range of visual impairments, not just AMD, according to additional studies carried out by other research groups.

The Australian researchers suggest any medical professional performing a cognitive assessment should use some quick and simple screening measures before tests are given to make sure any diagnosed or undiagnosed vision problems are taken into consideration.

My Takeaway 

I’d go one step further. Make sure that you or any loved one over the age of 65 gets regular testing for vision loss, whether suffering from dementia or not.

What’s more, this testing should include a visit with an ophthalmologist. They’re trained to notice diseases of the eye before they start—and help treat them once they’ve started—so you can stay on top of preserving your good vision and your cognitive function for as long as possible.

And, if you or a loved one has received a diagnosis of mild-cognitive impairment, dementia, or any other cognitive condition, get a vision check and ensure that the doctor handling your treatment for memory loss understands and considers any vision problems that exist.

Finally, as I mentioned at the start, the side effects of prescription medications and a deficiency of vitamin B-12 can also mimic cognitive dysfunction, so examine these as possible causes of memory loss as well. I’ve heard of a number of cases where starting a vitamin regimen or adjusting a prescription drug regimen dramatically improved symptoms of memory loss.


  1. https://www.unisa.edu.au/media-centre/Releases/2022/poor-eyesight-unfairly-mistaken-
    for-brain-decline/
  2. https://www.nature.com/articles/s41598-022-07924-8 

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