Vision and Perception Problems in Dementia: Misjudging, Mistaking and Misreading

Dementia can change how the brain makes sense of what the eyes see, causing misjudged distances, a dark rug seen as a hole, or a son mistaken for a husband. Here's why, and how to help.

By Jim Pavlish, Editor · Last updated: October 31, 2026 · Editorial policy

Short answer: dementia can damage the parts of the brain that interpret what the eyes see, even when the eyes are healthy. The Alzheimer's Society says this can cause misperceptions (a dark rug seen as a hole), misidentifications (a son mistaken for a husband) and trouble judging distance. Rule out eyesight problems first, then improve lighting, reduce clutter and shadows, and gently reassure rather than correct.

Your father stops at the edge of a black doormat as if it's a step down. Your mother reaches for her glass and knocks it over. Your husband calls you by his sister's name. Your aunt refuses to walk across a shiny floor.

These can look like stubbornness, clumsiness or "just confusion." Often they're a change in perception: how the brain makes sense of what the eyes take in.

This page is general information, not medical advice. Talk to the person's doctor about new or worrying changes, and see an optometrist or ophthalmologist for eye checks.

Eyes see, the brain interprets

The Alzheimer's Society explains that information from the eyes travels to the brain, which processes it and compares it with memories to work out what is being seen. Dementia can interrupt or slow down this process.

Even if the eyes are healthy, vision can be affected if the brain is damaged. According to the Society:

• The occipital lobes, at the back of the brain, process visual information. Damage here can make it hard to work out what's in front of you, leading to misperceptions.
• The temporal and parietal lobes help recognize faces and objects and judge distances. Damage here can lead to misidentifications and trouble with distance.

The Alzheimer's Association lists "trouble understanding visual images and spatial relationships" among its 10 warning signs of Alzheimer's. It says this may lead to difficulty with balance or reading, and to problems judging distance and telling color or contrast, which can affect driving. (Vision changes from cataracts, by contrast, are a typical age-related change.)

One rarer form of Alzheimer's mainly affects vision first; see Posterior Cortical Atrophy.

Common examples

From the Alzheimer's Society:

• Misperceptions: seeing one thing as something else, such as blue floor tiles as water, a dark rug or doormat as a hole, or a shadow as a spider
• Misidentifications: mistaking one person or object for another, such as a son for a husband, or a TV remote for a phone
• Visuospatial problems: difficulty judging distances or understanding 3D objects, making stairs, parking a car or reaching for things harder
• Using objects wrongly: trying to pay with a bus pass, or using the wrong coins

These problems can make a person nervous, less confident and more likely to fall. See Preventing Falls in Dementia.

Is it eyesight, perception or hallucination?

It's worth sorting these out, because the help is different.

Eyesight. Sight problems are more common with age, including glaucoma and macular degeneration, the Alzheimer's Society notes. It suggests an eye test to check whether glasses are needed or the prescription is right, and checking that glasses aren't scratched or dirty, with reading glasses clearly labeled. See Vision Loss and Dementia.

Hallucinations. These are seeing (or hearing, smelling or feeling) things that aren't there at all. The Society says people with dementia are often thought to be hallucinating when they are actually mistaken about something real, for example a busy carpet pattern seen as a "swarm of insects." Changing or covering the pattern may stop it. Hallucinations are most common in dementia with Lewy bodies. If you think someone is hallucinating, talk to their doctor. See Hallucinations and Delusions.

A sudden change. The Society says a sudden change over hours or days could be delirium, a medical emergency. Get urgent medical advice. See Delirium vs. Dementia.

How to help

Practical ideas from the Alzheimer's Society:

• Don't draw attention to mistakes. Gently point out what's really there. Being corrected can undermine confidence. If they realize the mistake, laughing about it together can help, if it feels right.
• Improve the lighting. More even light can help, and so can getting rid of shadows. Spotlights or harsh lighting can make corners look darker. An ornament's shadow might be the "dog" they keep seeing.
• Reduce visual clutter.
• Keep things where they've always been. Familiar surroundings let the person rely on memory and habit. Try not to move furniture.
• Offer an arm on tricky floors. If a shiny floor looks wet or icy, walk ahead or offer your arm so they can see it's safe.
• Say what you're handing over. Name the object and, if needed, how it's used. If they misjudge distance, place it on a table in front of them or in their lap.
• Describe the meal. Say what food and drink are on the table and where.
• Introduce yourself. Ask visitors to say their name when they arrive. Tell the person when someone comes in or leaves.
• Keep a note of when problems happen. If they're worse toward evening, it may be Sundowning or not enough light.
• Swap activities if needed. If reading has become too hard, try audiobooks.

For room-by-room ideas, see Home Safety.

Common questions

Why does my mom with dementia think the rug is a hole?

The Alzheimer's Society says dementia can damage the brain areas that interpret what the eyes see, causing misperceptions, such as seeing a dark rug or doormat as a hole. Reassuring them, offering your arm and improving lighting can help.

Can dementia affect your eyesight if your eyes are healthy?

Yes. The Alzheimer's Society explains that even with healthy eyes, damage to the brain can change how a person understands what they see. The Alzheimer's Association lists trouble with visual images, distance and contrast among the warning signs of Alzheimer's.

How can I tell a misperception from a hallucination?

A misperception is mistaking something real (a pattern, a shadow) for something else; a hallucination is seeing something that isn't there. The Alzheimer's Society suggests listening to what the person describes and checking the surroundings for a cause. Talk to the doctor about possible hallucinations.

Should someone with dementia still get eye tests?

Yes. The Alzheimer's Society recommends ruling out sight problems first, with an eye test to check glasses and the prescription.

The bottom line

Many "odd" reactions in dementia come from the brain misreading what the eyes see. Check eyesight first, then make the surroundings easier to read with better light, less clutter and familiar layouts. Gentle reassurance works better than correction.

Sources

1. Alzheimer's Society (UK): How can dementia change a person's perception?
2. Alzheimer's Society (UK): Supporting a person with dementia who's experiencing vision and perception problems
3. Alzheimer's Society (UK): Hallucinations and dementia
4. Alzheimer's Association: 10 Early Signs and Symptoms of Alzheimer's and Dementia

Not medical advice. This article is general information, not a diagnosis or treatment plan for any individual. Talk with a doctor about your situation.

Related articles

• Hallucinations and Delusions
• Preventing Falls in Dementia
• Home Safety
• Posterior Cortical Atrophy
• Vision Loss and Dementia
• When Someone With Dementia Doesn't Recognize You