This factsheet considers some specific visuoperceptual difficulties that people with dementia can have, and possible ways of helping them. Understanding potential perceptual problems and intervening with appropriate help, support and reassurance can greatly assist people with dementia to feel safe in their changing perceived reality.
People with dementia can experience a number of visuoperceptual difficulties due to normal ageing, eye conditions, and sometimes from additional damage to the visual system caused by specific types of dementia.
Vision difficulties can result in a variety of ‘visual mistakes’ (including illusions, misperceptions, misidentifications and sometimes even hallucinations). They can cause a person with dementia to misinterpret their environment and what is in it. The consequences of such difficulties can be more severe for people with dementia than for people without, since they may not know (or remember) that they are making ‘visual mistakes’, or be rational or able to ‘test reality’ accurately. They may also have difficulty explaining what they have seen.
Visuoperceptual difficulties have been reported for a number of dementias including Alzheimer’s disease, dementia related to Parkinson’s disease, Lewy body dementia, and vascular dementia (if stroke-type damage is on or near to the visual pathway in the brain). Of the various types of dementia, the visual difficulties in Alzheimer’s disease have been most studied to date.
Visual perception is complex since, whether people have good vision or not, they try to interpret and understand what they see. Sometimes trying to understand what was ‘poorly seen’ involves making a ‘best guess’ at what was seen. If what we perceive seems real to us, it can directly affect our behaviour.
Although ‘vision’ usually refers to seeing with the eyes, and ‘perceiving’ refers to making sense of the information that the eyes (and the other senses) are receiving, the two words are often used interchangeably.
To perceive accurately requires the ability to co-ordinate all the components of the visual system (eyes, optic muscles, retinas, optic nerve) and process information from other senses and thoughts. It also depends on overall health of the body, visual system and brain, alertness, mood, motivation and even the expectation of what ‘should’ be seen. Accurate vision also requires the co-ordination of every aspect of our cognitive (thinking) ability to manage and make sense of visual information (Jones G M M et al, 2006a).
There are many components to vision: adjusting and maintaining optimal focus; adjusting to different light levels; perceiving depth of field, black and white, colour, lines, objects, faces; distinguishing between faces; separating objects from background; making the accurate small eye movements required to follow moving objects and scan information. There are also many possible types and combinations of visual difficulties.
Advances in the neuroscientific understanding of normal vision are helping to better understand visual changes resulting from ageing, use of medication, illness or injury, and specific types of dementia.
Normal Age-related Changes in Vision
Visual changes resulting from normal ageing can include:
- reduced visual acuity (sharpness – nearby objects become blurred first)
- an increase in the amount of light needed to see
- an increase in the negative effects of glare
- more time required to adapt to marked changes in light level (from dark to light or vice versa)
- a reduction in size of the peripheral visual field
- decreased contrast sensitivity
- decreased depth perception
- changed colour vision (increased colour saturation required to see colours – gradual loss of the blue/violet part of the colour spectrum – dark colours and pastel shades become increasingly difficult to distinguish between)
- changes in the small eye movements (used to track moving objects, orientate oneself in new locations, and to read)
- blurring from ‘floaters’ (clumps of cellular debris in the vitreous humour gel in the eye)
- light flashes or momentary distortion of images (when vitreous humour in the eye begins to pull away from the retina)
- decreased ability to perceive the flickering of strobe lighting.
Most people have regular sight tests and adjust automatically to their changing vision as they get older. They can use glasses, accurately problem-solve, or learn to compensate for visual changes. However, people with dementia, increasingly, may not be able to do this.
Illnesses, Drugs, and Medications Can Affect Vision
As well as the effects of normal ageing on the visual system, a number of visual disorders are commonly associated with ageing. These include cataracts, glaucoma, macular degeneration and retinal complications from diabetes. These can all result in changes such as blurring, partial loss of visual field, through to genuine visual hallucinations and complete blindness.
Use of alcohol and other recreational drugs can also affect vision, as can withdrawal from them. Sometimes medications can cause or contribute to visual difficulties. A surprising number of medications commonly taken by older people can have visual side-effects. They include some drugs from the following categories: cardiovascular, non steroidal anti-inflammatory, antibiotics, anti-Parkinson, and even eye medications.
Additional Visual Difficulties in Some Types of Dementia
There can also be additional visuoperceptual difficulties in dementia related to Parkinson’s disease and Lewy body dementia. In vascular dementia, if strokes occur along or near the visual pathway, a wide range of visuoperceptual difficulties, including hallucinations, can result. Importantly, changes in vision from strokes may not be noticed by an individual.
Currently, most is known about damage to the visual system in Alzheimer’s disease (and ‘posterior cortical atrophy‘, a rare variant of Alzheimer’s disease, see Factsheet 479). The ‘plaque and tangle’ damage which characterises Alzheimer’s disease, initially accumulates in the brain areas linked to memory for processing new factual information. It lies close to a part of the visual pathway, which can also become affected from the spread of plaque and tangles. Later, other parts of the visual pathway can also be involved. Difficulties in both primary and complex visual functioning have been described for Alzheimer’s disease. (Note that some of these are similar to those described for normal ageing. However they can occur independently from, or in addition to, normal age-related visual changes and visual illness.)
Specific difficulties that have been reported in Alzheimer’s disease include:
- reduction in number and accuracy of small eye movements
- colour perception (loss of the blue, purple, green part of the spectrum)
- figure-background contrast discrimination
- depth and motion perception
- visual acuity (but not initially)
- object and facial recognition.
- assembling puzzles
- reading books, or doing visual tasks involving close eye movements
- watching TV shows with rapidly moving images.
- play board games
- keep handwriting in horizontal lines
- find objects readily (even though they may be in front of a person)
- copy images accurately
- walk or mobilise confidently.
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