Living with Dementia May 2008

Alzheimer's disease (AD) is often (but mistakenly) defined as simply a memory or cognitive disorder, but the true picture is more complicated.

Alzheimer's disease is more accurately described as a visual-perceptual-cognitive disorder. Failing to understand the complexities of the illness can lead to many misunderstandings about the difficulties that people with dementia can face.

Looking but not seeing

Seeing and perceiving is more than just taking in images in focus. Vision is seeing with the eyes. Perceiving is making sense of what eyes and the other senses are receiving. It requires the ability to co-ordinate all the components of the visual system with the brain's ability to process that information. It is a complex process, and requires the co-ordination of every aspect of our ability to manage and make sense of information.

Revising the expectation that 'hallucinations are frequent in Alzheimer's disease'

Hallucinations are where people see something although there is no stimulus to see it.  This is not the same as seeing something inaccurately- in a distorted, unclear way, or not recognising what is being seen, or, not being able to 'problem solve' that something is a visual illusion.  When there is damage to the visual system, people with dementia may not know they are seeing inaccurately. Also, limitations in language ability may make descriptions of what they've seen unclear to listeners.

Hallucinations in people with Alzheimer's disease are reported at between 13 and 73 per cent, with an average of 40 per cent. This suggests they are a common, and even expected, occurrence. Two studies looking at case notes have found that many events classified by GPs as 'hallucinations' were actually more accurately categorised as illusions, misperceptions, misidentifications or naming errors. The studies found that only about 3 per cent of people with AD had "possible visual hallucinations".

Visual and other types of sensory hallucinations were found more frequently in groups of people with other sorts of dementia and illness- especially those with infections.

Why do so many people with Alzheimer's disease appear to be seeing things incorrectly?

We need to take into consideration several factors:

• Normal deterioration in sight due to ageing.
• The possibility of illness affecting vision - such as cataracts, glaucoma, macular degeneration.
• Damage to the visual system as part of the damage to the brain caused by Alzheimer's disease.
• The interaction between mistakes in seeing and mistakes in thinking.

Mistakes in seeing and thinking

People with Alzheimer's disease appear to experience a combination of 'visual mistakes' and 'thinking mistakes', leading to a combined 'visuo-perceptual-cognitive' illness.

Some of the errors commonly made include:

• Mistaking reflections in shiny surfaces and mirrors.
• Misinterpretting patterns (and water and dirt marks).
• Anxiety about stepping over carpet rods, thinking they signify a change of level.
• Refusing to get into an empty lift if it appears full of people because of their own reflection (s) in multiple mirrors.
• Commenting on 'little people in the corner of the room' (people on television).

Minimising visual-perceptual problems

The single biggest thing that can help vision is to improve lighting levels. Better lighting can also help prevent falls, and has also been reported to reduce genuine visual hallucinations.

More tips are available in a forthcoming Society factsheet by neuropsychologist Dr Gemma Jones and colleagues, where this information comes from. Details of the factsheet will be provided once it is available.