Up to 20 per cent of patients with age-related macular degeneration may develop Charles Bonnet syndrome, a condition associated with visual hallucinations.
This is often disturbing for patients and can lead to them being misdiagnosed as suffering from dementia.
GPs and other health professionals should advise patients about the risks of developing such hallucinations, said Dr Winfried Amoaku, chairman of the scientific committee of the Royal College of Ophthalmologists. It is vital that neither they nor patients confuse the hallucinations with signs of psychoses or dementia, he added.
The college and the Macular Disease Society are launching a campaign this week to raise awareness of Charles Bonnet syndrome.
Dr Amoaku said it is caused by a lack of visual input to the brain's occipital lobe. Hallucinations can involve seeing faces, landscapes, or objects, as well as grids or patterns.
'GPs should advise patients who have poor eyesight about the risk of visual hallucinations and Charles Bonnet syndrome,' he said.
'Patients are reluctant to talk about these hallucinations. They don't want to talk to their relatives or their GP about it, because they don't know what they are.'
He added: 'The most important thing is to recognise that people are not crazy. Many people are content just to know what it is.'
Patients are likely to know what brings on hallucinations and can take steps to reduce them, he added. 'For some patients reading a newspaper may cause them, for others it may be sitting near bright light.'
Up to 100,000 people in the UK are thought to suffer from Charles Bonnet syndrome. Dr Amoaku warned that, as the population ages, prevalence of the condition will increase.
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