Charles Bonnet Syndrome (or visual hallucinations) can happen to anybody experiencing loss of visual stimulation.

There are many reasons for hallucinations. Sometimes these happen naturally while falling asleep or on waking. They can also be induced by illness, drugs or chemical imbalance in the brain.

With visual impairment, it is a totally different matter. When someone's eyesight fails and the visual image decreases, the brain takes over. It substitutes an image from memory, not imagination. The images vary. They are usually very vivid and exact. Sometimes they are frightening, sometimes pleasant, but almost always, at the very least, worrying.

A definition

Dr Bob Thompson, Chairman of the Macular Disease Society, gives a very good medical explanation: "Eyes do not see! It is the brain that does the seeing, which is why under certain circumstances, visual hallucinations can be such a frightening experience for some people who do not understand what is going on."

In simple terms, eyes do little more than convert light energy into electrical energy in the form of 'nerve impulses.' Specific patterns of nerve impulses are generated according to the nature of light falling on the retina. These impulses are transmitted to the visual cortex of the brain where they are further processed to access other areas of the brain.

When such information is first received by the brain, certain pathways are laid down involving specific areas and the information is stored as memory. The process is called 'cognition.' In short, a 'specific' image viewed by the eye gives rise to an equally specific pattern of nerve impulses which is not only seen by the brain, but stored as visual memory.

When an exact similar set of impulses is again received by the brain, the visual cortex initiates a search for the same stored pattern and the same image is seen once more by the brain.

Different types of hallucination

Charles Bonnet Syndrome bears no relation to mental instability. Patient know that what they are seeing is not real, and yet the vivid and clear image continue to taunt and disrupt their lives. These visions are not comparable to dreams - people never see the images when they are asleep. The vision unfolds on top of reality, rather like watching two films at once. Here are some of the common hallucinations recounted by the blind and visually impaired people:

• Sunflowers sitting on chairs
• Faces that change from tranquility to horrid monsters
• Victorian children (very common!)
• Men throwing knives
• Complete wedding scenes
• One very independent lady had to stop going out because huge forests appeared in front of her. She knew they were not actually there, but she could not see through them or beyond them.

Helpful tips

Discussing the condition helps immensely. Sometimes talking over feelings with a counsellor or psychiatrist can help provide people with ways of coping with the visions. If you are having problems with yours then talking to your GP may be a good way to find some help.

Disclaimer of Medical Liability

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The information provided should never be considered a substitute for professional health care by a qualified doctor or other health care professional, which will be tailored to the patient's individual circumstances. We cannot take responsibility if you rely on this information alone.