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Can blind people hallucinate? © Getty Images

Can blind people hallucinate?

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Charles Bonnet Syndrome means hallucinations are actually more common in visually impaired people.

Asked by: Christian Sant Cassia, Malta


Hallucinations are actually more common in visually impaired people. As many as 15 per cent of visually impaired or blind people may experience Charles Bonnet Syndrome (CBS), which takes its name from the 18th-century Swiss naturalist who first described the phenomenon experienced by his grandfather.

In a healthy eye, the optic nerve is accustomed to dealing with as much data as a high-speed broadband connection. When vision is reduced or lost due to damage to the eye (from cataracts or macular degeneration, for example) the neurons in the visual cortex are suddenly left with nothing to do. The visual cortex is already adapted to automatically fill in gaps in our visual field, to compensate for the blind spot.

It seems that, in CBS sufferers, this mechanism just takes wilder and wilder guesses. Victims report dancing monkeys, floating faces and other strangeness.

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luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.


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