Charles Bonnet syndrome
Also called: CBS · Visual release hallucinations
People who lose a lot of their sight often start to see things that are not there: patterns, faces, small people in costume, whole landscapes. They know the images are not real. It is caused by sight loss, not by mental illness.
How common
Does this happen to you?
How it works
Charles Bonnet syndrome is the name for visual hallucinations in people with poor sight and no mental illness1. It usually appears in older adults with macular degeneration, glaucoma, cataracts, or diabetic eye disease. Anything that cuts the amount of visual signal reaching the brain can cause it1.
The most accepted explanation is called deafferentation. The visual cortex is built to process a constant stream of input. When that input drops, the cortex does not shut down. The cells become more excitable and start to fire on their own1. The brain then presents that spontaneous activity as images. The same thing happens in people kept in the dark, and in the ear it produces musical ear syndrome.
The images range from simple to elaborate. Simple ones are lines, grids, and coloured patterns. Complex ones include faces, animals, buildings, and groups of small figures1. Some people see figures in costume from an earlier time3. The images are silent. They can last seconds or hours3. They appear more often when the person is inactive or drowsy1.
A key feature is insight. Most people with the syndrome know the images are not real, even when they look solid1. Charles Bonnet, a Swiss naturalist, first described the condition in 1760 in his grandfather, who had cataracts and saw people, birds, and carriages that were not there2.
How common it is
The figures come from studies of older people with sight loss1. Reported rates run from 10% to 40%, and a 2008 Australian study found 17.5%1. That is a share of people with serious sight loss, not a share of everybody. Two Asian studies found much lower rates, so the number moves with the group studied1. Underreporting is the biggest problem. Many people hide the images for fear of being thought mad, so the true share is probably higher than the reported figures1.
Is it a problem?
The hallucinations themselves are harmless. They are a side effect of sight loss, not a mental illness, and not a sign of dementia1. Many people with the syndrome hide it for fear of being thought mad. By one estimate, almost 60% of them hesitate to tell a doctor1.
Knowing the cause is usually enough to make it bearable. The images often become less frequent over one or two years3. Some people can make an image go away by blinking, moving their eyes, or changing the lighting1.
See a doctor if hallucinations come with:
- confusion,
- memory loss,
- hearing things.
Also see a doctor if you are not sure the images are unreal. Those are not the pattern of this syndrome.
Sources and further material
- Wikipedia Charles Bonnet syndrome
- Wikipedia Charles Bonnet
- aao.org What Is Charles Bonnet Syndrome? Patient page. Covers duration, content of the images, and how they fade over 1 to 2 years.
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Related oddities
Prisoner's cinema
After hours or days in darkness, people start to see light shows: colours, geometric patterns, and sometimes figures or scenes. Prisoners, truck drivers, pilots, and meditators all report it.
Closed-eye hallucinations
Close your eyes and you do not see nothing. You see speckle, drifting colour, and, as you fall asleep, moving patterns and even scenes. Almost everyone sees the speckle, and many people see more. Almost nobody talks about them.
Palinopsia
An image that keeps appearing after the thing you saw is gone. A faint afterimage after a bright light is normal and harmless. Copies that persist or return later need a doctor.
Musical ear syndrome
Some people with hearing loss hear clear, complete music that no one is playing. The brain replays stored songs to fill the silence. Most people with it know the music is not real.