Charles Bonnet Syndrome

Why it happens

The brain's visual areas normally receive a constant stream of signals from the eyes. When sight is lost, those areas receive less input and become overactive, generating their own images. This is similar to phantom limb sensations after an amputation. It is called deafferentation, or "release" hallucinations.

CBS is named after the Swiss naturalist Charles Bonnet, who described it in his grandfather, who had cataracts, in 1760.

Who is affected

CBS can occur with any condition that causes significant vision loss in both eyes, including:

• age-related macular degeneration, the most common cause
• glaucoma
• diabetic retinopathy
• cataracts
• stroke affecting the visual parts of the brain
• retinal conditions such as retinitis pigmentosa
• optic nerve damage

It is most often seen in older adults but can occur at any age. Hallucinations often begin when vision is declining, sometimes soon after a further drop in sight.

What people see

• Simple hallucinations: flashes, colors, shapes, grids, brickwork, lattices or lines
• Complex hallucinations: faces (sometimes distorted), people, often small and in costume, animals, vehicles, buildings, landscapes, flowers
• images that may be in color, still or moving, and very detailed
• images lasting seconds to hours, often when sitting quietly, in dim light or in the evening

Hallucinations are purely visual. People with CBS do not hear, smell or feel the images, and they generally understand they are not real, although they may be startled at first.

Many people do not mention them for fear of being thought "mad" or having dementia. Simply knowing the name and cause brings great relief.

Diagnosis

There is no specific test. A doctor makes the diagnosis when:

• there is significant vision loss
• hallucinations are only visual
• the person has insight that they are not real
• there are no other causes such as delirium, dementia, psychiatric illness, medicines, migraine or seizures

Doctors may check for other causes with a review of medicines, a memory assessment, blood tests and sometimes a brain scan. Lewy body dementia and Parkinson's disease can also cause vivid visual hallucinations, but with other features such as fluctuating alertness, movement problems or loss of insight.

Coping with Charles Bonnet syndrome

Techniques that help many people stop an episode:

• Eye movements: look from left to right about once a second, 15 to 30 times, without moving your head. Keep looking straight ahead between movements.
• Change the lighting: turn a light on if it is dim, or off if it is bright.
• Blink rapidly or close and open your eyes.
• Look directly at the image or move your gaze away.
• Get up and move to another room or activity.
• Talk aloud or listen to the radio.

Other measures:

• keep good lighting at home
• stay socially and mentally active; isolation and boredom make episodes more frequent
• treat sleep problems and fatigue
• use low vision aids and services to make the most of remaining sight

Treatment

There is no cure. Treating the underlying eye disease where possible (for example cataract surgery or macular degeneration injections) can reduce hallucinations. Medicines such as antipsychotics or anti-seizure drugs are occasionally tried for severe, distressing cases, but evidence is limited and side effects are common.

Outlook

For many people, hallucinations become less frequent after 12 to 18 months, although some have them for years. Hallucinations sometimes stop if vision is lost completely or improves. CBS does not lead to dementia or mental illness.

Frequently asked questions

What is Charles Bonnet syndrome?

Charles Bonnet syndrome is a condition where people with significant sight loss see vivid images that are not there, such as patterns, faces, people or animals. It happens because the brain fills in missing visual input. It is not a mental illness or dementia.

What do people with Charles Bonnet syndrome see?

They may see simple patterns such as grids, brickwork or colors, or complex images such as faces, small people in costume, animals, buildings or landscapes. The images are often detailed, can move, and usually last from seconds to hours.

Does Charles Bonnet syndrome mean dementia?

No. Charles Bonnet syndrome is caused by sight loss, not brain disease, and people keep insight that the images are not real. Doctors check for other causes, such as dementia or delirium, if there are memory problems, confusion or hallucinations involving other senses.

Does Charles Bonnet syndrome go away?

Often it improves with time. Many people find hallucinations become less frequent after a year or two, though some experience them for longer. Treating eye disease, good lighting, staying active and eye movement techniques can reduce episodes.

How do you stop Charles Bonnet hallucinations?

Try moving your eyes from side to side about once a second for 15 to 30 seconds without moving your head, blinking, changing the lighting, or getting up and doing something different. These techniques interrupt episodes for many people.