Charles Bonnet Syndrome

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What is Charles Bonnet Syndrome?

Charles Bonnet Syndrome (CBS) is defined as a condition where you experience hallucinations – seeing things that are not real. It is not known to be caused by mental health issues or dementia but tends to occur after losing a significant amount of sight. The initial loss of sight is often caused by the presence of other eye conditions. However the current understanding is that the hallucinations themselves are a result of the brain adapting to the sight loss by filling in the gaps across the field of vision.

Who was Charles Bonnet?

Painting of Charles Bonnet, a man wearing a white wig and a draped cloak and necktie.

Charles Bonnet


Charles Bonnet (1720 – 1793) a Swiss lawyer, naturalist and philosophical writer. In 1760, after documenting the symptoms experienced by his grandfather, Bonnet was the first to describe a condition in which the brain adjusted to vision loss by creating hallucinations. Bonnet’s own eyesight declined throughout his life, and he also experienced this condition, which would become known as Charles Bonnet Syndrome in 1937.

Symptoms of Charles Bonnet Syndrome:

The main symptom is visual hallucinations after significant sight loss. CBS does not develop for everyone who undergoes significant sight loss but the likelihood is increased if the sight loss occurred suddenly and / or in both eyes.  It is often linked to other eye conditions such as Age Related Macular Degeneration (AMD) and Cataracts. These conditions have been discussed in their own section of the knowledge hub. CBS relates only to sight, not the other senses. So hearing, smelling, feeling, and tasting things that are not perceptibly present are not defining symptoms. Most people with this condition know that the symptoms are not real.

The hallucinations can:

  • Be patterns like shapes or lines
  • Be of people, animals, objects or places
  • Be moving or still
  • Be in black or white or colour
  • Happen suddenly
  • Last for a few minutes or several hours

The NHS and all other significant public health bodies  along with Sight Support West of England strongly advise arranging an emergency GP appointment or calling 111 if you / someone you know is experiencing hallucinations. This helps to confirm or rule out the presence of other more serious health conditions and can speed up the management and recovery process (whether for CBS or otherwise).

How is Charles Bonnet Syndrome diagnosed:

There is no single specific test / procedure for diagnosing CBS. However the doctor can talk to you about your hallucinations and carry out various different tests and examinations on your eyes and brain in order to determine the cause. These tests can establish whether or not there are signs of other health conditions (neurological or psychological) that cause similar symptoms and whether your hallucinations are solely visual. In short; if the person has experienced significant sight loss, does not experience hallucinations that impact the other senses, is aware that the hallucinations are not real, and has not displayed signs of any other health condition that is known to cause hallucinations, then a diagnosis of CBS is very likely.

Treatments for / management of Charles Bonnet Syndrome:

Research into the treatment / management of CBS is ongoing (see the ‘Further information and Support’ section below). There is currently no known cure for CBS but the hallucinations do tend to diminish over time, becoming less frequent and often fading away entirely. If you are finding the hallucinations too overwhelming and upsetting, it is advised to discuss this with your GP who can refer you for Talking Therapy to help manage the situation better

There are some methods for managing CBS and which will perhaps help the recovery process.  Some ways you can stop hallucinations (or reduce their intensity / duration) are:

  • Turn on the lights or move somewhere lighter if you have a hallucination when it’s dark
  • Turn off the lights or move somewhere dark if it’s light when you have the hallucination
  • Move your eyes from left to right 15 to 30 times without moving your head, thereafter pause and repeat the same process a few times
  • Stand up and move around if you are not already doing so
  • Watch TV or listen to the radio
  • Any change of activity or distraction that you find helpful (either of these can remove the hallucination or at least the distress that is associated with it)
  • Reach out to touch the hallucination
  • Familiarise yourself with your surroundings and apply rehabilitation / mobility training to reduce the inconveniences caused by the hallucinations

Hallucinations might be worse and more likely to occur if you are tired or have low energy so making sure you are sleeping and resting sufficiently is essential. Hallucinations may also get worse if you have been feeling anxious, isolated, or stressed. You can talk to your GP about these issues if you are struggling to manage them alone (as many people do). As well as talking to one of our Sight Loss Advisors there are various services and sight loss organisations like the RNIB who provide helplines and befriending programmes which can also lend support. Some medications can worsen the hallucinations. These may include specific types of eye drops as well as medication for other non-eye related issues (e.g. Anticholinergics). In such cases alternative medication should be discussed with your GP.

Also making the most of any remaining vision may reduce the frequency of hallucinations. Some ways this can be achieved include using bright light bulbs at home and using a magnifying device for visual tasks. Also by getting regular eye tests, an optician can check for further changes in your eyes and provide advice on how to make the best use of your remaining sight.  A GP, optician, or ophthalmologist (eye doctor) can also refer you to a specialist low vision clinic for advice about specialist equipment that can help with your sight. Our Sight Loss Advisors  can refer you to the University West of England Low Vision Clinic in Bristol, where you will receive advice but not free equipment to loan.

Another treatment / management method currently undergoing research is non-invasive medical stimulation of the visual cortex of the brain. More specifically, Transcranial Direct Current Stimulation (TDCS). The Association of Optometrists reports a recent study funded by the Macular Society and conducted by Newcastle University and Kings College London, in which this treatment was tested. A weak electric current is passed between electrodes placed on the participants’ scalp. The 16 participants were all CBS patients and underwent 4 days of active and placebo TDCS treatment. It was concluded that this treatment could reduce the frequency of hallucinations, particularly in those with increased activity in the visual parts of their brain. No significant side effects of the treatment were identified.

Prevention risk factors:

Any universal methods of sustaining good eye health and vision are relevant for prevention (See ‘Further information and support’ section of this page). Prevention methods and risk factors for  Macular Degeneration and Cataracts (discussed in the relevant pages of our knowledge hub) are also important to consider and act upon, seeing as the likelihood of developing CBS is higher if you already have either of these conditions.

If hallucinations stop, it is possible for them to return if you lose further sight. There are also many cases of hallucinations returning for those people that develop an infection (e.g. chest infection or urinary tract infection). If you have medical history of such infections occurring regularly or if you develop such infections after being diagnosed with CBS, it is even more crucial to act upon all medical advice and guidance that has been provided for treating or managing them.

Further information and Support:

Charles Bonnet syndrome RNIB:

Charles Bonnet syndrome, Esme’s umbrella:

Charles Bonnet syndrome, macular Society: