Prevalence of severe vision loss hallucinations confirmed

Optometrists and ophthalmologists are being urged to broaden their understanding of Charles Bonnet Syndrome (CBS), after a major study has backed up how commonly patients with severe vision loss experience it.

With 2565 patients, the study – across the three major eye diseases, age-related macular degeneration (AMD), diabetic retinopathy and glaucoma – was one of the largest of its kind.

Author and Canadian National Institute for the Blind research vice-president, Dr Keith Gordon, said 19% of the vision clinic patients, all aged 40 or older, reported real or surreal hallucinations. The findings were published in the Canadian Journal of Ophthalmology this month.

Dr Gordon added: “Many doctors believe that this phenomenon is very rare, however, this study shows that it’s actually quite prevalent. People are afraid to tell their family, friends and even doctors that they’re experiencing hallucinations for fear of it being misunderstood as mental illness.”

Dr Gordon said CBS hallucinations are frequently simple, featuring patterns or shapes, but can also be complex. Patients experiencing CBS have reported seeing little men holding umbrellas, women in red dresses sweeping and soldiers marching.

One diabetic retinopathy patient, whose description was turned into a graphic representation (pictured), said: “After lunch when I sit in the living room I often see miniature people moving from the right to the left. They wear strange outfits like the Oompa Loompas from the Willy Wonka Chocolate factory film.”

Patients with greater levels of vision loss had a higher chance of experiencing CBS, the Bayer Health Care-funded study also found.

However, the cause of the vision loss and the age of the patient did not affect the likelihood of whether that person would hallucinate.

UK CBS expert and King’s College London senior psychiatry lecturer, Dr Dominic Ffytche, told OT that the study – which confirmed experts’ views on CBS prevalence – was a good opportunity for optometrists and doctors to familiarise themselves with the condition.

“There’s still a problem in getting the message through – 70% of patients aren’t aware that this might happen,” Dr Ffytche noted.

“We definitely need more knowledge, if only to support those that need help with this.”

He said the study found that, although many people are unconcerned by the hallucinations, one-third find them upsetting or distressing.

Dr Ffytche emphasised it was critical that optometrists know what symptoms fit a correct CBS diagnosis and what might point to another cause, such as dementia. CBS hallucinations affected sight but not hearing, smell or touch.

He advised optometrists who noted memory problems or confusion in a patient experiencing CBS should refer the person to their GP.

“Not all hallucinations are CBS. [Practitioners] need to know a little about alternatives so they don’t make the wrong diagnosis.”

Dr Ffytche explained that science was still exploring why some people experienced CBS and others did not. Experts have speculated that the hallucinations are attempts by the brain to fill in information that normally came from the eyes.

In the UK, CBS was thought to affect between 50,000 and 300,000 AMD patients, he said. For those whose symptoms did not ease with time or tricks like eye movements or switching light levels, some medications were available.