New study confirms prevalence of visual hallucinations in sight loss

Hallucination of fish

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.

The study by the Canadian National Institute for the Blind, was one of the largest of its kind. It looked at 2,565 patients across the three major eye diseases, age-related macular degeneration (AMD), diabetic retinopathy and glaucoma.

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.

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.”

Up to half of all people with macular degeneration are thought to experience visual hallucinations at some time. They are more likely to occur if both eyes are affected by sight loss. Hallucinations can be simple unformed flashes of light, colours or shapes. However, many people see geometrical grids and lattices. Some people also report seeing landscaped gardens or vistas, animals, people, or other vivid images.

The Bayer Health Care-funded study also found that patients with greater levels of vision loss had a higher chance of experiencing CBS.

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

The full study was published in the Canadian Journal of Ophthalmology this month.