Large Study Shows 1 in 5 People With Vision Loss Experience Hallucinations

A new study conducted by the Canadian National Institute for the Blind (CNIB) has found that one in five Canadians with vision loss who were surveyed experience visual hallucinations, known as Charles Bonnet Syndrome (CBS).
The study, titled “Prevalence of visual hallucinations in a national low vision client population”, published in the most recent issue of the Canadian Journal of Ophthalmology, is the largest and most comprehensive of its kind. It represents the first major study of CBS due to vision loss across all of the three most common eye diseases – age-related macular degeneration, diabetic retinopathy and glaucoma – with 2565 study respondents over 40 years of age who attended a CNIB low vision clinic.
“Many doctors believe that this phenomenon is very rare, however this study shows that it’s actually quite prevalent,” said Dr. Keith Gordon, study author and Vice-President of Research at CNIB. “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. With these findings, we are now able to shed more light on CBS and help raise awareness within the medical community and the general public about how prevalent it actually is.”
Widely considered quite rare among the medical community, the study shows that in fact CBS is a common condition among people with serious vision loss, characterized by temporary visual hallucinations. CBS is not a mental illness, nor is it a symptom of dementia or any other disease. Rather, it is a condition specifically related to vision loss. Lack of awareness of this condition can cause confusion and concern among those experiencing and diagnosing it. While it is not yet known exactly what causes CBS, researchers are beginning to believe it is related to an attempt by the brain to fill in information that would normally be obtained from the eyes.
CBS hallucinations only affect sight, not hearing, smell or touch. The hallucinations may seem “real” (like seeing cows in a field when the field is actually empty) or “surreal” (like seeing dragons). Most frequently, people will see patterns or simple shapes, however there are many accounts of more complex hallucinations, such as the following examples:
• Little men holding umbrellas at the end of the bed
• Women in red dresses sweeping the floor
• Cloakroom tickets lining the walls and ceiling
• Soldiers marching down the street
The CNIB study also showed:
• There was no higher probability of hallucinations between any of the three major eye diseases (age-related macular degeneration, diabetic retinopathy and glaucoma)
• Respondents who experienced greater levels of vision loss had higher chances of experiencing hallucinations
• Although vision loss occurs more frequently in older people, the risk of developing CBS does not increase as people age.
Participants in the study were asked if they saw patterns, shapes, people or animals that they knew were not actually there. Responses were cross-tabulated on the basis of age, sex, eye disease, and visual acuity. CNIB acknowledges funding support from Bayer Health Care for the “Prevalence of visual hallucinations in a national low vision client population” study.
For an audio/visual presentation about Charles Bonnet syndrome, visit