Introduction: The term Charles Bonnet syndrome (CBS) is used to describe visual hallucinations resulting from ocular pathology. As part of a larger case-control study we assessed factors which may predispose to this phenomenon in Age-related macular degeneration (AMD).
Methods: Three-hundred and sixty cases of late AMD underwent a detailed questionnaire about visual symptoms experienced. Potential ocular and environmental risk factors were compared in two groups; those experiencing symptoms of CBS (n = 97) and those not experiencing CBS symptoms (n = 263).
Results: Twenty-seven percent experienced CBS. Poor visual acuity was the only factor associated with the development of these images in AMD with an odds ratio of 3.50 (95% CI 1.64-7.48, p = 0.001) for those with best binocular visual acuity worse than 6/36. In those who experienced CBS, the images tended to be straight ahead (84.5%), colored (72.2%), have moving parts (62.9%), and occur on average once per day (34%). The most common visual image was of people (19.6%) followed by geometric patterns (15.8%). The majority (71.1%) felt the experience to be neither pleasant nor unpleasant. In 41% images were present throughout the course of their disease. There was no association between visual acuity and complexity of images.
Conclusion: The prevalence of CBS in late AMD is high, the main risk factor being poor better eye visual acuity. The most commonly experienced hallucinations were of people. Although most patients were unperturbed by the images, reassurance of their benign nature was welcomed. Practitioners should be aware that resolution of symptoms over time does not always occur.