70 year old male with no significant medical history except for glaucoma who was functioning independently at baseline was brought in to the hospital by family as patient reported seeing “diminutive ninjas” inside his house. He was awake, alert and oriented and was able to carry a normal conversation. The patient was initially reluctant to describe his symptoms although sympathetic questioning revealed well organized and brilliantly clear, complex visual hallucinations, that were sharper than his usual vision. Prior occurrence of these symptoms had led him to realize they were not real although was frustrated by them. He was noted to have paranoid delusions that his wife may be involved with his hallucinations. MOCA testing revealed score of 21. Lab studies were normal. Eye exam revealed severe visual impairment secondary to the glaucoma. MRI of his brain revealed right occipital encephalomalacia that was related to an old infarct. Psychiatry was consulted and a diagnosis of Charles Bonnet syndrome was made although it was noted that this fixed delusion is fairly atypical.
Charles Bonnet syndrome (CBS) was first described in 1760 when he noticed his grandfather, who was blinded by cataracts, describing birds and buildings that Bonnet could not see. The prevalence of complex visual hallucinations in patients with visual impairment is estimated to be 11‐15%. They are usually transient and are often noted to occur among the educated. The prevalence of CBS is grossly underestimated to be between 1.84 and 3.5% in the geriatric population. Even though patients may not voluntarily disclose visual hallucinations, they tend to respond to leading questions about the same. The proposed hypothesis is that in visually impaired individuals, the visual cortex compensates with abnormally increased activity and conjures up hallucinations from random firing of nerve cells.
Although it is a diagnosis of exclusion, the syndrome is often under‐diagnosed in clinical practice due to patients’ reluctance to admit to hallucinations for fear of being labeled mentally unstable in addition to physicians’ lack of awareness of the diagnosis. Physicians need to screen older adults with visual impairment for this syndrome and also be able to provide high quality education as reassurance and explanation can have a powerful therapeutic effect. Improving the visual function and addressing social isolation are also helpful in improving quality of life.