Charles Bonnet Syndrome

Charles Bonnet was an 18th Century Swiss naturalist and philosopher. His 87-year-old grandfather came to him with some unusual complaints. The elderly man was becoming nearly blind from cataracts in his eyes. However, he reported that he had begun to see men, women, birds, carriages, buildings, and complex tapestries and scaffolding patterns around him. He was still entirely sound of mind, and he knew the apparitions were not real.  Nonetheless, he was baffled by how vivid and compelling the visions were. Charles Bonnet found it inexplicable that a man could have such visions yet not be mad. He suspected that failing vision must have caused his grandfather’s otherwise normal brain to act in an unusual way.  In 1760, he devoted several pages to it in his book, Analytical Essay on the Faculties of the Soul.  This phenomenon of mentally healthy individuals seeing things in the midst of losing their vision has come to be known as Charles Bonnet Syndrome.

Charles Bonnet Syndrome has been found to accompany a variety of diseases or injuries to the eyes, including cataract, macular degeneration, clouding of the corneas, glaucoma, retinal detachment, and other ailments that rob an individual of their sight. Disturbances of the neural pathways that carry visual information from the eyes to the brain can also cause the syndrome. In some cases, the syndrome arises after damage to areas of the brain that process visual information, such as might occur from a stroke or head injury. The neurological processes that underlie Charles Bonnet Syndrome are not entirely understood. However, it is suspected that when the visual centers of the brain are deprived of input from the eyes, they can begin to fire somewhat randomly. The higher centers of consciousness in the brain then try their best to make sense of the abnormal input, and turn it into what it is familiar with, that is fully formed objects, patterns, and people.

Charles Bonnet Syndrome is fundamentally a neurological and ophthalmological condition. However, because sufferers report hallucinations, they are often first seen by a psychiatrist.  I recall a patient, a woman in her early 90’s, whose family brought her to my office after she began to report seeing visions of people outside of her home. They feared she was demented or going insane. However, she remained well aware that these visions of people were a product of her own mind. She was neither demented nor psychotic. Rather, her vision was becoming impaired due to an increasingly poor blood supply to the visual processing centers in the back of her brain and she was experiencing Charles Bonnet Syndrome. Indeed, her cognitive function remained well preserved throughout the time I saw her. She visited my office every two weeks and was able to repeat in fine detail what we had discussed in the previous session. She was always fully oriented to time and place and was well-versed in current events. She had a wonderful sense of humor, and I found her to be very pleasant company. Aside from providing some comfort in explaining to her and her family the reason that she was experiencing the hallucinations, there was really little else I had to offer her. I eventually discharged her from my care. I learned that she remained stable until a few months later, when other medical problems arose. Those problems sapped her vitality and led to her death.

Another patient, a 90-year-old woman, was brought to my office by her family after she had begun to complain of seeing “little people” in her living room. Seeing such “little people” is a not uncommon complaint in Charles Bonnet Syndrome. It can also occur in certain other neurological disorders. This phenomenon is common enough for clinicians to have given it a name, lilliputian hallucinations.  It derives from the little people that populated the fanciful land of Lilliput in Jonathon Swift’s book, Gulliver’s Travels. In speaking with her, she appeared quite certain that the little people she saw were not real. Moreover, she suspected that her mind was playing tricks on her, and that it had something to do with her failing vision. Again, the diagnosis was not psychosis, as the family had feared, but rather Charles Bonnet Syndrome.

Charles Bonnet Syndrome is not a psychiatric illness or symptom of dementia, but it tends to occur in the elderly who are vulnerable to developing other ailments, including forms of dementia. Over time, the memory and cognitive function of the 90-year old woman began to fail. She became increasingly confused and disoriented to time and place. She lost certainty about the nature of her visions, then started to believe that they were real. She began to spray the little men in her living room with an aerosol can of insecticide. She denied being afraid of them. Rather, she insisted she was simply annoyed at them for sitting in her house but refusing to answer when she asked why they were there.  She felt they were being intolerably rude. It was clear that she was developing dementia along with the Charles Bonnet syndrome she had at first exhibited. Every case is different, regardless of the condition. Nothing is simple.

Although Charles Bonnet Syndrome is usually considered in the context of visual hallucinations, auditory hallucinations can occur for similar reasons. That is, hearing loss can cause a person’s brain to compensate for the loss of auditory input and seemingly create its own sounds. These are not mere random buzzes or ringing in the ears as in common tinnitus. Like the full and florid visual hallucinations in the more commonly experienced form of Charles Bonnet Syndrome, these hallucinations are often complex and fully formed. Moreover, unlike the sounds suffered in tinnitus, they seem to be coming from the environment. This condition is sometimes referred to as Auditory Charles Bonnet Syndrome, but also Musical Ear Syndrome or Musical Hallucinosis. I have had two such cases in elderly patients. One patient had had significant hearing loss over the previous several years of time. One day while riding a bus, she “heard” the distant sound of a symphony orchestra. She first assumed it was a radio. But she heard it several more times over the following weeks. Although she knew her “ears” were playing tricks on her, she found it a delightful experience.  Indeed, what she heard were Beethoven symphonies, some of her favorites. Another patient was not so content with the symptoms. After years of increasing hearing loss, she began to hear choruses of air-raid sirens in the quiet of the night, often playing in strange harmonies. Although my explanation satisfied her intellectually, she continued to suffer from them.

In rare cases, patients with loss of sense of smell may report smelling unusual odors that they know have no basis in reality.  In a mechanism similar to that of Charles Bonnet Syndrome and Musical Hallucinosis, the brain generates its own odors to compensate for a loss of olfactory input.  The resulting hallucinations of odor are referred to as phantosmias, or “phantom smells.” Curiously, patients with Charles Bonnet Syndrome have occasionally reported visual hallucinations that spill over into smell—such as seeing miniature people who also have a specific scent of “spice” or “incense.”

Finally, there is a phenomenon related in mechanism to the Charles Bonnet Syndrome that involves loss of familiar sensations from parts of the body. This is the so-called “phantom limb” that can be experienced after the loss of an arm, leg, or other body appendage. Phantom limbs have been described since ancient times and a variety of explanations, some supernatural, have been offered in attempts to understand it. Until recent times, the predominant scientific explanation was that damaged nerve endings in the stump of lost limb continued to send signals into the nervous system that the brain interpreted as the limb still being there. However, studies of individuals with phantom limbs showed that the phenomenon was more complicated. For example, whereas an irritated stump might explain perceptions of the limb still being there, it could not explain that some individuals felt not only the limb to still be present, but also felt the presence of a long-worn ring on the finger or the feeling of still holding a habitually used cane. It is now known that, like the visual hallucinations of Charles Bonnet Syndrome, the phantom limb arises from a brain trying to make sense out of the loss of stimulation to which it had become accustomed.