More on Charles Bonnet Syndrome

Chuck Bonnet and the Hallucinations


In the year 1760, a Swiss naturalist named Charles Bonnet became concerned when his grandfather Charles Lullin began to experience a parade of “amusing and magical visions.” The eighty-nine-year-old Lullin was being visited by visions of people, birds, carriages, and buildings, all of which were invisible to everyone but him. Apparently these mysterious objects materialized spontaneously among the few bits of the world he was still able to perceive through his cataracts.

Bonnet’s grandfather did not demonstrate any other signs of marble loss, in fact he seemed quite sane aside from the vivid hallucinations. Moreover, the elderly man was keenly aware that the strange sights were all in his mind. Bonnet cataloged his grandfather’s curious circumstances, and over time the condition he described came to be known as Charles Bonnet Syndrome, or CBS. Numerous similar cases have been recorded in the decades since, and though it has long been regarded as a rare disease, recent evidence suggests that it is much more widespread than previously believed.

For those stricken with Charles Bonnet Syndrome, the world is occasionally adorned with vivid yet unreal images. Some see surfaces covered in non-existent patterns such as brickwork or tiles, while others see phantom objects in astonishing detail, including people, animals, buildings, or whatever else their minds may conjure. These images linger for as little as several seconds or for as much as several hours, appearing and vanishing abruptly. They may consist of commonplace items such as bottles or hats, or brain-bending nonsense such as dancing children with giant flowers for heads.

Most of those afflicted with Charles Bonnet Syndrome are people in the early stages of sight loss, and the hallucinations usually begin while their vision is still present but slowly diminishing. The most common culprit is macular degeneration, a disease where certain light-sensing cells in the retina malfunction and cause a slowly worsening blind spot in the center of one’s vision. Other eye diseases such as glaucoma and cataracts can cause the symptoms as well, and in a few rare cases it has been diagnosed in people without any detectable vision problems whatsoever. The likelihood of Bonnet visions also seems to increase in people who have limited social interaction, such as people who live alone.

Even people with damaged sight are often startled by the clarity of these hallucinations. The condition does not cause a series of vague, floating images; the visions are highly detailed, and quite often they will conform to their surroundings. A nonexistent man might sit down and relax in a real-life recliner, or a convoy of poached eggs may drape themselves on a legitimate mantelpiece. Sometimes a significant segment of reality is altered– such as staircase which becomes a steep mountain slope or a room which morphs in size and shape– making the world difficult to navigate. Real objects can even vanish for periods of time, leaving little or no evidence of their prior presence.

How a Bonnet vision might appear to someone with glaucomaHow a Bonnet vision might appear to someone with glaucomaA significant percentage of patients also describe floating, disembodied faces that squirm into their field of vision at random times. These often have wide, unblinking eyes; prominent teeth; and features reminiscent of a stone gargoyle.

Images of people are a common occurrence, though familiar faces are seldom seen. Most of the apparitions are strangers, although there are many reports of grieving people seeing their deceased loved ones during such hallucination episodes. These phantom people normally wear pleasant expressions on their faces as they loiter in eerie silence, and they make frequent eye contact with the viewer. Curiously, a great number of these imaginary characters are described as wearing hats, sometimes along with elaborate costumes.

Although these strikingly realistic images are usually non-threatening, they cannot be easily banished. Often variations of the same images appear repeatedly, but the items are seldom anything with any particular emotional meaning. In fact, they are frequently mundane items such as trucks or trees, though there are reports of dramatic scenes involving such things as funeral processions and dragons. The subjects of these visions are sometimes life-sized, but it is not uncommon for the hallucinations to appear in miniature, an effect called “lilliput hallucinations,” named after the small Lilliputian people from Gulliver’s Travels. Less frequently, visions will appear larger-than-life.

Although a Charles-Bonneter realizes at a rational level that the hallucinations are manufactured by the mind, it is nonetheless troubling to wake up to a room full of strangers, or to see vivid faces staring out of the shrubbery. It can also be disconcerting when visions of ordinary objects appear in ordinary places– such as a bottle on a table or a truck on the street– making fiction more difficult to separate from reality. In one case, a woman pointed out to her maid how cruel it was for her neighbor to leave the cows at pasture in the bitter winter cold, and she was embarrassed to learn that her maid could see no cows.

Some CBS visions are so outlandish that the viewers describe a moment of astonishment as they bid a premature farewell to their sanity. One woman was visited by several tiny chimney sweeps in stovepipe hats that paraded around her home, and another man spoke of a gaggle of monkeys in blue coats and red hats frolicking in his front yard day after day. Given the basic human tendency to trust one’s senses, these hallucinations can stir up lively struggles between emotion and reason. In an ironic demonstration of their intact rationality, many people afflicted with CBS choose not to report these strange visions for fear of having their sanity cast in doubt. In contrast, people with psychosis tend to immerse themselves in elaborate fictions to explain their hallucinations, and seldom question their own mental health.

The construction of the human eyeThe construction of the human eyeThe exact cause of Charles Bonnet Syndrome is not presently known, but the popular theory suggests that the brain is merely attempting to compensate for a shortage of visual stimuli. Consider that each human eye normally receives data at a rate of about 8.75 megabits per second, a bandwidth which is significantly greater than most high-speed Internet connections. The visual cortex is the most massive system in the human brain, and it is packed with pathways which manipulate the rush of visual data before handing it over to the conscious mind. When disease begins to kink this firehose of information, a legion of neurons are left standing idle.

It is worth noting that the human brain already has significant talent in dealing with partial blindness. Every human eye has a blind spot where the optic nerve passes through the retina, and the visual cortex automatically fills in these blind spots by extrapolating what should be there based on the surrounding detail. Since a person’s two blind spots do not overlap, the brain can also cross-reference the eye data when both eyes are active. In gradual-onset blindness, it is possible that these brain pathways attempt to fill in the new obscured areas. Since the eyes are sending reduced amounts of data with a greater frequency of errors, the visual cortex may produce more and more outlandish guesses.

You can indirectly perceive your own blind spot by using the image below. Simply sit close to your screen with your right eye covered, and focus on the word “Interesting.” Maintain that focus while slowly moving away from the screen, and at a particular distance the logo will disappear although the blue lines and the word “Damn” will still be visible. If you change your gaze, the logo will no longer be in the blind spot, and it will reappear.


Some have suggested that Bonnet visions are the product of the same mechanisms that generate dreams. Clearly the mind is starved of visual input during sleeping periods, so it stands to reason that both dreams and CBS hallucinations may be the result of the same thing: the visual cortex becomes bored due to lack of stimulation, and gratifies itself using stored imagery. This notion is further supported by sensory deprivation experiments, where subjects experience hallucinations when placed in complete darkness for long periods of time. But the explanation fits the problem imperfectly, because dreams include sound and sensations, whereas Bonnet-visions are confined to sight.

In cases where patients see gargoyle-like floating faces, it is likely that the lateral occipital region of the brain is contributing. That chunk of the visual cortex participates in plucking human faces out the river of incoming visual data, and it is the same wad of neurons that is tickled by any pattern that vaguely resembles a face, such as the front of a car. When this region becomes starved for input, it is quite possible that its lowers its standards considerably, and reveals faces that do not exist.

Formal studies have found that Charles Bonnet Syndrome has a higher rate of occurrence in those with higher education and those with creative leanings, a finding which suggests that the concept-association skills inherent in creativity and intelligence may be playing a role. The whole condition is also reminiscent of phantom limb syndrome, where people with missing limbs experience sensations as though the body parts are still present.

Of course there are some who believe that these bizarre Charles Bonnet visions have nothing to do with attention-starved brain cells, but rather they are real images from some alternate reality that is parallel to our own. The theory suggests that people cannot normally perceive these parallel realities because they are drowning in a flood of visual data from our own world. It is implied– though not stated outright– that these parallel realities must be strange places where people sometimes have flowers instead of heads, and preposterous guesses instead of evidence.

Visualizing the visual cortexVisualizing the visual cortexOne of the most thorough studies of the phenomenon was undertaken at the University Hospital in Nijmegen, the Netherlands, where 505 visually handicapped patients were involved. Of those, it was found that sixty-three had experienced complex visual hallucinations in the four-week period before screening. Psychiatric examination of the patients revealed no other disorders which might cause such side effects. This and other studies suggest that as many as 15% of people with vision loss experience Charles Bonnet Syndrome hallucinations to some degree. It is even rumored that Charles Bonnet himself followed in his grandfather’s footsteps, witnessing his own set of inexplicable visions when his eyes began to fail him later in life.

Given the high rate of Bonnet-visions among patients in these studies, it seems that it is not so rare as it was once thought. The small number of reported cases is probably due to the sufferers’ universal reluctance to describe their experiences; most of those afflicted with CBS will not speak of the hallucinations at all unless they are asked directly. One of the most effective treatments is to simply inform the patient that these visions are not a reflection on their mental well-being. This may not prevent future hallucinations, but in many cases it will greatly reduce the related anxiety.

Some Charles-Bonneters are able to banish their phantoms by changing the environment in some way– such as turning the lights on or off– though most of the time a patient is subject to their visions’ whims. Others have resorted to befriending the apparitions, making idle one-sided conversation as the imaginary guests stare quietly. Fortunately the condition is almost always temporary, and in most cases the visiting visions fade away forever after twelve to eighteen months.

Human perception is patently imperfect, so even a normal brain must fabricate a fair amount of data to provide a complete sense of our surroundings. We humans are lucky that we have these fancy brains to chew up the fibrous chunks of reality and regurgitate it into a nice, mushy paste which our conscious minds can digest. But whenever one of us notices something that doesn’t exist, or fails to notice something that does exist, our personal version of the world is nudged a little bit further from reality. It makes one wonder how much of reality we all have in common, and how much is all in our minds

Further reading:
Details on Charles Bonnet Syndrome and related studies
Macular Degeneration
Information on the human blind spot

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