There are so many weird illnesses and disorders out there — it’s one of the reason I love the study of medicine. If we’re lucky, we’ll get a glimpse at some of the stranger illnesses out there and then we’ll be able to use that experience to diagnose a patient with a rare condition.

Isn’t it wonderful when you are the one to diagnose a patient with something that every other provider has missed?!

I was leafing through a recent sleep medicine journal when I came upon an article about a patient with complex nocturnal visual hallucinations. In itself, the article sounded like something I would want to write about.

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When I dug a little further, I realized that the article was about Charles Bonnet syndrome (CBS). I remembered that I had heard briefly about CBS when I watched a clip from a TED talk by the renowned neurologist Oliver Sacks.

Charles Bonnet was a Swiss philosopher whose grandfather developed visual hallucinations when he lost his eyesight. CBS is seen in patients with macular degeneration, cataracts, diabetic retinopathy, and blindness. Visual hallucinations are the only things that occur, because no other senses are involved. Patients with CBS do not a mental illness or cognition problems and are very aware that they are seeing images that are not there.

The visual hallucinations that CBS patients experience differ from psychotic hallucinations. In psychotic hallucinations, patients are involved in the hallucinations. In CBS-induced hallucinations, patients simply see things, like watching a movie. They are not involved with the hallucination. Patients with CBS are usually, but not always, unafraid of what they see.

An interesting feature of this syndrome is that patients often have Lilliputian visions. In other words, they see characters or objects that are smaller than normal. They may see a person that is no bigger than their finger. One of the more common hallucinations in CBS is cartoon characters or characters with deformed faces. A lot of color may be involved. Patients with CBS also often see visions of people and places of bygone eras; researchers cannot explain why this occurs.

It is estimated that one million patients have CBS. Many patients do not report the visual hallucinations caused by CBS because they are afraid that they will be labeled insane or institutionalized. Because of this, the exact number of patients affected with CBS may be under reported. This is unfortunate because CBS can often be treated.

In many cases, the disorder resolves within 18 months — although many patients can have the syndrome for years. Behavioral therapy is often helpful. Surgical treatment, such as cataract removal, can cure the problem in some cases. Psychosocial support is essential — educating patients and assuring them that they are not mentally unstable is very important.

So, the next time a patient tells you he or she is seeing things that are not there, don’t automatically assume that the patient has a mental problem. If he or she is having visual problems, be sure to ask about hallucinations. Then, dig a little further to figure out if this could be CBS. You may be the key to a correct diagnosis!

Sharon M. O’Brien, MPAS, PA-C, is a practicing clinician with an interest is helping patients understand the importance of sleep hygiene and the impact of sleep on health.


  1. Lipford MC, Sandness DJ, St. Louis EK. J Clin Sleep Med 2015;11(4):491–493