Q: I have an 87-year-old patient with hand motion vision from diabetes. She says she sees specific images of animals and crowds of people. She describes them very vividly. Is she delusional, or is there an organic basis for this problem?

A: “This sounds like a classic case of Charles Bonnet syndrome, or CBS,” says Steven Ferrucci, O.D., chief of optometry at the Sepulveda VA Ambulatory Care Center in North Hills, Calif., and associate professor at Southern California College of Optometry. “CBS is defined as consistent or periodic complex visual hallucinations that occur in visually-impaired individuals with intact cognitive ability and no evidence of psychiatric disorders or neurologic lesions/abnormalities.” The syndrome is named after Charles Bonnet, the Swiss philosopher who first identified it.
“Classically, patients describe their hallucinations as distinct, very well-formed images, such as animals or people’s faces,” Dr. Ferrucci says. “Oddly enough, the faces are often of people unfamiliar to the patient, and are in very clear detail, much better than their level of vision would allow.”

Studies show that the syndrome can occur in as many as 10% to 40% of patients with visual impairment.1 But, it is largely under-reported because many patients are hesitant to disclose that they are having hallucinations. “They fear that they will be assumed to be crazy or suffering from dementia,” Dr. Ferrucci says.

The exact reason for these hallucinations is still uncertain, but the main theories have to do with spontaneous stimulation of neuronal activity in place of the sensory stimuli from the now-impaired optic nerve impulses.

That’s not so easy to explain to the patient. “Although it’s probably not 100% accurate, I explain the phenomenon to patients as akin to the ‘phantom limb’ that they may be familiar with. That is, when a patient loses a limb from trauma, for example, he sometimes states he can still feel his missing extremity, even though he knows it’s not there,” Dr. Ferrucci says. “With CBS, even though patients cannot see, the nerves in their eyes are tricking them into thinking they can still see—in the form of complex hallucinations.”

CBS is more common in elderly women, likely in the age range of about 75 to 84 years. Visual acuity typically ranges from 20/40 to 20/1600, with increased risk within 20/300 to 20/800.1 Age-related macular degeneration has been reported as the most common ocular disease associated with CBS. However, any ocular disease that results in decreased VA can cause CBS, including cataract, glaucoma, retinitis pigmentosa, retinal detachment and diabetic retinopathy.1

Hallucinations may last from one minute to one hour, with the majority lasting very briefly.

As the patient becomes accustomed to the vision loss, the frequency of hallucination tends to decrease after about a year or 18 months. “This is often comforting to the patient to learn that it is not likely permanent,” Dr. Ferrucci says.

Charles Bonnet syndrome is a diagnosis of exclusion, so a patient should have an MRI as well as a psychiatric consult to rule out neurologic lesions and any evidence of dementia or mental health problems. “However in my experience, these steps are rarely needed if the clinical presentation seems obvious,” he says. “Often, these patients just need reassurance that they are not going crazy, and that these types of hallucinations are relatively common in patients with vision loss.” Anti-psychotics and similar mediations may be helpful, but are rarely needed.

“The best treatment is to improve vision if possible, decrease glare and increase peripheral field using spectacles or low vision devices,” Dr. Ferrucci says. “A low vision referral may be helpful in many cases.”

1. Yacoub R, Ferrucci S. Charles Bonnet syndrome. Optometry. 2011 Jul;82(7):421-7.