A 93-YEAR-OLD Caucasian female was referred by her ophthalmologist to our University’s low vision clinic for complaints of bright sunlight glare and an inability to read her Bible and watch TV. Her medical history was positive for a history of congestive heart disease, hypertension, hyperthyroidism, gastro esophageal reflux disease, anemia, osteoarthritis, osteoporosis, anxiety disorder, dry AMD OU and dry eye disease OU. She did not have a history of neurological or psychiatric issues.

Upon inquiry about whether she experienced any visual hallucinations, the patient reported seeing beads, crisscross patterns and fern leaves when looking at a blank wall any time during the day. She said she was initially disturbed by the visual hallucinations, but now felt indifferent about them. (Given the high prevalence of visual hallucinations in people who have impaired vision, I ask every patient this question during his or her initial low vision evaluation.)

The patient’s BCVA was 20/60 OU. Confrontation fields, extraocular motilities and pupils were unremarkable. Goldmann applanation tonometry revealed 16mmHg OD and 15mmHg OS at 2:59 p.m. Dilated fundus examination showed posterior chamber intraocular lenses, geographic atrophy in the maculas and distinct optic nerve margins with temporal peripapillary atrophy — all OU.

Were these patient’s visual hallucinations due to an undiagnosed mental illness or Charles Bonnet Syndrome (CBS), also known as “phantom vision?” Here, I discuss CBS to help you decide.


Charles Bonnet was the first person to describe and publish about visual hallucinations associated with eye disease in 1760. His grandfather had undergone bilateral cataract surgery, yet his vision continued to decline with time, and he experienced visual hallucinations as his vision deteriorated. The term “Charles Bonnet Syndrome” was coined in 1967 by Swiss scientist George De Morsier, who conducted research regarding visual hallucinations.

CBS occurs as a result of damage along the visual pathway. Deafferentation theory (sensory deprivation theory) is the most commonly accepted reason for CBS, although its true etiology remains unknown. Specifically, when sensory visual input into the brain is removed from ocular pathology or there is damage along the visual pathway, spontaneous neuronal signals in the brain’s visual association cortex occur, increasing its excitability and, thus, creating a perception of visual hallucinations.

The type of hallucinations correspond well to specific brain locations. This has been documented by functional MRI studies. For example, the left middle fusiform gyrus is activated when patients see visual hallucinations of faces, and the collateral sulcus is activated when patients see textures, such as bricks, fences and maps.

The patient reported seeing crisscross patterns.

A total of 38 million Americans age 40 and older have blindness, low vision or an age-related eye disease, according to Prevent Blindness America. Studies reveal that the prevalence of CBS is upwards of 30% in individuals who have ocular disease. Although the condition tends to affect older adults, because of the incidence of age-related eye disease, keep in mind that it can affect people of all ages who suffer from vision loss.


Visual hallucinations last seconds to a few hours, with recurrence for years. Generally, CBS patients remain neutral about the hallucinations, probably because of a decreased frequency and duration through time. Patients are often relieved to learn that CBS is commonly associated with their ocular pathology, as opposed to mental illness or dementia. Even though these patients have impaired vision, the visual hallucinations are clearer and in better detail than their existing vision.

CBS is often categorized as simple or complex in nature:


  • Grid-like patterns
  • Photopsias
  • Shapes


  • Animals
  • Flowers
  • People
  • Plants


CBS is a diagnosis of exclusion. This means other etiologies that cause visual hallucinations, such as migraine auras-caused photopsias, vitreal conditions and retinal conditions, must be ruled out to make this diagnosis. In addition, we must refer these patients to their primary care physicians in order to dismiss pharmacologic side effects, illicit drug use, neurologic, psychiatric and metabolic etiologies, as well as miscellaneous conditions, such as transitional state between waking and sleeping, excessive fatigue, prolonged social isolation, food, water and sleep deprivation and narcolepsy-cataplexy syndrome, that may cause visual hallucinations. CBS patients have intact cognition, insight that the visual hallucinations are not real and absence of other psychological conditions.

Of course, a major roadblock to diagnosing CBS is a reluctance on these patients’ parts to report hallucinations for fear of not being taken seriously or of being labeled mentally unstable by their relatives, friends and health care providers. The best way to overcome this roadblock is to say to your low vision patients:

“Many patients who have low vision experience visual hallucinations, which is the brain’s way of making up for the lack of vision. If it is due to Charles Bonnet Syndrome, it has nothing to do with mental illness. If you’ve been seeing anything out of the ordinary, I’d like to try to optimize your vision to minimize and, hopefully, rid you of this common occurrence.”

With regard to optimizing the CBS patient’s remaining vision, investigate stronger prescription spectacles, contact lenses, optical aids and/or low vision rehabilitation. The idea is that doing so provides the sharpest images possible to the brain, discouraging it from delivering hallucinations. You may also want to investigate referring the patient for surgical intervention. For example, cataract surgery has been shown to eliminate visual hallucinations in cataract patients.

The patient also reported seeing beads.


The patient mentioned above was prescribed special +5.00D reading spectacles for reading and near tasks, a 2x spectacle telescope for watching TV and seeing people’s faces and a 4% gray absorptive filter for reducing outdoor glare. She was counseled about the nature of visual hallucinations and its prevalence in people who have ocular pathologies. Further, she was advised to (1) have a medical evaluation by her primary care physician to rule out metabolic, neurologic and other potential etiologies, (2) cognitive testing to rule out psychological etiologies and (3) a medication review by a pharmacist to evaluate whether pharmacologic etiologies existed. The diagnosis was CBS.

At her last follow-up visit in August 2016, she reported infrequent hallucination episodes and not being bothered by them. In addition, she said she was happy to be able to read her Bible, watch TV at a more comfortable position on her sofa and see loved one’s faces again.

With patients aging and living longer lives, more individuals will be affected by age-related vision loss and, thus, experience CBS. OM