Low-vision patients should be warned of Charles Bonnet syndrome Patients with low vision are more likely to experience visual hallucinations or phantom vision, the hallmark signs of Charles Bonnet syndrome, according to a study.

In 258 subjects with low vision and 251 matched controls with little or no vision loss, Charles Bonnet syndrome was diagnosed in 87 low-vision subjects (34%), but in only four control subjects (1.6%). Charles Bonnet syndrome occurred in patients with various visual acuities, but patients with visual acuity between 20/301 and 20/800 were twice as likely to have the visual disturbances.

Age-related macular degeneration was the most common cause of low vision, but there was not a statistically significant difference in prevalence according to the cause of low vision.

Patients described having episodes between one and 30 times a month, with an average of 10 episodes, but only eight of 87 subjects (9%) reported seeking medical advice. Of those seeking a medical opinion, only half said they were given an explanation for their symptoms. Episodes were reported to occur most frequently between 6 a.m. and noon and between 6 p.m. and midnight.

"The results of the present study show that no treatment is necessary, but it is imperative that ophthalmologists and their staff explain the nature of [Charles Bonnet syndrome] to patients and offer reassurance that this is a common phenomenon," the study authors said.

WHAT IT MEANS TO YOU: This study reminds us how common Charles Bonnet syndrome is, affecting one-third of all low vision patients. It is disappointing that only half of those seeking medical advice where given an explanation for their symptoms. This suggests that many eye doctors are unfamiliar with the condition. All clinicians that care for low vision patients should be aware of how common Charles Bonnet syndrome is, and be better equipped to discuss it with their patients.

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Can J Ophthalmol. 2009;44(1):49-52