Main

Sir,

Formed visual hallucinations in patients with normal cognition and insight (Charles Bonnet Syndrome (CBS)) have been reported after certain ophthalmic procedures, including macular laser photocoagulation1 and macular translocation.2 It is important for clinicians to recognise this condition as it is frequently misdiagnosed3 and the symptoms may bother some patients.4 We report a patient who developed formed visual hallucinations following bilateral laser peripheral iridotomies for angle-closure glaucoma.

Case report

A 90-year-old Chinese woman presented with blurring of vision secondary to bilateral nuclear sclerotic cataracts and chronic angle-closure glaucoma. Her best-corrected visual acuity was 6/18 in the right eye and hand motion in the left, and she had a left relative afferent pupillary defect. The intraocular pressures (IOP) were 21 mmHg on the right and 70 mmHg on the left. Gonioscopy disclosed closed angles in two quadrants in the right eye and in all quadrants in the left eye. Fundus examination revealed cup : disc ratios of 0.8 in the right eye and 0.95 in the left. The IOP was successfully controlled medically and sequential argon-Nd:YAG laser peripheral iridotomy (PI) was performed in both eyes.

Soon after the laser PI, the patient developed complex, formed visual hallucinations, which occurred several times a day and lasted between a few minutes and an hour each. These hallucinations persisted for 2 years of follow-up. The hallucinations were constant and stereotypical. Most commonly, she ‘saw’ several children running around and playing. They sometimes reached for her food, but they never spoke to her nor made any noises. At other times, she saw Indian workers or a corpse in her house. These hallucinations were clearer than the blurry images of real objects, of normal size and color, and fitted into the surroundings naturally. They occurred most commonly in the afternoons when the patient was either eating or watching television. Although she could sometimes experience visual hallucinations when her eyelids were closed, she was fully awake and conscious when they occurred. There were no factors that triggered the appearance or disappearance of the hallucinations.

She was aware that these images were not real, retained full insight and cognition, and did not experience hallucinations in other modalities.

Comment

CBS is a condition in which patients experience complex, formed visual hallucinations, with retention of insight and in the absence of organic brain disease or psychiatric illnesses.3,5,6,7 Although the exact aetiology is still unknown, it is commonly associated with poor eyesight secondary to a variety of ocular conditions, including glaucoma, cataracts, diabetic retinopathy, optic atrophy, and age-related macular degeneration.8 Au Eong et al2 reported two cases of transient CBS which started soon after macular translocation, when the retina was deliberately detached and the vision poor. The hallucinations ceased after retinal reattachment and visual improvement. Their observation of a temporal association of the state of retinal attachment and/or acute change of vision with the onset and cessation of hallucinations strongly supports the ‘sensory deprivation’ theory of hallucination.

In all, 10 cases of CBS after macular photocoagulation for choroidal neovascularization were previously reported,1 while some patients have experienced a cessation of symptoms after laser therapy.9 To the best of our knowledge, this is the first report of CBS following laser PI. Although the patient's poor visual acuity had been present for some time, she only developed visual hallucinations after the laser PI was performed. While the exact mechanism is unclear, it is possible that anterior segment inflammation and corneal changes following the laser iridotomy could have further affected her vision and precipitated the onset of hallucinations in a patient who was already at risk of developing CBS.

These findings are significant as CBS is frequently not recognized or misdiagnosed.3 It is believed that the prevalence of CBS is higher than generally thought because some patients do not reveal their symptoms for fear of being labelled a psychiatric case.4 Patients are often relieved to hear that their hallucinations are part of a recognized syndrome and not the result of a mental disorder.10

It is important for clinicians to recognize that CBS is associated with many conditions that impair vision, and to realize that symptoms may occur following some ophthalmic procedures, so that they can make the correct diagnosis and counsel patients accordingly, thus allaying their fears and concerns.