Reproduced from "Health and Ageing" April 1998. © Dr Stephen J Doyle and Maggie Harrison
Visual hallucinations, not unlike dreams, have been shared by nearly every culture since antiquity. They have generally been associated with mental illness or hallucinogenic drugs or people such as sailors, polar explorers or prisoners who have spent a long time in isolated circumstances. They are, however, a common occurrence in people with impaired sight, particularly in the elderly, writes Dr. Stephen Doyle, Ophthalmologist at Manchester Royal Eye Hospital. Robert Teunisse, a psychiatrist at the University Hospital in Nijmegen, the Netherlands, tells in a recent article about a typical example. The elderly woman sitting in his office seemed sane enough, but the story she told was decidedly odd. About two and a half years earlier, she said, she'd begun having strange visions. The first time it happened, she was sitting quietly at home when she suddenly saw three or four two-inch-high, stovepipe-hat-wearing chimney sweeps parading in front of her, ladders in hand. "She was thinking, 'Well, I'm going crazy now,' " recalls Teunisse,. "But they didn't harm her, so she thought, 'What the heck, I'll try to catch me one.' But when she went near, they disappeared. So she knew it was some kind of optical trick." Her only medical problem of note was that she had poor sight due to macular degeneration.
The woman wasn't crazy. Unlike most mentally ill people who hallucinate, she was perfectly aware that the images she saw were not real. She had Charles Bonnet Syndrome, first described by this Swiss naturalist in 1760 on account of the visual hallucinations experienced by his grandfather. He described them as "amusing and magical visions, coexisting with reason". It is now defined as "a persistent recurrent visual hallucinatory phenomenon of a pleasant nature, with a clear state of consciousness, compelling, but seen by the patient as unreal. It is associated with ocular pathology, and tends to be remarkably crisp and detailed, and at times Lilliputian" It is characterised by complex hallucinations in people who are psychologically normal.
Why these hallucinations should occur is not known, but the best explanation so far is that of the "dual-input model". According to this paradigm, both external sensory input and internal memory input contribute to image formation and a sustained level of sensory input is required to inhibit the emergence of pre-formed images from within the brain. If sensory input falls below a given threshold, a release of previously recorded perceptions into awareness may occur. A similar sort of thing may happen with dreaming. Patients with Charles Bonnet Syndrome show distinct similarities in the images they perceive. To begin, the bulk of the hallucinations are pleasant, or at least non-threatening. Often they are quite familiar forms and seem to occur with limited external stimuli when the patient is less active. They are generally of short duration and tend to abate spontaneously, although in some people they may occur every day for months.
If one talks to elderly people with poor sight, it is surprising to find out how common this problem is. A recent study of 500 elderly people with poor sight found 12% to have these visual hallucinations. There are not usually mentioned by the sufferers for fear of being thought mad and being "taken off to a mental institution"
Maggie Harrison is a Patient Support Officer for Henshaw’s Society for the Blond, a registered charity providing a wide range of services across northern England and North Wales. Maggie is based at Manchester Royal Eye Hospital where she provides advice, information and support for patients and their families, often at the distressing time of diagnosis. She deals mainly with elderly people and has met a significant number of patients suffering visual hallucinations.
"People are sometimes truly frightened by what the experience", says Maggie. "They’re also afraid of being misunderstood and they’re confused by knowing the hallucinations are not real, yet feeling that they are. One woman kept seeing very large spiders crawling across her living room floor. Although she knew the spiders were not really there, she could not be certain about it and felt unable to invite her friends to the house".
Maggie has found that by introducing the subject of hallucinations into her conversations with patients, they are far more likely to talk about their experiences. Pre-empting the discussion in this way has revealed a far higher number of people experiencing visions that had previously been thought. For example, in a two week period of active questioning, Maggie met four people suffering from visual hallucinations, yet in the four years since the Patient Support Service was launched in 1993, Maggie had met only nine out of 2500 patients who spontaneously admitted to having hallucinatory experiences.
She says; "For many people, hallucinations are an additional worry at a time when they are only just coming to terms with their sight loss. Many people keep quiet about it because they fear they will be thought mad and will have more restrictions imposed on them in addition to their lack of independence" Yet taking to someone can relieve patients’ anguish. Maggie recalls the case of a woman who was absolutely terrified by her hallucinations. When she finally talked about it, the transformation was remarkable; she felt reassured that she was not losing her mind and regained her confidence in the future.
Maggie believes that medical professionals need to be made aware of how common visual hallucinations are among patient with impaired sight. Often, these visions are dismissed as a figment of the imagination. Patients’ distress may go unrecognised, or worse, be belittled. They may be wrongly referred to psychologists or geriatric psychiatrists, or prescribed tranquillisers because no-one has made the connection with their visual impairment. Misunderstandings of this sort can seriously impede a patient’s progress towards independent living and makes coming to terms with their sight loss more difficult.
Charles Bonnet syndrome is more common in older people with a high level of education or a creative profession. Although Charles Bonnet Syndrome is mainly a problem of the elderly, it has been described in children who have lost their sight early in life and included "faces, animals, balls and buildings" Doctors should help families anticipate symptoms and provide reassurance that this can be a "normal" response to vision loss.