Imagine being an elderly woman, sipping her tea in an empty house, and suddenly seeing a girl entering through a closed door and vanishing. The apparition is crisp and well defined. Would you, as the woman did, wonder if your house was haunted?
If you are as scientifically minded as I am, you may reject such a supernatural explanation and gravitate toward one of the many medical causes of visual hallucinations. Maybe the woman was psychiatrically ill. Maybe she was having a seizure. Maybe her tea contained the remnants of her wild days at Woodstock.
What if I told you there was another explanation, and that these types of visual hallucinations are not uncommon among the elderly?
You see, the woman in question had a small brain tumour located in an area devoted to vision. She also had a very recent cataract. It turns out that age-related visual impairment, no matter its cause, can result in what is known as Charles Bonnet syndrome.
Bonnet was a Genevan biologist who first described this striking syndrome in his grandfather, who would hallucinate men and women, buildings and carriages, and whose own tapestries would change before his cataractous eyes to reflect posher tastes.
We now know it may be present in 10 to 40% of older adults with a visual impairment. Here are the characteristics of this syndrome which help differentiate it from a psychiatric illness: the person experiencing the hallucinations is in a state of clear consciousness and is not deceived by them; these hallucinations are overlaid with normal visual perceptions; they do not make any noise, they can’t be touched or smelled; they come and go and they often disappear when the eyes are closed. In fact, one of the strategies clinicians will tell patients with the syndrome is to simply look away or close their eyes if the hallucinations become bothersome. But perhaps the most interesting characteristic is that Charles Bonnet syndrome is almost always linked to a loss of vision.
The impairment in the visual system can be at the level of the lens (cataracts); of the retina (age-related macular degeneration); of the optic nerve (glaucoma); or at the level of the brain itself (occipital brain tumour). While many theories have been put forward to explain the process by which visual impairment can lead to these hallucinations, no clear answer has emerged. Perhaps the best hypothesis so far is that parts of the brain specialized in vision end up firing spontaneously because the eyes are not providing enough stimulus due to the loss of vision.
How people respond to these hallucinations varies. While some are distressed by them and may think they are losing their mind, many indulge their curiosity and find them interesting. Some of these visions nod their heads; others try on clothes; many are Lilliputian in size; and one woman even reported seeing “large chickens wearing shoes.”
Visual hallucinations in perfectly cogent people remind us that our brain is not always a reliable witness to the outside world. This has important consequences on the decisions we make based entirely on personal experience.
Meanwhile, if one of your elderly parents confesses to seeing chickens wearing shoes and they know it doesn’t make sense, you may ask them when was the last time they saw an optometrist. It may just be a symptom of vision loss.
