Charles Bonnet Syndrome (phantom vision)

Here are two informative articles about phantom vision, which affects between 10 and 40 percent of people with low vision.

The first article comes from an article in the Lighthouse International's Sharing Solutions newsletter, February 2004, on page 5: "I See Purple Flowers Everywhere: The Many Visions of Charles Bonnet Syndrome" (182 Kb .pdf) by Lylas G.Mogk,MD, and Marja Mogk, PhD; with Carol J. Sussman-Skalka,CSW, MBA.

Do you ever see things you know are not there but look real anyway? It's a common side effect among people with vision impairment. While we refer to it as "phantom vision," the technical term is "Charles Bonnet Syndrome." If you've experienced this, rest easy. Your mind is fine. It's your eyes that are playing tricks on you.

What Exactly Is Charles Bonnet Syndrome?

Charles Bonnet, an 18th century Swiss naturalist and philosopher, is credited as the first person to describe the syndrome. Like his grandfather, who had low vision and saw men, women, birds and buildings he knew were not there, Charles experienced similar phantom visions when his own vision deteriorated.

One explanation compares this condition to phantom limb experiences. People who have a limb amputated may still feel their toes or fingers, or may experience itching on an arm that is not there. This happens because the limb's nerves are still active and sending signals to the brain, which the brain interprets as sensations from the missing limb. Similarly, when retinal cells become impaired and are no longer able to receive and relay visual images to the brain, the visual system begins firing off images on its own.

Often, these images are not related at all to a person's life. Sam, who has macular degeneration, said, "I see little monkeys with red hats and blue coats playing in the front yard." Sam had no doubt that the monkeys he saw were not real ones. As a result, he wasn't concerned about his mind. However, he was worried about what others would think, so he kept it to himself…

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The article continues on to explain the percentage of people who may be affected by Charles Bonnet Syndrome and that it is not a psychiatric problem. The article describes some of the images seen that patients have reported.

A majority of people do not find their phantom vision disturbing, probably because the images they see are amusing, pleasing or entertaining.…

This article is based on, and includes quotes from, a chapter in Macular Degeneration: The Complete Guide to Saving and Maximizing Your Sight, written by Lylas G. Mogk, MD, and Marja Mogk, PhD, published by The Ballantine Publishing Group (2003).

This article appeared in Sharing Solutions – Fall 2004 Edition


The second article describing Charles Bonnet Syndrome comes from "Flashes and Paisley Prints" by Kate Chamberlin. Kate’s personal blog documents her "life and times as a writer who happens to be blind". Kate also experienced hallucinations during the 1980s while she was going blind.

For more of Kate's writing, see Kate's Blog at http://katechamberlin.com/.

Persistent Memory in Cats is Created by Doing, Not by Seeing

Cats remember where their paws have been. Researchers from the Department of Physiology at the University of Alberta, Edmonton, Alberta, Canada, report that cats can create memories of their environment without having to rely on vision. Stepping over and touching a physical obstacle with their forelegs creates a memory of the obstacle that persists for up to 10 minutes even after the obstacle is removed. Just seeing the obstacle does not appear to create a memory. The study found that visual memory lasts only a few seconds.

A cat's physical obstacle memory.
A cat's physical obstacle memory.

Keir G. Pearson studies the science of walking (the neurobiology of locomotion). For over 20 years, his test subjects included mice, cockroaches, locusts, humans, and felines. He is studying how animals learn to navigate complex environments, especially when they're moving around. His research has practical applications ranging from treating spinal cord injuries to building robots. "I'm interested in the general problem of how we remember the location of objects relative to the body as we move," Pearson says.

Over a 2-year period, Pearson compared cats' working memory of their recent movements with their visual memory and found that cats remember better with their bodies than with their eyes.

We put an obstacle in front of them and we stopped the cats after they stepped over it with their front legs, but not their back legs. We found that, even many minutes later, the cat would step high with their back legs, even though we had taken away the obstacle.

Pearson with his cat obstacle.
Keir Pearson with his cat obstacle. Credit: ExpressNews Staff, Univ. of Alberta
Felines' memories may in fact be longer but "many minutes" translates into about 10 minutes for the purpose of their experiments. Ten minutes is the maximum length of time Pearson and his fellow researcher David A. McVea were able to distract the animals, usually with a bowl of food.

To compare this working memory to the cat's visual memory, the researchers repeated the experiment, allowing the animals to see the obstacle (a small wooden block) but stopped them from moving forward before they made their first step over the obstacle.

The action of moving the front legs provided the information about the obstacle and the mechanism to establish a longer-term memory. The surprising thing to us was how short visual memory was. We thought it would last longer than a few seconds.

Similar research by Pearson's colleagues on other quadripeds such as dogs and horses, mirrored his results with cats exactly.

It's like driving; if you're a passenger, you really don't remember much about the trip, or the route, but if you've actually driven the car, you'll probably remember much better, and much longer.

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