A Faulty Eye Witness: Hallucinations

Treatment for Oliver Sacks eye cancer eventually required laser therapy, last summer. It killed the melanoma that riddled his eye – but obliterated his central visual field. Despite being a renowned neurologist, he never expected what would come next: mind games where his brain displayed things that simply didn’t exist.

Under skilled questioning by NPR’s Robert Krulwich, the researcher chronicled his visual hallucinations for several hundred people at the Metropolitan Museum of Art, last Friday night, as part of the first World Science Festival, convened in New York City.

Over an 18-month period beginning in January 2006, Sachs’ doctors tackled his cancer. Eventually, they decided they’d have to use lasers to kill it. When they removed the bandages, some time afterward, Sacks looked into a mirror and confronted a blind spot – “a blind continent” – where his face should have been.

But as he would quickly learn, that blind spot wouldn’t always stay blind. Moreover, the partial blindness in one eye could at times greatly affected his overall “vision”.

For instance, he was looking at a wash basin one morning and then closed both eyes. And still he saw a fully intact view of the sink. “The image continued as if my eyes were open,” he recalls.

How could this be? He didn’t imagine.

Sometimes, the blind spot also filled in. For instance, if Sacks stared at a solid red tablecloth, the dead visual field would become red too, providing a seamless carmine vista. The brain matched the vision associated with the dead zone to the color or pattern of what was being viewed in the area surrounding it. But this only occurred as long as the surrounding area wasn’t very complicated.

The strangest thing he charted, though, was the development of visual hallucinations. For instance, he described walking on the street one day in the company of his physician. Striding briskly towards them were two men in startling white shirts. At one point, his doctor asked Sacks to close his good eye. Then asked him what he saw.

He told his doctor that he saw the two men continuing to walk towards them. But after a short while, he noted that despite their pace, they didn’t seem to be making any real progress. Isn’t that strange, he asked his doctor? It was almost as if his brain recorded a three-second tape of the advancing men and then replayed it like a loop over and over.

Eventually, Sacks opened his good eye and looked around – and the men he had seen an instant earlier were nowhere to be seen in front or behind him. They were now long gone.

Surprised by this trick his brain had played, Sacks probed the scientific literature and found scattered reports of visual hallucinations in others who also had experienced profound visual loss.

In general, Sacks notes, his hallucinations tend to be fairly mundane. For instance, as he looks at a solid-color background, zig-zags and half-formed letters will begin to emerge. They have the naïve shapes of characters that a young child might start to draw – and they often flicker. Always transparent, they’re only vaguely visible.

At first, these mind games “intrigued and alarmed” Sacks. But most of all, they puzzled him. Which just prodded his inquiries into how common such hallucinations are. And it now appears, he says, that perhaps 80 percent of people who have experienced profound visual loss see something like his transparent geometric images.

Krulwich asked him: Is there anything you can do about them?

“You can’t wish them there. And you can’t wish them away,” Sacks responded.

Other people who’ve experienced dramatic eye damage may encounter fanciful landscapes populated with strangers. Sacks described one instance recorded by Swiss naturalist Charles Bonnet two centuries ago. They came to light in a new translation of the man’s journals.

Bonnet’s grandfather, nearly blind from cataracts, developed especially “flamboyant” hallucinations. One occurred when two girls — his granddaughters, I believe Sacks said – had just come to see him. The man, a bit unsure at what he was sort of seeing, asked if the girls were accompanied by two handsome young men. No, they told him, but they wished they were.

This condition would come to be known as Charles Bonnet syndrome. It afflicts normal people who have lost substantial vision, and saddles them with vivid and unusual hallucinations. They can involve animals, carriages, almost anything.

For the syndrome’s victims, Sacks suspects, such dramatic hallucinations amount to almost a waking dream. When our eyes deprive the brain of visual stimuli, as when we sleep or our optic neurons become severed, a stimuli-deprived brain may feel compelled to occasionally invent imagery, he says.

How odd. But not rare. According to Sacks, some 10 percent of people who sustain serious or complete vision loss experience the Bonnet syndrome, yet the condition is not well recognized because few people describe these visual tricks their brains play, even to their nearest and dearest.

Why? Krulwich asked.

I guess because they figure no one will believe them, Sacks says. But he’s one man who does.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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