A professor of ophthalmology explains those moving specks of light, geometric shapes, flashes and colors.
Closing your eyes can be trippy, with a kaleidoscope of shapes and colors visible behind shut lids. What are we seeing behind closed eyes? Ivan Schwab, professor of ophthalmology at University of California, Davis, and a clinical spokesperson for the American Academy of Ophthalmology, explains.
Eyes Wide Shut
Those who sleep with blindfolds on can attest that, even in the absence of any visible light, the visual field fires up. “It’s like a non-drug hallucination,” says Dr. Schwab, who wrote “Evolution’s Witness: How Eyes Evolved,” explaining how vision has changed across nearly four billion years.
When the eyelids are closed but without a blindfold, most people can see wispy clouds, moving specks of light, geometric shapes, flashes of white, snow and a range of colors, he says. “Kids love doing this, because it’s fun, and they are curious.”
The pathway of vision is from the eyes to the brain, Dr. Schwab explains. If you apply pressure to the eyeball when the eye is closed, you may see an explosion of color. “Photoreceptors, cells in the retina that detect light, don’t know the difference between stimuli, and only have one option for reacting—sending a message to the brain,” Dr. Schwab says. “Pressure will cause them to act the same as if they were being stimulated by light.”
A similar effect can be created under special conditions in a laboratory using a magnetic source placed behind the head, where the visual cortex lies.
What you’re seeing in both cases are called phosphenes, he says, a sensation of light and colors produced by stimulation other than light.
This Is Your Eye Talking
The plethora of things a person can see when eyes are closed are collectively called entoptic phenomena.
They include phosphenes and other visual effects generated by the eye or brain. These phenomena visible to the closed eye might include white blood cells within the capillaries around the part of the retina called the fovea, which pulsate with one’s heartbeat; white dots with tails; floaters and vertical or horizontal lines.
Without a blindfold, up to 80% of light gets through the closed lid, and once the eyes are dark-adapted, lots of phospenes can appear. “Most people can see bright sunlight and maybe even a little bit of form through closed eyes,” Dr. Schwab says. “These images are being produced inside the brain so, in effect, the visual system is creating these forms, colors or patterns using remnant available light.”
Researchers have written about eighth-century Taoist monks in China who attempted to reach a different psychic plane, says Dr. Schwab, slowing their heart rate and concentrating deeply. “They could generate these phosphenes during a hypnagogic state—which is that moment right before you fall asleep,” he says. During that twilight phase of being neither asleep nor awake, the monks reported their eyes—on demand—producing images of yellow-green rings and purple clouds.
Modern science has shown “the photoreceptors aren’t always totally shut down, and they can occasionally fire without light stimuli,” says Dr. Schwab. Simply put, what we see when our eyes are closed are extraneous signals that go to the brain, he says. “The brain says, ‘Did you see something?’ But it’s just visual noise.”
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