1. Most people can see a million colors
Scientists estimate that the average person can see at least a million colors thanks to the eye's cone cells, which send signals to the brain that allow us to perceive different hues. If that sounds impressive, consider that people with a rare condition called tetrachromacy have an extra type of cone cell and can see as many as 100 million colors as a result!
2. You spend 10 percent of your waking hours blinking
Blinking keeps your eyes lubricated and protects them from dust and debris, which may help explain why we do so much of it: The average person blinks between 15 and 20 times per minute, or 14,400 to 19,200 times a day — that's about 10 percent of your waking life, or upwards of 5 million times in a year.
3. The quick-healing cornea has no blood vessels
The cornea is the transparent covering over the front part of the eye — and unlike other body parts, it doesn't have its own blood supply (instead, it receives oxygen from the air). The cornea does, however, have nerve endings, which is why scratching your eye can hurt quite a bit. Fortunately, most abrasions heal quickly, within 24 to 72 hours.
4. Blue-eyed people share a common ancestor
If you have a pair of baby blues, you're among the 8 to 10 percent of the population worldwide with blue eyes, which are the result of a mutation that causes the irises to lack pigment. Researchers believe this mutation first appeared in a person who lived in Europe between 6,000 to 10,000 years ago, meaning all blue-eyed people alive today share a common ancestor.
5. How you feel affects what you see
For people struggling with depression, saying that the world seems drab, flat, or gray may be more than a metaphor. Research has found that individuals with major depression experience measurable differences in how their eyes perceive contrast, which validates the idea that mental health can influence how we see our surroundings.
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6. Night vision occurs slowly
If you feel like your eyes need time to adjust to a dark room, that's because they do. Night vision takes between 20 and 30 minutes to “turn on” through a process known as dark adaptation. Even once our eyes have adjusted, our surroundings appear mostly black-and-white because the rod cells that allow us to see in dimly lit conditions aren't responsible for color vision.
7. Fooled by your eyes? Blame the brain
When it comes to vision, eyesight is only part of the equation — visual information is captured by our eyes but processed by more than 30 areas of the brain. Optical illusions, for example, work by tricking the brain into incorrectly interpreting what your eyes see or by creating a new image that isn't there at all.
8. Your eye color is one-of-a-kind
Just like fingerprints, the colors and patterns within the iris, or colored part of the eye, are unique (so unique, in fact, that iris scans have been found to be more successful than fingerprint recognition technology). Even identical twins who share DNA don't have identical irises.
9. 20/20 vision isn't “perfect”
We often call 20/20 vision “perfect,” but that measurement simply means someone is able to see an eye chart as expected from 20 feet away — meaning it's possible to see even more sharply. One study of professional baseball players, for example, found that more than three-quarters of players had 20/15 vision or better, meaning they could see clearly from 20 feet what the average person sees at 15.
10. Color blindness is a guy thing
Some form of color blindness, or color deficiency, affects approximately 1 in 10 men, most often resulting in trouble distinguishing between red and green tones. Less commonly, someone might not be able to tell blues and yellows apart.