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14 Unbelievable Facts About The Human Eye

My EYES. H/t this fascinating Quora thread.

1. Your retinas actually perceive the outside world as upside-down – your brain flips the image for you. / Via

If you want to see the world as your retinas do, try a pair of prism glasses. Just don't, you know, walk near sheer drops or operate heavy machinery while wearing them.

2. In addition to being upside-down, images arrive at your retina split in half and distorted. / wikicommons / Via

Each half of your brain receives one half of the image, and then they scramble the images together to compose the whole picture you're used to seeing.

3. Your retinas cannot detect the colour red. / Via

Although your retinas have red, green and blue colour receptors, the "red" receptor only detects yellow-green, and the "green" receptor detects blue-green. Your brain combines these signals and turns them into red.

4. Your peripheral vision is very low-resolution and is almost in black-and-white.

Thinkstock /

You don't realise it because your eyes move to "fill in" the peripheral detail before you notice the difference.

5. Got blue eyes? You share an ancestor with all other blue-eyed people across the world.

6. And if you have brown eyes, you're old school. / Via /

All humans originally had brown eyes. Blue eyes appeared as a mutation about 6,000 years ago.

7. If you're blind, but were born with sight, you probably still see images in your dreams.

8. On average, you blink 17 times a minute. / Via /

That's 14,280 times in a 14-hour day, and 5.2 million times a year.

9. "20/20 vision" doesn't equal perfect vision. It just means you can see 20 feet in front of you as well as the average person can.

10. If you're shortsighted, your eyeball is longer than normal. If you're farsighted, it's shorter than average.

11. Your eyes are almost the same size as they were when you were born. And newborn babies can see clearly up to 15 inches away. / Via /

Which is, handily, generally where their mothers' faces are when they're breastfeeding.

12. Your tears have different compositions based on whether something's irritating your eye, or you're crying, or yawning.

Gaumont Buena Vista International / / Via /

13. Your eye is constantly making tiny jerking movements called "microsaccades" to stop objects from fading from your vision. / Via

A process called Troxler's phenomenon causes static objects in your gaze to disappear if you stare at them for too long (see image below). Microsaccades stop this from happening.

14. And finally, your eye can distinguish between 50,000 shades of grey.

Universal / / Via /

Which makes Christian Grey seem kinda... tame.

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