1. Your retinas actually perceive the outside world as upside-down – your brain flips the image for you. Tap to play or pause GIF Tap to play or pause GIF coolgifcollection.tumblr.com / Via quora.com 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. upload.wikimedia.org / wikicommons / Via quora.com 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. Tap to play or pause GIF Tap to play or pause GIF tu-eres-el-unico-para-mi.tumblr.com / Via quora.com 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 / quora.com 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. Tap to play or pause GIF Tap to play or pause GIF redbull250ml.tumblr.com / Via quora.com / eyecare2020.com 6. And if you have brown eyes, you're old school. Tap to play or pause GIF Tap to play or pause GIF tumblr.com / Via quora.com / eyecare2020.com 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. Tap to play or pause GIF Tap to play or pause GIF FOX / thesimpsonsforever.tumblr.com / Via quora.com 8. On average, you blink 17 times a minute. Tap to play or pause GIF Tap to play or pause GIF gifloop.tumblr.com / Via quora.com / eyecare2020.com 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. Tap to play or pause GIF Tap to play or pause GIF whatgiftoday.tumblr.com / Via quora.com / eyecare2020.com 10. If you're shortsighted, your eyeball is longer than normal. If you're farsighted, it's shorter than average. Tap to play or pause GIF Tap to play or pause GIF tumblr.com / Via quora.com / eyecare2020.com 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. Tap to play or pause GIF Tap to play or pause GIF tumblr.com / Via quora.com / eyecare2020.com 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. Tap to play or pause GIF Tap to play or pause GIF Gaumont Buena Vista International / watermelanieseeding.tumblr.com / Via quora.com / eyecare2020.com 13. Your eye is constantly making tiny jerking movements called "microsaccades" to stop objects from fading from your vision. Tap to play or pause GIF Tap to play or pause GIF black-and-white-gifs.tumblr.com / Via quora.com 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. Tap to play or pause GIF Tap to play or pause GIF briantobin.info 14. And finally, your eye can distinguish between 50,000 shades of grey. Tap to play or pause GIF Tap to play or pause GIF Universal / lovingeverlark.tumblr.com / Via quora.com / eyecare2020.com Which makes Christian Grey seem kinda... tame.