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Monday, December 19, 2016

Fun Eye Facts

1- The average blink lasts for about 1/10th of a second. 
2- Eyes heal quickly. With proper care, it only takes about 48 hours for the eye to repair a corneal scratch. 
3- Vision is such an important part of life that it requires about half of the brain. 
4- Newborns don’t produce tears. They make crying sounds, but the tears don’t start flowing until they are about 4-13 weeks old. 
5- Doctors cannot transplant an eyeball. The optic nerve that connects the eye to the brain is too sensitive to reconstruct. More than 1 million nerve fibers connect each eye to the brain.
6- The cells in your eye come in different shapes. Rod-shaped cells allow you to see shapes, and cone-shaped cells allow you to see color. 
7- You blink about 12 times every minute. 
8- Your eyes are about 1 inch across and weigh about 0.25 ounce. 
9- Even if no one in the past few generations of your family had blue or green eyes, these recessive traits can still appear in later generations. 
10- Each of your eyes has a small blind spot in the back of the retina where the optic nerve attaches. You don’t notice the hole in your vision because your eyes work together to fill in each other’s blind spot. 
11- Out of all the muscles in your body, the muscles that control your eyes are the most active. 
12- Your eyes start to develop two weeks after you are conceived. Your eyeballs stay the same size from birth to death, while your nose and ears continue to grow. Newborn babies can see clearly up to 15 inches away. 
 13- The entire length of all the eyelashes shed by a human in their life is over 98 feet with each eye lash having a life span of about 5 months. 
14- Corneas are the only tissues that don’t have blood. 
15- Humans and dogs are the only species known to seek visual cues from another individual’s eyes, and dogs only do this when interacting with humans. 
16- A fingerprint has 40 unique characteristics, but an iris has 256, a reason retina scans are increasingly being used for security purposes. 
17- People who are blind can see their dreams if they weren’t born blind. 
18- 80 percent of what we learn is through our eyes 
19- Eyes are the second most complex organ after the brain. 
20- Your eyes can get sunburned. Severely sunburned eyes, known as photokeratitis, is a result of prolonged exposure to the sun’s ultraviolet rays and can cause a burning sensation and blurred vision. These damaging UV rays do not just come directly from the sun, but also from the reflection of these rays from water and sand.
21- Your retinas actually perceive the outside world as upside-down – your brain flips the image for you. 
22- In addition to being upside-down, images arrive at your retina split in half and distorted. 23- Your retinas cannot detect the color red. Your retinas have red, green and blue color 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. 
24- Your peripheral vision is very low-resolution and is almost in black-and-white. You don’t realize it because your eyes move to fill in the peripheral detail before you notice the difference. 
25- 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. 
26- If you’re shortsighted, your eyeball is longer than normal. If you’re farsighted, it’s shorter than average. 
27- Your eye is constantly making tiny jerking movements called “microsaccades” to stop objects from fading from your vision. 
28- Your eye can distinguish between 50,000 shades of gray. 

     Dust, water vapor and pollution in the air will rarely let you see more than 12 miles, even on a clear day. Due to the curvature of the Earth at sea level, the horizon is only about 3 miles away, but if the Earth were flat you could perceive bright lights hundreds of miles distant. 
     On a dark night, you could even see a candle flame flickering up to 30 miles away. How far the human eye can see depends on how many particles of light, or photons, a distant object emits. The farthest object visible with the naked eye is the Andromeda galaxy, located 2.6 million light-years from Earth. The galaxy's 1 trillion stars collectively emit enough light for a few thousand photons to hit each square centimeter of Earth every second. So, on a dark night it can be detected with the naked eye. 
     Under ideal conditions the brightness of a candle flame, and the way a glowing object dims according to the square of the distance away from it, vision scientists conclude that one could make out the faint glimmer of a candle flame up to 30 miles away. 
     But how far away can we perceive that an object is more than just a twinkle of light? Human-scale objects are resolvable as extended objects from a distance of just under 2 miles. For example, at that distance, we would just be able to make out two distinct headlights on a car. 
     The best vision possible with human eyes is 20/8 vision, meaning a person can see things as well from 20 feet away as most people can see at a distance of only 8 feet. Normal vision is 20/20 which means that a given person can resolve the same objects that other people can at a distance of 20 feet. As a comparison, eagles have 20/4 or 20/5 vision, meaning that at 20 feet away, they see objects as well as a person would at a distance of only 4 or 5 feet.

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