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The Human Eye: 51 Facts About Your Eyes

Your eyes are incredibly complex. They work hard from the minute you wake up to the minute you go back to sleep, constantly taking in information about the world around you.

We’ve put together 51 facts about your eyes that will help you realise just how remarkable they truly are:

1. The human eye works just like a camera. In the same way that a camera lens focuses light onto a photosensitive surface, your eyes focus light onto the retina.

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2. Eyes first evolved around 500 million years ago. Scientists estimate that eye first evolved 500 million years ago, originally in a very simple form that could probably only distinguish light from dark.

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3. The most common eye colour in the world is brown. With over 55% of the world’s population having brown eyes, it remains the most common colour. Eye colour is determined by genetics, because they dictate how much melanin is produced in your iris.

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4. Some people are born with mismatched eye colours. This condition is known as heterochromia, and is usually the result of a relative lack or excess of pigment in one eye. It is most often inherited, but may also occur due to disease or injury.

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5. The cornea is the transparent covering of the iris and pupil. It protects your eyes from dirt and germs, as well as some of the sun’s UV rays. If your cornea becomes damaged you will experience distorted vision, because the light that enters your eye is interfered with.

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6. 20/20 vision just means you have normal eyesight. Contrary to popular belief, having 20/20 vision isn’t anything remarkable. Rather, it means that you can read a chart from 20 feet away in normal lighting conditions.

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7. Wider pupils can suggest excitement. Any positive thought can serve to dilate your pupils. For example, when you look at someone you are attracted to, they will expand up to 45%. However, dilating pupils can also mean you are scared.

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8. It’s a myth that liars make less eye contact. In fact, a well-practised liar will try to overcompensate as an attempt to “prove” they are telling the truth, by making too much eye contact and holding a gaze.

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9. A woman’s eyesight can be affected by pregnancy. While hormones are raging and physical changes are occurring, it is possible for a woman to experience problems with her sight. These are usually minor and temporary conditions such as blurred vision and dry eyes, and will go away once the child is born.

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10. Your eyes become tired when you read or stare at a computer for extended periods of time. This is because you blink less often and you are not relaxing the muscle inside your eye. If this happens to you often, you should make sure that you have an up-to-date prescription.

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11. Human corneas are very similar to a sharks’ cornea. This similarity means that sharks’ eyes can be used as replacements in human eye surgeries.

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12. The “floaters” in your vision are permanent. They are mainly made up of protein strands floating inside the eye’s vitreous, casting shadows on the retina. Because the vitreous is completely stagnant, they will remain there indefinitely unless surgically removed.

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13. It’s impossible to sneeze with your eyes open. Your eyes and nose are connected by cranial nerves, so the stimulation from a sneeze travels up one nerve to the brain, then down another nerve to the eyelids, typically prompting a blink.

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14. Smokers have almost double the chance of experiencing dry eye. Tobacco smoke is known to irritate eyes - even second hand exposure to the smoke can worsen dry eye, particularly for contact lens wearers.

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15. The sun’s rays have been linked to eye damage. Several eye conditions, such as cataracts and pterygia, have been associated with exposure to UV rays. To protect your eyes from the dangers of the sun, you should wear well fitted sunglasses, preferably a wraparound style.

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16. Many eye injuries are surprisingly quick to heal. Our bodies understand that our eyes are very important to us, and many eye injuries can be recovered from very quickly. For example, with the correct care, a minor corneal scratch will heal in around 2 days.

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17. While a fingerprint has 40 unique characteristics, an iris has 256. This is why retinal scans are increasingly being used for security purposes. A retinal scanner uses infrared light to map the unique pattern of blood vessels on a person’s retina. This pattern is so intricate that even identical twins do not have the same configuration.

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18. We have two eyeballs for depth perception. Our eyes work together to help us judge the size and distance of objects, so that we can safely navigate around them.

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19. Tears help protect our eyes from infection. Any dirt and dust that has managed to pass the defence of our eyelashes and brows is washed away by tears. They keep our eyes clean and moist and a filled with antibodies that fight infection.

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20. Our eyes close automatically to protect us from perceived dangers. The superb reflex control of our eyelids allows them close automatically when they detect that an object is too close to the eye or there is sudden bright light.

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21. We actually see things upside down and our brain turns the image the correct way up. As a result of having a curved cornea, the light that enters our eyes is refracted and creates an upside down image on the retina.

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22. There are colours that are too complex for the human eye to comprehend. These are known as “impossible colours”, which cannot be perceived due to being outside the strength of our three types of cone cell in the retina. However, some of these colours can be seen by mixing colour signals from the two eyes, or by looking at special “fatigue templates”.

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23. Eye transplants are currently impossible due to the sensitivity of the optic nerve. Surgeons are currently unable to wire the optic nerve to the brain because it contains over 1 million nerve cells. This means a transplanted eye would not transmit signals to the brain and therefore fail to produce sight.

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24. You should throw away your eye makeup after three months. Creamy or liquid eye makeup, such as mascara, is the perfect breeding ground for bacteria. This can cause eye infections.

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25. You should never share eye makeup with friends. Swapping your eye makeup can lead to nasty infections. This is because makeup applicators can easily carry bacteria and you don’t want to trade germs with others.

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26. Eye tests can detect Schizophrenia. The mental disorder can be diagnosed with 98.3% precision using a simple examination of the eyes. The test checks for abnormalities of eye movement.

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27. The cornea is the only tissue in the human body which doesn’t contain blood vessels. The cornea must remain clear in order to refract light correctly. If blood vessels were present, they would interfere with this process.

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28. In space, an astronaut cannot cry. Due to the lack of gravity in space, tears do not fall. Instead they collect in little balls and make a person’s eyes sting.

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29. Astigmatism refers to a curvature of the cornea or lens. It is a common and usually not a serious problem. It causes distorted vision and toric lenses are prescribed to aid the individual’s sight.

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30. Just behind our pupil is the lens - which is round, flat and thicker toward the middle. It is made of transparent, flexible tissue and, together with the cornea, helps to focus light onto the retina.

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31. Part of the retina is insensitive to light. Human eyes contain a small blind spot, known as the Punctum Caecum. It is rarely noticed, if ever, because our brains are able to use information from the other eye to fill in the vision gap.

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32. Diabetes affects the blood vessels of your eyes. If these blood vessels become blocked or leak then the retina, and perhaps your vision, will be harmed. This is called Diabetic Retinopathy and affects 40% of people who suffer from Type 1 diabetes and 20% of people who suffer from Type 2 diabetes.

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33. Diabetes is usually first detected during an eye test. Sufferers of type 2 diabetes often have no noticeable symptoms. If this is the case, then the condition is often first noticed during eye examinations due to tiny haemorrhages leaking from blood vessels at the back of the eye.

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34. You blink on average 4,200,000 times a year. The purpose of blinking is to lubricate the eyes. Adults blink around 15 - 20 times a minute, which researchers say is more than the required amount to keep the eyes moist.

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35. Babies blink a lot less than adults. There are several theories as to why babies only blink one or two times a minute. Some researchers believe that it is because a baby’s eye-opening is much smaller and therefore requires less lubrication. Others believe it is because they spend so much time sleeping and tired eyes blink more.

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36. Oily fish, vitamin A and vitamin C all help to preserve good eyesight. Studies have found that eating oily fish at least twice a week (such as salmon or mackerel), can help reduce the risk of age-related macular degeneration - a common cause of blindness in old age. Vitamin A and vitamin C also maintain good eye health.

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37. On average, people are likely to look at each other between one and seven seconds before looking away. Constant eye contact can be intimidating and unpleasant for the other person. When listening to someone else, however, it is good to maintain eye contact 90% of the time.

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38. Your eye is the fastest reacting muscle in your body. It contracts in less than 1/100th of a second. The eye muscles collaboratively carry out a total of seven corresponding movements that allow you to trail moving objects.

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39. Around 99% of the world’s population will first need reading glasses between the ages of 43 and 50. As we age, the lenses in our eyes slowly lose the ability to focus. This means that the vast majority of us will need some form of vision correction in our adult lives.

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40. Cleaning your contact lenses with water will do more harm than good. Never try and clean your contact lenses with water, whether it is bottled or from the tap. This can lead to serious eye infections.

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41. Your eyes contain 7 million cones which help you see colour and detail, as well as 100 million cells called rods which help you see better in the dark. In order to work well, cones need more light than rods. Rods cannot perceive colour, just black, white and gray. However, they are very sensitive and tell us the shape of something.

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42. The human eye only sees three colours. The retina has three types of cones; one is sensitive to the colour red, one is sensitive to the colour blue and the other is sensitive to the colour green. These three cones work together to sense combinations of light waves that help us see millions of other colours and shades.

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43. Flitting eyes suggest distress or tension. Sometimes, when a person’s eyes are darting around, it is because they are trying to find a solution or an answer in a difficult situation.

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44. Anisocoria is a condition where a person’s pupils are not the same size. It can be present at birth or can be developed over time, however it is very rare. Sometimes, people with this condition will notice that the difference in size is only temporary, and they return to their normal sizes again.

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45. Red-green colour blindness is primarily found in men. The genes for the red and green colour receptors are found on the X chromosome, of which men only have one. Women, on the other hand, have two X chromosomes and the stronger of the two is superior. This means that even if one is faulty, a woman will still retain correct vision.

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46. Your eyes start to develop just two weeks after conception. This is one of the reasons why it is so important for a pregnant woman to take care of her own body so that her unborn child can develop properly.

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47. At birth, babies can only see in black, white and some shades of gray. This is because certain nerve cells in their retina and brain are not fully developed. However, they develop the ability to see in colour as quickly as a week later.

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48. People with blue-eyes share the same ancestor. Originally, all human beings had brown eyes, until a genetic mutation occurred between 6,000 and 10,000 years ago. Every single blue-eyed person shares this very distant relative.

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49. Male and female brains process colours slightly differently. Research has shown that men and women see colours slightly differently. It is likely that the male hormone, testosterone, affects the way a male brain processes information taken in by the eye. However, the difference is only very small.

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50. Red-eye in photos is caused by light from the flash bouncing off the capillaries in people’s eyes. When camera flash is used at night, or in dim lighting, it can reflect from the subject’s retina and show up on the picture as red eye. If the subject of the photo doesn’t look directly at the camera, there is less chance of red-eye.

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51. Playing Tetris can treat a lazy-eye. Canadian doctors have found that the puzzle game is effective in training both eyes to work together. In fact, it works better than the conventional eye patch.