Home Science 40 Facts About Human Eyes

40 Facts About Human Eyes

by Sankalan Baidya
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Human eyes can be puzzling. They are extremely complex and it is because of these complexities that they keep surprising us so much! Here are some amazing facts about human eyes that you may enjoy.

Interesting Eyes Facts: 1-10

1. Number of working parts present in human eyes is more than 2 million.

2. Human eyes are capable of focusing at 50+ things at any given second.

3. Humans don’t really use their eyes to see. It is the brain! Poor vision, blurry vision etc. are all results of technical problems in brain‘s visual cortex.

4. Human eyes have fastest lens known to mankind. They are way faster than any known camera lens. While camera lenses take a few seconds to focus on objects at different distances, human eyes can adjust focus almost instantly without any noticeable lag.

5. Human eyes blink 17 times every minute on an average. This sums up to 14,280 blinks each day and 5.2 million blinks every year.

6. Eyes blink less when reading and more when talking.

7. One blink can last anywhere between 100 to 150 milliseconds. This means a person can blink up to 5 times in one second. This means that eye muscles are the fastest muscles in human body.

8. There are 107 million cells in a single eye that are sensitive to light. This means that there are 214 million photosensitive cells in two eyes.

9. Of these 107 million cells, only 7 million cells known as cones are responsible for detecting color. Remaining 100 million cells known as rods are responsible for distinguishing between white and black.

10. Every individual in this world having blue eyes have only one common ancestor. The first ever person with blue eyes lived about 10,000 years ago. It was then that every human had only brown eyes.

Interesting Eyes Facts: 11-20

11. Human eyes don’t have green, hazel or blue pigments in ocular fluid or iris. Eye color is dependent on cellular density and melanin content in iris stroma. The lighter the cellular density and melanin content, the greater is the variation in eye color. Thus, eye color can change when lighting conditions change. This phenomenon is similar to the blueness of sky.

12. Human brain is responsible for correcting vision when someone wears a pair of glasses capable of flipping images upside down. This means that even though a person will be seeing upside down images, the brain will adapt and make the person believe that he or she is actually seeing upright images.

13. Muscles responsible for controlling eyes are the most active muscles in entire human body.

14. The external muscles responsible eye movements are the strongest known muscles in entire human body. They don’t really need to be that strong. These muscles are 100 times more powerful than the actual strength they need to make the eyes move.

15. Almost half of any human’s active part of the brain is responsible for generating vision.

16. Human eyes are capable of seeing a candle flame from a distance of 14 miles provided all environmental conditions are perfect.

17. Human eyes are capable of processing 36 KB of information each hour.

18. A human eye can see 1 million colors. It also has an extraordinary ability to distinguish between different shades of a same color. For instance, human eyes can actually distinguish between 500 different gray shades.

19. The range of sight for human eyes is 200 degrees.

20. Only 1/6th of the entire eyeball is actually exposed to the outside world.

Interesting Eyes Facts: 21-30

21. Human babies are always born color blind.

22. Human newborn babies are incapable of producing tears until they reach the age of 4 to 13 weeks.

23. Human tears are composed of water, mucous and fat. Eyes become dry if any of these three components are not present in correct proportion. In case eyes become dry, brain produces these components in greater quantities.

24. A corneal scratch can actually heal completely within 48 hours if proper care is provided. This makes human eyes the fastest healing organs in body.

25. A person can be born with two different eye colors. This eye condition is medically known as heterochromia.

26. One eyeball weighs 7.5 grams.

27. Human eyes have a static contrast ratio of 100:1 and a dynamic contrast ratio of 1,000,000:1.

28. 20/20 or normal vision is just an arbitrary measure. When anyone is capable of reading a chart (used for eye testing) from a distance of 20 feet under normal lighting conditions is said to have normal vision. That never means that a person cannot read it from a greater distance.

29. 20/16 is a better vision than 20/20 and 20/8 is the best seen so far. During eye testing, people are asked to read a chart up to the second last line. Anyone doing that has 20/20 vision. Person capable of reading the last line from a distance of 20 feet under normal lighting conditions is called to have 20/16 vision. 20/8 vision is by far the best ever recorded. It actually means that if a person with normal or 20/20 vision is capable of seeing something from a distance of 8 feet, a person with 20/8 vision can see the same thing from a distance of 20 feet!

30. Human eyes are capable of adapting to blind spots. Diseases like glaucoma create blind spots in human vision. This could have been extremely uncomfortable. However, human mind is capable of adapting to those blind spots and make them disappear. The brain suppresses these blind spots in affected eyes and the good eye is made to fill in the blanks, leaving with normal vision.

Interesting Eyes Facts: 31-40

31. Eye examination is often the first medical examination that helps to identify diabetes. The symptoms of type 2 or brittle diabetes are not just difficult to identify but are often left unidentified because the patients simply don’t know that they are suffering from diabetes. Eye examination reveals small hemorrhages at the back of the eyes. These hemorrhages appear from blood vessels that leak because of diabetes.

32. Cataract is very normal and everyone gets it. It is very similar to hair graying with age. This means that cataract sets in with age. Under normal health conditions a person will invariably get cataract at the age of 70.

33. Blinking eyes is a very important function. This function spreads tears all over the eye surface and this in turn helps to remove debris from eyes, kills microbes and keeps the eyes moist.

34. A normal human will have 3 types of cones (cells that perceive color). Thus all humans are called trichomats. However, there are some women, who through a process called mutation, are known to have 4 cones. They can see up to 100 million colors. These women are called tetrachromats.

35. They can see shades that have no name and cannot be seen on color swatches. However, they really don’t know that they see more colors than any other average human.

36. Only some insects and birds are known to be trichromats apart from humans and hence, they can enjoy the same richness of the world as humans do. Some of these insects and birds can even see spectrum’s ultraviolet part, making their vision far richer than that of humans. Dogs and monkeys on other hand are dichromats because they have only two cones.

37. No human in this world can sneeze without closing eyes.

38. Human eyes are the only organs in whole body that NEVER rest. Their performance never alters even with non-stop functioning. However, the muscles controlling the eyes and eyelids need rest. It is because of this that eyes blink.

39. Human eyes are not as fast on computer screen as they are on paper. Humans read on computer screen at a rate 25% slower than the speed with which they read on paper.

40. There are no blood vessels present in cornea making it the only living tissue in human body without blood vessels.

Did you know while crying, nose becomes runny because of the tears draining into the nose from eyes?

Sources: 1, 2, 3, 4

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7 comments

Engineer July 30, 2016 - 2:59 pm

3 is not correct. Visual issues arise from many sources in the eye (e.g. the lens may not focus light on the retina or have aberrations).

Reply
Sankalan Baidya July 30, 2016 - 3:24 pm

Could you please elaborate with proper sources and citations?

Reply
DR venkatesh October 14, 2018 - 9:06 pm

Visual disturbances can arise from many problems starting from cornea to retina to brain.
even dry eyes can cause blurry vision. cataracts are one of the commonest cause of preventable blindness. Brain is perfectly functioning normal.

Reply
Faylinn August 23, 2016 - 6:27 pm

I find it very interesting that those with blue eyes have only one common ancestor. How exactly are we able to know that and do we know who this ancestor is? I’m just curious, because the professionals of today weren’t around 10,000 years ago and I’m not sure how they would determine that to be true.

Reply
DEVENDRA BHAR July 13, 2018 - 2:10 pm

no comments

Reply
Sankalan Baidya July 14, 2018 - 1:22 pm

You made a wise choice sir!

Reply
Haha,nope. October 16, 2019 - 8:30 pm

This site was sucky.

Reply

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