12 Unbelievable Facts About Human Eyes That You Didn’t Know!

Even as you read this, your eyes are working at an incredible pace and doing it silently and stealthily. Ask yourself though – how much do you know about this incredible organ? For instance, did you know that every time you light up a cigarette, you are reducing your night vision? Or that an average blink lasts 300-400 milliseconds?

Here are some other facts about human eyes, so that you can appreciate the superhuman strength of the deceptively simple human eye.

1. The focusing muscle of the human eye moves about 1000,000 times every day.

Image source: giphy

It’s crazy how much the focusing muscle of the eye gets done. On an average, this spectacular muscle of the human eye moves about 1000,000 times every single day. If that doesn’t blow your mind, let’s put it in perspective. For your leg muscles to get the same kind of workout, you would have to walk 50 miles, every day.(source)

2. Until about 10,000 years ago, all human beings had brown eyes. Blue eyes are a more recent phenomenon caused by a genetic mutation, a sign that humans are still evolving. 

Image source

Originally, every single human being had brown eyes. However, about 10,000 years ago, someone who lived near the Black Sea developed a genetic mutation that turned brown eyes to blue.  There are many theories about how blue eyes have still persisted, so many generations later. For instance, one theory suggests that blue eyes act as sort of a paternity test. This means that since there is strong evolutionary pressure on a man not to invest his paternal resources in another man’s child, he would actively seek out blue-eyed mates. Since it is impossible for two blue-eyed partners to create a brown-eyed baby, this instinct may have led to the genetic preservation of blue eyes.(source)

3. How far can the human eye see? Assuming a flat earth and complete darkness, the human eye is sensitive enough to spot a candle flame, flickering up to 30miles (48 km) away.

Image source

Although the Earth’s surface curves out of sight at a distance of 3.1 miles (5 km), our ability to see extends far beyond that distance. If Earth were completely flat, or if you were standing on top of a mountain surveying a larger-than-usual patch of the planet, you could see bright lights that are hundreds of miles away! On a particularly dark night, you could even see a candle flame flickering in the distance, specifically up to 30 miles away.

The eye’s ability to perceive things in the distance depends on how many particles of light, or photons, an object emits. After extensive research, vision scientist Selig Hecht discovered that the absorption of 5 to 14 photons, or, equivalently, the activation of just 5 to 14 rod cells is enough to tell your brain that you’re seeing something. The farthest object that is visible to the naked eye is the Andromeda galaxy, wherein its constituent 1 trillion stars collectively emit enough light for a few thousand photons to hit each square centimeter of Earth every second.(source)

4. Both our left and right eyes have independent blind spots.  

The human eye has a blind spot on the retina, at the point where the optic brain leads back to the brain. However, the wonderful thing is that the left and right eyes have blind spots that are aligned symmetrically. What this means is that one eye’s field of vision will compensate for the other’s loss of vision, most of the time.

Are you now wondering if you can locate the blind spots in both your eyes? Yes, you can. There’s a rather simple test that can help you identify the blind spot in each of your eyes. In order to find the blind spot on the right eye – shut your left eye, focus the right eye on a single point and see if anything vanishes from your line of sight, about 20 degrees to the right. That’s your blind spot. Repeat the same steps for your left eye.(source)

In order to find the blind spot of the right eye, it is necessary to close the left eye, focus the right eye on a single point, and see if anything vanishes from vision some 20 degrees right of this point. The following diagram has a set of characters on the left hand side, and black circle on the right. Keeping your head motionless, with the right eye about 3 or 4 times as far from the page as the length of the red line, look at each character in turn, until the black circle vanishes.

5. The human eye evolved from a plain spot of photoreceptive cells.

Image source: wikipedia

In fact, eyes went through a few stages of evolution, from photoreceptor proteins to the eye as we know it, today. The earliest predecessors of the eye were photoreceptor proteins, found in unicellular organisms, called ‘eyespots’. Eyespots can only sense brightness. Then, it became important for organisms to be able to discriminate the direction that light was coming from. This was made possible by the multicellular eyepatch, gradually depressed into a cup, which first granted the ability to discriminate brightness in directions, then in finer and finer directions as the pit deepened.

The development of the retina came next. When a photon is absorbed by the chromophore(part of a molecule responsible for its colour), a chemical reaction causes the photon’s energy to be transduced into electrical energy and relayed, in higher animals, to the nervous system. These photoreceptor cells form part of the retina, a thin layer of cells that relays visual information to the brain.

Then, things happened very quickly. The next stage was the discovery that reducing the width of the light opening became more efficient at increased visual resolution, than simply deepening the cup. These kind of eyes still lacked a cornea or lens which, sure enough, came to be in the next stage of eye evolution.(source)

6. The human eye, an incredible organ, can distinguish about 10 million different colors.

Image source: wikipedia

Essentially, there are three primary colours – red, green and blue – that make up the millions of colors distinguishable to the human eye. Each eye contains three receptors, one for each primary colour, that are responsible for the creation of the experience of color, when stimulated in various combinations. This is known as the Young-Helmholtz Trichromatic Theory. Thus, it follows that those who have defective cones cannot see certain colours and are known to be color-deficient.(source)

7. If the human eye was a digital camera, it would have a resolution equivalent to 576 megapixels.

Image source

However, the eye is not like a single frame snapshot camera but, instead, like a video stream. The eye works tirelessly, moving rapidly in small, angular amounts so that it can continually update the image of what we are seeing in our brain. Considering we have two eyes, this power also gets multiplied by 2, which further increases the resolution and, thereby, the amount of detail we perceive. This basically makes our eyes more powerful than any digital camera, as the eye plus brain assembles a higher resolution image than possible, because of the number of photoreceptors in the retina. This resolution is roughly estimated at a whopping 576 megapixels.(source)

8. Human corneas are so similar to shark corneas that they may, one day, be used as a replacement in human eye surgery.

Image source: www.medibank.com.au

Sharks can actually prove extremely useful to humans. Optometric researchers are investigating the possibility of using shark corneas as a replacement to human corneas in transplant surgeries. Apparently, shark corneas are rather similar to our corneas. If this were to become a reality, it would be pathbreaking.(source)

9. Green-eyed people make up only 1-2% of the entire human population, and naturally occurring violet-colored eyes exist.

Image courtesy: Steve McCurry(taken from)

If you know someone with green eyes, they are a part of very tiny percentage of the human population. While green eyes are dominant over blue eyes, there are very few people that carry the gene responsible for green eyes. Therefore, within the ‘light-eyed community’, the number of blue-eyed people greatly outnumber those with green eyes. Thus far, scientists have found evidence linking the presence of certain other traits, such as having red hair, or gender with the occurrence of green eyes.

Even rarer than green eyes are violet eyes. However, violet eyes are steeped in lots of mystery and surrounded by many myths.(source)

10. No, carrots don’t make your eyesight better. This was actually a lie that the British came up with to cover up the fact that they had come with a new, cutting-edge technology, during WWII. 

Image source: www.ph-microscope.com

Unfortunately, if you’ve been chomping on carrots in the hope that you can toss your spectacles away, once and for all, you’re going to be disappointed. This famous ‘cure’ for better eyesight is actually just an elaborate cover-up, a story of wartime espionage. During the World War II, British pilots had the advantage of a game-changing tool, RADAR, that let them spot their enemies at night. However, to ensure that their enemies did not find out about RADAR, and then copy it, they claimed that their pilots had high-carrot diets to thank for their night-time vision!(source)

11. Lightning fast vision protein in the human body has been named after the adorable pokemon, Pikachu. 

Image source: f00.inventorspot.com

The newly-discovered protein, Pikachurin, has been named after Pikachu, in honour of his blink-and-miss moves and electrifying powers. The team of 18 Japanese scientists who discovered Pikachurin all work at the Osaka Bioscience Institute. This newly-discovered protein is essential for eye-to-brain transmission of visual signals and also for the way the eye tracks moving objects, in its field of vision.

Essentially, without the fantastic Pikachurin, it can take upto three times longer for visual signals to reach the brain.(source)

12. Humans get ‘red eye’ in photos because the flash reflects off of the blood vessels in our retinas. In dogs and other animals, eyes look green because they have an extra layer of cells behind their retinas.

Image source: nivea.psycho.univ-paris5.fr

The mystery of the frustrating red eye has been decoded. When taking photographs, if light reflects off of the blood vessels in our retinas, it gives us devilish, red-tinted eyes. Similarly, animals tend to take on an unnatural, ghostly green glow in photographs, sometimes. The reason their eyes look green is because they have a special layer of cells, either in or behind their retinas, that acts like a mirror in reflective light and helps them see better at night.

To make sure you never ruin another picture with ‘red eye’, try to shoot at an angle so that the light source is not directly above your camera.(source)