Eye and vision - Hypermarket of knowledge. Interesting facts about human eyes and vision How a person sees: a physiological point of view

– these are windows to the world and a mirror of our soul. But how well do we know our eyes?

Did you know how much our eyes weigh? Or how many shades of gray we can see?

Did you know that Brown eyes Are these blue eyes with a brown layer on top?

Here are some interesting facts about eyes that will surprise you.

Human eye color

2. Pupils of the eyes expand by 45 percent when we look at someone we love.

3. The human cornea is so similar to the shark cornea that the latter is used as a substitute in eye surgeries.

4. You can't sneeze with your eyes open.

5. Our eyes can distinguish about 500 shades of gray.

6. Each eye contains 107 million cells, and they are all sensitive to light.

7. Every 12th male representative is color blind.

8. Human eye sees only three colors: red, blue and green. The remaining colors are a combination of these colors.

9. The diameter of our eyes is about 2.5 cm, and they weigh about 8 grams.

The structure of the human eye

11. Your eyes will always remain the same size as at birth, and the ears and nose do not stop growing.

12. Only 1/6 part eyeball visible

13. On average, over a lifetime we we see about 24 million different images.

14. Your fingerprints have 40 unique characteristics, while your iris has 256. This is the reason why retinal scans are used for security purposes.

15. People say “in a blink of an eye” because it is the fastest muscle in the body. The blink lasts about 100 - 150 milliseconds, and you you can blink 5 times per second.

16. The eyes process about 36,000 pieces of information every hour.

17. Our eyes focus on about 50 things per second.

18. Our eyes blink on average 17 times per minute, 14,280 times per day and 5.2 million times per year.

19. The ideal duration of eye contact with a person you meet for the first time is 4 seconds. This is necessary to determine what eye color he has.

Brain and eyes

21. The images sent to our brain are actually upside down.

22. Eyes use about 65 percent of brain resources. This is more than any other part of the body.

23. Eyes began to develop about 550 million years ago. The most with the naked eye there were particles of photoreceptor proteins in single-celled animals.

24. Each an eyelash lives for about 5 months.

26. Octopus eyes do not have a blind spot; they evolved separately from other vertebrates.

27. About 10,000 years ago all people had brown eyes until a person living in the Black Sea region developed a genetic mutation that led to the appearance of blue eyes.

28. The wriggling particles that appear in your eyes are called " floaters". These are shadows cast on the retina by tiny filaments of protein inside the eye.

29. If you flood cold water into a person's ear, the eyes will move towards the opposite ear. If you flood warm water into the ear, the eyes will move to the same ear. This test, called the caloric test, is used to determine brain damage.

Signs of eye disease

31. Schizophrenia can be detected with 98.3 percent accuracy using a conventional eye movement test.

32. People and dogs are the only ones who look for visual cues in the eyes of others, and dogs only do this when interacting with people.

33. Approximately 2 percent of women have a rare genetic mutation, due to which they have an additional retinal cone. This allows them to see 100 million colors.

34. Johnny Depp is blind in his left eye and nearsighted in his right.

35. A case has been reported of conjoined twins from Canada who share a common thalamus. Thanks to this they could hear each other's thoughts and see through each other's eyes.

Facts about eyes and vision

37. History Cyclops appeared thanks to the peoples of the Mediterranean islands, who discovered the remains of extinct dwarf elephants. Elephants' skulls were twice the size of a human's, and the central nasal cavity was often mistaken for the eye socket.

38. Astronauts can't cry in space due to gravity. Tears gather in small balls and begin to sting your eyes.

39. Pirates used blindfolds to quickly adapt your vision to the environment above and below deck. Thus, one eye got used to bright light, and the other to dim light.

© Fernando Cortes

40. The flashes of light you see in your eyes when you rub them are called "phosphene".

41. There are colors that are too complex for the human eye, and they are called " impossible colors".

42. If you place two halves of ping pong balls over your eyes and look at a red light while listening to a radio tuned to static, you will see bright and complex hallucinations. This method is called Ganzfeld procedure.

43. We see certain colors because this is the only spectrum of light that passes through water - the area where our eyes appeared. There was no evolutionary reason on earth to see a wider spectrum.

44. Apollo mission astronauts reported seeing flashes and streaks of light when they closed their eyes. It was later discovered that this was caused by cosmic radiation irradiating their retinas outside of Earth's magnetosphere.

45. Sometimes people suffering from aphakia - the absence of a lens - report that see the ultraviolet spectrum of light.

46. ​​Bees have hairs in their eyes. They help determine wind direction and flight speed.

47. About 65-85 percent of white cats are blue eyes- deaf.

48. One of the firefighters of the Chernobyl disaster had eyes that turned from brown to blue due to the strong radiation received. He died two weeks later from radiation poisoning.

© irina07 / Getty Images

49. To keep an eye out for nocturnal predators, many species of animals (ducks, dolphins, iguanas) sleep with one eye open. One half of their brain hemisphere is asleep while the other is awake.

50. Almost 100 percent of people over 60 years of age are diagnosed with herpes eye upon opening.

The human eye is often cited as an example of amazing natural engineering - but judging by the fact that it is one of 40 variants of devices that appeared in the process of evolution different organisms, we should moderate our anthropocentrism and admit that by design human eye is not something perfect.

It’s best to start the story about the eye with a photon. A quantum of electromagnetic radiation slowly flies directly into the eye of an unsuspecting passerby, who squints from an unexpected glare from someone’s watch.

The first part of the eye's optical system is the cornea. It changes the direction of light. This is possible due to such a property of light as refraction, which is also responsible for the rainbow. The speed of light is constant in vacuum - 300,000,000 m/s. But when moving from one medium to another (in this case, from air to the eye), light changes its speed and direction of movement. Air has a refractive index of 1.000293, and the cornea has a refractive index of 1.376. This means that the light beam in the cornea slows down by a factor of 1.376 and is deflected closer to the center of the eye.

A favorite way to split partisans is to shine a bright lamp in their face. This hurts for two reasons. Bright light is powerful electromagnetic radiation: trillions of photons attack the retina, and its nerve endings are forced to transmit a crazy number of signals to the brain. From overstrain, nerves, like wires, burn out. This forces the iris muscles to contract as hard as they can, desperately trying to close the pupil and protect the retina.

And flies up to the pupil. Everything is simple with it - it is a hole in the iris. Using the circular and radial muscles, the iris can constrict and dilate the pupil accordingly, regulating the amount of light entering the eye, like the diaphragm in a camera. The diameter of the human pupil can vary from 1 to 8 mm depending on the lighting.

Having flown through the pupil, the photon hits the lens - the second lens responsible for its trajectory. The lens refracts light weaker than the cornea, but it is mobile. The lens hangs on ciliary muscles, which change its curvature, thereby allowing us to focus on objects at different distances from us.

Visual impairment is associated with focus. The most common are myopia and farsightedness. In both cases, the image is not focused on the retina, as it should, but in front of it (myopia) or behind it (farsightedness). This is due to the eye, which changes shape from round to oval, and then the retina moves away from the lens or approaches it.

After the lens, the photon flies through the vitreous body (transparent jelly - 2/3 of the volume of the entire eye, 99% is water) straight to the retina. Here photons are detected and arrival messages are sent along nerves to the brain.

The retina is lined with photoreceptor cells: when there is no light, they produce special substances - neurotransmitters, but as soon as a photon hits them, the photoreceptor cells stop producing them - and this is a signal to the brain. There are two types of these cells: rods, which are more sensitive to light, and cones, which are better at detecting movement. We have about one hundred million rods and another 6-7 million cones, in total more than one hundred million light-sensitive elements - that’s more than 100 megapixels, which no “Hassel” could ever dream of.

The blind spot is a breakthrough point where there are no light-sensitive cells at all. It is quite large - 1-2 mm in diameter. Fortunately, we have binocular vision and there is a brain that combines two pictures with spots into one normal one.

At the moment of signal transmission, a problem with logic arises in the human eye. The underwater resident octopus, which does not particularly need vision, is much more consistent in this sense. In octopuses, a photon first hits the layer of cones and rods on the retina, immediately behind which a layer of neurons waits and transmits the signal to the brain. In humans, light first breaks through layers of neurons - and only then hits the photoreceptors. Because of this, there is a first spot in the eye - a blind spot.

The second spot is yellow, this is the central area of ​​the retina directly opposite the pupil, just above the optic nerve. The eye sees best in this place: the concentration of light-sensitive cells here is greatly increased, so our vision in the center of the visual field is much sharper than the peripheral one.

The image on the retina is inverted. The brain knows how to correctly interpret the picture, and restores the original image from the inverted one. Children see everything upside down for the first couple of days while their brain installs its Photoshop. If we put on glasses that reverse the image (this was first done back in 1896), then after a couple of days our brain will learn to interpret such an inverted picture correctly.

The structure of the human eye resembles a camera. The lens is the cornea, lens and pupil, which refract light rays and focus them on the retina. The lens can change its curvature and works like autofocus on a camera - instantly adjusts good vision near or far. The retina, like photographic film, captures the image and sends it in the form of signals to the brain, where it is analyzed.

1 -pupil, 2 -cornea, 3 -iris, 4 -lens, 5 -ciliary body, 6 -retina, 7 -choroid, 8 -optic nerve , 9 -blood vessels of the eye, 10 -eye muscles, 11 -sclera, 12 -vitreous.

The complex structure of the eyeball makes it very sensitive to various injuries, metabolic disorders and diseases.

Ophthalmologists of the portal "All about vision" in simple language described the structure of the human eye, giving you a unique opportunity to visually familiarize yourself with its anatomy.

The structure of the main structures of the eye

Constant hydration of the entire surface of the eyeball is provided by the lacrimal glands, which ensure adequate production of tears, forming a thin protective tear film, and the outflow of tears occurs through special lacrimal ducts.

The outermost layer of the eye is the conjunctiva. It is thin and transparent and also lines the inner surface of the eyelids, providing easy gliding when the eyeball moves and the eyelids blink.
The outer “white” layer of the eye, the sclera, is the thickest of the three eye layers, protects the internal structures and maintains the tone of the eyeball.

The scleral membrane in the center of the anterior surface of the eyeball becomes transparent and has the appearance of a convex watch glass. This transparent part of the sclera is called the cornea, which is very sensitive due to the presence of many nerve endings. The transparency of the cornea allows light to penetrate into the eye, and its sphericity ensures the refraction of light rays. The transition zone between the sclera and the cornea is called the limbus. This zone contains stem cells that ensure constant regeneration of cells in the outer layers of the cornea.

Next shell- vascular. It lines the sclera from the inside. From its name it is clear that it provides blood supply and nutrition to intraocular structures, and also maintains the tone of the eyeball. The choroid consists of the choroid itself, which is in close contact with the sclera and retina, and structures such as the ciliary body and iris, which are located in the anterior part of the eyeball. They contain a lot blood vessels and nerves.

The ciliary body is part of the choroid and a complex neuro-endocrine-muscular organ that plays an important role in the production of intraocular fluid and in the process of accommodation.

The color of the iris determines the color of a person's eye. Depending on the amount of pigment in its outer layer, it ranges in color from pale blue or greenish to dark brown. In the center of the iris there is a hole - the pupil, through which light enters the eye. It is important to note that the blood supply and innervation of the choroid and iris with the ciliary body are different, which is reflected in the clinical picture of diseases of such a generally unified structure as the choroid.

The space between the cornea and the iris is the anterior chamber of the eye, and the angle formed by the periphery of the cornea and the iris is called the anterior chamber angle. Through this angle, the outflow of intraocular fluid occurs through a special complex drainage system into the eye veins. Behind the iris is the lens, which is located in front of the vitreous body. It has the shape of a biconvex lens and is well fixed by many thin ligaments to the processes of the ciliary body.

The space between back surface iris, ciliary body and anterior surface of the lens and vitreous called the posterior chamber of the eye. The anterior and posterior chambers are filled with colorless intraocular fluid or aqueous humor, which constantly circulates in the eye and washes the cornea and lens, while nourishing them, since these eye structures do not have their own vessels.

The innermost, thinnest and most important membrane for the act of vision is the retina. It is a highly differentiated multilayer nerve tissue which lines choroid in her posterior region. The optic nerve fibers originate from the retina. It carries all the information received by the eye in the form of nerve impulses through a complex visual pathway to our brain, where it is transformed, analyzed and perceived as objective reality. It is the retina that ultimately receives or does not receive the image, and depending on this, we see objects clearly or not very clearly. The most sensitive and thin part of the retina is the central region - the macula. It is the macula that provides our central vision.

The cavity of the eyeball is filled with a transparent, somewhat jelly-like substance - the vitreous body. It maintains the density of the eyeball and fits into the inner shell - the retina, fixing it.

Optical system of the eye

• The cornea refracts light rays more than any other structure, then passing through the pupil, which acts as a diaphragm. Figuratively speaking, just as in a good camera the diaphragm regulates the flow of light rays and, depending on the focal length, allows you to obtain a high-quality image, so the pupil functions in our eye.
• The lens also refracts and transmits light rays further to the light-receiving structure - the retina, a kind of photographic film.
• Liquid eye chambers and the vitreous body also have light-refracting properties, but not as significant. However, the state of the vitreous body, the degree of transparency aqueous humor eye chambers, the presence of blood or other floaters in them can also affect the quality of our vision.
• Normally, light rays, having passed through all transparent optical media, are refracted so that when they hit the retina, they form a reduced, inverted, but real image.

Thus, the eye is very complex and amazing. Impairment in condition or blood supply, any structural element eyes may have a negative impact on the quality of vision.

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We are used to mercilessly straining our eyes while sitting in front of monitors. And few people think that in fact this is a unique organ, about which even science still knows not everything.

website offers everyone office workers think more often about the state of your vision and at least sometimes do eye exercises.

• The pupils of the eyes dilate almost half when we look at the one we love.
• The human cornea is so similar to the shark cornea that the latter is used as a substitute in eye surgery.
• Each eye contains 107 million cells, all of which are sensitive to light.
• Every 12th male representative is color blind.
• The human eye is capable of perceiving only three parts of the spectrum: red, blue and yellow. The remaining colors are a combination of these colors.
• Our eyes are about 2.5 cm in diameter and they weigh about 8 grams.
• Only 1/6 of the eyeball is visible.
• On average, we see about 24 million different images throughout our lives.
• Your fingerprints have 40 unique characteristics, while your iris has 256. This is the reason why retinal scans are used for security purposes.
• People say “in a blink of an eye” because it is the fastest muscle in the body. Blinking lasts about 100 - 150 milliseconds, and you can blink 5 times per second.
• The eyes transmit a huge amount of information to the brain every hour. Bandwidth This channel is comparable to the channels of Internet providers in a large city.
• Brown eyes are actually blue under the brown pigment. There is even a laser procedure that can turn brown eyes blue forever.
• Our eyes focus on about 50 things per second.
• The images that are sent to our brain are actually upside down.
• The eyes load the brain with work more than any other part of the body.
• Each eyelash lives for about 5 months.
• The Mayans found squint attractive and tried to make sure their children were squinted.
• About 10,000 years ago, all people had brown eyes, until a person living in the Black Sea region developed a genetic mutation that resulted in blue eyes.
• If you only have one eye red in a flash photo, there is a chance that you have an eye tumor (if both eyes are looking in the same direction towards the camera). Fortunately, the cure rate is 95%.
• Schizophrenia can be detected with 98.3% accuracy using a conventional eye movement test.
• Humans and dogs are the only ones who look for visual cues in the eyes of others, and dogs only do this when interacting with humans.
• About 2% of women have a rare genetic mutation that causes them to have an extra cone retina. This allows them to see 100 million colors.
• Johnny Depp is blind in his left eye and nearsighted in his right.
• A case has been reported of conjoined twins from Canada who share a thalamus. Thanks to this, they could hear each other's thoughts and see through each other's eyes.
• The human eye can make smooth (not jerky) movements only if it is following a moving object.
• The story of the Cyclops comes from the peoples of the Mediterranean islands who discovered the remains of extinct pygmy elephants. Elephants' skulls were twice the size of a human's, and the central nasal cavity was often mistaken for the eye socket.
• Astronauts can't cry in space because of gravity. Tears gather in small balls and begin to sting your eyes.
• Pirates used blindfolds to quickly adapt their vision to the environment above and below deck. Thus, one eye got used to bright light, and the other to dim light.
• There are colors that are too “complex” for the human eye; they are called “impossible colors.”
• We see certain colors because this is the only spectrum of light that passes through water, the area where our eyes originate. There was no evolutionary reason on earth to see a wider spectrum.
• Eyes began to develop about 550 million years ago. The simplest eye was particles of photoreceptor proteins in single-celled animals.
• Sometimes people with aphakia, the absence of a lens, report seeing ultraviolet light.
• Bees have hairs in their eyes. They help determine wind direction and flight speed.
• Apollo mission astronauts reported seeing flashes and streaks of light when they closed their eyes. It was later discovered that this was caused by cosmic radiation irradiating their retinas outside of Earth's magnetosphere.
• We “see” with our brains, not with our eyes. Blurred and poor-quality images are a disease of the eyes, as the sensor receiving the distorted image. Then the brain will impose its distortions and “dead zones”.
• About 65-85% of white cats with blue eyes are deaf.

From seeing distant galaxies light years away to perceiving invisible colors, the BBC's Adam Hadhazy explains why your eyes can do incredible things. Take a look around. What do you see? All these colors, walls, windows, everything seems obvious, as if this is how it should be here. The idea that we see all this thanks to particles of light - photons - that bounce off these objects and enter our eyes seems incredible.

This photon bombardment is absorbed by approximately 126 million light-sensitive cells. Different directions and energies of photons are transmitted to our brain in different forms, colors, brightness, filling our multi-colored world with images.

Our remarkable vision obviously has a number of limitations. We can't see the radio waves coming from our electronic devices, we can't see the bacteria under our noses. But with advances in physics and biology, we can identify the fundamental limitations of natural vision. "Everything you can discern has a threshold, the most low level, above and below which you cannot see,” says Michael Landy, a professor of neuroscience at New York University.

Why we see purple and not brown depends on the energy, or wavelength, of photons hitting the retina, located at the back of our eyeballs. There are two types of photoreceptors, rods and cones. Cones are responsible for color, and rods allow us to see shades of gray in low light conditions, such as at night. Opsins, or pigment molecules, in retinal cells absorb electromagnetic energy from incident photons, generating electrical impulse. This signal travels through the optic nerve to the brain, where conscious perception of colors and images is born.

We have three types of cones and corresponding opsins, each of which is sensitive to photons of a specific wavelength. These cones are designated S, M, and L (short, medium, and long wavelengths, respectively). Short waves we perceive them as blue, long ones as red. The wavelengths in between and their combinations become a complete rainbow. “All the light we see, except that created artificially using prisms or clever devices like lasers, is a mixture different lengths waves, says Landy."

Of all the possible wavelengths of a photon, our cones detect a small band from 380 to 720 nanometers - what we call the visible spectrum. Beyond our perceptual spectrum there is the infrared and radio spectrum, the latter having a wavelength ranging from a millimeter to a kilometer in length.

Although most of us are limited to the visible spectrum, people with aphakia (lack of a lens) can see in the ultraviolet spectrum. Aphakia is usually created due to surgical removal cataracts or birth defects. Normally, the lens blocks ultraviolet light, so without it, people can see beyond the visible spectrum and perceive wavelengths up to 300 nanometers in a bluish tint.

A 2014 study found that, relatively speaking, we can all see infrared photons. If two infrared photons accidentally hit a retinal cell almost simultaneously, their energy combines, converting their wavelength from invisible (say, 1000 nanometers) to visible 500 nanometers (a cool green color for most eyes).

A healthy human eye has three types of cones, each of which can distinguish about 100 different shades of color, so most researchers agree that our eyes can distinguish about a million shades in total. However, color perception is a fairly subjective ability that varies from person to person, making it difficult to pin down exact numbers.

"It's pretty hard to put that into numbers," says Kimberly Jamison, a research scientist at the University of California, Irvine. “What one person sees may only be part of the colors another person sees.”

How many minimum photons do we need to see?

For color vision to work, cones typically need much more light than their rod counterparts. Therefore, in low light conditions, the color "fade out" as the monochromatic sticks come to the fore.

Under ideal laboratory conditions and in areas of the retina where rods are largely absent, cones can be activated by only a handful of photons. Still, sticks perform better in diffuse light conditions. As experiments in the 1940s showed, one quantum of light is enough to attract our attention. "People can respond to a single photon," says Brian Wandell, a professor of psychology and electrical engineering at Stanford. “There is no point in being even more sensitive.”

The scientists then flashed a blue-green light in front of the subjects' faces. At a level above statistical chance, participants were able to detect light when the first 54 photons reached their eyes.

After compensating for the loss of photons through absorption by other components of the eye, the scientists found that five photons activated five separate rods that gave the participants the sensation of light.

What is the limit of the smallest and furthest thing we can see?

This fact may surprise you: there is no inherent limit to the smallest or farthest thing we can see. As long as objects of any size, at any distance, transmit photons to retinal cells, we can see them.

"All the eye cares about is the amount of light that hits the eye," Landy says. - Total number of photons. You can make the light source ridiculously small and distant, but if it's emitting powerful photons, you'll see it."

For example, popular belief says that on a dark, clear night we can see the light of a candle from a distance of 48 kilometers. In practice, of course, our eyes will simply be bathed in photons, so wandering quanta of light from great distances will simply get lost in this mess. "When you increase the intensity of the background, the amount of light you need to see something increases," says Landy.

All the individual stars that we see in the night sky are located in our galaxy - . The most distant object we can see with the naked eye is outside our galaxy: the Andromeda Galaxy, located 2.5 million light-years away. (Although this is controversial, some individuals claim that they can see the Triangulum Galaxy in an extremely dark night sky, and it is three million light years away, you just have to take their word for it).

The trillion stars in the Andromeda Galaxy, given the distance to it, blur into a vague, glowing patch of sky. And yet its size is colossal. In terms of apparent size, even though it is quintillions of kilometers away, this galaxy is six times wider full moon. However, so few photons reach our eyes that this celestial monster is almost invisible.

How sharp can vision be?

Why can't we distinguish individual stars in the Andromeda Galaxy? The limits of our visual resolution, or visual acuity, impose their limitations. Visual acuity is the ability to distinguish details such as dots or lines separately from each other so that they do not blur together. Thus, we can think of the limits of vision as the number of “points” that we can distinguish.

In theory, research has shown that the best we can see is about 120 pixels per degree of arc, a unit of angular measurement. You can think of it as a 60 by 60 black and white chessboard that fits on the fingernail of an outstretched hand. "It's the clearest pattern you can see," Landy says.

A vision test, like a chart with small letters, follows the same principles. These same limits of acuity explain why we cannot distinguish and focus on one dim biological cell several micrometers wide.

But don't write yourself off. A million colors, single photons, galactic worlds quantillions of kilometers away - not too bad for a bubble of jelly in our eye sockets connected to a 1.4 kg sponge in our skulls.