The eye is one of the most important human organs. We usually use it to explore the world around us. You can communicate and move thanks to your eyesight. Find out how the eyes are built.

Sight- like other senses - warns against danger. Due to its location at a "strategic" point on the body, it can provide the brain with the most information. The eyeball rests in the socket on the fatty lining. It has a diameter of 22-24 mm and weighs approx. 7 g.

Eyes: eye structure

  • Pupil

This is the hole in the center of the iris. It narrows in bright light, and widens in dim light. It is possible thanks to the work of the muscles of the iris - the pupil dilator and sphincter.

  • Volleyball

The deepest layer of the eyeball, made of nerve cells sensitive to light and color. It is like a photosensitive photographic film - it is where impressions are recorded, which, by means of nerve impulses, go to the brain and are read there. The most important part of the retina is the macula.

  • Twardówka

The outer wall of the eyeball. It is an opaque, strong fibrous membrane. It is thanks to her thateyekeeps its spherical shape. Attached to it are muscles that allow the eye to move. In children it has a bluish color, and in the elderly it is yellowish due to fat deposits.

  • Vitreous body

It is made of gelatinous tissue which gives the eyeball the proper elasticity. Fills 4/5 of the eye volume.

  • Cornea

This is the most convex part of the eyeball and the most important optical element. It concentrates light rays so that they reach the lens at the right angle. The cornea must be constantly moisturized and this is served by tears, which also have bactericidal properties.

  • Lens

It is transparent, it is located behind the iris. It refracts rays that fall into the eye and transforms them into an image. When it automatically thickens (becomes convex), we see exactly up close. When it flattens - from a distance. It is accommodation, that is, adaptability. With age, the lens may become cloudy. Then a cataract develops, also known as a cataract.

  • Iris

Its purpose is to doselight entering through the pupil into the eye. Works like a camera shutter. Pigment is stored at the back of the iris (pigment epithelium). The color of the eyes depends on its quantity. When there is a lot of it, the eyes are brown-black, while little - blue.

  • Yellow spot

Located on the retina. It is the site of the greatest concentration of suppositories, making it the most sensitive to colors and light.

  • Blind spot

The image runs from the retina to the brain via the optic nerve. Its connection to the eyeball is called a blind spot. It is not sensitive to light.

Eyes: how is the image formed?

Light entering the eye passes through the cornea, anterior chamber, lens and vitreous body to reach the retina. The cornea, together with the aqueous humor, the lens and the vitreous body focus the light rays so that a sharp image of the viewed object appears on the retina.

This is due to a lens that can change shape, and thus the optical power. This allows for precise observation of objects at different distances from the eye. We call this ability accommodation.

As the rays pass through the lens, they refract and hit the retina at the back of the eye. This is where an image is created and transmitted to the brain via the optic nerve.

Eyes: upside down image

The image of the object on the retina is upside down due to the physical structure of the eye. In the first days of life, the human brain learns to see the correct arrangement of things, using a lens that reverses the image.

Once the eye fixes this mechanism, it will do it automatically. But it takes time. This means that at the beginning of our lives we see the world standing on its head.

Eyes: convergence

When you look at a very distant object, the eyes' viewing axes are almost parallel. If it starts getting closer, the muscles will reposition the axis so that we can still see it. This is a phenomenon of convergence.

The closer the observed object is, the smaller the axis intersection angle. The brain analyzes this angle and thus evaluates the distance of the object being viewed. It is thanks to the fact that we have a pair of eyes that we do not fall over or bump into furniture.

Eyes: color differentiation

The eye receives only light that is within the range of the so-called the optical window, i.e. visible light. This is the wavelength range of light from approx. 400 nm (violet color) to approx. 700 nm (red color). Above 700 nm there is infrared, and below 400 nm ultraviolet, both invisible to us. The suppositories (approx. 7million in each eye), and for the shades of gray - the rods (about 125 million).

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Eye diseases and vision disorders