As the famous Russian proverb says, "eyes are the mirror of the soul." On them you can read the character of a person. Through the eyes of people see the world, see the beautiful that is happening around.
How does this wonderful organ work? What is the structure of the eye?
The central part of the eye is the eyeball. It is connected to the brain by a special optic nerve. The eyeball is shaped like an oval. It consists of front and rear poles, which are connected by a straight line - the optical axis. The length of the optical axis in a healthy person is 24 mm. The eye equator, which divides the eyeball into two parts, is slightly shorter than the optical axis. Its length is 23.6 mm. The vertical diameter of the eyeball is 23.3 mm. The eyeball has three membranes that protect its core from negative influences from the outside. This is the outer fibrous membrane, the middle choroid and the inner retina. The corneal-scleral capsule performs a protective function: it prevents foreign bodies from penetrating the lens and vitreous body. The thickness of the cornea in different places varies from 0.6 mm to 1 mm. In terms of optical performance, it is the most powerful refractive index. The structure of the eye is laid so that the cornea does not contain blood vessels. But it contains a large number of nerve endings. It is thanks to the hypersensitivity of the sclera that a person blinks and squints at the slightest danger to the eye. The sclera on the outside of the eye reaches a thickness of 1 mm., While on the inside it is very thin. Its circular sinus regulates the outflow of intraocular fluid.
The structure of the eye is laid in such a way that normal eye pressure is always maintained. The space behind the cornea is filled with chamber moisture, which in its biochemical composition is similar to cerebrospinal fluid. The back wall of the anterior chamber of the eye is the iris, on which the pupil is located. The iris contains pigments that are responsible for the color of the eyes. The eye color trait is transmitted genetically, and dark eye color is the dominant trait in relation to light. More precisely, the presence of pigment is the dominant feature , and blue or light brown eyes are possible with a low content of this pigment. If the coloring pigment is completely absent, then the person is an albino. Blood vessels give the white eye a pinkish tint. In the iris are two muscles responsible for the size of the pupil. In bright light, the pupil decreases, and in the dark, on the contrary, it becomes wider. The ciliary body is responsible for the production of intraocular fluid.
The structure of the eyes is perfect from the point of view of optical physics. It is amazing that nature has created such a sensitive mechanism that humanity is still not able to copy. The retina has ten layers. It is she who is responsible for the formation of the image and the perception of colors and shades. On how healthy the retina is, the number of shades distinguishable by a person depends. The cone and rod receptors consist of four parts: the outer segment, the constriction, the inner segment and the synaptic region. The rods are more sensitive to light due to the pigment rhodopsin, and cones with iodopsin better record movement. It is noteworthy that in many representatives of the animal world the structure of the eye provides only for the presence of rods, but not cones.
To study the biophysical nature of vision, the structure and function of the eye must be considered in conjunction with the structure of nerve cells and endings that transmit information from the retina to the occipital lobe of the brain. A vein and an artery exit from the central region of the nerve disk of the eye. The image transmitted by the left eye is formed in the right half of the brain, and the image fixed by the right eye is formed in the left.
This article, which describes the structure of the eye, contains only general facts. If you want to understand the detailed structure of the organs of vision and the principles of their functioning, you have to read countless reference books and textbooks on ophthalmology.