The eye is the sensory organ of sight. Sight is the most precious human sense that, more than any other, enables man to know and experience the outside world and to navigate in it. By sight, man receives about eighty percent of all impressions of the world around him. Therefore, a person's mental and physical development, his relationship between people, his happiness and satisfaction largely depend on good eyesight. The loss of any organ is not as hard for a man to bear as the loss of an eye. Such an important organ has been well protected by nature. The eyes are located in the bony cavities, the eye sockets. Eyelids, eyebrows and eyelashes protect them from external harmful influences. The lacrimal glands, sebaceous glands, numerous muscles and blood vessels support and maintain the visual ability of the eye.

The "red eye" can also be called the "burning eye". It is the most common eye disorder. Only a small proportion of people with “red eye” seek medical help. This burning sensation as well as redness of the eye are the two most characteristic signs of inflammation of the mucous membrane of the eye (conjunctivitis). Sudden, acute inflammation of the lining of the eye usually begins with itching, tearing, and burning in the eye. There is often a feeling as if there is a foreign body in the eye. The disturbances are most pronounced in the evening when the formation of tears is reduced, so there is a feeling as if the eye is bruised, as if the eyes are full of sand. When the lower eyelid is moved downwards, it is seen that the mucosa, which coats the inner side of the eyelid, is slightly swollen and bright red in color. The mucous membrane of the sclera has dilated blood vessels, which can be seen as winding red lines that go all the way to the edge of the cornea. The entire visible part of the eye gives the impression of redness, which is why people say "red eye".

Many people have occasional or permanent disturbances when looking, and describe them as if they see spots, shadows, dots, sparks in the eye or in front of the eye. Such disorders are usually transient and harmless, more often accompanied by other diseases in which the eye is completely healthy. Mandatory medical examination is necessary only because of those disturbances that last for a long time, especially if "dark spots", "dark islands" appear in one part of the visual field. It can be a sign of a more serious disease, often one of the first symptoms of brain disease, tumors, bleeding.

Black and white spots in front of the eyes, especially if accompanied by dizziness, can occur in the elderly after strong head movements. Due to senile changes in the cervical vertebrae, when the neck moves, there may be a stronger narrowing of the blood vessels that enter the brain through the neck. Decreased blood in the brain, even for a short time, can cause such disturbances. Sparks, flicker, and even dark swelling in one half of the eye can be seen in one type of headache called migraine. With a severe headache, which usually affects only half of the head, moving shapes, rainbow colors are seen in front of the eyes, there is a fear of light, disturbances occur in attacks and disappear with the cessation of headaches.

Colored vision is when all observed objects are seen in one color, and even colored objects are even colored. Colored vision is not a normal occurrence and always requires a medical examination. Most often, everything is colored yellow (xanthopsy). This is seen in jaundice and poisoning by a heart drug, digitalis. In rare cases, yellow vision can also occur due to poisoning by some other drugs, sometimes due to DDT poisoning. Blue-colored objects are not seen often (alcohol poisoning, syphilis of the nervous system). Everything painted red is a bit more common (bleeding in the vitreous, snow blindness). Colored vision can occur after the eye lens has been removed by surgery, as well as after instilling eye drops that dilate the pupil, especially if you are looking at a smooth surface. Sometimes even blind people complain of seeing colored light, most likely due to stimulation of the vision center in the brain.

Blindness means loss of vision. Complete blindness is one in which a person does not distinguish light from darkness in both eyes, and only one eye can be blind. Blindness is much more often the result of diseases that occur after the birth of a child. Once upon a time, the most common cause of blindness was gonorrhea of the eye. It is a purulent inflammation of the eye with an ulcer on the cornea. The child became infected at birth from a mother who suffered from gonorrhea (gonorrhea). Sudden blindness that comes on completely suddenly, mostly affects one eye. The result is an injury to the eye or an injury to the main blood vessel that supplies blood to the most important part of the eye’s retina. If this artery closes with a blood clot or some other foreign body such as an air bubble, fat droplets, cell clusters, then the retinal cells are left without oxygen and blindness can occur instantly. Sudden blindness, usually within a few minutes, can be caused by a sudden rise in pressure inside the eye, i.e. acute glaucoma.

Night blindness is popularly called "chicken blindness", vision is greatly reduced, and can even disappear completely, during the day when there is enough light, vision is normal. People suffering from this disease start complaining about their ailments only in the evening. How many times are they recognized by this because they constantly complain that their light is too dim. The most common cause is vitamin A deficiency. Due to the fact that normal foods contain a lot of this vitamin, night blindness occurs mainly during hunger, due to excessive and poor diets and very rarely in spring due to vitamin A deficiency in winter foods. Night blindness can be cured in a few hours with food rich in vitamin A. With injections of this vitamin, healing occurs in a few minutes.

The eye recognizes many different colors. Special cells located in the retina of the eye, the so-called cones. The cones feel only three basic colors: red, green and blue. All other colors that a person sees are created by mixing these three basic colors. If the eye lacks cones sensitive to a color, that color cannot be distinguished. There are acquired or inherited diseases accompanied by blindness for all colors or, more often, only for some. In general, color blindness is called color blindness, according to Dalton, the English chemist and physicist who first described the phenomenon. A person who is completely blind to all colors is called a monochromat. Failure to recognize red is called protanopia, green deuteranopia, and blue tritanopia. The most common is blindness for red and green.