Pupil is what? Description, structure, functions and features. The reaction of pupils to light

If you just close your eyes for a minute and try to live in total darkness, you begin to understand how important vision is for a person. What helpless people become, who have lost the ability to see. And if the eyes are a mirror of the soul, then the pupil is our window into the world.

Structure of the eye

The human body is a complex optical system. Its main purpose is to transfer the image through the optic nerve to the brain.

The eyeball, having the shape of a sphere, is located in the orbit and has three membranes: fibrous, vascular and retina. Inside it are watery moisture, the lens and the vitreous.

The white segment of the eyeball is covered with a mucosa (sclera). The front transparent part, called the cornea, is an optical lens with a large refractive power. Under it is the iris, which performs the function of the diaphragm.

The stream of light reflected from the surfaces of objects falls first to the cornea and, refracted, enters through the pupil onto the lens, which is also a biconvex lens and enters the optical system of the eye.

The next item on the path of the person's visible image is the retina. It is a shell of cells sensitive to light: cones and rods. The retina covers the inner surface of the eye and transmits information to the brain through the nerve fibers through the optic nerve. It is in him that there is a finite perception and awareness of what he saw.

Pupil function

There is a phraseology popular in the people: "cherish as the apple of the eye", but few people nowadays know that the puppet in the old days was called the pupil. This expression is used a long time ago and it shows how we should treat our eyes - as the most valuable and expensive.

The pupil of a person is regulated by two muscles: a sphincter and a dilator. They are controlled by various groups of nerves related to the sympathetic and parasympathetic systems.

The pupil is, as a matter of fact, a hole through which the light enters the retina of the eye. It acts as a regulator, tapering in bright light and expanding at its lack. Thus, the pupil of the eye protects the retina from a burn and increases visual acuity.

Mydriasis

Is it the norm when a pupil is dilated? It depends on a number of factors. In a medical environment, this phenomenon is called mydriasis.

It turns out that the pupils react not only to light. Their expansion can be triggered by an excited emotional state: strong interest (including sexual nature), stormy joy, unbearable pain or fear.

The above factors cause natural mydriasis, which does not affect visual acuity and eye health. As a rule, such a state of the pupil quickly passes, if the emotional background comes back to normal.

The phenomenon of mydriasis is characteristic of a person who is in alcoholic or narcotic intoxication. In addition, dilated pupils often indicate serious poisoning, such as butulism.

Pathological mydriasis can often be observed in patients with traumatic brain injury. Constantly widened pupils indicate the presence of a number of possible diseases in man:

• Glaucoma;
• migraine;
• Paralysis of the oculomotor nerve ;
• Encephalopathy;
• Thyroid dysfunction;
• Syndrome Eddie.

Many people know from movies that when fainted, ambulance doctors first examine their eyes. The reaction of pupils to light, as well as their size, can tell a lot of physicians. A slight increase indicates a shallow loss of consciousness, while "glass", almost black eyes, signal a very serious condition.

Miosis

An excessively narrowed pupil is a condition opposite to mydriasis. Ophthalmologists call it miosis. This deviation also has a number of reasons, it can be an innocuous visual defect, but often it is an occasion to immediately consult a doctor.

Specialists distinguish several varieties of miosis:

1. Functional, in which narrowing occurs for natural reasons, such as poor light, sleep, infant or senile age, hyperopia, overwork.
2. Medicamentous miosis is the result of taking medications, which, in addition to the basic function, have an effect on the operation of the eye muscles.
3. Paralytic - characterized by a complete or partial lack of motor capacity of the dilator.
4. Myosis of irritation - observed with spasm of the sphincter. It is often found in tumors in the brain, meningitis, encephalitis, as well as in people with multiple sclerosis and epilepsy.
5. Syphilitic miosis - can manifest at any stage of the disease, although with timely therapy is extremely rare.

Anisocoria

According to statistics, every fifth person on Earth has pupils of different sizes. This asymmetry is called anisocoria. In most cases, the differences are insignificant and visible only to the ophthalmologist, but some people can see this difference with the naked eye. The regulation of the pupil diameter for this particular feature occurs asynchronously, and in some cases the size changes only on one eye, while the other remains stationary.

Anisocoria can be both hereditary and acquired. In the first case, this structure of the eye is caused by genetics, in the second - by trauma or some kind of disease.

Pupils of different diameters are found in people suffering from such ailments:

• Defeat of the optic nerve;
• aneurysm;
• Brain injury;
• Tumors;
• Neurological diseases.

Policia

The double pupil is the rarest kind of anomaly of the eyes. This congenital effect, called polycoria, is characterized by the presence of two or more pupils in one iris.

There are two types of this pathology: false and true. The false variant implies that the pupil closes unevenly with the membrane, and it seems that there are several holes. In this case, the reaction to light is present only in one.

True polycore is associated with the pathology of the development of the eye cup. The shape of the pupils is not always round, there are holes in the form of an oval, a drop, a keyhole. The reaction to light, albeit not very pronounced, is in each of them.

People with this pathology feel considerable discomfort, the defective eye sees much worse than normal. If the number of pupils is more than 3, and they are large enough (2 mm or more), a child up to a year is likely to undergo a surgical operation. Adults are prescribed to wear corrective contact lenses.

Age features

Many young mothers often notice that the pupils are dilated. Is it worth raising panic because of this? Single cases are not dangerous, they can be caused by poor illumination in the room and features of the excitable nervous system. Seeing a beautiful toy or frightened by the terrible Barmalea, the child reflexively dilates the pupils, which soon again return to normal.

If such a condition is observed constantly - this is an excuse to sound the alarm and urgently seek medical attention. It can talk about diseases of a neurological nature, and unnecessary consultation with a specialist is definitely not a hindrance.

The pupils' reaction to light changes with age. Adolescents have the greatest possible expansion, in contrast to older people, for whom constantly narrowed pupils are a variant of the norm.