Eyes are a fairly important organ for the normal functioning of the body and a full life. The main function is the perception of light stimuli, thanks to which the picture appears.
Features of the structure
This peripheral organ of vision is located in a special cranium cavity, called the eye socket. The sides of the eyes are surrounded by muscles, through which he holds and moves. Consists of several parts:
- The eyeball itself, which has the shape of a ball about 24 mm in size. It consists of a vitreous body, crystalline lens and watery moisture. All this is surrounded by three shells: protein, vascular and reticulate, arranged in the reverse order. Elements, through which the picture is obtained, are located on the mesh shell. These elements are receptors that are sensitive to light;
- The protective apparatus, which consists of the upper and lower eyelids, the orbit;
- Attachment. The main components are the lacrimal gland and its ducts;
- The oculomotor apparatus, which is responsible for the movements of the eyeball and consists of muscles;
- The optic nerve.
Basic functions of
The main function that vision performs is to distinguish between the various physical characteristics of objects, such as brightness, color, shape, size. In combination with the action of other analyzers( hearing, smell and others) allows you to adjust the position of the body in space, as well as determine the distances to the object. That is why the prevention of eye diseases should be carried out with an enviable regularity.
Presence of pupillary reflex
With the normal functioning of the eyes, with certain external reactions, there are so-called pupillary reflexes, in which the pupil narrows or widens. The pupillary reflex, the reflex arc of which is an anatomical substratum of the pupil's reaction to light, indicates the health of the eyes and the whole organism as a whole. That's why with some diseases the doctor first of all checks the presence of this reflex.
What is a reaction?
The pupil response or the so-called pupillary reflex( other names - iris reflex, iris reflex) is some change in the linear dimensions of the pupil of the eye. Constriction, as a rule, is caused by contraction of the muscles of the iris, and the reverse process - relaxation - leads to the dilatation of the pupil.
Possible causes
This reflex is called by a combination of certain stimuli, the most important of which is the change in the level of illumination of the surrounding space. In addition, the change in the size of the pupil can occur for the following reasons:
- the effect of a number of medications. That is why they are used as a way to diagnose the state of drug overdose or excessive depth of anesthesia;
- change the point of focus of a person's view;
- emotional outbursts, both negative and positive in equal measure.
If there is no reaction
The absence of a pupil's reaction to light can indicate different conditions of a person that pose a danger to life and require immediate intervention by specialists.
Scheme of pupillary reflex
Muscles that control the pupil's work can easily influence its magnitude if they are given a certain stimulus from outside. This allows you to regulate the flow of light that comes directly into the eye. If the eye is covered from incoming sunlight and then opened, the pupil, which previously expanded in the dark, immediately diminishes in size when light appears. The pupillary reflex, the reflex arc of which begins on the retina, indicates the normal functioning of the organ.
Iris has two types of muscles. One group is represented by circular muscle fibers. The parasympathetic fibers of the optic nerve are innervated. If these muscles contract, then this process causes a narrowing of the pupil. Another group is responsible for the dilatation of the pupil. It includes radial muscle fibers that are innervated by sympathetic nerves.
The pupillary reflex, whose pattern is quite typical, occurs in the following order. Light that passes through the layers of the eye and is refracted in them, falls directly on the retina. Photoreceptors, which are located here, in this case are the beginning of the reflex. In other words, it is here that the path of the pupillary reflex begins. The innervation of the parasympathetic nerves affects the operation of the sphincter of the eye, and the arc of the pupillary reflex contains it in its composition. The process itself is called the efferent shoulder. There is also the so-called center of pupillary reflex, after which various nerves change their direction: some of them go through the legs of the brain and enter the orbit through the upper gap, others - to the sphincter of the pupil. This ends the way. That is, the pupillary reflex is closed. The absence of such a reaction can indicate any violations in the human body, which is why this is given so much importance.
Pupillary reflex and signs of its defeat
When examining this reflex, several characteristics of the reaction itself are taken into account:
- the size of pupil narrowing;
- form;
- uniform reaction;
- pupility of the pupils.
There are several most common pathologies that indicate that the pupillary and accommodative reflexes are impaired, which indicates a malfunction in the body:
- Amavrotic immobility of pupils. This phenomenon is a fallout of a direct reaction when the blind eye is illuminated and a friendly reaction, if the vision of problems is not observed. The causes most often are various diseases of the retina itself and the visual pathway. If the immobility is one-sided, is a consequence of amaurosis( lesion of the retina) and is associated with the dilatation of the pupil, although insignificant, then there is a possibility of anisocoria( pupils become of different sizes).With such a violation, other pupillary reactions are not affected in any way. If the amaurosis develops on both sides( that is, both eyes are simultaneously affected), the pupils do not react at all and even remain exposed when exposed to the sun's rays, that is, the pupillary reflex is completely absent.
- Another type of amaurotic immobility of the pupils is the hemianopic immobility of the pupil. Perhaps the defeat of the visual path itself is observed, which is accompanied by hemianopsia, that is, blindness of the half of the visual field, which is expressed by the absence of a pupillary reflex in both eyes.
- Reflexive immobility or Robertson's syndrome. It consists in the complete absence of both direct and friendly reaction of the pupils. However, unlike the previous type of lesion, the reaction to convergence( the narrowing of the pupils in the event that the view is focused on a certain point) and the accommodation( the change in the external conditions in which the person is located) is not violated. This symptom is due to the fact that there are changes in the parasympathetic innervation of the eye in the event that there is a lesion of the parasympathetic nucleus, its fibers. This syndrome may indicate the presence of a severe stage of syphilis of the nervous system, less often the syndrome reports on encephalitis, brain tumors( namely, in the region of the legs), and also about craniocerebral trauma.
- Absolute, or complete immobility of the pupil( that is, it does not narrow, and does not widen at all).When a beam of light beams is applied to the pupil, the absence of both direct and friendly reaction to the stimulus is diagnosed. This reaction develops not instantaneously, but gradually. As a rule, it begins with a violation of physiological pupillary reactions - mydriasis( dilated pupil), lack of pupillary mobility.
Causes may be inflammatory processes in the nucleus, root or trunk of the nerve responsible for eye movements, the focus in the ciliary body, tumors, abscesses of the posterior ciliary nerves.