Anatomy of the eye as an organ of vision

The human body is a complex system in which all elements are closely interrelated and the work of some organs is simply impossible without the functioning of others. For example, the sense organs or analyzers allow not only to explore and perceive the surrounding world, but are also the primary link of self-consciousness, creativity and other complex mental processes.Eyes are the most significant sense organ, because through vision we get more than 90% of information.They have a complex anatomy and represent a natural optical system that can adapt to any external conditions.

Eye as an organ

Like any analyzer, the eye includes three main elements:

• Peripheral part, whose task is to read visual stimuli and recognize them;
• Nerve pathways through which information enters the central nervous system;
• A site of the brain, where the analysis and interpretation of all the information obtained. Treatment of visual stimuli occurs in the occipital region of each hemisphere.

Despite the development of modern medicine, the analyzers have not yet been thoroughly investigated. In many respects this is due to their complex structure and direct connection with the brain - the most unexplained organ of the human body.

The peripheral part of the human visual analyzer is the eyeball located in the orbit or orbit, which protects it from injuries and injuries.Its full-fledged work is provided by the optic nerve, 6 different muscles, a protective system (eyelids, eyelashes, glands), as well as a system of blood vessels. The eyeball itself has a spherical shape with a volume of up to 7 cm3 and a mass of up to 78 grams. From the anatomical point of view, the eye includes 3 membranes - fibrous, vascular and retina.

Structure of the eye

Basic structures

The fibrous membrane is represented by a sclera, cornea and limb - a place where one part passes into another

Sclera

The most voluminous element of the fibrous membrane (80% of the total volume). It consists of a dense connective tissue, necessary for fixing the eye muscles.It is the sclera that helps maintain the tone and shape of the eyeball.In the posterior pole there is a peculiar grating surface, which is necessary for innervation. In fact, the sclera is the framework for all other elements of the eyeball.

Cornea

This colorless element of the fibrous membrane is considerably smaller than other structures in size. A healthy cornea is a transparent spherical element, up to, mm thick, with a pronounced luster and high photosensitivity.Its main task is to refract and conduct beams of light. The refractive power of this structure in a healthy person is 40 diopters.

Nutrition and cell exchange in the eyeball supports the middle or choroid. It is represented by the iris, the ciliary body, and the system of blood vessels (choroid).

Iris

It is localized directly behind the cornea of ​​the eyeball and has in the center of the pupil a self-regulating opening, 2-8 mm in diameter, which acts as a diaphragm. Melanin is responsible for the color of the iris.His task is to protect the eye from the excess of sunlight.

Ciliary body

This is a small area, localized at the base of the iris. In its thickness there is a muscle, which provides the curvature and focus of the lens. It is the ciliary muscle that is key in the process of accommodation of the eye.

Choroid

This is the choroid of the eye, the task of which is to provide nutrition to all structural elements. In addition, it takes an active part in the regeneration of decaying visual substances over time.

Lenticular

This element is located immediately behind the pupil. In fact, it is a natural lens, which, due to the ciliary body, can change the curvature and take part in focusing on objects different in remoteness. Its refractive force is 20 to 30 diopters, depending on the tone of the muscle.

Retina

This is a photosensitive shell of the eye, with a thickness of, 7 to, mm, which are represented by 10 different layers of cells. Some anatomists compare the retina with the film of the camera, since its main task is the formation of images with the help of cones and rods (specialized photosensitive cells). The rods are present on the peripheral part of the retina and are responsible for twilight and black-and-white vision, and the cones in the central zone are the macula (yellow spot).

Auxiliary elements

Many researchers combine additional auxiliary elements of the eye into one group. As a rule, this includes eyelashes, eyelids with a thin mucous membrane (conjunctiva) lining it from the inside, in the thickness of which are lacrimal glands. Their main task is to protect the eyeball from mechanical impact, dust and dirt.

The eye is a complex mechanism in which all parts work synchronously and can not do without each other. That is why ophthalmic diseases are so often accompanied by complications, because if the functioning of one element is disturbed, difficulties arise in others.

Optical system

The main task of the visual analyzer is to get a clear and clear image, which is then sent through the nerve fibers to the brain where the information is analyzed.Contrary to the established opinion, we do not see the object itself, but only the rays reflected from it, which subsequently focus on the surface of the retina. Light rays before entering the retina go through a complex and long path that lies through 3 refractive surfaces - the cornea, the lens and the vitreous.

The process of refraction of light rays in the human eye system is called refraction, and the mechanism itself is described in detail in optics.

Refraction in the eyeball occurs exactly 4 times.First, the light beam is refracted in the anterior and posterior parts of the cornea, then into the lens and slightly refracted by the liquid internal media. Visual acuity is directly dependent on the refractive power of these elements. The average refractive power of the human eye is 60 diopters (59 D for distinguishing distant objects and 7, D for nearby objects).

On the retina, the image appears significantly reduced, upside down and projected from right to left. Subsequent recognition of the object already occurs in the occipital region of the brain.

There are 3 main characteristics of the human optical system:

• Binocular vision. The perception of the image of objects at the same time with two eyes, while not normally feeling a duality. It is believed that always one eye is leading, and the second - a slave;

• Stereoscopy. The ability to see not flat but voluminous images, in other words, the human eye can estimate the distance to the object, its true shape, and also the real size;
• Visual acuity. Thanks to it, it is possible to recognize two points equidistant from each other.

Due to the presence of photosensitive cells - cones, the visual analyzer is able to distinguish the colors of objects. This possibility is not available in all mammalian species.

Age development of the visual analyzer and its optical power

The beginnings of the visual system appear on the 3rd week of embryonic development, and fully the formation of vision only ends 12-14 years.In neonates, you can see the excessive bulge of eyeballs due to the unformed size of the orbit. Up to 2 years, the eye increases in size by 40%, and by 5 years by 70% of the original volume. In addition, in the first years of life the cornea is much thicker, and the lens has a greater elasticity, but it disappears with the development of the nucleus. In pathologies, ophthalmic disorders occur in the form of clouding or lens densification.

Comparison of the sizes of the eyes of an adult and a newborn

After 14 years, the eye structures practically do not change, depletion of structural elements begins after 45-50 years, depending on individual characteristics.With age, the refraction of the lens changes, which leads to the development of hyperopia or nearsightedness.

Central vision occurs only on 2-3 months of a person's life and in the future it is constantly being improved.First, there is the ability to distinguish objects, and with the development of the intellect, it becomes possible to recognize them. By 6 months the newborn can react to the appearance of familiar faces, by the end of the first year there is the ability to recognize simple geometric shapes. Only to 2-3 years the ability to recognize painted images of objects develops. Full perception of the forms and sizes, as well as normal visual acuity are observed only to 6-7 years. Including, therefore, it is inappropriate to give the child to study before this time.

The visual acuity of the baby is very small and is, 02 3. By the age of 2 she rises to, and to 5-7 comes to norm (, ).Newborn children for a long time see objects turned upside down, until the visual cortex of the hemispheres has developed sufficiently.

At birth, the child does not have a conscious sight at all. His eyes are only able to react to bright light by narrowing the pupils, and eyeballs themselves move asynchronously independently of each other. This is why binocular vision develops significantly later than other visual functions.

Adaptation

The human eye is able to adapt to lighting conditions, so that we can distinguish objects from different sources of light.This visual function is called adaptation. It is possible due to the change in the size of the pupil, due to which the ability to transmit light varies, as well as the different photochemical reactions of rods and cones. Complete pupil contraction occurs within 5 seconds, and the maximum expansion lasts up to 5 minutes. There are three types of adaptation:

• Color. Provides a correct perception of color depending on external conditions;
• Dark. Occurs when going from the highest brightness to the lowest. Complete sensitivity of the eye to darkness is observed after 1 hour of stay in conditions of poor illumination. The ability to distinguish and see objects in the dark is provided by pupil dilating and the functioning of the rods;
• Light. Occurs when passing from a small brightness to a larger one. During this process, there is a rapid decomposition of rhodopsin in rods, and cones, on the contrary, actively recruit an enzyme. Thus, blinding is a photochemical reaction. Light adaptation in the norm does not last more than 10 minutes.

Different people have different rates of mechanism for the production and decomposition of rhodopsin in rods and cones. That's why some people see well in the dark.

Accommodation

It is understood as a person's ability to equally well see objects near and far away, as well as fast focusing of vision when looking from one object to another.The process is automatic and can not be controlled. The signal for the beginning of accommodation is a fuzzy image of the object on the retina, after which the ciliary muscles and The cinnamon ligaments under the action of a signal from the brain begin to contract or relax, triggering the lens. In the elderly, the ability to accommodate is weakened by decreasing the elasticity of the lens and sealing the muscular accommodative fibers.

During focusing on nearby objects, the muscles tend to strain, while on the distant objects they relax. That is why it is so important to translate the view from one object to another from time to time during work, which requires a long concentration of vision. This simple exercise allows you to change the load on the visual muscles.

Visual acuity

This is one of the main characteristics of the visual system, which provides many structural elements of the eye.It is the ability of the eyes to perceive points that are equidistant from each other.Its value is inversely proportional to the angle of the central view, the smaller it is, the more accurately we see the objects. Normally, the eye should separately perceive objects removed for 1 minute of the arc (, 16 degrees). To diagnose this parameter, the tables of Sivtsev or Golovin are used.

Simultaneous check on the table of Sivtsev and Golovin

Care Tips

During a lifetime, visual functions deteriorate strongly due to the anatomical features of this organ. Therefore, to monitor the health of the eyes should be from a young age to protect themselves from the development of serious diseases.There are a number of ways to preserve eye health and visual acuity for a long time.

Hygiene

These are the factors that are worth paying attention to to protect eyes from diseases, reduce the risk of vision loss.

• Read and work is necessary with competent lighting to create comfortable conditions for the eyes. It should not be too bright, but not dim;
• During reading, it is desirable to place the light behind, as if from a shoulder. Keep the document is recommended at a distance of 30-35 cm from the eyes, with a long work behind the monitor - 50-60 cm;
• You must constantly monitor the hydration of the mucous membrane.This provides maximum protection against dust and dirt, and reduces the likelihood of injury to the conjunctiva. To avoid excessive dryness, moisturizing drops can be used;
• Eyes get tired after about 45-50 minutes of intensive work. To reduce muscle tension, you need to take breaks and visual gymnastics;
• Do not touch the eyes with unwashed hands.During this, pathogens can be introduced, which leads to infection. Plus, it is recommended to wash eyes twice a day;
• In summer, you need to wear sunglasses to avoid the harmful effects of ultraviolet radiation;
• When there are any signs of the disease, you do not need to pull with an ophthalmologist. Treatment is much more effective in the early stages.

Exercises

Proper rest of the eyes is an important condition for maintaining visual acuity and this can provide gymnastics for the eyes.If there is no possibility to take a break during work, it is possible to perform simple exercises, which allow to lower the tension of the visual apparatus.

1. Blink intensively for 2 minutes at high speed. The rhythm can be changed, makes various pauses between blinking;
2. Look at the farthest object in your field of vision. Look closely at it for 30 seconds, then switch to another object. Repeat the action several times;
3. Close your eyes tightly for 5-7 seconds, and then open them as much as possible. Do 10 repetitions;
4. Using the three fingers of each hand, pinch the upper eyelids. Approximately 2-4 seconds, hold them in sufficient tension, and then relax. Repeat the exercise 3 times.

During morning and evening washing it is useful to make a hydromassage eye with a gentle jet of water.

Video

conclusions

The human eye is a complex mechanism that can perform optical operations with incredible accuracy and speed.Health and visual acuity play an important role for a full life, therefore it is necessary to look after your eyes from a young age, take vitamin complexes for the eyes, call the doctor on time and remember the simple rules of prevention of ophthalmic diseases.