Lens functions. Human eye: structure

The human eye is a complex optical system whose task is to transfer the correct image to the optic nerve. The components of the organ of vision are fibrous, vascular, reticular membranes and internal structures.

The fibrous membrane is the cornea and sclera. Through the cornea, the refracted light rays enter the organ of vision. Opaque sclera acts as a framework and has protective functions.

Through the vascular membrane, the eyes are energized with blood, which contains nutrients and oxygen.

Under the cornea is the iris, which provides the color of the human eyes . In the center of it is a pupil, capable of changing the size depending on the lighting. Between the cornea and the iris, there is an intraocular fluid that protects the cornea from germs.

The next part of the choroid is called the ciliary body, due to which the intraocular fluid develops. The vascular membrane is in direct contact with the retina and provides it with energy.

The retina is made up of several layers of nerve cells. Thanks to this organ, the light is perceived and the image is formed. After this, information is transmitted through the optic nerve to the brain.

The internal part of the organ of vision consists of the anterior and posterior chambers filled with transparent intraocular fluid, the lens and the vitreous body. The vitreous humor has a jelly-like appearance.

An important component of the human visual system is the lens. Functions of the lens - ensuring the dynamism of eye optics. He helps to see different objects equally well. Already at the 4th week of development of the embryo, the lens begins to form. The structure and functions, as well as the principle of work and possible diseases of it, we consider in this article.

Structure

This organ is similar to a biconvex lens, the anterior and posterior surfaces of which have different curvatures. The central part of each of them is the poles, which are connected by an axis. The length of the axis is approximately 3.5-4.5 mm. Both surfaces are connected along a contour, which is called the equator. The adult person has the dimensions of the optical lens of the eye 9-10 mm, on top of it covers a transparent capsule (front bag), inside which is a layer of epithelium. On the opposite side there is a posterior capsule, it does not have such a layer.

The possibility of growth of the ophthalmic lens is provided by epithelial cells, which constantly multiply. Nerve endings, blood vessels, lymphoid tissue in the lens are absent, it is entirely epithelial. The transparency of this organ is affected by the chemical composition of the intraocular fluid, if this composition changes, perhaps clouding of the lens.

Lenticular composition

The composition of this organ is 65% water, 30% protein, 5% lipids, vitamins, various inorganic substances and their compounds, as well as enzymes. The main protein is crystalline.

Principle of operation

The lens of the eye is the anatomical structure of the anterior part of the eye, in norm it should be perfectly transparent. The principle of lens operation is the focusing of light reflected from the object into the macular area of the retina. To make the image on the retina clear, it must be transparent. When light enters the retina, an electrical impulse arises that passes through the optic nerve into the visual center of the brain. The task of the brain is to interpret what the eyes see.

Lens functions

The role of the lens in the functioning of the human eye system is very important. First of all, it has a light-conducting function, that is, it ensures the passage of the light flux to the retina. The light-conducting functions of the lens are provided by its transparency.

In addition, this body takes an active part in the refraction of the light flux and has an optical strength of about 19 diopters. Thanks to the lens, the accommodation mechanism is provided, by means of which the focusing of the visible picture is spontaneously regulated.

This organ helps us to easily translate the view from distant objects to those that are near, which is provided by the change in the refractive power of the eyeball. When the muscle fibers that surround the lens contract, the capsule tension decreases and the shape of this optical eye lens changes. It becomes more convex, due to which you can clearly see objects located near. When the muscle relaxes, the lens becomes flat, this allows you to see objects located in the distance.

In addition, the lens is a septum that divides the eye into two sections, thereby protecting the anterior parts of the eyeball from excessive vitreous pressure. Also this is an obstacle to the path of microorganisms that do not enter the vitreous. This is the protective function of the lens.

Diseases

The causes of diseases of the optical lens of the eye can be very diverse. This is a violation of its formation and development, and a change in the location and color that occur with age or as a result of injuries. There is also an anomalous development of the lens, which affects its shape and color.

Often there is a pathology, such as cataracts, or clouding of the lens. Depending on the location of the cloud zone, there is anterior, layered, nuclear, posterior and other forms of the disease. Cataract can be both congenital and acquired during life as a result of injuries, age changes and a number of other causes.

Sometimes trauma and rupture of threads that ensure the correct position of the lens can lead to its displacement. With complete rupture of the threads, a dislocation of the lens occurs, a partial break leads to subluxation.

Symptoms of lens damage

With age, the visual acuity of a person decreases, it becomes much harder to read from a close distance. The slowing of metabolism leads to changes in the optical properties of the lens, which becomes denser and less transparent. The human eye begins to see objects less contrast, the image often loses color. When more pronounced turbidity develops, visual acuity is significantly reduced, cataracts occur. The location of turbidity affects the degree and speed of vision loss.

Age cloudiness develops long, up to several years. Because of this, impaired vision on one eye may go unnoticed for a long time. But even at home, you can determine the presence of cataracts. To do this, you need to look at a blank sheet of paper with one, then the other eye. If there is a disease, it will seem that the leaf is dull and has a yellowish tinge. People with this pathology need bright light, in which they can see well.

Lens clouding can be caused by the presence of an inflammatory process (iridocyclitis) or a prolonged intake of drugs that contain steroid hormones. Various studies have confirmed that with glaucoma, the opacity of the optic lens of the eye is faster.

Diagnostics

Diagnosis consists of checking visual acuity and examining the structure of the eye with a special optical device. The ophthalmologist evaluates the size and structure of the lens, determines the degree of its transparency, the presence and localization of opacities, which lead to a decrease in visual acuity. In the study of the lens, a method of lateral focal illumination is used, in which the front surface of the lens within the pupil is examined. If opacities are absent, the lens is not visible. In addition, there are other methods of research - examination in transmitted light, study with a slit lamp (biomicroscopy).

How to treat?

The treatment is mainly surgical. Pharmacy chains offer various drops, but they are not able to regain the transparency of the lens, nor do they guarantee the cessation of the development of the disease. The operation is the only procedure that provides full recovery. To remove cataracts, extracapsular extraction can be applied, with sutures applied to the cornea. There is another method - phacoemulsification with minimal self-sealing cuts. The method of removal is chosen depending on the density of opacities and on the state of the ligamentous apparatus. Equally important is the experience of the doctor.

Since the ocular lens plays an important role in the work of the human vision system, various injuries and disruptions to its functioning often lead to irreparable consequences. The slightest signs of visual impairment or discomfort in the eye area is an occasion for immediate contact with a doctor who will diagnose and prescribe the necessary treatment.