home Analyzes The most important elements of the internal mesh shell are. Features of the structure of the retina

The most important elements of the internal mesh shell are. Features of the structure of the retina

The retina of the eye, or retina, is photosensitive, inner shell eyeball. It consists of photosensory cells and represents the peripheral part visual analyzer.

The retina consists of photoreceptor cells that provide absorption of the visible electromagnetic spectrum, its primary processing and conversion into nerve signals. It received its name from the ancient Greek physician Herophilus (c. 320 BC). Herophilus compared the retina of the eye to a fishing net.

The retina of the eye consists of 10 layers

The anatomy of the retina is a very thin, ten-layer formation:

The pigment layer comes into contact with the vitreous body, forming Bruch's membrane. Another name for it is vitreous plate, as it is completely transparent. The thickness of the plate does not exceed 2 - 4 microns.

The function of the membrane is to counteract the contraction of the ciliary muscle at the time of its accommodation. The entry through Bruch's membrane is nutrients and water into the retinal pigment layer and choroid.

With age, the membrane thickens and changes its protein composition. Exchange processes change and slow down, pigment formation may be observed, which is evidence age-related diseases retina.

His inside it comes into contact with the vitreous body of the eye, and the outer one is adjacent to its choroid along its entire length - up to the pupil. The nervous membrane of the eye originates from ectoderm cells. It is presented in two parts:

External - containing pigment;
Internal - divided into two sections (posterior and anterior). The posterior one has light-sensitive receptors in its structure, while the anterior one lacks them. They are delimited from each other by a serrated edge located at the border of the transition of the ciliary body.

Upon examination, the retina is completely transparent and allows you to clearly see the red choroid underneath. On the red background of the fundus, a whitish round spot is visible.

The optic disc, or the place where the optic nerve exits the retina. Ophthalmologists called this place a “blind spot”, since there are no visual receptors here and, therefore, the process of visual perception is impossible.

The retina performs very important role in eye nutrition

The optic disc has a diameter of 1.7 mm. and is located slightly medial to the posterior pole of the eye. Laterally and slightly closer to the temporal side of the posterior pole, is the macula - this is the " yellow spot", here is the place with the greatest acuity of visual perception.

Macula in diameter is only 1 mm. and it is colored red-brown. The thickness of the retina in an adult is about 22 mm. It lines 72% of the entire inner surface fundus. The retinal pigment layer is nourished by choroid eyes.

For humans and other primates there are their own distinctive features in the structure of the retina. If in humans and other primates the “yellow spot” is presented in the form of a rounded depression, then in dogs, cats and some species of birds it is in the form of a “visual stripe”.

The central part of the retina is represented as a fovea and the part adjacent to it. The total radius is 6 mm. Here it is largest cluster cones. In the peripheral part there is a decrease in the number. In the inner layer of the retina, ending in a jagged edge, there are no photosensitive receptors at all.

Microscopic structure of the retina

The retina of the eye has a very complex structure

The retina of the eye consists of three radial layers of cells and two layers of synapses. Ganglion neurons are by-product evolution and are located in the deepest layers of fiber, and the photosensitive “rods” and “cones” are located away from the center. The retina of the eye is an inverted organ.

Therefore, before light reaches the photosensitive receptors, it must pass through the entire multilayer retina. But the difficulty lies in the fact that opaque epithelium and choroid stand in its way.

In front of the receptors there may be capillaries with shaped elements blood that is in blue light look like very small, moving, transparent dots. This phenomenon is called the “Shearer phenomenon.” Bipolar neurons are located between the photoreceptor and ganglion neurons. Through them there is a connection between the first and second.

Horizontal and amacrine neurons make horizontal connections in the retina. Between the layers of photosensitive and ganglion neurons are the outer and inner plexiform layers. The first communicates between cones and rods, and the second switches the signal from bipolar to ganglionic and amacrine neurons in the horizontal and vertical directions.

Consequently, the outer nuclear layer of the retina contains photosensory cells, the inner nuclear layer contains bipolar, horizontal and amacrylic cells, and the ganglion layer contains ganglion cells and displaced amacrylic cells. Radial glial cells Müller's cells penetrate the entire retina.

The limiting outer membrane is a complex of synaptic connections between the ganglion layer and the photoreceptor layer. The axons of ganglion cells form the nerve fiber layer. Müller cells form the internal limiting membrane.

Axons that do not have a protein shell, approaching the inner border of the retina, turn around and form at an angle of 90 degrees optic nerve. The retina of each human eye may contain 110-125 million rods and 6-7 million cones.

Their distribution in the layers of the retina is uneven. The central part of the retina contains more cones, while the peripheral part contains mainly rods. The central part of the visual spot is filled with cones that are reduced in size; they are arranged in a mosaic manner and form compact hexagonal structures.

The functions of cones and rods are different. Rod receptors have hypersensitivity to light, but are unable to distinguish colors. Cone receptors require more light and, given sufficient light, are capable of distinguishing colors. The rods contain a special substance, the so-called rhodopsin or visual purple.

Under the influence of light, rhodopsin decomposes and this helps the receptors to capture the slightest exposure to light. Cones contain the substance iodopsin - visual pigment. The decomposition of these substances activates electrolytic processes that promote light perception and the transmission of nerve impulses from the eye to the visual part of the brain. The brain is able to receive this information and process it to obtain a certain image.

The outermost layer of the retina, which is adjacent to the choroid, contains a lot of pigment, colored black. It is located in the form of grains and helps the organ of vision to work when at different levels lighting. The black pigment focuses the light beam onto itself and prevents the process of scattering light rays inside the eye itself.

With the help of modern nanotechnology it was possible to create artificial eye and implant it into the human body. Before this, the patient was completely blind, but after the operation he gained the ability to move independently and distinguish objects

A tiny plate of special alloy, which contains 60 electrodes. IN special glasses They built in a video camera that directs the image to a converter that transmits the signal to the electrodes. The electrodes are connected to the optic nerve, which transmits a signal to the brain. The patient needs to carry devices for power supply and information processing.

Retinal diseases

Retinal tear

Exists a large number of hereditary and acquired eye diseases. As a result of such diseases, the retina of the eye can also be damaged. Here are some of them.

Types of pathological changes in the retina

Most often, pathological inclusions, hemorrhages, rupture, swelling, atrophy or changes in the position of the layers are found on the retina. TO pathological inclusions may include: drusen, infarction, exudates. Among the hemorrhages in the retina one can note: round, streak-shaped, preretinal, subretinal.

Retinal edema may be diffuse or cystic. A retinal tear is a round or horseshoe-shaped formation. Retinal atrophy manifests itself in the form of various types of pigmentation. The delamination is observed as delamination or delamination.

Vascular diseases of the retina

TO vascular diseases retina can be classified as:

central vein thrombosis, which most often occurs in people aged 50 lei and older;
occlusion of the central artery in the retina, occurring in men aged 60 years and older;
diabetic retinopathy (proliferative, preproliferative, non-proliferative);

Degenerative and dystrophic diseases

These include:

age-related macular degeneration;
pigmentary degeneration;
retinal disinsertion. There are tractional, exudative and rhegmatogenous retinal detachments.

What the retina is, what functions it performs, the video will tell you:

The retina of the eye is an important light-receiving element. Its structure is very complex, it includes several layers that are responsible for performing various functions. With the development of pathological processes, a violation occurs visual function, which may result in partial or complete loss of vision.

The structure of the retina of the eye

The retina is a complexly organized structure, in which several layers of cells can be distinguished:

The pigment layer is located directly on the border with.
The photoreceptor layer contains and, which ensure the transformation of light waves in the dark and daylight hours, respectively.
The outer limiting membrane is necessary to separate the different layers from each other. This is necessary to transform chemical energy into an electrical impulse.
The photoreceptor nuclei are located in the outer nuclear layer.
The processes of photoreceptors and bipolar neurons are localized in the outer reticular layer.
The inner nuclear layer contains the nuclei of bipolar neurons.
The inner reticular layer contains cells that limit the photoreceptors.
Ganglionic multipolar layer.
Fibers related to the optic nerve.
Internal dividing membrane.

Physiological role of the retina

Among the functions performed by the retina are:

Color-perceiving;
Light-perceiving;
Creating the volume of an object.

At normal operation of all structures of the eyeball, the image is focused strictly in the plane of the retina. Due to this, it becomes possible to create a clear, three-dimensional, bright image.

Video about the structure of the retina

Symptoms of retinal damage

The symptoms of retinal pathology can hardly be called specific, but it is necessary to know them. This will help you make an appointment with an ophthalmologist on time. On initial stages pathology, any discomfort may be absent. In the future, the following symptoms may develop:

Decreased overall visual acuity;
Appearance foreign objects(glare, lightning,) before the eyes;
Narrowing of the field of view;
Appearance of circles or dark spots.

Diagnostic methods for retinal damage

If a person experiences similar symptoms, the ophthalmologist should conduct a diagnostic search, which includes:

, which is a very simple and accessible technique.
eyes;
Fluorescent;
Optical coherence tomography.

After receiving the examination data, the ophthalmologist determines correct diagnosis and treatment.

It should be recalled once again that the retina has a rather complex structure, which allows it to perform difficult tasks. It is capable of perceiving color and light impulses, which are then transformed into a nerve impulse. Due to electrical discharges, information reaches the central structures of the brain and higher visual centers. Perceiving photoreceptors are peculiar neurons, and therefore these cells are very vulnerable and practically cannot be regenerated. At pathological process with the involvement of the retina, a significant decrease in visual function and blindness often occurs. Therefore, it is important to diagnose the pathology in the early stages.

Retinal diseases

Various kinds pathological changes may affect the retina:

Hemorrhage into the retinal substance;
Chorioretinitis, which is manifested by inflammation of the retina and choroid;
retina (can be partial or complete);
(dystrophic process affecting the macula);
Anomalies of retinal development;
Degenerative processes in the substance of the retina;
Retinopathy associated with for various reasons(diabetic retinopathy is more common).

All these diseases can cause irreparable harm visual function, including leading to blindness of the patient. As a result, a person becomes unadapted to life, the quality of which noticeably decreases. In this regard, it is necessary to carry out a set of diagnostic and then therapeutic measures in a timely manner.

The retina is a thin layer nerve tissue, located with inside back of the eyeball. The retina is responsible for perceiving the image that is projected onto it using the cornea and lens, and converts it into nerve impulses, which are then transmitted to the brain.

The retina is most firmly connected to the underlying membranes of the eyeball along the edge of the optic nerve head. Retinal thickness different areas varies: at the edge of the optic disc it is 0.4–0.5 mm, in the central fovea 0.2–0.25 mm, in the fovea only 0.07–0.08 mm, in the area of the dentate line about 0.1 mm.

The complex structure allows the retina to be the first to perceive light, process and transform light energy into irritation - a signal in which all the information about what the eye sees is encoded.

The most important part of the retina is the macula (macular area, macula). The macula is responsible for central vision, as it contains a large number of photoreceptors - cones. They give us the opportunity to see well in daylight. Diseases of the macula can significantly reduce vision.

Structure of the retina

The retina is a rather complex structure. Microscopically, 10 layers are distinguished in the retina, counting from the outside to the inside. The main layers are the pigment epithelium and light-sensitive cells (photoreceptors). Then comes the outer limiting membrane, outer nuclear layer, outer reticular (synaptic) layer, inner nuclear layer, inner reticular layer, ganglion layer, nerve fiber layer, internal limiting membrane.

The first layer is the pigment epithelium

The pigment epithelium extends throughout the optic part of the retina and directly borders the underlying choroid, having a connection with the vitreous plate.

The pigment epithelium is a single layer of densely packed cells containing large amounts of pigment. Cells pigment epithelium have the shape of a hexagonal prism and are located in one row. Such cells are part of the so-called hematoretinal barrier, which ensures the selective entry of certain substances from blood capillaries choroid into the retina.

The second layer is light-sensitive cells (photoreceptors)

Cone-like and rod-like cells, or more simply, rods and cones, received this name because of the shape of the outer segment. This type cells is considered the first neuron of the retina.

Sticks They are regular cylindrical formations with a length of 40 to 50 microns. The total number of rods in the entire retina is about 130 million. They provide vision in low light, for example, at night, and have very high light sensitivity.

Cones in the retina human eye 7 million and they only work in bright lighting conditions. They are responsible for central shaped vision and color perception.

The retina is the layer of the eye located in the inner part of the eye. The retina is formed by ten layers. In general, the organ of vision is one of the most complex in the body; it includes the eyeball itself and an auxiliary apparatus located in the orbit. We can only see part of the eyeball, but in fact it is larger and spherical in shape, consisting of a nucleus and three membranes: the outer (visible sclera), the middle (vascular layer) and the inner retina.

The retina is bounded, on the one hand, by the vitreous body, and on the other, by the choroid. It has two sections - anterior and posterior. Scientists divide the first into ciliary and iris. It does not have cells sensitive to light, and therefore received the name “blind”. The other region, the posterior one, occupies a large area and is located so that it is adjacent to a group of cells next to the optic nerve and the dentate line. There are two leaves in it - the inner one, sensitive to light waves, and the outer one (containing dyes).

The retina in an adult is 22 mm in size and covers about 72% of the inner surface of the eyeball.

As mentioned above, the retina of the eye is formed by ten layers. It contains several types of neurocytes. If you examine the retina in a section, you can see three types of neurons located along the radius: outer - photoreceptor, middle - intercalary, and inner - ganglion. The area between them is occupied by pleximorphic (from Latin - plexus) layers of the retina. They are processes of neurons (receptor cells that perceive light, neurons with one axon and one dendrite, and neurons capable of generating nerve impulses), long and short processes. Axons are responsible for transmission nervous excitement from one neurocyte to other neurons or connected to the central nervous system organs and tissues. And short processes send nerve impulses from organs and tissues or other neurons to the surface of a specific nerve cell. Also, the retina contains interneurons. In them, one can distinguish associative retinal neurons that receive input signals from bipolar neurocytes, they are called amacrine, and cells whose dendrites are in direct contact with the axons of photoreceptor cells are called horizontal.

— Pigment layer.
He is educated epithelial tissue and has such an arrangement that it comes into contact with the choroid of the eye. It is surrounded on all sides by rod-shaped and cone-shaped neurons, and partly extends onto them through finger-like protrusions. Because of this, layers can interact closely with each other. When a light wave affects the molecules of chromolipoproteins, inclusions of neurocytes containing pigment are directed to the processes - this prevents the scattering of light waves between nearby rods and cones. Neurocytes, which contain dyes, capture and eliminate separated parts of light-sensitive receptor cells. In addition, they supply metabolites, salts and oxygen from the choroid, which nourishes the retina and recreates the continuously dissociating visual purple substance to the photoreceptors and back, thus controlling the coordinated work of substances that conduct electricity, in the retina of the eye and determine its activity and security. Cells containing dyes remove fluid from the space between the layers of retinal pigment epithelial and neuroepithelial tissue, allowing the layers to adhere tightly optical retina to the uveal tract, in case of damage they participate in the repair of injuries.

- Photoreceptor layer of the retina, it is the most important, performing main function– perception of light. It contains neurosensory rod and cone cells, the outer parts (dendrites) of which are cylinder-like and exist in the form of rods or cones. In light-sensitive neurocytes, external and inner part and the ending of an axonal or non-neuron. Rods contain the pigment rhodopsin, and cones contain the pigment iodopsin. As we can see, the retina has a complex structure.

Photosensitive neurons have different functions: cones process information in bright light, and rods process information in dim light (dark vision). When there is no light at all, both types of cells work. In the center of the light-receiving tissue of the eye is blind spot. This is where the optic nerve exits the eye. It does not have photosensitive elements and therefore does not perceive light. Next to the blind spot is the area of the retina that best perceives light fluxes - the yellow spot. The middle of its recess is called the central fossa. It is responsible for clear and clear vision and contains exclusively cones. In addition, the macula is the thinnest part of the retina, and the blind spot is the thickest.

- External border plate. This is a stripe that connects neurons. Through this membrane, into the space between the layers of pigment epithelial tissue and neuroepithelial tissue of the retina, the outer parts of light-receiving neurocytes pass.

- Outer granular layer. Its structure is determined by the rods and cones, which contain the nuclei.

- Outer reticular layer. Another name is the mesh layer. It separates the outer and inner layers of the nuclei.

— Inner granular layer, contains kernels nerve cells second order (bipolar cells) and the nuclei of horizontal, amacrine and neuroglial cells.

— The inner reticular layer is the intertwined processes of neurons. They form the gap from the inner nuclear layer to the ganglion cell layer.

— The layer of ganglion multipolar cells of the light-receiving tissue of the eye are second-order neurocytes (cells that conduct electrical signals). When moving away from the center, this layer reduces the number of its cells. This is how the retina adapts to environmental changes.

— The optic nerve fiber layer is the long processes of cells that conduct electrical signals (second-order neurons) that form the optic nerve.

— The internal border plate is what is adjacent to vitreous body. It covers the retina on the inside and is the main membrane of the retina. These are the bases of the processes of Müller neurons (neuroglia).

The retina contains Müller cells throughout; they perform isolating and supporting functions. They also participate in the formation of bioelectric impulses and transport metabolites. Neuroglial cells fill the small openings between retinal neurons and separate their receiving sites.

The pathway of the nerve impulse carried out by the rods is formed by the rod photoreceptor, bipolar and ganglion cells, and amacrine neurocytes different types(associative neurons). Rod photoreceptors communicate only with cells that have one axon and one dendrite.

Features of the cone pathway include the presence in the outer plexiform layer of the junction of cones, which connect them with bipolar neurons of several types and form a light and dark pathway for nervous excitation. For this reason, we find polar sensitivity channels in the cones of the macular surface. Number of photoreceptors associated with a large number There are fewer bipolar cells, and there are more receptors associated with one bipolar cell, as the distance from the macula increases. When the process of isolation of the neurotransmitter has occurred (due to the formation of receptor biopotential), the retina begins to activate neurons. After this, the received data is sent along the optic nerve to the centers of the brain responsible for analyzing visual images.

Ability to see clearly and clearly - unique feature not only humans, but also animals. With the help of vision, orientation occurs in space and environment, obtaining a large amount of information: it is known that with the help of a person receives up to 90% of all information about objects and the environment. Unique structure and cellular composition allowed the retina not only to perceive sources of light stimulation, but also to distinguish their spectral characteristics. Let's look at how the retina works, the functions and features of its neuronal organization. But we will only talk about its structure not from the point of view of a person carrying the burden of scientific knowledge, but from the point of view of an average citizen.

Functions of the retina

Let's start with the main points. The answer to the question, what are the main functions of the retina of the eye, is quite simple. First of all, this is the perception of light stimulation.

By its nature, light is an electromagnetic wave with a certain vibration frequency, which determines the perception of different colors by the retina. The ability to color vision is a unique feature of mammalian evolution. With help scientific achievements, modern equipment, new luminescent chemical compounds, it was possible to look deeper into the structure of the organs of vision, clarify biochemical processes and better understand how the retina implements its functions. And, as it turns out, there are a lot of them, and each one is unique.

Retina and functions

Many people know that the retina is located inside the eye and is its innermost layer. It is known that it contains so-called photosensitive cells. It is directly thanks to them that the retina performs the functions of photoreception.

Their names come from the shape of the cells. Thus, rod-shaped cells were called “rods”, and cells similar to a chemical vessel called “flask” were called “cones”.

Rods and cones differ from each other not only in their features histological structure. The main difference between them is how they perceive light and its spectral characteristics. The rods are responsible for the perception of light flux in the twilight - precisely when, as they say, “all cats are gray.” But cones are responsible for the perception of color vision.

Functional features of cones

Among the cones, there are three special classes: cones, responsible for the perception of the green, red and blue parts of the spectrum, respectively. Each cone contributes to the formation of color vision by processing the image projected by the lens. In painting, the formation of the final color depends on the proportions in which the paint was initially taken by the artist. In a similar way, the retina transmits information about the spectral characteristics of light: depending on how the cones of each group are discharged by impulses, we see a particular color.

For example, if we see green color, then the cones responsible for the green region of the spectrum are most strongly discharged. And if we see red, then, accordingly, for red. Thus, the functions of the human retina consist not only in the perception of light flux, but also in the primary assessment of its spectral characteristics.

Layers of the retina and why they are needed

Perhaps someone thinks that immediately after the lens, light directly hits the rods and cones, and they, in turn, connect with the fibers of the optic nerve and carry information to the brain. Actually this is not true. Before reaching the rods and cones, light must travel through all the layers of the retina (there are 10 of them) and only then affect the light-sensitive cells (rods and cones).

The outermost is the pigment layer. Its task is to prevent the re-reflection of light. This layer of pigment cells is a kind of black chamber of a film camera (it is the black color that does not create glare, which means that the image becomes clearer and reflections of light disappear). This layer ensures the formation of a sharp image using the optical media of the eye. In very close proximity to the layer of pigment cells, rods and cones are adjacent, and this feature makes it possible to see sharply. It turns out that the layers of the retina are located, as it were, backwards. The innermost layer is a layer of specific cells that, through mediator cells in the middle layer, process incoming information from rods and cones. The axons of these cells gather together from the entire surface of the retina and leave the eyeball through the so-called blind spot.

In this place there are no light-sensitive rods and cones, and the optic nerve emerges from the eyeball. Moreover, this is where the vessels enter that provide trophism to the retina. The state of the body can be reflected in the state of the retinal vessels, which is a convenient and specific criterion for diagnosing various types of diseases.

Localization of rods and cones

Nature intended that rods and cones be unevenly distributed over the entire surface of the retina. The fovea (the area of best vision) has the greatest concentration of cones. This is due to the fact that this area is responsible for the clearest vision. As you move away from the fovea, the number of cones decreases, and the number of rods increases. Thus, the periphery of the retina is represented only by rods. This structural feature provides us with a clear vision when high level illumination and helps to distinguish the outlines of objects at low levels.

Neuronal organization of the retina

Just behind the layer of rods and cones are two layers of nerve cells. These are layers of bipolar and ganglion cells. In addition, there is a third (middle) layer of horizontal cells. The main purpose of this group is primary processing afferent impulses that come from rods and cones.

Now we know what the retina is. We have already examined its structure and functions. It is also necessary to mention the most interesting facts related to this topic.

In order to reach the pigment layer, light must pass through all the layers of nerve cells, penetrate the rods and cones and reach the pigment layer!

Another feature of the structure of the retina is the organization of ensuring clear vision in daytime. The bottom line is that in the central fossa, each cone connects to its own ganglion cell, and as it moves away to the periphery, one ganglion cell collects information from several rods and cones.

Retinal diseases and their diagnosis

So what is the function of the retina? Of course, this is the perception of the light flux, which is formed by the refractive media of the eye. Violation of this function leads to disturbances in clear vision. There are a large number of retinal diseases in ophthalmology. These are diseases caused by degenerative processes, and diseases based on dystrophic and tumor processes, detachment, hemorrhages.

The main and primary symptomatology, which may indicate retinal diseases, is a disorder. In the future, optical circles and many other symptoms may appear. It must be remembered that if visual acuity decreases, you should immediately consult an ophthalmologist and undergo the necessary examination.

Conclusion

Vision is a huge gift of nature, and the retina, its functions and its structure are a finely organized element of the eyeball, both structurally and functionally.

Timely consultation and preventive examinations with an ophthalmologist will help identify diseases of the visual analyzer and begin treatment on time. Fortunately, modern medicine has unique technologies that allow you to literally get rid of visual disturbances in 20-30 minutes and regain the ability to see clearly. And knowing what function the retina performs, you can restore it.