What are the layers of the retina? What are their functions? You will find answers to these and other questions in the article. The retina is called a thin shell with a thickness of 0.4 mm. It is located between the choroid and the vitreous body and lines the hidden surface of the eyeball. Let's look at the layers of the retina below.
Signs
So, you already know what the retina is. It is attached to the wall of the eye only in two places: along the border of the optic nerve disk and along the serrated edge of the wall (ora serrata) at the beginning of the ciliary body.
These signs explain the mechanism and clinic of retinal detachment, its ruptures and subretinal hemorrhages.
Histological structure
Not everyone can list the layers of the retina. But this information is very important. The structure of the retina is intricate and consists of the following ten layers (list from choroid):
- Pigmented. This isthe outer layer of the retina adjacent to the hidden surface of the vascular membrane.
- Layer of cones and rods (photoreceptors) - color and light-perceiving components of the retina.
- Membranes (marginal outer plate).
- Nuclear (granular) outer layer of the nucleus of cones and rods.
- Reticular (mesh) outer layer - processes of cones and rods, horizontal and bipolar cells with synapses.
- Nuclear (granular) inner layer - body of bipolar cells.
- Reticular (mesh) inner layer of ganglion and bipolar cells.
- Multipolar ganglion cell layer.
- Layer of optic nerve fibers - axons of ganglion cells.
- Boundary inner membrane (lamina), which is the most hidden layer of the retina, bordering the vitreous body.
Those fibers that extend from the ganglion cells form the optic nerve.
Neurons
The retina forms three neurons:
- Photoreceptors - cones and rods.
- Bipolar cells that synaptically connect the processes of the third and first neurons.
- Ganglion cells, processes of which form the optic nerve. With many ailments of the retina, selective damage to its individual components occurs.
Retinal pigment epithelium
What are the functions of the layers of the retina? The retinal pigment epithelium is known to:
- participates in the development and electrogenesis of bioelectric reactions;
- together with choriocapillaries and Bruch's membraneforms a blood-retinal barrier;
- maintains and regulates ionic and water balance in the subretinal space;
- ensures the rapid revival of visual pigments after their destruction under the influence of light;
- is a light bioabsorber that prevents destruction of the outer portions of cones and rods.
Pathology of the pigment layer of the retina is observed in babies with hereditary and congenital ailments of the retina.
Cone structure
What is the cone system? It is known that the retina contains 6.3-6.8 million cones. They are located most densely in the fovea.
There are three types of cones in the retina. They differ in visual pigment, which perceives rays with different wavelengths. The diverse spectral susceptibility of cones can explain the mechanism of color perception.
Clinically, the abnormality of the cone structure is manifested by various transformations in the macular zone and leads to a disorder of this structure and, as a result, to a decrease in visual acuity, impaired color vision.
Topography
The surface of the retina is heterogeneous in its functioning and structure. In medical practice, for example, in documenting the abnormality of the fundus, its four zones are listed: peripheral, central, macular and equatorial.
The indicated zones in the functional meaning differ in the photoreceptors contained in them. So, cones are located in the macular zone, and its conditioncolor and central vision is determined.
Rods (110-125 million) are located in the peripheral and equatorial regions. The defectiveness of these two areas leads to a narrowing of the field of vision and twilight blindness.
The macular zone and its constituent segments: foveola, fovea, fovea centralis and avascular foveal region are functionally the most important areas of the retina.
Macular segment parameters
Macular zone has the following parameters:
- foveola - diameter 0.35 mm;
- macula - diameter 5.5 mm (about three diameters of the ONH);
- avascular foveal sphere - about 0.5mm diameter;
- central fovea - a point (depression) in the center of the foveola;
- fovea - diameter 1.5-1.8 mm (approximately one diameter of the optic nerve).
Vascular structure
The circulation of the retina is provided by a special system - the choroid, the retinal vein and the central artery. The vein and artery have no anastomoses. Related to this quality:
- disease of the choroid in the pathological process involves the retina;
- Obstruction of a vein or artery or their branches causes malnutrition of the entire or specific area of the retina.
Clinical and functional specificity of the retina in babies
In the diagnosis of diseases of the retina in babies, it is necessary to take into account its originality at birth and age-related kinetics. By the time of birththe retinal structure is practically molded, except for the foveal region. Its formation is completely completed by the age of 5.
Accordingly, the development of the central vision occurs gradually. The age specificity of the retina of children also affects the ophthalmoscopic picture of the fundus of the eye. In general, the appearance of the fundus of the eye is determined by the state of the optic disc and choroid.
In newborns, the ophthalmoscopic picture differs in three variants of a typical fundus: red, hot pink, pale pink parquet appearance. Pale yellow - in albinos. By the age of 12-15, in adolescents, the general background of the fundus of the eye becomes the same as in adults.
The macular area in newborns: the background is light yellow, the contours are blurred, clear edges and the foveal reflex appear by the first year of life.
The Problem of Illness
The retina is the shell of the eye that is inside it. It is she who is involved in the perception of the light wave, modifying it into nerve impulses and moving them along the optic nerve.
The problem of retinal diseases in ophthalmology is practically the most topical. Despite the fact that this anomaly accounts for only 1% of the total structure of eye diseases, disorders such as diabetic retinopathy, blockage of the central artery, rupture and detachment of the retina often become a factor in blindness.
Color blindness (weakening of color perception), chicken blindness (decline of twilight vision) and others are associated with retinal defectsdisorders.
Functions
We see the world around us in colors thanks to the organ of vision. This is done by the retina, which contains unusual photoreceptors - cones and rods.
Each type of photoreceptor performs its functions. So, during the day, the cones are extremely “loaded”, and when the flow of light decreases, the sticks are actively included in the work.
The retina of the eye supplies the following functions:
- Night vision is the ability to see perfectly in the dark. Sticks provide us with such an opportunity (cones do not work in the dark).
- Color vision helps to distinguish colors and their shades. With the help of three types of cones, we can see red, blue and green colors. Color blindness develops with a disorder of perception. Women have a fourth, extra cone, so they can distinguish up to two million colors.
- Peripheral vision gives the ability to perfectly identify the area. Peripheral vision works thanks to rods placed in the paracentral zone and on the periphery of the retina.
- Object (central) vision allows you to see well at various distances, read, write, perform work for which you need to consider tiny objects. It is activated by retinal cones located in the macula area.
Building features
The structure of the retina is represented as the thinnest shell. The retina is divided into two parts, unequal in general parameters. The largest zone is the visual zone, which consistsfrom ten layers (as mentioned above) and reaches the body of the ciliary. The front of the retina is called the "blind spot" because it does not have photoreceptors. The blind zone is divided into ciliary and iris in accordance with the areas of the choroid.
Heterogeneous layers of the retina are located in its visual part. They can only be studied at a microscopic level, and they all ply deep into the eyeball.
The functions of the pigment layer of the retina we considered above. It is also called the vitreous plate, or Bruch's membrane. As the body ages, the membrane becomes thicker and its protein composition changes. As a result, metabolic reactions slow down, and pigment epithelium appears in the form of a layer in the boundary membrane. The ongoing transformations speak of age-related ailments of the retina.
We continue our acquaintance with the layers of the retina further. The adult retina covers about 72% of the total area of the hidden surfaces of the eye, and its size reaches 22 mm. The pigment epithelium is more closely associated with the choroid than with other structures of the retina.
In the center of the retina, in the area that is closer to the nose, on the reverse side of the surface is the optic nerve head. There are no photoreceptors in the disc, and therefore it is referred to in ophthalmology as a "blind spot". In photographs taken under microscopic examination of the eye, it appears as a pale oval shape, 3 mm across and slightly raised above the surface.
It is in this zone that the initialstructure of the optic nerve. The middle part of the disc has a depression through which the vessels extend. They supply the retina with blood.
You must admit that the neural layers of the retina are rather intricate. We continue further. On the side of the optic disc, at a distance of about 3 mm, there is a spot. In its central part there is a recess, which is the most sensitive area of the retina of the human eye to the light flux.
The central fovea of the retina is called the "yellow spot". It is it that is responsible for a clear and clear central vision. It contains only cones. In the central part, the retina is represented only by the fovea and the surrounding area, which has a radius of about 6 mm. Then comes the peripheral segment, where the number of rods and cones decreases imperceptibly towards the edges. All inner layers of the retina end with a jagged border, the structure of which does not imply the presence of photoreceptors.
Illnesses
All diseases of the retina are divided into groups, the most famous of which are:
- retinal detachment;
- vascular diseases (occlusion of the main retinal artery, as well as the nodal vein and its branches, diabetic and thrombotic retinopathy, peripheral retinal dystrophy).
With dystrophic ailments of the retina, its tissue particles die off. Most often it occurs in older people. As a result, spots appear before the eyes, vision decreases, peripheral vision deteriorates.
When macular age-related degeneration are inflamedmacula cells - the central zone of the retina. In humans, central vision deteriorates, the shapes and colors of objects are distorted, a spot appears in the center of the eye view. The disease has a wet and dry form.
Diabetic retinopathy is a very insidious disease, as it develops against the background of an increased amount of sugar in the blood and has no symptoms at the beginning of the process. Here, if treatment is not started in time, retinal detachment may occur, which leads to blindness.
Macular edema refers to swelling of the macula (the center of the retina), which is responsible for central vision. An anomaly can appear due to the presence of a number of ailments, for example, diabetes, as a result of the accumulation of fluid in the layers of the macula.
Angiopathy refers to lesions of retinal vessels of different parameters. With angiopathy, a defect in the vessels appears, they become tortuous and narrow. The cause of the disease is vasculitis, diabetes mellitus, eye injury, high blood pressure, cervical osteochondrosis.
A simple diagnosis of vascular and degenerative diseases of the retina includes: measurement of eye pressure, study of visual acuity, determination of refraction, biomicroscopy, measurement of visual fields, ophthalmoscopy.
For the treatment of ailments of the retina can be recommended:
- anticoagulants;
- vasodilators;
- retinoprotectors;
- angioprotectors;
- B vitamins, nicotinic acid.
With detachments and ruptures of the retina, severe retinopathy, at the discretion of the ophthalmologist,surgical techniques are used.
