What are retinal layers ? What are their functions? You will find answers to these and other questions in the article. The retina is called a thin shell 0.4 mm thick. It is placed between the choroid and the vitreous body and lines the hidden surface of the eyeball. The layers of the retina will be discussed 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 disc and along the dentate 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 retinal layers. But this information is very important. The structure of the retina is intricate and consists of the following ten layers (list from the choroid):
- Pigmented. This is the outer layer of the retina adjacent to the hidden surface of the vascular film.
- A layer of cones and rods (photoreceptors) - color and light-reflecting components of the retina.
- Membranes (border outer plate).
- Nuclear (granular) outer layer of the nucleus of cones and rods.
- The reticular (mesh) outer layer - the processes of cones and rods, horizontal and bipolar cells with synapses.
- The nuclear (granular) inner layer - the body of bipolar cells.
- Reticular (reticular) inner layer of ganglion and bipolar cells.
- Layer of multipolar ganglion cells.
- A layer of fibers of the optic nerve - axons of the cells of the ganglia.
- The borderline inner membrane (lamina), which is the most hidden retinal layer, bordering the vitreous.
Those fibers that leave the ganglion cells form the optic nerve.
Neurons
The retina forms three neurons:
- Photoreceptors - cones and rods.
- Bipolar cells that synaptic connect the processes of the third and first neurons.
- Ganglion cells, the 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 retinal layers? Pigmented retinal epithelium is known to:
- participates in the development and electrogenesis of bioelectric reactions;
- together with the choriocapillaries and Bruch's membrane forms a hematoretinal barrier;
- maintains and regulates the ionic and water balance in the subretinal space;
- provides rapid revival of visual pigments after their destruction under the influence of light;
- is a bioabsorbent of light, which prevents the destruction of the outer sections of cones and rods.
Pathology of the retinitis pigmentosa is observed in infants with hereditary and congenital retinal ailments.
Cone structure
What is the cone system? The retina is known to contain 6.3–6.8 million cones. Most densely placed in 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 interpret the mechanism of color sensation.
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, and color vision impairment.
Topography
In its functioning and structure, the surface of the retina is heterogeneous. In medical practice, for example, in documenting the abnormality of the fundus, four zones are listed: peripheral, central, macular and equatorial.
These zones in the functional value differ in the photoreceptors contained in them. So, in the macular zone there are cones, and its state determines the color and central vision.
In the peripheral and equatorial regions bacilli (110-125 million) are located. The deficiency of these two sites leads to a narrowing of the field of vision and twilight blindness.
The macular zone and its constituent segments: foveola, fovea, central fossa and avascular foveal region are functionally the most important areas of the retina.
Macular Segment Parameters
The macular zone has the following parameters:
- foveola - diameter 0.35 mm;
- Macula - 5.5 mm across (about three diameters of the optic disc);
- avascular foveal sphere - a diameter of about 0.5 mm;
- central fossa - a point (deepening) in the center of the foveola;
- fovea - a diameter of 1.5-1.8 mm (approximately one diameter of the optic nerve).
Vascular structure
The retinal circulation is provided by a special system - the choroid, retinal vein and central artery. Veins and arteries lack anastomoses. In connection with this quality:
- an ailment of the choroid in the pathological process involves the retina;
- obstruction of the vein or artery or its branches causes malnutrition of the whole or a certain area of the retina.
Clinical and functional specificity of the retina in babies
In the diagnosis of retinal ailments in infants, it is necessary to take into account its originality at birth and age kinetics. By the time of the birth of the structure of the reticular membrane is almost formed, with the exception of the foveal region. Its formation completely ends by 5 years of life of the baby.
Accordingly, the development of central vision is gradual. The age specificity of the retina of children affects the ophthalmoscopic picture of the bottom of the eye. In general, the type of fundus of the eye is determined by the condition of the optic nerve disc and choroid.
In newborns, the ophthalmoscopic picture differs in three variants of the typical fundus: red, hot pink, pale pink parquet appearance. Pale yellow - in albinos. By 12-15 years of age in adolescents, the general background of the bottom of the eye becomes the same as in adults.
The macular zone in newborns: the background is light yellow, the contours are blurry, clear edges and the foveal reflex appear by the first year of life.
The problem of ailments
The retina is the shell of the eye that is inside it. It is she who participates in the perception of a light wave, modifying it into nerve impulses and moving them along the optic nerve.
The problem of retinal ailments in ophthalmology is almost 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, central artery obstruction, rupture and retinal detachment often become a factor of blindness.
Color blindness (weakening of color perception), night blindness (decline in twilight vision) and other disorders are associated with retinal defectiveness.
Functions
We see the world around us in colors thanks to the organ of vision. This is done due to the retina, on which unusual photoreceptors are placed - cones and rods.
Each type of photoreceptor performs its function. So, during the day the cones are “loaded” to the maximum, and when the light flux decreases, the rods are actively included in the work.
The retina provides the following functions:
- Night vision is the ability to see well in the dark. We are given the opportunity to sticks (in the dark, the cones do not work).
- 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 disturbance in perception. Women have a fourth, additional cone, so they can distinguish up to two million color shades.
- Peripheral vision gives the ability to perfectly identify the terrain. Lateral vision works thanks to sticks located in the paracentral zone and on the periphery of the retina.
- Objective (central) vision allows you to clearly see at various distances, read, write, perform work, for which you need to consider tiny objects. It is activated by retinal cones located in the area of the macula.
Structural features
The structure of the retina is presented in the form of a very thin shell. The retina is divided into two parts, unequal in general parameters. The largest zone is the visual, which consists of ten layers (as mentioned above) and reaches the ciliary body. The front of the retina is called the “blind zone,” since there are no photoreceptors in it. The blind zone is divided into ciliary and iris in accordance with the areas of the choroid.
Inhomogeneous layers of the retina are in its visual part. They can be studied only at the microscopic level, and they all ply deep into the eyeball.
The functions of the pigment layer of the retina we examined 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 a pigment epithelium also appears in the boundary membrane as a layer. The transformations taking place indicate age-related ailments of the retina.
We continue our acquaintance with the layers of the retina further. The retina of an adult covers about 72% of the entire area of the hidden surfaces of the eye, and its size reaches 22 mm. Pigmented epithelium is associated with the choroid more closely than with other retinal structures.
In the center of the retina, in the area that is located closer to the nose, on the back of the surface is the optic disc. There are no photoreceptors in the disk, and therefore it is referred to as a “blind spot” in ophthalmology. In the photo taken by microscopic examination of the eye, it looks like a pale oval shape, having a diameter of 3 mm and slightly rising above the surface.
It is in this zone that the initial structure of the optic nerve begins from the axons of the ganglionic neurocytes . The middle part of the disk has a recess through which the vessels stretch. It is they who supply the retina with blood.
Agree, the nerve layers of the retina are pretty intricate. We continue further. A spot is located on the side of the optic nerve disk , at a distance of about 3 mm. In its central part is a recess, which is the most sensitive to the light flux zone of the retina of the human eye.
The central fossa of the retina is called the "yellow spot." It is she who is responsible for a clear and clear central vision. It contains only cones. In the central part, the retina of the eye is represented only by the fossa and the surrounding area, which has a radius of about 6 mm. Then comes the peripheral segment, where the number of rods and cones is imperceptible to the edges. All inner layers of the retina end with a dentate border, the structure of which does not suggest the presence of photoreceptors.
Ailments
All diseases of the retina are divided into groups, the most famous of which are:
- retinal disinsertion;
- vascular ailments (occlusion of the main retinal artery, as well as the nodular vein and its branches, diabetic and thrombotic retinopathy, peripheral retinal dystrophy).
With dystrophic ailments of the retina, its tissue particles die. Most often this happens in older people. As a result, a person has spots in front of his eyes, vision decreases, peripheral vision worsens.
With age-related macular degeneration, the cells of the macula, the central zone of the retina, become inflamed. In humans, central vision deteriorates, the shapes and colors of objects are distorted, a spot appears in the center of the eye's view. The ailment 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 healing is not started in time, detachment of the retina may occur, which leads to blindness.
Macular edema is called edema of the macula (center of the retina), which is responsible for central vision. An anomaly can occur 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 is called retinal vascular lesions of various parameters. With angiopathy, a vascular defect appears, they become crimped and narrow. The cause of the disease is vasculitis, diabetes, eye injury, high blood pressure, osteochondrosis of the cervical spine.
A simple diagnosis of vascular and dystrophic diseases of the retina includes: measuring eye pressure, studying visual acuity, determining refraction, biomicroscopy, measuring the fields of vision, ophthalmoscopy.
For the treatment of retinal ailments, the following can be recommended:
- anticoagulants;
- vasodilator drugs;
- retinoprotectors;
- angioprotectors;
- B vitamins, nicotinic acid.
With retinal detachments and tears, severe retinopathies, surgical methods can be used at the discretion of the ophthalmologist.