Vision is the most important analyzer that allows a person to perceive about 80% of information about the outside world. A person who has never encountered vision problems rarely thinks about how one of the most important mechanisms in his body works.
Eyeball
The complex structure of the human eye allows us to distinguish between colors, distances to objects, their shape and other aspects that are important in the perception of the outside world. During normal operation of the ocular apparatus, all layers of the eyeball must perform their specific functions.
Information is perceived by the peripheral part of the visual system, which also includes protective mechanisms:
- Eye socket.
- Or rather the eyelid.
- Lower eyelid.
The eyeball itself is located directly in the orbit and is surrounded by muscle fibers, nerve plexuses and fiber. In the structure of the eye, three shells are distinguished:
- Fibrous membrane (outer).
- Vascular (medium).
- Photosensitive (internal).
The essence of the fibrous membrane
The outer shell of the eyeball is a kind of front part of the eye, which is also divided into two sections:
- The first transparent, which is called the cornea.
- The second, which occupies a large part, is whitish, which is commonly called sclera.
Between the indicated sections, a circular scleral groove passes.
The fibrous membrane of the eye consists of sufficiently dense connective fibers. Due to the density and elasticity of both the cornea and sclera, they allow you to give the eye a certain shape.
The structure of the cornea
The transparent layer of the fibrous membrane, called the cornea, makes up only a fifth of the entire outer layer. The cornea itself has a transparent consistency, and at the point of transition into the sclera it forms a limb.
In its shape, the cornea of the eye is an ellipse with a diameter of about 12 mm and a layer thickness of only 1 mm. This membrane has absolutely no vessels, is absolutely transparent, and all its cells are optically oriented. It is believed that the cornea of the eye grows to the size characteristic of an adult, already by 10-12 years of life of the child.
Despite its subtlety, this part of the fibrous membrane is divided into several layers:
- Epithelial.
- Bowman's shell.
- Stroma (the thickest layer of the cornea of the eye).
- Descemet's shell.
- Back epithelial layer.
The structure of the fibrous membrane is designed in such a way that a huge number of nerve receptors are located in the cornea, therefore it is extremely sensitive to external influences. The cornea transmits light, but due to its refractive ability it modifies and refracts the rays.
There are no blood vessels in this layer, for this reason all metabolic processes are very slow.
Corneal function
It is customary to distinguish two main functions that the layer of the cornea of the eye performs:
- Protective function. The high strength of the cornea, together with increased sensitivity and rapid regeneration of the upper layer of the epithelium, allows the cornea to fully cope with the task assigned to it.
- Light transmission and light refraction. Acting as an optical medium, due to its shape and transparency, it provides the correct refraction of light rays. The degree of this refraction depends on the individual characteristics of a person.
What is sclera?
The second important part of the fibrous membrane of the eyeball is the sclera, or as it is also commonly called, the protein membrane. Due to its density, it helps maintain the necessary shape of the eyeball and protects its internal contents.
In a healthy state, this layer has a whitish hue and is colloquially called “eye protein”.
The sclera is attached to the eye muscles. The layer thickness is heterogeneous, but sufficient to perform surgical procedures without piercing the sclera through and through.
The entire layer consists of a dense fibrous fabric, which has a high degree of elasticity. It contains a large number of collagen fibers, which in the front part of the layer are oriented parallel to the equator, in deeper layers they acquire a loop-like shape.
The blood supply to the sclera is scarce, it does not contain a large number of blood vessels. In contrast to the cornea, in the protein membrane there are practically no nerve endings and its sensitivity is extremely small, which increases the risk of pathological processes in this part of the eyeball.
When carrying out any surgical procedures on the eye, it must be borne in mind that four important vortical veins pass through the sclera.
Sclera functions
For the full operation of the ocular apparatus, the functions of the fibrous membrane in the sclera are reduced to the following:
- Protective. It is considered to be the main function. Sclera allows you to protect other layers of the eyeball from external influences, including from mechanical damage.
- Wireframe. The sclera structure supports the spherical shape of the eyeball. It is to her that the ligaments, nerve endings, blood vessels and muscle are attached, which are also responsible for the synchronization of the eyes.
- Optical Unlike the cornea, the sclera is opaque, which limits the amount of light entering the retina. This provides a person with a good level of vision.
- Stabilization. The scleral layer is directly involved in the stabilization of eye pressure, which affects the work of all departments of the eyeball. With constant changes in intraocular pressure, the collagen fibers of the sclera wear out.