The optic nerve belongs to highly specialized nerves and in structure resembles the cerebral cortex. The functions of the optic nerve are the transmission of nerve impulses obtained by various light stimuli from the retina to the visual center of the cerebral cortex.
Optic nerve: structure.
Retinal nerve fibers are combined into one optic nerve. It consists of four departments: intraocular, intracranial, intraorbital and intracranial. The intraocular section is a disc with a diameter of about 1.5 mm. The orbital part has a length of about 3 cm. The optic nerve has a length of 5-6 mm in the bone canal and 4-17 mm in the intracranial canal.
The location of the nerve endings in various areas of the retina is constructed according to a certain structure. So, when approaching the disk, the layer of nerve fibers has a large thickness, while the nerve fibers in the disk are bent at right angles, forming the intraocular section of the optic nerve.
The optic nerve starts from the disc and has an ending in chiasm. The optic nerve in an adult has a length of 35 to 55 mm. It is covered with three meninges: hard, soft and arachnoid. The space between these shells is filled with a special liquid with a complex chemical composition.
The optic fibers from both eyes exit into the cranial cavity, where they connect in the region of the Turkish saddle. The place of their association is called chiasm. It partially overlaps the visual fibers. Crossing is subject to those fibers that come from the inner parts of the retina. Crossover data are very important for the correct diagnosis of certain diseases. After crossing, optic tracts are formed, which at the base of the brain bend around its leg and end in the cranked bodies, the anterior quadrupole, as well as in the posterior region of the optic tubercle. Cranial bodies are most important when transmitting visual impulses to the cerebral cortex. Those fibers that end in the optic tubercle carry out the reflex regulation of visceral and somatic reflexes. And the anterior quadruple is used to transmit pupil reflexes. The optic fibers pass to the nuclei of the oculomotor nerve, in which they enter the eye, ending in the muscles of the iris.
Processes of a pathological nature that develop in the optic nerve have a close relationship with its structure. Due to the large number of capillaries that are contained in the partitions and surround the optic nerve, as well as increased sensitivity to toxins, conditions are created for toxic effects on the visual nerve endings and infection with infectious diseases. With an increase in intraocular pressure, the disk becomes the most vulnerable spot, as a result of which, with glaucoma, it is pressed and a fossa forms. High intracranial pressure delays fluid outflow in the interblock space, resulting in compression of the nerve and swelling of the interstitial substance contained in it.
The disk is also adversely affected by hydrodynamic and hemodynamic shifts, which lead to a decrease in intraocular pressure. Any changes in the optic nerve always lead to a violation of the functions of peripheral or central vision, while there may be a deterioration in twilight vision and color differences. Diseases relating to the optic nerve are degenerative, allergic or inflammatory in nature. Sometimes there are tumors and abnormalities in the development and structure of the optic nerve.