Eye diseases. The structure of the retina and optic nerve (the most important)

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Eye diseases. The structure of the retina and optic nerve (the most important)

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5. The structure of the retina and optic nerve

The retina contributes to the lining of the entire inner surface of the vascular tract. It is also a peripheral part of the visual analyzer. Under microscopic examination, ten layers are distinguished in it. At the place corresponding to the transition of the choroid itself into the flat part of the ciliary body (the region of the dentate line), only two layers of epithelial cells are preserved from its ten layers, passing to the ciliary body, and then to the iris. In the region of the dentate line, as well as at the exit of the optic nerve, the retina is tightly fused with the underlying formations. For the rest of its length, it is held in a constant position by the pressure of the vitreous body, as well as the connection between the rods and cones and the retinal pigment epithelium, which is genetically related to the retina, and anatomically closely related to the choroid.

There are three types of neurons in the retina: rods and cones, bipolar cells, and multipolar cells. The most important area of the retina is the yellow spot, located at the posterior pole of the eyeball. The macula has a central fossa. In the area of the central fovea of the macula, instead of ten layers, only three or four layers of the retina remain: the outer and inner border plates and the layer of cones and their nuclei located between them. However, newborns have all ten layers in the macula area. This, along with other reasons, explains the child’s low central vision. In the central zone of the retina, predominantly cones are located, and towards the periphery the number of rods increases.

Nerve cell fibers (about 100) form the optic nerve, passing through the lamina cribrosa of the sclera. The inner part of the optic nerve is called the disc (nipple). It has a somewhat oval shape, its diameter in newborns is 000 mm, in adults it reaches 0,8 mm. In the center of the disc are the central retinal artery and vein, which branch and participate in feeding the inner layers of the retina. Topographically, in addition to the intraocular one, the intraorbital, intracanalicular and intracranial parts of the optic nerve are distinguished. In the cranial cavity, the optic nerve forms a partial decussation of the nerve fibers of the chiasm. The optic tracts emerge from the chiasm in the form of two separate trunks, ending in the primary visual centers (external geniculate bodies, visual tuberosities). Through the internal capsule in the form of a bundle, the optic fibers go to the cortical visual centers, ending in the occipital lobe, in the region of the avian spur furrow (field seventeen to nineteen according to Brodmann). It is in this area that the visual image of the surrounding world is formed.

Author: Shilnikov L.V.

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