Eye diseases. The structure of the eyeball, cornea and sclera (the most important)

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Eye diseases. The structure of the eyeball, cornea and sclera (the most important)

Lecture notes, cheat sheets

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3. The structure of the eyeball, cornea and sclera

The eyeball has an irregular spherical shape. Its anterior section is more convex. The anteroposterior size of the eye is on average 16 mm in a newborn, 19 mm by one year of life, 20 mm by three, 21 mm by seven, 22,5 mm by fifteen, and 23 mm by age twenty. The weight of the eyeball of a newborn is about 3,0 g, and that of an adult is 8,0 g.

The eyeball has three shells: outer (represented by the cornea and sclera), middle (represented by the vascular tract) and inner (represented by the retina). Inside the eyeball are aqueous humor, lens, vitreous body, blood vessels.

The cornea is the anterior transparent part of the capsule of the eye. Its horizontal size in a newborn is 9,0 mm, by one year 10,0 mm, by three years 10,5 mm, by five years 11,0 mm, and by nine years it acquires the same dimensions as in adults, 11,5 .0,5 mm. The vertical dimension of the cornea is 78 mm smaller. The radius of curvature of the cornea is 1,12 mm. The thickness of this shell in the center in a child is 0,8 mm, in an adult 85 mm. The cornea contains up to XNUMX% water.

The cornea normally has transparency, specularity, shine, sensitivity, and sphericity. The cornea is the most powerful refractive medium in the eye (60,0 D in newborns and 40,0 D in adults).

The cornea is nourished by diffusion of nutrients from the marginal looped network and moisture from the anterior chamber. Sensitive innervation of the cornea is carried out by the trigeminal nerve, and trophic innervation is also due to the branches of the facial and sympathetic nerves.

The sclera is a dense opaque fibrous membrane, occupies 5/6 of the entire outer shell of the eye and anteriorly passes into the transparent cornea, and the surface layer of the sclera passes into the transparent shell later than the middle and deep ones. Thus, at the transition point, a translucent limbus border is formed.

In the posterior pole of the eye, the sclera becomes thinner and has a large number of holes through which the fibers of the optic nerve exit. This area of the sclera is called the lamina cribrosa and is one of its weak points. The plate under the influence of increased pressure can stretch, forming a deep excavation of the optic disc.

Outside, the sclera is covered with episclera, which forms the inner wall of Tenon's space. All oculomotor muscles are attached to the sclera. It has openings for the blood vessels and nerves of the eye.

In newborns and children of the first years of life, the sclera is thin, elastic, the choroid is visible through it, so the sclera has a bluish tint. With age, it becomes white, and by old age it turns yellow due to the degeneration of its tissue. Thin, elastic sclera in children of the first years of life under the influence of high intraocular pressure can stretch, which leads to an increase in the size of the eye (hydrophthalmos, buphthalmos).

The outer shell is the main optical medium, it gives the eye a shape, maintains a constant volume.

Author: Shilnikov L.V.

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