The eyeball, or organ of vision, despite its miniature size, has a very complex anatomical structure. Macroscopically, this organ has the appearance of a ball, which is not quite ideal, because its visible front part has a greater curvature than the back surface hidden from the eyes. This fact also determines the uneven size of the eye in different directions. Due to the bulge of the cornea, the anteroposterior organ of vision is the largest. On average, an adult healthy person approaches 24 mm. The transverse and vertical axes are approximately the same: the average size of the transverse axis of the eye is 23.6 mm and 23.3 mm for the vertical.
The structure of the eyeball
In the organ of vision, three important membranes are distinguished, which perform different functions from each other.
- Outer or fibrous membrane. It distinguishes two parts, which are completely unequal in anatomical terms. The largest part of the fibrous membrane belongs to the sclera, or the protein membrane, the rest to the cornea. The sclera is an absolutely opaque fabric with a whitish hue. Thanks to its color, the eyeball, in particular its opaque part, was called the protein. In clinical practice, the condition of the sclera can determine various pathological conditions that occur in the eye and in the body as a whole. So, redness of the eyeball can talk about acute inflammatory phenomena in the organ of vision: conjunctivitis, keratitis, uveitis, etc. And the yellowing of the protein coat indirectly indicates a liver disease - hepatitis. The eyeball, which is also represented in front by the cornea, appears in this place painted in brown, green or blue. However, this is not the cornea itself, but the iris shining through it. The cornea is absolutely colorless and transparent, it has no blood vessels, only a clot of nerve endings, allowing it to be the most sensitive element in the body. If the eyeball is represented in the percentage of parts of its fibrous membrane, then the cornea accounts for less than 16%.
- The middle, or choroid. It is adjacent to fibrous, but not throughout its entire length, but only in its scleral part. Where the sclera passes into the cornea, the vascular tract is separated from it and goes at a certain distance from the cornea. In the middle shell there are three parts: the iris, the ciliary (ciliary) body and the choroid. The iris serves as a kind of diaphragm that regulates the luminous flux, going deep into the eye, to its light-perceiving structures. The pupil takes over the function of the regulator, which can expand with a deficit of light and narrow with an excess of it. The ciliary body is necessary for the continuous production of intraocular fluid, which is necessary for nourishing the eye and maintaining tone in it. The choroid, or the choroid itself, is represented by a network of vessels supplying the internal structures of the eye.
- The inner, or mesh shell. This is the most important part of the organ of vision, which responds to light and transfers the received visual information further to the brain cortical structures. The retina is a very thin and fragile tissue, in which, as a rule, two main areas are distinguished: ciliary, which does not have highly differentiated cells, and optically active, in which these cells are. Their separation (the dentate line) can be seen in a study such as cycloscopy, when the fundus is examined .
In addition to the membranes, the eyeball has a vitreous body, which gives it a characteristic rounded shape and is involved in light refraction, as well as the lens, which is involved in accommodative processes and refraction of light beams.