In a continuation of our articles about how the visual process works we’ll next cover the function of the cornea. As the outermost structure of the eye it only seems right to that it be the next topic covered.
What is the function of the cornea?
The cornea is as smooth and clear as glass but is strong and durable. The cornea helps the eye in several ways:
The surface of the cornea is where light begins its journey into the eye. The cornea’s mission is to gather and focus visual images. Because it is out front, like the windshield of an automobile, it is subject to considerable abuse from the outside world. It helps shield the rest of the eye from germs, dust, and other random debris. This protective task of the cornea is shared with the eyelids, the eye socket, tears, and the sclera. The cornea acts as the eye’s outermost lens and functions like a window that controls and focuses the entry of light into the eye. The cornea is responsible for 65-75 percent of the eye’s total focusing power. When light hits the cornea, it bends the light onto the lens. The lens then refocuses the light onto the retina. In order to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina. The cornea also serves as a filter, screening out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the lens and the retina would be highly susceptible to injury from UV radiation.
The cornea is masterfully engineered so that only the most expensive manmade lenses can match its precision. The smoothness and shape of the cornea, as well as its transparency, is vitally important to the proper functioning of the eye. If either the surface smoothness or the clarity of the cornea suffers, vision will be disrupted.
Although appearing to be one clear membrane, the cornea is composed of five distinct layers of tissue, each with its own function.
- Epithelium is the thin outermost layer of fast-growing and easily-regenerated cells.
- Bowman’s layer consists of irregularly-arranged collagen fibers and protects the corneal stroma. It is 8 to 14 microns thick.
- Stroma, the transparent middle and thickest layer of the cornea is made up of regularly-arranged collagen fibers and keratocytes (specialized cells that secrete the collagen and proteoglycans needed to maintain the clarity and curvature of the cornea)
- Descemet’s membrane is a thin layer that serves as the modified basement membrane of the corneal endothelium.
- Endothelium is a single layer of cells responsible for maintaining proper fluid balance between the aqueous and corneal stromal compartments keeping the cornea transparent.
Here’s a great video on the visual system.
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