The cornea is the eye’s outermost layer. It is the clear, dome-shaped surface that covers the front of the eye and plays an important part in the eye’s visual acuity. The cornea is the transparent layer which covers the iris and pupil in the front of the eye. Corneal tissue consists of five basic layers: epithelium, Bowman’s layer, stroma, Descemet’s membrane and endothelium. Although the cornea is clear, it contains a highly organized group of cells and proteins. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor that fill the chamber behind it.
The cornea, one of the protective layers of the eye, serves two functions:
First, along with the eyelid, eye socket, and sclera (white part of the eye), and the tear film, the cornea shields the eye from dust, germs, and other harmful matter. Second, as the eye’s outermost lens, it is the entry point for light into the eye. When light strikes the cornea, it bends, or refracts, the incoming light onto the lens. The lens further refocuses the light onto the retina, a layer of light-sensing cells lining the back of the eye.
To see clearly, the cornea and lens must focus the light rays precisely on the retina. This refractive process is similar to the way a camera takes a picture. The cornea and lens in the eye act as would a camera’s lens. The retina approximates the film. If the cornea is unable to focus the light properly, then the retina receives a blurry image.
LASIK, PRK and Lens refractive procedures can frequently correct problems of focus such as near sightedness (myopia), far sightedness (hyperopia) and astigmatism.
Corneal and external diseases involve the cornea, anterior chamber of the eye, iris, lens, conjunctiva and eyelids, including cataracts; corneal allergies, infections and irregularities; refractive errors (nearsightedness, farsightedness and astigmatism); conjunctivitis (pink eye); dry eye; tear disorders; keratoconus; pterygium; Fuch’s Dystrophy and many others.
Some trauma, including projectile foreign bodies, lacerations and blunt trauma can cause scarring that clouds the cornea.
Hereditary conditions including degenerations and dystrophies may also cloud the cornea. The most common hereditary condition seen in young people is keratoconus, a condition in which the cornea assumes a cone shape. This is common in children with Down’s syndrome and in people with allergic conjunctivitis. These patients may be able to use contact lenses or glasses for a period of time, but may eventually develop scarring and high astigmatism that cannot be corrected without corneal transplantation. Collagen cross- linking with riboflavin usually halts the progression of keratoconus and may prevent the need for corneal transplant.
Fuchs dystrophy is a genetic condition affecting the inner lining cells of the cornea – the endothelium. The cells gradually fail in their function to keep the cornea clear. It may become necessary to perform a corneal transplant.
The eye surface can be severely damaged by a number of problems, including:
These problems can result in extensive damage on the eye surface, leading to new blood vessel formation and scarring — damage which results in loss of vision.
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