The eyes are complex sensory organs. They are designed to optimize vision under conditions of varying lighting. The basic elements are similar to those of an average photography camera.
The primary function of the eye is to focus light. For the eye to see, light rays must be bent or "refracted" to meet at a single point through the cornea, the clear window at the front of the eye that provides most of the focusing power. The transparent dome cornea is a firm covering and is susceptible to dryness and abrasion injuries.
The iris of the eye is the color portion behind the cornea. Our eye color is a function of the amount of pigment within the iris (brown eyes have the most pigment, while blue eyes have the least). The iris contains muscles that open and close its central opening called the pupil in response to decreases and increases in light exposure (exactly like the camera aperture).
Light then travels through the lens, where it is fine-tuned to focus properly on the retina, the nerve layer that lines the back of the eye and connects to the brain. The retina acts like the film in a camera, and clear vision is achieved only if light from an object is precisely focused onto it. If the light focuses either in front of or behind the retina, the image you see is blurred. A refractive error means that the shape of eye structures does not properly bend the light for focusing.
Now that you have had a brief introduction to the structure of the eye, it is easier to explain what part of the eye is used when you become an eye donor. The father of one of the staff members of MedicineNet.com was an eye donor, and upon his death was able to give vision to someone who needed it.
The cornea is the part of the eye that is used for transplant when you become an eye donor. A corneal transplant is "...a surgical procedure, which involves replaceing a disc-shaped segment of an impaired cornea with a similarly shaped piece of a healthy donor cornea." (1) Only the cornea can be transplanted. The entire eye, however, may be used for research and educational purposes.
Corneal transplant is one of the most frequently performed human transplant procedures. Since 1961, more than 549,889 corneal transplants have been performed, restoring sight to men, women, and children ranging in age from nine days to 103 years. Over 90% of all corneal transplant operations successfully restore the corneal recipient's vision.(1)
So you ask, why should I become an eye donor? There is no substitute for
human tissue. The transplantation process depends upon the priceless gift of
corneal donation from one human to the next. Donated human eyes and corneal
tissue are used for research, education, and transplantation. Anyone can become
an eye donor. Cataracts, poor eyesight, or age do not prevent you from being a
donor. It is important for individuals wanting to be donors to inform family
members of their wishes.(1)
For information about eye care, please read the Eye Care article.
(1) Portions of the above information was provided with the kind permission of the Eye Bank Association of America (http://www.restoresight.org/general/about_ebaa.htm).