Your eye is a complex organ connected to your brain by the optic nerve. The optic nerve sends visual signals from the eye to the brain, where they are interpreted as images. The optic nerve is relatively small, varying in length between 1.3 and 2.2 inches, and at its widest point, inside your cranial cavity, it is still less than one-fifth of an inch wide. Yet the optic nerve is made up of more than one million tiny nerve fibers, much like a fiber optic cable. Once these nerve fibers are cut, they cannot be reconnected. That is why it's impossible to transplant a whole eye. Even if a surgeon could implant the eye into the eye socket, the eye still would not be able to transmit signals to the brain through the optic nerve and thus would not provide sight.

By contrast, corneal transplantation is not only possible, it is a procedure more than a century old.

A healthy, clear cornea is necessary for good vision. If your cornea is injured or affected by disease, it may become swollen or scarred. A cornea with scarring, swelling or an irregular shape can cause glare or blurred vision. In a corneal transplant, the damaged or unhealthy cornea tissue is removed and clear donor cornea tissue is put in its place. Read more about corneal transplant surgery options.

While corneal transplants are the most common type of eye-related transplantation, it is not the only one. Surgeons have also been able to successfully perform eyelash transplantation. However, the procedure carries significant risks, including scarring, and is not recommended as a cosmetic procedure.

In patients suffering from disorders of the sclera or the conjunctiva (the external eye), doctors have been able to transplant amniotic membranes which have aided in the healing and regeneration of ocular surface tissues.

Doctors continue to explore whether it is possible to transplant other parts of the eye. In July 2010, French doctors announced that they had transplanted eye lids and tear ducts as part of a full-face transplant for a man with a genetic disorder. Researchers are also focusing on how to replace damaged retinal cells with healthy transplants.

In fact, it has been shown in recent clinical trials that human stem cells can be cultivated to become retinal pigment epithelium (RPE) cells. In the near future, we can expect RPE transplants. This is good news for people suffering from macular degeneration and Stargardt's Disease.

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