Is An Eye Transplant Really A Possibility?
A successful eye transplant would certainly be a wonderful thing if, like a heart transplant, or a kidney transplant, the entire eye could be totally replaced with a new (or slightly used) one. Unfortunately, the technology has not yet reached the point where a defective eye can be removed from its socket and a working eye inserted in its place, and there is no guarantee that total eye replacement will ever become a possibility.
Eye Transplant Is A Misnomer
We occasionally hear about successful eye transplants, but one has to look beyond the headlines, as the headlines are misleading. When one undergoes an eye transplant it is more correct to refer to it as a corneal transplant. In a corneal transplant, only the transparent front portion of the eye is removed and replaced. Not the entire eye. This transparent part of the eye is where light first enters, before it reaches the iris, the lens, and finally the retina. A common defect involving the cornea is a cataract, which clouds the image that is to be recorded on the retina. A cataract can be removed without having to replace the cornea, but if the cornea itself is damaged it will have to be replaced to fully restore sight.
“Eye Transplants” Are Commonplace
A corneal transplant is one of the more common organ transplant procedures. Many more people receive corneal transplants than receive heart, kidney, or bone marrow transplants. An eye transplant (corneal transplant) is generally successful, the reason being that the cornea does not contain blood vessels, so rejection of transplanted tissue is rare. As is the case with a heart or kidney transplant, the cornea to be transplanted must be donated. The donor being someone who prior to his or her death has elected to donate one or more organs. Since the cornea in the average person is generally quite healthy, there is seldom a shortage of donor corneas. When a person dies, the cornea begins to cloud over. Transparency can be restored, but there is a time limit. If however the cornea is surgically removed shortly after a donor's death, it can successfully be stored in an eye bank for a relatively long period of time.
A Problem With Splicing
Transplanting an entire eye, as previously noted, is not currently possible. It may never be possible, although advances in science and technology continue to amaze us. If an entire eye is to be replaced it must be removed, which means the optic nerve must be severed. The optic nerve sends signals to the brain, and what we see is due to activity within the brain itself. No optic nerve, no signals for the brain to process. Cutting the optic nerve is not like cutting a telephone line. It is more like cutting through a fiber optics cable. The optic nerve is a very tiny cable however, and contains over a million fibers. Imagine trying to correctly splice together a million microscopic fibers in the relatively short period allowed during a surgical procedure. You can see the challenge involved in any attempt to successfully transplanting an entire eye.
A report has been published describing a surgical procedure which partially restored sight to a person who had lost the sight in one eye. This surgery was referred to as a "miracle" eye transplant, although it wasn't a transplant at all. What the procedure consisted of was the implanting of a microchip behind the retina of the defective eye. When light (an image) strikes the retina, the microchip, which contains just under two thousand sensors, sends signals to the optic nerve and to the brain, enabling the person to see. A thousand or so sensors isn't the same as a million signal transmitting fibers, but the person with the microchip implant was able to read letters of the alphabet, a giant step beyond being totally blind. Efforts in this area are continuing, and one can reasonably expect improved results as the years go by.
Tadpole Eye Transplants? - It's A Start
Another intriguing area of research involves growing a replacement eye or a portion of an eye through the use of stem cell technology. Some success has been achieved in growing replacement eyes using this technology, but this is work involved the use of tadpoles, not humans or other mammals. The results have encouraged further research, but there is admittedly a vast difference between a tadpole eye transplant and a human eye transplant. Research has also been done using mice as subjects. Those results have not been as successful as was the case with tadpoles, but the experiments on mice raise the possibility that certain portions of an eye, but not the total eye, could be replicated. Optimists see the possibility of successful eye transplants within the lifetime, while skeptics generally regard complete eye transplants as the stuff of science fiction, and likely to remain so. But, as we said before, advances in science and technology will no doubt continue to amaze us.
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