The cornea is the transparent, outer covering of the front of the eye. Besides offering protection to the eye, it also acts as a refracting surface and works to focus the light entering the eye. In fact, it is the cornea that does over 60% of the focusing the eye needs to be able to see objects clearly. It is in many ways like the crystal on a watch - it protects the watch and at the same time gives a clear view though it.
The cornea is one of the most sensitive parts of the body and there are more nerve endings here than anywhere else in the body. Since the cornea contains no blood vessels, there is nothing to affect its transparency or its shiny surface. Even though the cornea is made up of five separate layers, it is only 0.5 millimeters thick.
Because the cornea is not just smooth and clear but also strong, it acts as the eye's shield and protects it from dust, germs and other external matter that may enter the eye and cause injury. Along with the eyelids and the tear ducts, the cornea keeps the eyes clean in a manner that would put the most advanced washing machine or car wash to shame.
In regard to your vision, the cornea functions like a camera lens. It refracts incoming light onto the lens in the eye. The lens takes this partly focused light and does the fine focusing needed to direct it correctly to the retina, a layer of light sensing cells at the rear of the eye that begins the process of converting the light into images. What the retina senses is sent to the brain, which refines the inputs and converts them into images that we can understand. Think of the cornea as the camera lens and the retina as the film. If the light is not focused correctly on the film, the image captured is blurred.
Have you ever seen a photographer use a filter to block out some types of light from the picture he is taking? The cornea does that work also. It limits the amount of ultraviolet light that enters the eye. An excess of ultraviolet light and radiation can cause serious damage to the eye.
Because the cornea is so strong, it is easy to take it for granted. No one thinks twice about the occasional speck of dust in the eye. It's cleaned out as soon as possible and we carry on. It may happen however, that a big speck, or one that is rubbed into the eye in an unthinking reaction, could scratch the cornea. If the scratch is slight the cornea is self healing and covers it up and often we do not even realize what has happened. But if the scratch goes deeper and is beyond the ability of the cornea to quickly cure itself, the eye can become painful and red, with blurred sight and a great sensitivity to light. This kind of damage is not serious, but needs medical care and may take days or even weeks to heal. If the scratch should go very deep, the cornea could become scarred which will cause vision impairment and a corneal transplant may be needed.
A transplant of the cornea entails taking out that part of the cornea that has become scarred or cloudy because of age or sickness and replacing it with a clear cornea. The transplant is usually sourced from an eye bank. The new cornea is sewn in place with a very fine thread that may need to remain for months or even years, until the doctor is certain that the transplant has taken hold. Once he is sure, the stitches are easily removed. Eye drops are also prescribed after the surgery to both speed up the healing process and prevent infection.
Corneal transplants are very common these days and an average of 40,000 are done every year in the US alone. Because of the new developments in surgical methods and the technology available, the success rates of corneal transplants are extremely high.
A very common problem affecting the cornea is what is called dry eye. The eye must remain moist to stay lubricated, heal minor wounds and to protect the eye from infection. The moisture comes from the tear ducts which are always secreting some amount of liquid. If the tear ducts are unable to secrete enough, the eye becomes dry and feels scratchy as if dust is in it. This problem is usually treated with eye drops, but if the symptoms are noticed, self medication is not advised. With the eyes it is always better to consult a doctor.
Bookmark This Page