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The cornea is the transparent tissue that covers the front of the eye. (Read about "The Eye") It provides a physical barrier that protects the eye. It is also the part of the eye that helps focus light to create an image on the retina. The retina is the paper-thin tissue at the back of the eye that starts the translation of light into vision. If the shape of the cornea isn't right, the image on the retina will be distorted. Since refraction is the bending and focusing of light, imperfections in the focusing power of the eye are called refractive errors.
The Food and Drug Administration (FDA) and the American Academy of Ophthalmology (AAO) say there are four primary types of refractive errors:
Glasses or contact lenses can compensate for the eye's imperfections. AAO points out that glasses, when they have a special coating, can also help protect your eyes from harmful light rays, such as ultraviolet (UV) light rays. (Read about "Eyes and Sun") Sometimes the entire lens of the glasses is the same prescription. Sometimes it's divided; for example, bifocals can have a correction for reading on the bottom half of the lens and another for seeing distance on the top. People may also combine prescriptions to read a computer screen through the top portion of a lens. (Read about "Computers and Health")
Contact lenses are another option for correcting vision. FDA says there are three basic options: hard contacts (which do not allow oxygen transmission through the lens), rigid gas-permeable contacts (which do allow oxygen transmission through the lens) and soft contacts. Soft lenses, which are the most popular, can be disposable or planned-replacement. Lenses can also be prescribed for either daily wear or for extended wear. Extended wear lenses may be left in the eyes while the wearer is both awake and asleep. There are advantages and risks to all types of lenses. FDA cautions that people should never wear their contact lenses for longer periods than recommended by their eye care professional. You can discuss the many different options, as well as necessary precautions, with your doctor or eye care professional. This is essential because the National Eye Institute (NEI) says that corneal infections, although relatively infrequent, are the most serious complication of contact lens wear. (Read about "Keratitis")
In addition to removable lenses, FDA has more recently approved a plastic lens that is permanently implanted into the eye to correct moderate to severe nearsightedness. FDA says there are restrictions and potential complications with this type of lens that should be carefully discussed with your doctor.
FDA has also approved a contact lens that is worn overnight and removed during the day. During the day, nearsightedness is corrected or reduced, according to FDA. Again, there are restrictions and potential complications with this type of lens that should be carefully discussed with your doctor.
Surgery, called refractive surgery, can also be used to correct the focusing power of the eye. There are a number that are used. Perhaps the best known is LASIK.
LASIK stands for Laser-Assisted In Situ Keratomileusis. FDA says LASIK permanently changes the shape of the cornea, using an excimer laser.
LASIK is done using a topical anesthetic. During the procedure, a flap is cut in the cornea. FDA says a hinge is left at one end of this flap. The flap is folded back revealing the stroma, the middle section of the cornea. Pulses from a computer-controlled laser vaporize a portion of the stroma and the flap is replaced.
LASIK can significantly improve vision in people with refractive problems, but it is not for everyone. FDA says the following conditions are among those that can make someone a poor candidate for the procedure:
There are other surgical treatments that can be used on refractive errors. Procedures that have been approved by the FDA include:
The Federal Trade Commission (FTC) suggests that people considering LASIK or another type of refractive surgery get as much information as possible beforehand. Among other things, they should ask their doctor how long he or she has been doing LASIK, how much improvement they can expect, what are the risks or potential complications they face and what specific procedures do patients need to follow both before and after surgery in order to reduce the risk of complications.
FDA also warns that dry eye can be a complication of refractive surgery. According to FDA, dry eye not only causes discomfort, but can reduce visual quality due to intermittent blurring and other visual symptoms. FDA says that for some people, the condition may be permanent, and intensive drop therapy and use of plugs may be needed. (Read about "Dry Eye")
All Concept Communications material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.
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