Refractive Error and Refractive Surgery
The cornea is the clear surface of the eye that helps focus light to create an image on the retina. It works in much the same way the lens of a camera focuses light to create an image on film. Usually the shape of the cornea and the eye are not perfect and the image on the retina is out of focus, (blurred) or distorted. These imperfections in the focusing power of the eye are called refractive errors. There are three primary types of refractive errors: myopia, hyperopia, and astigmatism. People with myopia, or nearsightedness, have difficulty seeing distant objects as clearly as near objects. People with hyperopia, or farsightedness, have difficulty seeing near objects as clearly as distant objects. Astigmatism is a distortion of the image on the retina caused by an irregularity or steepness on the surface of the cornea. Combinations of myopia and astigmatism or hyperopia and astigmatism are common. Glasses or contact lenses are designed to compensate for the various refractive errors and thereby help the individual focus more clearly. Surgical procedures aimed at improving the focusing power of the eye are called refractive surgery. LASIK (laser assisted in situ keratomileusis) and PRK (photorefractive keratectomy) are the two most common refractive surgical procedures.
LASIK
LASIK permanently changes the shape of the cornea by using an excimer laser to ablate (remove by vaporization) a small amount of tissue. First, the eye is numbed with topical anesthetic eye drops. Next, a tissue flap is created on the surface of the cornea with either a mechanical cutting device called a microkeratome, or a special laser called the femtosecond laser. This corneal tissue flap is then replaced to its normal position at which point the procedure is essentially complete.
PRK
PRK also permanently changes the shape of the cornea. Instead of creating a flap which is replaced towards the end of the procedure, the surface layer of the cornea called the epithelium is mechanically removed after numbing the surface of the eye. A certain amount of the corneal bed determined by your eyeglass prescription is then ablated using the excimer laser. Once the laser is complete a bandage contact lens is placed on the eye to promote healing and help keep the eye comfortable until epithelium grows and covers the exposed corneal bed. This usually takes several days.
Am I a candidate for LASIK or PRK?
LASIK and PRK are excellent procedures if you are a good candidate. Certain eye conditions may prevent you from being a good candidate for LASIK and PRK. Your ophthalmologist will determine if you are a good candidate according to your eye exam and ocular/medical history. Ideal candidates are those who are at least 21 years old with no changes in their eye glass prescription for at least 1 year.
LASIK and PRK are mainly used to correct distance vision. These procedures do not correct presbyopia, the age-related process which gradually decreases focusing for near (reading) vision. At Hampton Eye, we offer FREE screenings to determine if you are a good candidate for LASIK or PRK.
