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Surgery for Refractive Errors
Surgical and laser procedures (refractive surgery) can be used to correct nearsightedness, farsightedness, and astigmatism. These procedures are used to reshape the cornea so that it is better able to focus light on the retina. The goal of refractive surgery is to decrease dependence on eyeglasses or contact lenses. Before deciding on such a procedure, people should have a thorough discussion with an ophthalmologist and should carefully consider their own needs and expectations, along with the risks and benefits.
The best candidates for refractive surgery are healthy people aged 18 and older with healthy eyes who are not satisfied with eyeglasses or contact lenses and who enjoy activities, such as swimming or skiing, which are difficult to do with eyeglasses or contact lenses. Many people undergo this surgery for convenience and cosmetic purposes. However, refractive surgery is not recommended for all people with refractive errors.
People who usually should not have refractive surgery include those who have
Additional people who usually should not have refractive surgery are those who are
The doctor determines the exact refractive error (eyeglass prescription) before surgery. The eyes are thoroughly examined, and special attention is paid to the surface cells of the cornea (including whether the cornea has a loose or well-anchored surface layer), the shape and thickness of the cornea (using pachymetry (see page Tests for Eye Disorders : Pachymetry), the pupil size, the intraocular pressure, the optic nerve, and the retina. Refractive surgical procedures are generally brief and cause little discomfort. Eye drops are used to numb the eye. Because the eye is not held still, the person must not move the eye during the procedure. Usually, a person can go home soon after the procedure.
After refractive surgery, most people have distance vision that is good enough to do most things well (for example, driving or going to the movies), although not everyone has perfect 20/20 vision without eyeglasses after the procedure. More than 95% of people do not need corrective lenses for distance vision. The people most likely to have 20/20 distance vision after surgery are those who have weak or moderate eyeglass prescriptions before refractive surgery. Even if they do not wear eyeglasses for distance vision, most people older than 40 still need to wear eyeglasses for reading after refractive surgery.
Complications may include overcorrection, undercorrection, excessive inflammation, a feeling as though something is in the eye (foreign body sensation), infection, double vision, astigmatism, sensitivity to bright light, glare and halos around lights, dryness, haze, difficulty with seeing or driving at night, wrinkling of the cornea, and deposition of cells or other material in the cornea. Rarely, even with eyeglasses, a person may have worse vision after refractive surgery. Because treating undercorrection is usually easier than treating overcorrection, surgeons prefer not to overcorrect. If undercorrection or overcorrection occurs, further correction can usually be done.
The two most common refractive surgery procedures are laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).
LASIK is used to correct nearsightedness, farsightedness, and astigmatism. In LASIK, a very thin flap is created in the central part of the cornea with a laser or a cutting device called a microkeratome. The flap is lifted, and computer-controlled pulses of highly focused ultraviolet light from an excimer laser vaporize tiny amounts of corneal tissue under the flap to reshape the cornea. The flap is then laid back in place and heals over several days.
LASIK causes little discomfort during and after surgery. Vision improvement is rapid, and many people are able to go back to work within 1 to 3 days.
Complications include possible flap-related problems and long-term thinning and bulging of the cornea (ectasia). If a flap problem develops, surgery is stopped but sometimes may be tried again after about 6 to 9 months. One potential flap problem is a flap dislocation, usually occurring only after severe eye injury and causing blurry vision. This problem can usually be fixed with immediate treatment. Very rarely, flap problems develop when, for example, an irregular incision, an irregular flap, or a flap that heals with ridges causes blurring or star bursts or halos (see page Other Eye Symptoms : Glare and Halos) around lights that can not be corrected and can permanently impair function, such as driving at night. Ectasia can cause blurring, increasing nearsightedness, and irregular astigmatism.
People who have any conditions that prevent them from having refractive surgery, as well as those who have thin corneas or a loose corneal surface layer, may not be good candidates for LASIK.
PRK requires use of an excimer laser to reshape the cornea. PRK is used primarily to correct nearsightedness, astigmatism, and farsightedness. Unlike LASIK, no flap is created. The cells on the surface of the cornea are removed at the start of the procedure. As in LASIK, computer-controlled pulses of highly focused ultraviolet light remove small amounts of the cornea and thus change its shape to better focus light onto the retina and improve vision without eyeglasses or contact lenses. This procedure usually takes less than 1 minute per eye.
Complications include possible haze formation (causing blurred or cloudy vision) if a large amount of corneal tissue is removed. Also, people need to use corticosteroid eye drops for 3 months after surgery. Use of corticosteroid eye drops may cause glaucoma. Therefore, doctors closely monitor people who are using corticosteroid eye drops.
Although there is more discomfort and longer healing time than with LASIK (because the removed surface cells need to grow back), PRK can be done on people who cannot have LASIK, such as those with a loose corneal surface layer or thin corneas.
Other techniques are available that may have advantages over or different risks than LASIK and PRK.
For people who are very nearsighted and who are not suitable candidates for laser vision correction, a plastic lens can be placed inside the eye, in front of or behind the iris (PIOL implantation). The person's own natural lens is left in place.
Risks of PIOL implantation include cataract formation, glaucoma, infection, and swelling of the cornea.
Some people can have laser vision correction after PIOL placement.
Sometimes the natural lens is removed, and the plastic lens is placed behind the iris (clear lensectomy with IOL implantation). Clear lensectomy with IOL implantation may be better for people with severe farsightedness who are over age 40. Because these techniques require that an opening is made in the eye, there is a very small risk (but significantly higher than for LASIK) of severe infection inside the eye. Clear lensectomy should usually be avoided in young people who are very nearsighted because they have an increased risk of detachment of the retina (see page Detachment of the Retina) after surgery.
INTACS are used for people with mild nearsightedness and minimal astigmatism. Small plastic arcs are implanted into the middle layer of the cornea near its outer edge. The plastic arcs change the shape of the cornea to improve focus. Because no tissue is removed during the procedure, the INTACS procedure can be reversed by removing the small plastic arcs.
Risks include astigmatism, undercorrection, overcorrection, infection, glare, and seeing halos.
Currently, INTACS are mostly used to treat disorders such as keratoconus and ectasia that occurs after LASIK surgery when eyeglasses or contact lenses no longer provide adequate vision or are uncomfortable.
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