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Surgery for Refractive Errors

By Deepinder K. Dhaliwal, MD, L.Ac, Professor, Department of Ophthalmology, University of Pittsburgh School of Medicine

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Surgical and laser procedures (refractive surgery) can be used to correct the refractive errors nearsightedness, farsightedness, and astigmatism. These procedures are commonly used to reshape the cornea so that it is better able to focus light on the retina. Another type of refractive surgery for people who have severe nearsightedness involves insertion of a thin lens inside the eye.

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 (a medical doctor who specializes in the evaluation and treatment [surgical and nonsurgical] of eye disorders) 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

  • A change in their eyeglass or contact lens prescription in the past year

  • An autoimmune or connective tissue disease

  • Eye disease

  • Keratoconus (cone-shaped corneas)

  • Severe dry eyes

  • Poor wound healing

Additional people who usually should not have refractive surgery are those who are

  • Taking certain drugs (for example, isotretinoin or amiodarone)

  • Younger than 18 (with a few exceptions)

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 a test called 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 should try not to 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 mild to 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.

Side effects of refractive surgery include temporary symptoms of

Occasionally, these symptoms do not go away. Dryness can cause vision to blur.

Possible complications of refractive surgery may include

  • Overcorrection

  • Undercorrection

  • Infection

Other complications include excessive inflammation, double vision, 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, infection or inflammation can lead to decreased vision in the eye.

Rarely, even with eyeglasses, a person may have worse vision after refractive surgery.

Types of refractive surgery

The two most common refractive surgery procedures of the cornea are

  • Laser in situ keratomileusis (LASIK)

  • Photorefractive keratectomy (PRK)

Laser In Situ Keratomileusis (LASIK)

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 often be fixed with immediate treatment. Very rarely, flap problems develop when, for example, a flap heals with ridges causes blurring or star bursts or halos. These flap problems cannot be corrected easily and can permanently impair function, such as driving at night unless a rigid contact lens is used. Ectasia can cause blurring, increased nearsightedness, and irregular astigmatism. Other complications include severe, intermittent blurring resulting from dry eyes and, rarely, vision-threatening infection or inflammation of the cornea.

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.

Photorefractive Keratectomy (PRK)

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. A contact lens is placed on the eye after the surgery and acts as a bandage (called a bandage contact lens). It helps the surface cells grow back and helps relieve pain. This procedure usually takes 5 minutes 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 several months after surgery. Use of corticosteroid eye drops may cause glaucoma. Therefore, doctors closely monitor people who are using corticosteroid eye drops. Severe, vision-threatening infection of the cornea is a rare complication.

Although there is more discomfort and longer healing time with PRK 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 Refractive Surgery

Other techniques are available that may have advantages over or different risks than LASIK and PRK.

Phakic intraocular lenses (IOLs)

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 (phakic IOL implantation). The person's own natural lens is left in place.

Risks of phakic IOL implantation include cataract formation, glaucoma, infection, and swelling of the cornea.

Some people can have laser vision correction after phakic IOL placement to further correct vision.

Clear lensectomy

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 after surgery.

Intracorneal ring segments (INTACS)

INTACS are used for people with mild nearsightedness and minimal astigmatism. Small plastic arc-shaped segments 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 segments.

Risks include astigmatism, undercorrection, overcorrection, infection, glare, and seeing halos.

Currently, INTACS are mostly used to treat disorders such as keratoconus and ectasia after LASIK or PRK surgery when eyeglasses or contact lenses no longer provide adequate vision or are uncomfortable.

Radial keratotomy and astigmatic keratotomy

In radial keratotomy and astigmatic keratotomy, surgeons change the shape of the cornea by making deep incisions using a diamond blade.

Radial keratotomy has been replaced by laser vision correction and is rarely used.

Astigmatic keratotomy is still often done at the same time as cataract surgery.

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