Refractive eye surgery

Also known as: Vision correction, laser-assisted in situ keratomileusis (LASIK), laser epithelial keratomileusis (LASEK), photorefractive keratectomy (PRK)

Anatomy or system affected: Eyes

Definition: A surgical procedure that changes the way in which the eye refracts light, thus correcting vision disorders

Indications and Procedures

When light rays enter the eye, the cornea and lens bend (refract) the rays to focus them on the retina. When the eye is shaped in such a way that light rays are not sharply focused on the retina, an error in refraction occurs. Refractive eye errors that can be alleviated or cured with surgery are myopia, hyperopia, and astigmatism. Myopia (nearsightedness) is caused by a cornea that is too sharply curved, causing light rays to focus in front of the retina rather than on it, resulting in blurry distance vision. With hyperopia (farsightedness), the cornea is too flat, so light rays focus beyond the retina rather than on it, causing blurred vision when viewing near objects. Astigmatism is caused by a cornea that is uneven, curving, and flattening in different spots on the eye, which makes it difficult to see objects at any distance. According to the World Health Organization, 2.2 billion people suffer from vision impairment worldwide.

Laser-assisted in situ keratomileusis (LASIK) is the most common refractive surgery in use. By 2023, more than sixteen million of these surgeries had been performed in the United States. LASIK can be used if the patient is nearsighted, farsighted, and with or without astigmatism. The surgeon conducts an intensive eye examination prior to the surgery to determine whether the cornea needs to be flattened or curved and in what specific area. Then anesthetic drops are used to numb the eye.

The surgeon uses a blade or a special cutting laser to cut a hinged flap about the size of a contact lens from the front of the eye. The flap is folded back to allow access to the tissue in the cornea that needs reshaping. After the tissue is properly shaped with another kind of laser called an excimer laser, the flap is folded back in place. Usually, no stitches are required. The procedure is painless and takes fifteen to twenty minutes, depending on the condition of the eye before surgery and whether both eyes are reshaped. Patients can usually leave the doctor’s office within two hours. Postsurgery care involves the use of medicated eyedrops and wearing an eye shield at night. Healing is usually complete in five to seven days. The vision shows some immediate improvement, and in about two to three months, most patients will have between 20/20 and 20/40 vision.

Laser epithelial keratomileusis (LASEK) is similar to LASIK up to the point of surgery. During a LASEK procedure, however, a thinner layer of the cornea is folded back. This is of particular benefit to people who have thinner-than-normal corneas. Also, people who work in jobs where there is a high risk of injury prefer LASEK. A thinner flap means less damage to the patient’s vision should the flap be torn before it is healed. Healing is rapid, and full vision is recovered.

Photorefractive keratectomy (PRK) is used with patients who have a low-to-moderate degree of nearsightedness or farsightedness or farsightedness with astigmatism. Unlike the LASEK procedure, which is very similar, with PRK, the thin layer of the cornea is removed altogether. The surgeon then uses a laser to either flatten or curve the cornea, depending on the patient’s need. A contact lens is placed on the raw cornea, to be worn as a bandage for three or four days. It takes the eye three to six months before vision improves completely. With PRK, the recommendation is to do only one eye at a time. It is the least used of the three procedures. Healing after the LASEK or LASIK methods is faster and involves less discomfort and scarring.

Uses and Complications

Some risks are associated with refractive surgery. Undercorrection occurs when too little tissue is removed from the eye, more often in treatments for nearsightedness. Another surgery to remove more tissue may be required. Overcorrection, when too much tissue is removed from the cornea, can occur when the eye moves during surgery. It is difficult to fix, and additional surgery may be needed to remedy the condition. Astigmatism can also be caused by uneven tissue removal.

Double vision, glare, and halos around bright lights are also risks of refractive surgery. These conditions can be greatly helped with eyedrops that contain cortisone, but sometimes a second surgery is needed. Cases of dry eyes, sometimes severe, also occur. Special plugs for tear ducts are used to prevent tears from draining away from the surface of the eyes, keeping them moist. Flaps folded back during surgery can sometimes become infected and tear and swell. The flap removed during PRK may also grow back abnormally.

Perspective and Prospects

In 2002, the LASIK procedure was improved by a technique known as wavefront-guided LASIK. Wavefront sensors measure the acuity and quality of a patient’s vision twenty-five times more accurately than previous testing methods. They record how the eye processes light and show unique distortions in each individual eye. This enables the surgeon to make a more precise cut. In the 2010s, doctors began using a topography-guided laser to treat even the smallest of ocular imperfections. Use of a femtosecond laser during surgery has also reduced the incidence of post-surgery complications.

Alternative refractive surgery procedures include conductive keratoplasty, which uses radio frequency (RF) energy instead of a laser to reshape the cornea, and phakic intraocular lenses (IOLs), which are essentially surgically implanted contact lenses that can correct severe myopia. These and other procedures widen the range of options for people seeking surgical vision correction.

The total cost of LASIK refractive eye surgery varies widely but is generally between $1,500 and $3,000 per eye. The use of the wavefront technology adds another $500. Many insurance companies consider refractive eye surgery elective and will not pay for it. The Food and Drug Administration (FDA) urges people who are considering refractive eye surgery to check a doctor’s credentials before the operation.

Bibliography

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Braham, Lewis. “Eye Surgery: It’s Getting Sharper.” Business Week, October 18, 2004, pp. 142–143.

Fiscbetti, Mark. “Clear Favorite.” Scientific American 290 (May, 2004): 106–107.

"LASIK Eye Surgery." Mayo Clinic, November 4, 2011.

"LASIK—Laser Eye Surgery." American Academy of Ophthalmology, 2013.

“LASIK Statistics - Safety and Success Rates in 2023.” Vision Center, 2 May 2023, www.visioncenter.org/resources/lasik-statistics. Accessed 28 July 2023.

Rapuano, Christopher J., ed. Refractive Surgery. San Francisco: American Academy of Ophthalmology, 2012.

Sunshine, Wendy Lyons, and Adam Martin. “Lasik Woes: Here’s Help.” Health 18, no. 1 (January/February, 2004): 50–54.