Surgery for Refractive Errors

ByDeepinder K. Dhaliwal, MD, L.Ac, University of Pittsburgh School of Medicine
Reviewed/Revised Feb 2024

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 of each option.

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

  • Conditions that impair wound healing, such as autoimmune or connective tissue diseases

  • Active eye disease such as severe dry eye

  • Keratoconus (cone-shaped corneas)

  • A recurrent herpes simplex infection involving the cornea

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

  • 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 tests called topography, tomography, and pachymetry), the pupil size, the intraocular pressure, the optic nerve, and the retina.

Refractive surgical procedures are generally quickly done and cause little discomfort. Eye drops are used to numb the eye. The person should try to keep their eye fixed on a designated target 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 will have perfect 20/20 vision after the procedure. The people most likely to have 20/20 distance vision after surgery are those who had mild to moderate eyeglass prescriptions before surgery. More than 95% of people will not need to wear corrective lenses for distance vision. However, 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

It is important to have high-quality surgery with an experienced refractive surgeon to minimize complications.

Types of refractive surgery

The two most common refractive surgery procedures of the cornea are

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 during surgery, the surgery is stopped but sometimes may be tried again after about 6 months. Another flap problem is a flap dislocation, which usually occurs after a severe eye injury and causes blurry vision. This problem can often be fixed with immediate treatment. Very rarely, flap problems develop when, for example, a flap heals with ridges and causes blurring or star bursts or halos. If these flap problems cannot be corrected, they 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 is used primarily to correct nearsightedness, astigmatism, and farsightedness. PRK requires use of an excimer laser to reshape the cornea. 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 also 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 sometimes be done on people who cannot have LASIK, such as those with a loose corneal surface layer or slightly thin corneas.

Other Refractive Surgery

Other techniques that may have advantages over or different risks than LASIK and PRK include

Small incision lenticule extraction (SMILE)

SMILE is used to treat nearsightedness. In SMILE, a doctor uses a laser to cut a small lenticule (disk) of corneal tissue. This tissue is then removed through a very small incision in the adjacent cornea. The reshaped cornea corrects the refractive error in a person with nearsightedness.

SMILE is similar to LASIK (laser in situ keratomileusis) in terms of effectiveness and safety. However, because SMILE does not create a flap of tissue like in LASIK, flap-related complications (such as flap dislocation) are avoided. In addition, because the incision is very small, the risk of dry eye is lower.

SMILE does carry a slightly higher risk of an intra-operative complication if the eyeball-stabilizing device loses suction. However, this complication does not usually impair vision since it can be managed effectively.

Phakic intraocular lenses (IOLs)

For people who have moderate to severe nearsightedness, 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 (these occur rarely).

Phakic IOLs achieve better vision than laser vision correction in people with moderate to high levels of nearsightedness. Some people can have laser vision correction after phakic IOL placement to further correct vision.

Corneal inlays

Corneal inlays are implanted into a pocket or flap in the eye to treat presbyopia (gradual loss of ability to focus on nearby objects). These inlays are placed only in the cornea of the person's weaker eye.

Corneal inlays can improve near vision with the trade-off of a 1- to 2-line decrease in distance vision on an eye chart, and they can be surgically removed if desired.

With corneal inlays, there is the risk of corneal haze or inflammation, which requires long-term use of corticosteroid eyedrops and can result in glare, halo, and difficulty reading in dim light. Some people develop dry eye or scar tissue.

Clear lensectomy

Sometimes the natural lens is removed, and a plastic lens is placed in the lens capsule (clear lensectomy with IOL implantation). This is the same procedure as cataract surgery, but there is no cataract or cloudy lens. 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 be made in the eye, there is a very small risk (but significantly higher than for LASIK) of severe infection inside the eye. Clear lensectomy is often 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 in the cornea using a diamond or stainless steel blade or laser.

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. Risks include infection, undercorrection, overcorrection, and corneal perforation.

Drugs Mentioned In This Article
Test your KnowledgeTake a Quiz!
Download the free Merck Manual App iOS ANDROID
Download the free Merck Manual App iOS ANDROID
Download the free Merck Manual App iOS ANDROID