Refractive Eye Surgeries Health Article

Definition

Refractive eye surgeries are medical procedures used to correct such refractive errors as myopia, hyperopia, and presbyopia. The three most widely utilized refractive surgeries approved by the U.S. Food and Drug Administration (FDA) are photorefractive keratectomy (PRK); laser-assisted in-situ keratomileusis (LASIK); and laser thermal keratoplasty (LTK). PRK and LASIK use an excimer laser to correct myopia by reshaping the cornea. The two techniques differ in how the surface layer of the cornea is treated.

Purpose

Refractive surgeries are performed to correct hyperopia, myopia, and presbyopia in patients who don't want to wear eyeglasses or contact lenses. After refractive surgery, most patients are able to see well enough to pass a driver's license exam without glasses or contact lenses. Some patients will still need corrective lenses, but the lenses won't need to be as strong or thick.

Precautions

Medical history is important in determining the appropriate refractive surgery patients. Patients for LASIK and PRK must be older than 18 years of age, have healthy corneas, and have vision that has been stable for the past year. People who may not be good candidates are pregnant women or women who are breastfeeding; patients with very small or very large refractive errors; those with low contrast sensitivity; people with scarred corneas or macular disease; or those with autoimmune diseases or diabetes. Patients with glaucoma should not have LASIK because the intraocular pressure (IOP) of the eye is raised during the procedure. A patient with persistent lid infections (i.e., blepharitis) may not be a good candidate because of an increased infection risk.

LTK patients must be at least 40 years old; have stable vision for at least six months; fall in the low-to-moderate range of hyperopia (+0.75–+2.50 diopters); and have no more than 0.75 diopters of astigmatism. Pregnant or nursing women, patients with clinically significant corneal dystrophy or scarring in the 6 mm or 7 mm central zone, patients with a history of herpetic keratitis, patients with an autoimmune disease, collagen vascular disease, clinically significant atopic syndrome, insulin-dependent diabetes, or an immune-compromised status should not have LTK.

Description

Refractive surgeries that correct myopia are similar in nature. PRK and LASIK are both performed with an excimer laser, which uses a cold beam of ultraviolet light to reshape the cornea so that light will focus properly on the retina. In myopia, the cornea is either too steep or the eye is too long for a clear image to be focused on the retina. PRK and LASIK flatten the cornea so that the image will focus more precisely on the retina.

In PRK, the surface of the cornea is removed by the laser. In LASIK, the outer layer of the cornea is sliced, lifted, and moved aside while the cornea is reshaped with the laser. The outer layer is then replaced to speed healing. For LASIK and PRK, the patient's eye is numbed with anesthetic drops. No injections are necessary.

Before LASIK, the cornea's surface is marked with a dye marker so that the flap of cornea can be precisely aligned when it is replaced. The ophthalmologist places a suction ring from a microkeratome, a lathe-like surgical instrument, on the corneal limbus (where the clear cornea meets the white of the eye). When the device is properly positioned, the surgeon applies suction by using a foot pedal, causing the eye's pressure to elevate to 80 mmHg from a minimum of 65 mmHg. During this time, the microkeratome lathes the top 10% of the total corneal thickness, which creates a thin flap of tissue. The thin layer is folded back, the cornea is reshaped with the laser beam, and the flap layer is replaced. Because the flap is not permanently removed, patients have a faster recovery time and experience far less discomfort than with PRK. A physician or ophthalmic assistant administers antibiotic drops, and the eye is patched until the following day's checkup.

In PRK, a small area of the surface layer of the cornea is vaporized. It takes about three days for the surface cells to grow back, and vision will be blurred.

PRK and LASIK take only a few minutes. Patients are usually able to return home immediately after surgery.

The LTK system resembles a slit lamp used in a general eye exam, so it is non-threatening to patients. Before the procedure, an ophthalmic assistant administers three sets of anesthetic eyedrops with three minutes between each set. Ophthalmologists use a retractor to keep the eyelids open, and the other eye is patched. There is a three-minute waiting period after insertion of the laser to evaluate the tear film for irregularities or uneven dry spots on the cornea. The patient focuses on a fixating light, and the 16-spot nomogram for the degree of correction is programmed into the LTK unit's computer. The laser is applied for three seconds.

After the procedure, the ophthalmic assistant or physician will give the patient topical antibiotic drops. There is no postoperative patching. Some patients may experience a foreign-body sensation for a few hours after LTK. It sometimes takes a few weeks for vision to stabilize. Patients are usually seen one day postoperatively.

The cost of refractive surgery can vary with geographic area and the surgeon. In general, the procedure costs $1,350–$2,500 per eye for PRK and about $500 more per eye for LASIK. LTK is slightly more expensive than LASIK, at about $3,000 per eye. Refractive surgery usually isn't covered by insurance.