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.
Preparation
Refractive eye surgery patients should be carefully screened by an ophthalmic assistant or physician before surgery is approved to avoid some possible complications. This screening should include a comprehensive eye exam, either completed by the ophthalmologist or a co-managing optometrist at least a few days before the surgery. At this time, the physician or ophthalmic assistant should chart any dry eye or corneal disease that may hinder surgery. They should also perform corneal topography, which creates a topographical map of the patient's eye.
Assistants need to advise patients to discontinue wearing contact lenses prior to the visual exams to make sure vision is stable, and advise the doctor of contact lens wear.
Before surgery, ophthalmic staff administer eyedrops and a sedative to the patient. The physician tests the patient's vision, and the patient rests while waiting for the sedative to take effect. Immediately before the surgery, ophthalmic staff administer local anesthetic eyedrops.
Ophthalmic staff also will check the microkeratome settings before surgery and test their accuracy. Some complications from refractive surgery result from a faulty microkeratome.
Aftercare
The patient returns to the surgeon for a follow-up visit the next day. After that, postoperative treatment may be handled by a co-managing optometrist. The doctor usually prescribes antibiotic and anti-inflammatory eyedrops. PRK patients have a longer recovery time and may need steroidal eyedrops for months. After LASIK, antibiotic and anti-inflammatory drops are prescribed for one week.
LTK patients are treated similarly, with antibiotic drops and an over-the-counter pain reliever. Patients may have a foreign-body sensation for a few hours. It may take a few weeks for the eye to stabilize.
The attending physician will require the patient to return for a few months so that the patient's eye health and vision stability can be monitored. After that, yearly checkups are recommended.
Complications
There is a risk of under- or over-correction with LASIK and PRK. If vision is under-corrected, a second procedure can be performed to achieve results that may be closer to 20/20 vision. About 5–10% of PRK patients return for an enhancement, as do 10–25% of LASIK patients. Patients with very high myopia (over -15.00 diopters) may experience improvement after LASIK, but are not likely to achieve 20/40 vision or better without glasses.
Severe dry eye syndrome is a possible complication of LASIK, and has been reported more often as the number of procedures performed has increased. The condition may be permanent. Physicians may prescribe intensive artificial tear therapy; and the use of punctal plugs or other procedures may be required.
Haze is another possible side effect, and is more likely to occur after PRK. Corneal scarring, halos, glare at night, or an irritating bump on the cornea are other side effects. Infection and vision loss are also possible with these procedures, but are extremely rare.
Most LASIK complications are related to the creation and realignment of the flap. The microkeratome must be in good working order and sharp. LASIK requires surgical skill and the complication rate is related to the experience level of the surgeon. In one study, the rate of LASIK complications declined from 3% for surgeons during their first three months using this technique, to 1% after a year's experience in the technique, to 0% after 18 months of experience.
Because LTK was approved in mid-2000, many of its complications have not yet been identified. Potential complications include corneal infiltrate or ulcer, uncontrolled intraocular pressure, late onset of haze, decrease in best spectacle-corrected visual acuity, or retinal detachment. In some cases the procedure is not successful at all.
Results
Most patients experience vision improvement immediately after refractive surgery. Vision tends to become sharper a few days after surgery and then stabilizes. Final visual acuity is achieved within three to six months with LASIK and six to eight months with PRK.
LASIK is more complicated than PRK because of the microkeratome procedure. However, LASIK generally has faster recovery time, less pain, and less chance of halos and scarring than PRK. LASIK can treat higher degrees of myopia (-5.00–-25.00 diopters). LASIK also requires less use of steroids.
An LTK patient's vision will be overcorrected (improvement will be initially dramatic) for one to three months. The effect of improved near vision may diminish over time as distance vision improves.
Cataract—A condition in which the lens of the eye turns cloudy and interferes with vision.
Cornea—The clear, curved tissue layer in front of the eye. It lies in front of the colored part of the eye (iris) and the black hole in the center of the iris (pupil).
Diopter (D)—A unit of measure of the power or strength of a lens.
Excimer laser—An instrument that is used to vaporize tissue with a cold, coherent beam of light with a single wavelength in the ultraviolet range.
Hyperopia—The inability to see near objects as clearly as distant objects, and the need for accommodation to see objects clearly.
Intraocular lens (IOL) implant—A small plastic device (IOL), usually implanted in the lens capsule of the eye to correct vision after the lens of the eye is removed. This is the implant that is used in cataract surgery.
Macular degeneration—A condition usually associated with age, in which the area of the retina called the macula is impaired. This condition interferes with vision.
Microkeratome—A precision surgical instrument that can slice an extremely thin layer of tissue from the surface of the cornea.
Myopia—A vision problem in which distant objects appear blurry. Myopia results when the cornea is too steep or the eye is too long and the light doesn't focus properly on the retina. People who are myopic or nearsighted can usually see near objects clearly, but not far objects.
Refractive surgery—A surgical procedure that corrects visual defects.
Retina—The sensory tissue in the back of the eye that is responsible for collecting visual images and sending them to the brain.
There regression has been noted with LTK. The LTK mean rate of change decreases progressively, reaching only .02 diopters per month between 18 and 24 months. If the regression continues at the expected rate, the corrective effect would dissipate no sooner than 11 years after the procedure.
Health care team roles
Allied health professionals play an important role in preparing patients for refractive surgery. Advanced and intermediate-level ophthalmic technicians perform refractions and help determine the patient's eligibility for refractive surgery. These professionals also may perform corneal topography.
Specially trained ophthalmic nurses assist during the surgery. They check the microkeratomes and administer eyedrops. Advanced ophthalmic technologists, who are specially trained for such additional duties as taking ophthalmic photographs and using ultrasound, may administer eye medications, perform ophthalmologic tests, maintain ophthalmic surgical equipment and assist in refractive surgery.
Patient education
Refractive surgeons should carefully screen patients for these procedures and make sure the patients are aware of possible complications before the procedure begins. Some highly myopic patients expecting "perfect" vision will be disappointed when they discover they still need eyeglasses for distance vision.
Ophthalmic staff also need to stress that while LTK vision improvements may be startling at first, those changes are likely to fade. These patients should be advised they may still need glasses for fine print. Aging and the onset of presbyopia will still affect their vision.
Training
Ophthalmologists are advised to observe other surgeons perform these procedures before they begin. Laser companies offer seminars to help doctors perfect their techniques. Other groups, such as the American Society of Cataract and Refractive Surgery, keep physicians informed of the latest advances. Co-managing optometrists are advised to observe surgeries and attend seminars to learn more about follow-up treatments.
Ophthalmic assistants who want to assist in these surgeries can receive additional training from certified education programs.
PERIODICALS
Belmont, Sandra C. "Correcting Hyperopia: Is LTK Your Next Move?" Ophthalmology Management 4 (June 2000): 6-10.
Brint, Stephen F., et al. "Photorefractive Keratectomy versus Laser in Situ Keratomileusis: Comparison of Optical Side Effects." Ophthalmology 107 (2000): 925-933.
Chynn, Emil William. "Refractive Business. No Time Like the Present." Ophthalmology Times (15 Feb. 1998): 11-12.
Gorman, David, and Arthur M. Cotliar. "Refractive Surgery Options: RK vs PRK vs LASIK." Newsweek, 16 June 1997, S38.
Vinals, Antonio. "No Regression Seen 2 Years After LASIK." Ophthalmology Times (1 Mar. 1998): 1, 34.
Vinals, Antonio. "Study Documents LASIK Learning Curve." Ophthalmology Times (1 Mar. 1998): 1, 35.
ORGANIZATIONS
American Academy of Ophthalmology. PO Box 7424, San Francisco, CA 94120-7424 (415) 561-8500. <http://www.eyenet.org>.
American Society of Cataract and Refractive Surgery. 4000 Legato Road, Suite 850, Fairfax, VA 22033-4055. (703) 591-2220. <http://www.ascrs.org>.
Food and Drug Administration. 5600 Fishers Lane Rockville, MD 20857. (888) 463-6332. <http://www.fda.gov>.
