Background

Normally, the cornea and lens refract light rays onto the retina, and the resulting image is transmitted to the brain via the optic nerve. (Figure 1) If the eye is too long or too short, light rays are not properly refracted onto the retina, and the images sent to the brain appear blurred. This is known as a refractive error and is measured in units called diopters (D). When eyeglasses or contact lenses are worn, refractive errors are corrected by the addition or subtraction of focusing power to or from the cornea and lens. Eyeglasses or contact lenses provide the refractive power needed to help the eye focus images directly on the retina.

Myopia is a refractive error in which distant objects become blurred because the eye is too long and its focusing power causes light rays to focus in front of the retina. In myopic individuals, concave prescription lenses subtract focusing power. Prescriptions are preceded by a negative sign (e.g., −2.00 D). Hyperopic (farsighted) individuals wear prescription lenses that are convex and preceded by a positive sign (e.g., +2.00 D).

Corrective lenses for astigmatic individuals are shaped to compensate for the uneven curvature of the cornea and allow light rays to focus on a single point on the retina.

Besides wearing eyeglasses or contact lenses, another method of correcting refractive errors is refractive eye surgery, which is a surgical procedure that corrects refractive errors by reshaping the eye and permanently changing its focusing power. The goal is to reduce or eliminate the refractive error, to attain emmetropia (normal vision), and to reduce or eliminate the need for eyeglasses or contact lenses. Refractive surgery accomplishes this goal by removing corneal tissue thus reshaping the cornea. The four types of refractive eye surgery are radial keratotomy (RK), photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and intra ocular lenses (IOL). Of the four, LASIK is the most popular surgery now being performed.

Radial Keratotomy (RK)

With RK surgery, the patient sits in an operative chair or lies on an operating table. The operative eye is labeled, and the opposite eye is patched to ensure that the patient maintains fixation with the operative eye. Topical anesthetics are administered, and a lid speculum or separator is placed to hold the eye open.

Guided by an operative microscope, numerous partial-thickness keratotomies (incisions) are made in a radial or spoke-like pattern in the peripheral cornea. (Figure 2) Normal intraocular pressure causes the area around the incisions to steepen, flattening out the central cornea.

RK reduces refractive errors and improves visual acuity in patients with low to moderate levels of myopia. A significant percentage of patients who have this surgery will become farsighted over time, and a substantial number will require corrective lenses or another operation to achieve better vision. Both eyes may be corrected at one time, but more often only one eye is corrected at a time. Correction of the second eye occurs after the stabilization of the first eye. Under correction, the presence of residual myopia is a condition that can occur after primary surgery and may be treated with follow-up surgery (enhancement surgery). Hyperopic over correction, another result of the primary surgery, may sometimes be managed with interrupted or purse-string sutures, or LASIK. RK is now seldom used because it's accuracy is lower than with laser techniques.

Photorefractive Keratectomy (PRK)

PRK corrects low to high levels of myopia by removing a predetermined amount of tissue from the corneal surface. This is done by using the high-energy pulses of an excimer laser beam (photoablation). The patient fixates, and a round optical zone is marked on the cornea to indicate the borders of the tissue to be removed.

A small portion of a corneal epithelium (outer covering) is removed from the surface, and a section of the corneal stroma (layered connective tissue) is lasered. (Figure 3) Healing takes place through re-epithelialization (the process of becoming covered by healthy tissues).

Two lasers were approved for manufacture and marketing by the Food and Drug Administration (FDA) in 1996 and are currently being used for PRK surgery. PRK is an effective treatment for low to moderate levels of myopia but is limited due to a high likelihood of myopic worsening glare and myopic regression, particularly in patients with higher levels of myopia. Compared with RK, there are longer times to refractive stabilization, as well as more occurrences of corneal haze, reduction in contrast sensitivity, and disturbances by glare and nighttime halos. According to the FDA, there is an approximate 5% chance of patients still needing eyeglasses all the time for distances up to 15 feet, and a 15% chance of needing eyeglasses occasionally. For approximately 5% of patients, vision is slightly worse after surgery. Of those having the surgery, 95% achieved 20/40 or better vision and 65% obtained 20/20 vision.

Laser In Situ Keratomileusis (LASIK)

LASIK surgery corrects low to high levels of myopia. It is now being used for hyperopia and astigmatism as well. It is performed with the excimer laser but differs from PRK in that photoablation is performed underneath a protective flap of corneal tissue. A microkeratome, a knife used for incising the cornea, is positioned over the operative eye, and a corneal flap (not more than one fifth of the cornea) is cut. (Figure 4) This flap, which remains attached, is elevated, and the excimer laser is used to evaporate the stromal bed, resculpturing the eye under the flap. The bed is then irrigated with saline solution, the flap replaced, and healing takes place through adhesion.

In July 1998, the FDA approved the manufacture and marketing of two additional lasers used for LASIK surgery. LASIK appears to be an effective treatment for low to very high myopia. Postoperative complications may diminish visual sharpness and myopic regression is possible, but such complications are not as common as when PRK is used. Since it is a relatively new procedure the outcome over 5 years is unknown.

Intra Ocular Lenses (IOL)

In April 1999, the FDA granted pre-market approval for ocular lense implants in adults 21 years of age or older. These implants are transparent, acrylic half-circles which are about as thick as contact lenses. A small incision is made into the periphery of the cornea and the implants are inserted. The lense flattens the eye causing the needed correction for mild nearsightedness and mild astigmatism. The lenses are considered permanent implants but may be removed if necessary, with vision returning to the pre-surgery level.

There is limited information on the procedure and the FDA review panel has expressed concerns about the potential loss of clarity in the cornea over a 30-50 year period. The FDA has requested the lens manufacturer to maintain a very close watch on patients who receive surgery, which costs $2,000 to $2,500 per eye.

Patient Selection

Patient selection varies by geographic location, clinic, physician, and type of surgery being performed. There are, however, some general guidelines that are used. Selected candidates are more than 18 years of age and have no history of an ocular surface or systemic disease, no glaucoma, normal ocular pressure, stable eyesight for 12 to 18 months, and an acceptable corneal thickness. Other considerations may include the ability or inability of the patient to comply with surgical or postoperative protocols, the patient's diabetes mellitus status, presence or absence of glaucoma, whether prior eye surgery had been performed, pregnancy or breast-feeding status, and any early signs of cataracts. A thorough discussion with the physician will help determine if an individual will meet the requirements.

Cost of the Procedures

• The patient cost for refractive eye PRK surgery (laser) is typically between $1200 and $2000 per eye.
• The patient cost for LASIK surgery is typically between $2000 and $2500 per eye.
• If a location can be found that does RK surgery, the patient cost is typically between $1200 and $1600 per eye.
• The patient cost for IOL is typically between $2000 and $2500.

These costs cover a wide variety of items. Costs may include the initial exam fees, computer mapping of the eye, pre- and postprocedure exams, physicians' fees, monitoring exams for the next year, and enhancements. Fully understanding what the cost includes is an important part of the final decision of whether to have the surgery.

Safety and Complications

Conclusion

The popularity of refractive eye surgery is increasing due in part, to hearing about the success of a neighbor, friend, or relative who has had the surgery. In a number of studies, patients report high satisfaction with the surgeries. However, there are adverse effects that can result from any kind of surgery. For this reason, a close analysis of whether to have the surgery should be done by anyone considering this procedure. Individuals who are considering surgery should carefully weigh the benefits and risks before making a decision. The technology used with excimer laser surgery is undergoing rapid change and is, in some instances, still in the experimental stage. The expertise of the surgeon plays a large role in determining the overall risk of the procedure. The new techniques are promising, but further studies should be done on the long-term safety and efficacy of these techniques.

Many patients, especially the young and high myopic individuals, may not achieve the results they are looking for. Some will not achieve a complete independence from eyeglasses, and, for some, eyesight will worsen as a result of the surgery. There are no studies that provide long-term results of LASIK surgeries. The short-term results are encouraging; however, the possibilities of regression, cataract formation, and the outcomes of having future eye surgery are not known. Each potential patient should carefully research the procedure being considered.

Questions to consider when evaluating refractive eye surgery include:

• Which surgery is best?
• Who is the best doctor for that surgery?
• How many surgeries has the doctor performed?
• What is the total cost?
• Is there health insurance coverage for the procedure and for the costs of possible complications caused by the surgery?

The most important question is the one only the patient can answer:

• Is the success rate high enough and the failure rate small enough to risk having the surgery?

In conclusion, refractive eye surgeries for myopia are elective procedures. These irreversible procedures have different degrees of benefits and risks associated with them. Persons considering refractive eye surgery should carefully weigh the decision between continued use of eyeglasses or contact lenses versus eye surgery.