Surgery to Correct Refractive Errors
Several surgical procedures can correct refractive errors. Some patients who undergo surgery no longer need eyeglasses or contact lenses, and others experience improved vision. The type and degree of refractive error determines whether or not a patient is a good candidate for surgery. There are risks involved and favorable outcomes are not guaranteed.
Radial Keratotomy (RK)
In this procedure, the cornea is reshaped to eliminate myopia and, in some cases, astigmatism. The eye is anesthetized and deep cuts are made in the cornea, like spokes in a wheel. The number of incisions and their location is determined by the degree of nearsightedness. The incisions cause the sides of cornea to bulge outward and the center to flatten, bringing the point of focus closer to the retina. Antibiotic and cycoplegic drops that paralyze the focusing ability of the eye are instilled after surgery and a patch is usually placed over the eye for about 2 hours.
Visual acuity may fluctuate for 6 months or longer and a second operation may be needed to further reduce myopia. About 50% of patients achieve 20/20 vision and about 85% achieve 20/40 vision. Improved techniques have significantly reduced the amount of regression (refractive power migrates back toward myopia) experienced by patients.
Glare around bright lights at night caused by a larger pupil and the peripheral incisions or an irregular cornea, can persist for up to 3 years and is the most common side effect following radial keratotomy.
Laser In Situ Keratomileusis (LASIK)
Currently, LASIK is the most commonly performed surgery for refractive errors. The procedure takes between 10 and 15 minutes for both eyes. It can correct nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. As in radial keratotomy, the cornea is reshaped to correct the refractive error.
After the eye is anesthetized with drops, the surgeon makes a corneal flap, a raised thin layer of the cornea, with an instrument called a microkeratome. This part of the procedure is a keratectomy. The flap is lifted and moved to one side. Using a computer-controlled laser, and on newer systems, an eye tracker, which follows the patient's minute eye movements, the surgeon removes tissue under the corneal flap to reshape the cornea.
To treat myopia, the cornea is made flatter by removing tissue from its center. For hyperopia, the cornea's center is made steeper. To treat astigmatism, the cornea is made rounder. The flap is replaced when the necessary tissue has been removed.
Healing occurs rapidly and stitches are not needed. Postoperative care varies from practice to practice. For example, some surgeons may cover the eyes with clear shields to protect them, while others find it unnecessary. The eyes should be rested the day of surgery and rubbing them should be avoided for a few days. Engaging in contact sports should be avoided for a couple of weeks and swimming for about a month.
Most patients experience some discomfort for 24–48 hours and notice improved vision within 1 to 5 days. However, visual acuity may not stabilize for several months.
The best results are achieved in patients with mild to moderate myopia. Approximately 93% have 20/40 vision or better following LASIK. For severely myopic patients and those with other types of refractive errors, LASIK may be less effective. Some patients who achieve 20/20 vision following LASIK report that it is not as crisp as the 20/20 they had with contact lenses, particularly the hard, gas-permeable type. This phenomenon is referred to as "loss of contrast sensitivity."
Rare complications include seeing glare or halos around bright lights at night, pain, blurry vision, eye dryness, infection, and problems with night vision.
Photorefractive Keratectomy (PRK)
PRK also uses a computer-controlled laser to reshape the cornea. In this procedure, the laser is used on the anterior part (surface) of the cornea, rather than under a corneal flap, as in LASIK. The corneal surface is prepared by removing the epithelium (outermost layer).
Healing takes longer with PRK, and patients usually experience discomfort and pain. Patients may require 3 to 5 days off from work following PRK, compared to an average of 1 day after LASIK. They also wear a bandage contact lens for 3–5 days after to help alleviate pain. Results are similar to LASIK, especially for patients with low to moderate myopia. Higher amounts of myopia do not respond well to PRK. The risk for complications is low, but the incidence of corneal scarring is slightly higher.
Intracorneal Ring (IRC)
IRC is used to correct mild myopia. It involves surgically placing a plastic ring into the cornea, which flattens the central area and corrects myopia. Unlike other surgeries, this does not permanently alter the eye. When the ring is removed, the cornea returns to its previous shape.
The eye is numbed with drops. A tiny incision is made near the upper edge of the cornea and the IRC is inserted between the tissue layers in the cornea. The procedure takes about 15 minutes.
Almost 100% of patients have 20/40 vision following IRC placement and 75% achieve 20/20. Complications are rare and include night vision difficulty, over- or undercorrection, glare, and increased astigmatism.
Clear Lens Replacement (CLR)
While not a common procedure for correcting refractive errors, the placement of an intraocular lens can help patients who are not candidates for RK, LASIK, or PRK. In this procedure, the eye's crystalline lens is removed and replaced with an artificial intraocular lens. Unlike other surgeries that alter the shape of the cornea, this one adjusts vision by changing the focusing power of the lens.
Generally, this procedure is not performed on patients younger than 40 because the implanted lens can cause difficulty in seeing close objects. Often reading glasses are required following the procedure. New types of intraocular lenses, however, are being developed that can be inserted into an eye without having to remove the natural crystalline lens. This type of lens, called a phakic intraocular lens, is currently undergoing FDA testing.
Most complications are minor and can usually be treated. Possible serious complications include retinal detachment, infection, or bleeding in the eye, but these are rare.