Surgical procedures now make it possible to permanently eliminate or significantly reduce the need to wear glasses or contact lenses, even for people with very large refractive errors that require thick lenses. Appropriate surgery can modify the eye to focus light rays properly on the retina. Various operations can reduce or correct nearsightedness, farsightedness, and astigmatism, and it is now possible to reduce the magnitude of higher-order optical distortion such as spherical aberration. Newly developed intraocular lenses can even correct presbyopia, the reduced ability to focus from far to near that everyone begins to experience in their forties and that would otherwise occur with cataract surgery.
There are two basic types of corrective refractive surgery. One changes the curvature of the cornea (outer surface of the eye). The other changes the internal optics of the eye, either by replacing the natural lens of the eye or by using an intraocular lens in addition to the natural lens.
Refractive surgery became popular in the United States through radial keratotomy (RK), which was introduced from Russia in the early 1980s. In this operation, incisions made in the outer part of the cornea cause the central part of the cornea to flatten. This can correct a mild to moderate degree of nearsightedness. Astigmatism can be corrected with astigmatic keratotomy, in which circumferential incisions are made in the outer part of cornea. Radial keratotomy has been largely replaced by better procedures, but astigmatic keratotomy is still performed widely, especially together with cataract surgery.
With cataract surgery, the pre-existing spherical refractive error can be remedied by choosing an intraocular lens of appropriate power, and astigmatism can be corrected by utilizing a toric intraocular lens or by making astigmatic keratotomy incisions at the time of cataract surgery or later. In addition, an excimer laser can be used either before or after cataract surgery to maximize the accuracy of the refractive correction.
For most refractive errors, excimer laser surgery has replaced radial and astigmatic keratotomy because of its ability to remedy precisely a wider range of refractive errors. Computerized topography and computerized aberrometry can be used preoperatively to determine the best procedure and postoperatively to determine whether additional correction might be needed. The topographic apparatus measures the true elevation of each portion of the cornea and gives the surgeon an accurate picture of the corneal surface. The aberrometers measure the total refractive error of the eye and can be synchronized with an excimer laser system to correct higher-order aberrations. The modern excimer laser system can minimize new higher order aberrations that would otherwise be induced by the refractive corneal laser procedure. New topography-guided ablations have been used around the world and are awaiting FDA approval in the United States. Lens exchange procedures and introduction of an intraocular lens to augment the natural lens of the eye are also assuming a greater role in correcting refractive errors. Many of the new intraocular lenses have aspheric (nonspherical) optics that further reduce higher order aberrations that might otherwise be seen after cataract and refractive lens exchange procedures.
The current refractive surgical procedures include:
Photorefractive keratotomy (PRK):Photorefractive keratotomy (PRK): An excimer laser is used to correct low to moderate degrees of farsightedness, nearsightedness, and astigmatism. The thin corneal epithelial layer is removed, and some tough underlying tissue is ablated. The recovery period varies, and the final refractive state may not be reached for two or three months. The eye may be uncomfortable for a few days until the corneal surface layer regrows over the operative site. Newer medication regimens have eliminated discomfort for most patients. Postoperative haziness of the cornea (with cloudy vision) used to be common with this procedure, but topical treatment with the drug Mitomycin-C at the time of surgery usually prevents such haze.
Laser in-situ epithelial keratomileusis (LASEK): The outermost corneal layer (epithelium) is treated with dilute alcohol to harden it to increase its handling properties and is dissected aside. The excimer laser is used to reshape the cornea, and the epithelial layer is then replaced. A newer variation of this procedure (EpiLASIK) uses a precise mechanical instrument to push aside the superficial layer of the cornea, and with such newer instruments the alcohol treatment is unnecessary.
Laser in-situ keratomileusis (LASIK): An outer flap of the corneal epithelium and supporting tissue is made with the microkeratome and a precise underlying ablation is made with the excimer laser. As with the above procedures, each laser pulse removes just 0.25 microns (1/100,000 of an inch) of tissue. LASIK techniques can be used to correct astigmatism and farsightedness as well as nearsightedness. The results are nearly always predictable and recovery is usually very rapid. There is usually no postoperative pain or other discomfort. The availability of Mitomycin-C treatment and EpiLASEK equipment has led to increased use of PRK, but LASIK is still the most commonly performed refractive surgical procedure.
Refractive lens replacement: For people who are severely farsighted or severely nearsighted, an alternative approach is replacement of their natural lens with an artificial lens of a more appropriate power. This procedure is useful for anyone who is beginning to develop distortions in the lens of the eye, especially patients over fifty years of age. This is essentially the same as cataract surgery, an operation that has been perfected over the years. This approach is logical for patients who are beginning to develop a cataract or who are within the cataract age group. In patients with extremely high refractive errors, it is often the only choice.
“Standard” single vision intraocular lenses focus at just one distance. Such lenses can provide an increased range of focus when both eyes are used together the monovision technique is used. With monovision, near focus with one eye and a distance focus with the other eye can be combined to reduce dependence on glasses. However the recent development of intraocular lenses which actually focus for far and near can allow the patient to use both eyes for distance and both eyes for near. Bausch & Lomb’s Crystalens® actually changes position and shape to provide a clear focus at different distances. It utilizes the natural focusing muscle (ciliary muscle) of the eye to provide a continuous focus from far to near by inducing a forward movement and optical arching of the lens implant. This lens usually allows adequate focusing for reading vision. About 10% of patients sdo not focus adequately to read fine print without a reading glass, but they still obtain good distance and intermediate vision without correction. We often incorporate a very small amount of monovision to provide a fuller range of vision to these patients.
There are also several varieties of bifocal intraocular lenses which present the retina simultaneously with several focused images for different distances and the patient’s brain chooses the appropriate image to obtain well-focused vision. One of the newest lenses of this variety is Abbott Medical Optics’s Tecnis Multifocal Lens®. This lens (and the above-mentioned Crystalens) also have an aspheric surface to minimize higher order aberrations and improve vision.
Phakic intraocular lens implantation: A special intraocular lens is placed either in front of or behind the iris so that it works with the eye’s natural lens to bend the light rays more appropriately. This type of lens implant can correct very high degrees of myopia, and is particularly beneficial to younger patients since it allows them to retain the ability to focus near with their natural lens. Some uncommon problems, such as cataract formation, have been reported. Cataract formation in itself is not difficult to deal with with regular cataract surgery if this becomes necessary. The FDA has approved two such lenses: Advanced Medical Optics’s Verisyse® which clips to the front of the iris; and Staar Surgical Company’s Visian ICL®, a posterior chamber lens that fits behind the iris and is sometimes referred to as an “intraocular contact lens.”
Benefits vs. Risks
People contemplating refractive surgery should discuss the potential benefits and risks with an ophthalmic surgeon who is well regarded by the medical and optometric communities. As with any type of surgery, complications can occur. With corneal procedures, it is not unusual for patients to experience flare around lights at night, especially younger patients who have large pupils. Undercorrection or overcorrection may occur with any procedure and may necessitate a second “enhancement” procedure. Sometimes glasses may be required even after this surgery, and rarely, corneal irregularity may require use of contact lenses. In many cases, LASIK surgery may be used to refine the result of lens exchange surgery.
With LASIK, complications in the cutting of the corneal flap can lead to corneal irregularity. Rarely, wrinkles occur in the cap, requiring lifting and refloating of the cap, and sometimes corneal epithelial tissue grows under it and has to be removed. The excimer laser ablation itself could be off-center, resulting in reduced vision, halos around lights, and astigmatism. Newer scanning-spot excimer lasers enable greater accuracy of treatment and prevention and correction of higher-order optical distortions. Newer highly accurate tracking systems make decentration of laser treatment much less likely.
Lens exchange surgery carries with it the possibility of any complication that could occur with cataract surgery, such as infection, bleeding, and retinal detachment. These are rare nowadays, and, whereas in the past lens replacement surgery caused the patient to lose the ability to focus for near, newer focusing lenses remedy this problem. Two special advantages of lens exchange surgery are that the patient will not develop further refractive changes in the lens as he ages and the patient will never develop a cataract.
Satisfaction with modern refractive surgery is very high, and complications are rare. Most patients do well, gaining a whole new world of freedom from dependence on eyeglasses or contact lenses. Even so, the risk involved may not justify the use of surgery if adequate vision and comfort can be achieved with eyeglasses or contact lenses. Individuals who wish to explore the possibility of refractive surgery should seek a qualified eye surgeon who is thoroughly experienced in a wide variety of procedures.
About the Authors
The authors are ophthalmologists who specialize in refractive surgery. Dr. Herbert Nevyas is a former Chief of the Division of Ophthalmology and Clinical Professor of Ophthalmology at the Medical College of Pennsylvania. Their main office and ambulatory surgical center are located in the Philadelphia area at Two Bala Plaza, Bala Cynwyd, PA 19004. Telephone: (610) 668-2777.
For Additional Information
This article was revised on March 25, 2010.