Your Guide to Refractive Surgery
Herbert J. Nevyas, M.D.
Anita Nevyas-Wallace, M.D.
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 enable light rays to converge 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 trefoil, coma, and spherical aberration.
Modern 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. Astigmatic keratotomy, consisting of circumferential incisions in the cornea, also became popular at this time. Radial keratotomy has been replaced by newer procedures, but astigmatic keratotomy is still performed widely, especially together with cataract surgery.
When cataract surgery is performed, the pre-existing spherical refractive error can be remedied by the choice of intraocular lens power. The astigmatic refractive error can be treated at the same time by appropriate astigmatic keratotomy incisions, performed either in the midperiphery or near the outer boundary of the cornea.
For most refractive errors, excimer laser surgery has replaced radial and astigmatic keratotomy because of its ability to remedy 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 indicated. The newest topographic diagnostic apparatus measures the true elevation of each portion of the cornea and gives the surgeon an accurate picture of the corneal surface. The newest aberrometers measure the total refractive error of the eye and can be synchronized with an excimer laser system to correct even higher-order aberrations. Lens-replacement 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.
The current refractive surgical procedures include:
Photorefractive keratotomy (PRK): An excimer laser is used to correct low to moderate degrees of nearsightedness, and astigmatism. The thin and weak corneal epithelial layer is removed, and the tougher corneal stromal tissue is ablated. The correction is fairly precise but not completely predictable. The recovery period varies, and the final refractive state may not be known for several months. During the procedure, the corneal surface is removed and left to heal in, which means that the eye may be painful for a few days until the corneal surface regrows. Postoperative haziness of the cornea (with cloudy vision) used to be common with this procedure, but topical treatment with Mitomycin-C at the time of surgery usually presents 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. This procedure produces less postoperative discomfort than LASEK or PRK.
Laser in-situ keratomileusis (LASIK): An outer flap of the corneal stroma 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. There is usually no postoperative pain or other discomfort. This procedure is preferred throughout the world by eye surgeons who have sufficient experience and have access to the necessary equipment. The availability of Mitomycin-C and EpiLASEK has led to increased use of PRK, but LASIK is still the most commonly performed refractive surgical procedure.
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 is essentially the same operation as cataract surgery, an operation that has been perfected over the years. In patients who are beginning to develop a cataract or who are within the older cataract age group, this approach is logical. In patients with extremely high refractive errors, it is often the only choice. Newer lenses that allow both distance and near vision are now being introduced. Diffractive lenses that create a simultaneous distant and near image on the retina have been used for several years, but these lenses have the disadvantage of decreasing contrast sensitivity and causing glare at night.
A newer lens is the accommodating intraocular lens. The FDA has approved only one variety, the Crystalens, manufactured by Eyeoptics Inc. This lens utilizes the natural focusing muscle (ciliary muscle) of the eye to allow it to provide a continuous focus from far distance to near by inducing a forward movement of the lens implant with accommodation effort. This lens usually allows adequate focusing for reading vision. However, about 10% of patients do not focus adequately to read and require a reading glass. These patients still obtain good intermediate vision without correction.
Phakic intraocular lens implantation: A special 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. In younger patients, this procedure preserves the ability to focus with the natural lens. Some problems, such as cataract formation, have been reported, but the most refined forms of this procedure look promising. The FDA has approved two such lenses: Advances Medical Optics's Verisyse/Artisan, which clips to the front of the iris; and Staar Surgical Company's Visian ICL, a posterior chamber lens 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 the patient to experience flare around lights at night, especially younger patients who have large pupils. Undercorrection or overcorrection may occur and may necessitate a second "enhancement" procedure. Sometimes glasses may be required even after this surgery; and rarely, corneal irregularity may require even continued use of contact lenses. Occasionally, LASIK surgery is use to refine the result of lens procedure surgery.
With LASIK, complications in the cutting of the corneal flap can lead to corneal irregularity. Sometimes 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 have largely replaced the older broad-beam lasers, which enable greater accuracy of treatment and correction of higher-order optical distortions.
Lens-replacement surgery carries with it the possibility of all the complications 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 vision, newer lenses allow this. Two advantages of lens-replacement surgery are that these patients will not develop refractive changes in the lens and will never develop a cataract. Phakic lens implantation bears with it the rare possibility of infection and also of producing a cataract that eventually requires cataract surgery.
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 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 August 23, 2005.