Medical Edge Newspaper Column

Correcting Vision Problems: Three Good Methods

May 27, 2007
Dear Mayo Clinic:
I'm 48 years old and have been wearing hard contacts since I was 10. Apparently, as we approach 50 our eyes don't produce as many tears, so my hard lenses have become uncomfortable. What's the latest information on refractive surgery, and which kind has the highest success rate?

Answer:
Refractive surgery refers to procedures aimed at correcting "refractive error" -- an abnormality in the eye's focusing power that manifests itself in nearsightedness, farsightedness, or astigmatism. Nearsightedness occurs when the curvature of the cornea -- the transparent membrane that arcs over the front part of the eye -- is too steep. Farsightedness results if the cornea is too flat. And astigmatism is the problem when the cornea's curvature varies around its circumference (too steep in some directions along its surface, too flat along others).

If discussions with your doctor lead to the conclusion that refractive surgery, as opposed to eyeglasses, is for you, three time-tested procedures are available -- laser-assisted in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and (laser epithelial keratomileusis (LASEK) -- that give comparably good long-term results. LASIK is performed on most patients, though, while PRK and LASEK tend to be used on individuals who would be at risk for complications from LASIK.

PRK is the original method, developed in the 1990s. The surgeon first uses "controlled corneal abrasion" to polish off some of the epithelium (the outer layer that normally protects the cornea). Next, he or she directs an excimer laser -- which doesn't produce heat -- to correct the patient's refraction error by selectively removing tissue from the cornea's surface, thus changing its curvature. For example, with a nearsighted individual, the objective is to flatten the cornea enough that it will focus images normally.

The problem with PRK has been that it takes two to three days for the cornea's protective layer to heal, and patients can experience pain and persistent blur during that time. The need for an alternative method that was quicker and relatively pain-free -- while remaining accurate, stable, and of high optical quality -- led to development of LASIK.

In the LASIK procedure, the surgeon uses a precision-cutting instrument to create a thin, hinged flap in the outermost corneal tissue. The open flap gives the surgeon access to the so-called stroma (transparent tendon material) below, and an excimer laser is employed to reshape this tissue in accordance with the patient's needs. The flap is then closed, and being thin it will conform to the new curvature. Note that the epithelium has been minimally disturbed -- it is cut only enough to create the thin seam of the flap, so there is little pain and the healing occurs rapidly -- within a few hours.

LASIK is usually the method of choice. But in recent years, PRK has been making a small comeback because of a new bandage-like contact lens that temporarily protects the cornea while it heals. Another refractive-surgery procedure, LASEK, in which the surgeon creates a thinner flap than in LASIK because it is confined to the epithelium, has also been added. Nevertheless, PRK and LASEK are largely reserved for individuals with contraindications to LASIK; their corneas are either too thin, too steep, or have other characteristics that would increase the risk of a poor optical result. Better screening methods are now available for identifying such patients, which in my practice have run as high as 25 percent.

Three more factors to consider in your own case:

• People who've worn contacts for a long time can have a condition called contact lens-induced corneal warpage. Be sure to have the curvature measured at least twice before undergoing surgery to confirm that it is stable and of high optical quality.
• Refractive surgery may produce dry-eye symptoms for days or even months after the procedure. This risk is heightened if you already have dry eyes before surgery.
• Even with the best possible surgical outcome, at your age it is likely you'll still need reading glasses to see up close.

-- Leo J. Maguire, M.D., Ophthalmology, Mayo Clinic, Rochester, Minn.