Astigmatic Keratotomy (AK)

Astigmatic keratotomy is a variation of Radial Keratotomy (RK), which was the first truly successful refractive vision correction procedure. The RK procedure was designed to correct mild to moderate cases of myopia (nearsightedness), while the AK procedure was used to correct moderate astigmatism. Although major improvements were made in both the RK and AK procedures through the years, both have been largely replaced by more modern refractive surgery techniques such as laser in-situ keratomileusis (LASIK).

To understand how refractive surgery works, it is first necessary to understand the visual function of the eye. The eye works like a camera with two lenses. The first lens is the cornea, a clear membrane that covers the front of the eye. The second lens is the eye's natural crystalline lens that is located behind the pupil. The cornea is responsible for about 70 percent of the eye's focusing power, while the natural lens fine-tunes the image before it is focused on the retina at the back of the eye. The retina works like the film in a camera, receiving light images and sending them through the optic nerve to the brain. (See Anatomy of the Eye.)

A perfect eye has an evenly rounded cornea that allows light to fall exactly on the retina resulting in perfect vision. Astigmatism is a refractive eye disorder that exists because the shape of the cornea is less than spherical. It is more oblong, somewhat like the back side of a spoon. Thus, light rays, or visual images, are bent out of shape either horizontally or vertically before they strike the retina. Because astigmatism often exists in conjunction with nearsightedness, the RK and AK procedures were often combined and performed at the same time.

For the AK procedure, incisions are made in the surface of the cornea in a sideways manner. They are made where the corneal curve is the steepest, rounding out the cornea. The AK incisions can be made in a straight line or in an arc-like form, depending on the data generated by the preoperative testing, evaluation process, and the surgeon's judgment. The incisions are made outside of the central zone, or visual axis, of the cornea.

After surgery, your eyes may feel gritty, be sensitive to light, and appear red. Antibiotic eye drops help guard against infection. Although the AK procedure was done successfully for many years with good results in correcting astigmatism, newer forms of refractive eye surgery are more precise and produce more consistent results.