Performed since the early 1970’s, refractive surgery procedures improve vision due to nearsightedness (myopia), farsightedness (hyperopia) and astigmatism. With the advent of the laser for refractive surgery (Photorefractive keratectomy or PRK,), a new era in eye care is unfolding. It has been found that the excimer laser procedure combined with the creation of a corneal flap (lamellar Keratoplasty or LK) is an excellent technique for reshaping the surface of the cornea to correct nearsightedness and astigmatism. The combination of both procedures is called Laser Assisted In-Situ Keratomileusis (LASIK) and offers the accuracy of refractive lasers with the benefits of the LK procedure’s speedy recovery.
With a refractive error, there is a defect in the way light passes through the eye. Light rays do not refract (bend) properly to achieve a single focus point. Instead, light rays focus in front of the retina (nearsighted), behind the retina (farsighted), or at two different points (astigmatism).
Refractive errors usually result from a defect in the length of the eye or shape of the cornea.
A computer, programmed by the doctor for each person’s own correction factors, controls the laser and the reshaping to the cornea. The procedure is performed while the patient lies on her/his back. In treating myopia, (as shown to the left)
The laser segment of the procedure starts with a narrow diameter beam. As the laser beam expands or moves, a tiny lens-shaped disc is created. The focal point of the beam only penetrates the cornea about two thousandths of an inch (about half the thickness of a human hair). Only a small area in the center of the cornea is treated, essentially producing a concave lens over the visual axis. Finally, the corneal flap is replaced (without stitches) and the LASIK procedure is complete.
With hyperopia (left), the shape of the cornea is essentially steepened to allow images to correctly focus on the retina. For astigmatism (right), the laser beam scan back and forth along the cylindrical axis to reshape the eye.