Photorefractive Keratectomy

Photorefractive Keratectomy, commonly known as PRK, is a common alternative to LASIK. It was developed in the early '80s, and is the predecessor to LASIK surgery. Unlike conductive keratoplasty, PRK can be used for nearsightedness.

Vision problems that can be remedied with glasses are a result of the eyeball not being a perfect sphere. Light enters the eye through the cornea, which does not change in shape normally. Light then passes through the lens, which can change shape from almost spherical to relatively flat, depending on the distance of the object being viewed. A perfectly functioning eye has a clear lens that focuses light directly on the retina. Problems arise when the eye is not perfectly spherical. People with nearsightedness or myopia have eyeballs that are too long. The lens is unable to flatten enough to focus light directly on the back of the eye -- the point of focus falls in front of the retina. People suffering from hyperopia or farsightedness have eyes that are too short, and light is projected past the back.

As light goes through the eye, it is refracted several times. Refraction is simply the bending of light when it goes from one substance to another. Refraction is why swimming pools appear more shallow than they really are and why fish in a round bowl sometimes appear to have distorted shapes and why magnifying glasses enlarge objects.

Photorefractive keratectomy involves removing a layer of the cornea so that light is refracted more directly onto the lens, which in turn can more easily project an image onto the retina. While LASIK removes cells under a flap of corneal tissue, PRK removes the outermost layer of the cornea. PRK causes more discomfort and takes longer to heal and provide clear vision, which is why it has mostly been replaced by LASIK. However, PRK can be performed on people with a cornea that is too flat or who have a pupil that is too big for LASIK to be practical.