At greater levels, the procedure is less predictable. While technique has evolved, the basic principles have remained. These incisions induce peripheral steepening of the cornea, which in turn causes flattening of the central cornea. This results in images coming into focus on the retina. The amount of correction can be altered with the length and depth of the incisions.
Visual recovery is rapid, with little discomfort.
RK patients with satisfactory postoperative visual acuity, however, may still be bothered by fluctuating vision, glare, decreased contrast sensitivity, or photophobia. The results of this study have been the standard for evaluating RK results. The excimer laser used in PRK delivers pulsed ultraviolet light to penetrate only a small distance into corneal tissue and works by breaking chemical bonds instead of destroying tissue with heat. Recently, FDA approval was obtained for its use in treating astigmatism and low to moderate levels of hyperopia. Although PRK does not involve use of a surgical blade to make corneal incisions, it is still considered a surgical procedure.