PRK, or photorefractive keratectomy, makes use of a specialized cool laser beam, called an excimer laser, to remove excess corneal tissue. The removal of this tissue corrects the shape of the eye so that light entering the eye can be properly focused on the retina. The outer surface layer called the epithelium, is removed to expose the underlying corneal tissue. Once this tissue is revealed, the excimer laser is used to reshape the cornea. The main distinction between PRK and LASIK is that PRK does not make use of a corneal flap. Instead, the epithelium is allowed to gradually heal through the body’s natural healing process. To protect the exposed cornea, surgeons fit patients with a lightweight contact lens to serve as a bandage for the eye. The contact lens also reduces discomfort. The lens is usually only worn for a few days, two to three days post-operative, at which time the eye is allowed to heal as normal with no bandage.
LASIK is the most widely known and performed type of laser eye surgery in the United States. LASIK stands for Laser Assisted In-Situ Keratomileusis, which literally means to "reshape the cornea from within using a laser.” LASIK differs from PRK in that a small flap is made in the stroma of the eye. This flap, made by either a microkeratome or IntraLase, is then peeled back to expose the underlying corneal tissue. An excimer laser is then used to reshape the cornea to correct any refractive errors. Once the cornea has been reshaped, the cornea flap is put back into place and smoothed out. The flap acts as a natural bandage to help the eye heal and protect the delicate cornea. The benefit of LASIK is that the use of the flap helps the cornea heals more quickly than it would using the PRK technique, and reduces much of the discomfort felt during the healing process.
Many ophthalmologic surgeons are now offered the next evolution in LASIK surgery, which they called Customized LASIK. The general procedure used to correct refractive errors is the same as is used for traditional LASIK procedures, with the addition of wavefront devices used to map the unique surface of the patient’s eye. The wavefront device passes a narrow ray of light through the systems and into the eye, measuring any optical distortions that result as the light exits back out the eye. Any irregularities identified are then fed back into the system so that the laser can automatically correct for aberrations on the surface of the eye. Proponents of Customized LASIK claim that the use of wavefront technology enables surgeons to treat higher order aberrations that can contribute to low-light visual disturbances such as halos and glare not corrected by traditional LASIK, eyeglasses, or contact lenses. Customized LASIK can provide patients who suffer from higher order aberrations with an increase in visual clarity.
The final type of laser eye surgery is LASEK, or Laser Assisted Sub-Epithelial Keratectomy. LASEK is especially helpful for patients who have a thin or flat cornea, making them questionable candidates for LASIK and Customized LASIK procedures. During LASEK, a small trephine blade is used to cut into the outer skin of the eye, called the epithelium. Once the cut has been made, the eye is bathed in a mild alcohol solution to allow the edges of the epithelium to soften. This permits the surgeon to gently tease the epithelium flap out of the way to expose the underlying tissue. An excimer layer reshapes the eye under the flap to correct any refractive errors, after which the flap is replaced over the treated cornea. As with LASIK, the replacement of the flap in LASEK speeds up the natural healing process and serves to minimize discomfort resulting from the procedure.
Although the end result of PRK, LASIK, Customized LASIK, and LASEK is the same – the reduction of refractive errors – the method by which these corrections are made differ. Each procedure has its advantages and disadvantages and is best suited for certain types of patients. Individuals who are considering laser eye surgery to correct their vision and reduce dependency on corrective lenses are urged to contact their ophthalmologist to inquire about available options and learn if they are a strong candidate for one of more of these procedures.
