PRK / LASIK ~ LASIK, PRK, laser vision correction, eye care, hyperopia - farsightedness, myopia - nearsightedness, astigmatism and excimer laser information.

PRK- PHOTOREFRACTIVE KERATECTOMY

The corneal epithelium is removed.

Cross section showing flatter shape.

PRK is the most common procedure utilizing the excimer laser. It is used to correct myopia, astigmatism, and hyperopia. With PRK, no scalpels are used and no incisions are made. The majority of surgical time is spent preparing both the laser and the patient's eye for the operation. The eye is prepared by anesthetizing it with drops.

Your GEA surgeon then prepares the eye by gently removing the eye's protective epithelium, (a layer of cells that naturally regenerates itself every few days) to reveal the next layer of corneal tissue known as Bowman's layer.

Laser preparation involves programming the laser to the individual characteristics of each patient's eye. Computer-controlled pulses of cool laser light are then applied to delicately reshape the curvature of the eye. Deeper cell layers remain virtually untouched.

Flattening of the cornea.

The strategy for treating myopia is to make the cornea flatter (a little less convex). Flattening of the cornea is achieved by removing more tissue from the center than the periphery. The flattening is controlled bye an iris diaphragm shutter that opens to control the pattern of the laser beam. The shutter is controlled by the computer program. The iris diaphragm shutter opens more slowly for higher amounts of myopia. In this way, more flattening is achieved in the center of the cornea to correct higher amounts of myopia.

The strategy for treating astigmatism is to flatten the steep meridian of the cornea. Recall that astigmatism occurs when the cornea is steeper in one meridian and is shaped like a football or back surface of a teaspoon. Also note that the meridian 90 degrees away is flatter. Preferential flattening of the steeper meridian is achieved by removing more tissue from the steeper meridian of the cornea. This is achieved by opening a slit shutter to control the pattern of the laser beam. The opening slit shutter is controlled by the computer program. The combination of myopia and astigmatism is corrected bye combining the opening slit and opening iris diaphragm together, creating an oval pattern on the cornea.

Steepening of the cornea.

The strategy for treating hyperopia is to steepen the cornea. Steepening of the cornea is achieved by removing more tissue from the mid-periphery than the center of the cornea. The steepening is controlled by the computer directing an opening slit to be focused on the mid-periphery of the cornea. The computer directs the opening slit to move 360 degrees around on the corneal surface, thus making the mid-peripheral cornea steeper symmetrically. Directing the slit to mid-periphery of the cornea is achieved optically by an off-set lens placed in the path of the laser beam (Click here for illustration). The opening slit opens more slowly for higher amounts of hyperopia. In the case of hyperopia and astigmatism the computer directs the opening slit to pause momentarily over the flatter astigmatic meridian of the hyperopic astigmatic cornea. This corrects, simultaneously, both the hyperopia and astigmatism.

Note that the strategy to treat astigmatism occurring with myopia is the exact opposite of astigmatism occurring with hyperopia. The above strategies are used for both PRK and LASIK.

The whole PRK procedure itself is usually completed in less than five minutes and is painless. Since a layer about as slender as a human hair is typically removed, the cornea maintains its original strength. Immediately, after the procedure a bandage contact lens is placed on the eye to improve your comfort while healing. The corneal epithelium grows back under the contact lens in 2-4 days after the myopic procedure and 6-8 days after the hyperopic procedure. Daily eye examinations are required during this initial healing process to ensure an infection does not develop.

Analgesic anti-inflammatory and antibiotic drops are given to reduce inflammation, promote healing, and prevent infection. The eye has a burning sensation and light sensitivity of varying degrees and relaxants are prescribed for the first few days. The patient is advised to rest for the remainder of the day following surgery.

Epithelial cells repopulate.

Your vision will be blurry while the contact lens is in place. However, vision is relatively good once the epithelium has grown back and the cornea surface has become smooth again (usually 3-4 days). The vision becomes the crispest or sharpest at variable amounts of time after the contact lens is removed. The average time prior to crisp vision is one week. To complete the healing process, PRK patients use steroid anti-inflammatory drops for up to three months under the direct supervision of their eye doctor.