•  LASIK – uses the Microkeratome to make a flap on the cornea, which gets temporarily put aside, while lasers are used to remove the layers of tissue under the cornea. Where and how much tissue is taken out determines the amount and type of correction.  (For farsightedness, the tissue removed is mostly around the edge, leaving a small build up in the center of the eye, which effects the vision.  For nearsighted eyes, the tissue is made flatter in the center of the eye, changing the vision.) Then the flap is replaced.  After surgery, it takes a few hours to heal.  LASIK can be used to improve farsightedness, nearsightedness, or astigmatism.  LASIK is considered state-of-the-art and is the most commonly used laser eye surgery.

•  PRK – (Photorefractive Keratoplasty) uses a laser to remove tissue, but, unlike LASIK, it also removes the surface layer.  But the surface of the cornea contains elements that are critical for stable vision.  So, though the eye replaces and heals the surface over time, those elements were taken out, causing problems for the eye.  Visual stability can take years to achieve after surgery.  (The reason for the instability is because after the surgery, the eye tries to heal itself in a process called remodeling.  With LASIK, the surface is never violated, therefore the tendency for remodeling is greatly reduced.)

•  RK – (Radial Keratotomy) corrects mild forms of nearsightedness, by making small incisions in a radial pattern on the cornea, therefore flattening it.  But a major concern about RK is the way that the incisions weaken the eye.  Another concern is that eyes with RK can experience progressive flattening, making them farsighted over time.  The effect is worse for eyes undergoing larger amounts of correction, and that is why today RK is usually replaced by LASIK surgery.  RK is the oldest of the modern refractive procedures.

•  ALK – (Automated Lamellar Keratoplasty) corrects nearsightedness by removing a thin layer from the surface of the cornea, leaving it aside, and removing a layer of the cornea underneath it.  But when the surface layer is replaced, some of the cornea has been taken away, leaving it thinner and flatter than it was originally.  ALK has the advantage of leaving the corneal strength intact, unlike RK.  The disadvantage is that it is not as precise as the laser in removing tissue, and therefore it sometimes takes multiple procedures to obtain the right amount of correction.  ALK has recently been replaced by LASIK.

Contacts