Laser In Situ Keratomileusis (LASIK)
The LASIK procedure also uses the excimer laser to reshape the cornea, but this is done under a thin corneal flap, which preservers the surface epithelial cells. Rather than scraping away the epithelial cells to expose the corneal stroma as in PRK, a specialized surgical instrument known as a microkeratome (which works somewhat like a carpenter's plane) creates a flap of corneal tissue that is attached by a hinge. This flap is gently pulled back like a clear, hinged pancake and the corneal stroma is exposed. The laser part of the LASIK procedure takes place in the exposed corneal bed (corneal stroma). The laser application itself lasts about 30 to 90 seconds.
After the exposed corneal bed is treated by the laser and minute amounts of cells are vaporized, the flap is replaced in its original position. The flap is held in position by the eye's natural suction facility and natural sticky sugars, and provides increased comfort and decreased recovery time for the patient.
Photorefractive Keratectomy (PRK)
This is a procedure in which the front surface of the cornea is directly sculpted by the excimer laser. The surgeon prepares the eye by gently removing the surface layer known as the corneal epithelium. This layer regenerates itself within a few days. As in the LASIK procedure, computer-controlled pulses are directed at the exposed surface (the corneal stroma) to reshape the cornea. Less than ten percent of the cornea is affected, with the deeper layers remaining untouched.
Differences Between LASIK and PRK
Refractive vision correction performed under a flap (LASIK) offers numerous advantages over refractive vision correction performed on the cornea's surface (PRK). Notably, there is a more rapid improvement in vision and decreased discomfort with LASIK since the surface epithelial cells have been preserved and do not need to regrow. This is undoubtedly the reason that LASIK has become the corrective surgery of choice for both doctors and patients. However, in some patients, PRK is a safer alternative that may promise better outcomes. Patients who might benefit from PRK include those in whom the cornea might too thin for LASIK, or in some patients with corneal irregularities or scars.
A brief comparison of PRK and LASIK is outlined in the following chart.
|Initial examination||Similar to PRK||Similar to LASIK|
|Procedural difference||Corneal flap made with microkeratome||Surface epithelium removed|
|Excimer laser procedure||Similar to PRK||Similar to LASIK|
|Postoperative discomfort||Usually minimal||Variable|
|Visual recovery||Starts improving at one day||Starts improving at three days|
|Possible side effects||Glare/halo/ghosting Corneal flap problems||Glare/halo/ghosting Corneal haze|
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