Glasses or contact lenses are designed to compensate for the imperfections of the eye. Surgical procedures aimed at improving the focusing power of the eye are called refractive surgery. With Lasik surgery, precise and controlled removal of corneal tissue by a special laser reshapes the cornea and changes its focusing power.
Before Lasik there were other techniques developed to reshape the cornea for example Photorefractive Keratectomy. Often the exact same laser is used for the two types of surgery. The major difference between the two surgeries is the way that the stroma, the middle layer of the cornea, is exposed before it is vaporized with the laser. In PRK, the top layer of the cornea, called the epithelium, is scraped away to expose the stromal layer underneath. In LASIK, a flap is cut in the stromal layer and the flap is folded back.
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