PRK : Photorefractive keratectomy ( PRK ) and Laser-Assisted Sub-Epithelial Keratectomy ( LASEK ) are laser eye surgery procedures intended to correct a person's vision and reduce their dependency on glasses or contact lenses . The procedures permanently changes the shape of the anterior central cornea using an excimer laser to ablate (burn off) a small amount of tissue from the corneal stroma at the front of the eye, just under the corneal epithelium . The outer layer of the cornea is removed prior to the ablation. A computer system tracks the patient's eye position 60 to 4,000 times per second, depending on the brand of laser used, redirecting laser pulses for precise placement. Most modern lasers will automatically center on the patient's visual axis and will pause if the eye moves out of range and then resume ablating at that point after the patient's eye is re-centered.

The outer layer of the cornea, or epithelium , is a soft, rapidly regrowing layer in contact with the air that can completely replace itself from limbal stem cells within a few days with no loss of clarity. The deeper layers of the cornea, as opposed to the outer epithelium, are laid down early in life and have very limited regenerative capacity. The deeper layers, if reshaped by a laser or cut by a microkeratome , will remain that way permanently with only limited healing or remodelling. In LASEK the corneal epithelium is preserved with a chemical solution, peeled off, and replaced after the laser ablation is complete. With PRK the epithelium removed is discarded and allowed to regenerate. Both procedures are distinct from LASIK ( L aser- A ssisted in- SI tu K eratomileusis ), a form of laser eye surgery where the epithelium is not removed.

LASEK is a procedure that permanently changes the shape of the cornea using an excimer laser to ablate a small amount of tissue from the front of the eye, just under the eye's outer layer or epithelium

Custom Wavefront LASIK

Epi-LASIK is a refractive surgery technique designed to reduce a person's dependency on eyeglasses and contact lenses . Invented by Dr. Ioannis Pallikaris ( Crete , Greece ), the technique is basically an automatic LASEK without alcohol :

IntraLase "Bladeless" LASIK which the epithelium is not removed from the corneal flap, the epithelium is kept off the eye during the procedure and replaced afterward to act as a natural bandage.