Photorefractive keratectomy (PRK) and laser-assisted sub-epithelial keratectomy (or laser epithelial keratomileusis) (LASEK) are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lenses. LASEK and PRK permanently change the shape of the anterior central cornea using an excimer laser to ablate (remove by vaporization) 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 specifications of the laser that is used. The computer system redirects laser pulses for precise laser 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 tear film 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 microtome, will remain that way permanently with only limited healing or remodelling.

With PRK, the corneal epithelium is removed and discarded, allowing the cells to regenerate after the surgery. The procedure is distinct from LASIK (laser-assisted in-situ keratomileusis), a form of laser eye surgery where a permanent flap is created in the deeper layers of the cornea. However, PRK takes longer to heal and can, initially, cause more discomfort.

LASEK and PRK are two different procedures. While both procedures interact with the epithelium atop the cornea, the PRK procedure removes this entirely, while LASEK brushes the material away for the procedure, before being placed back for healing after laser surgery. The procedure can be used to treat astigmatism, nearsightedness, and farsightedness. During the procedure, the epithelium is displaced using a diluted alcohol solution.

PRK has advantages over LASIK in that it avoids added complications associated with the flap created during surgery. The procedure may also reduce the chances of dry eye symptoms after surgery. Due to the PRK procedure not requiring a surgical flap, athletes or individuals concerned with trauma introduced by the flap may see benefits to LASEK. Patients that wear contact lenses will typically need to stop wearing these for a specified time before the procedure.

PRK disadvantages include a longer recovery time for vision in contrast to LASIK which may be between five days and two weeks for blurred vision to properly clear. Another disadvantage is that patient may be required to apply steroid eye drops for a few weeks longer than that of a LASIK procedure.

When LASEK is compared to LASIK, LASIK can have better outcomes with corneal haze while LASEK has a lower rate of flap complications than LASIK.