Surface based excimer laser treatments are called Photorefractive Keratectomy (PRK) or Laser Epithelial Keratomileusis (LASEK) or EpiLASIK.
In PRK, the surface cells of the cornea are first mechanically brushed off or loosened with alcohol and the laser energy is applied to the firm corneal tissue, called the stroma. This leaves behind a surface ‘scratch’ which causes discomfort for about 72 hours after the procedure. The procedure itself is absolutely painless.
The surface defect takes up to three or four days to heal. After treatments, during the healing and settling down phase, vision may be worse than before the treatment, but rapidly improves over the first few days.
With LASEK, the epithelium (the top layer of the cornea) is loosened with alcohol which is held on the eye with a cup. The epithelium is raised as a flap with a blunt instrument and some sponges. The laser energy is applied to the exposed stroma as in PRK and then the epithelium is replaced.
The main difference between PRK and LASEK is the preservation of the epithelium. A contact lens is applied and left on the eye for about five days. After treatment, during the healing and settling down phase, vision may be worse than before the treatment, but with LASEK this very rapidly improves over the first few days.
LASEK is popular as there is no cutting involved, and hence no additional risks, as in LASIK.
EpiLASIK treatment is between LASEK and LASIK. An automated instrument separates the top layer (epithelium) from the firm tissue (stroma).The instrument is like the one used for LASIK but creates a flap like the one in LASEK. The recovery is more like LASEK.
PRK/LASEK and EpiLASIK treats the surface of the cornea once the epithelium has been removed. Vision improves with these surface procedures over a few days. LASEK and EpiLASIK are technically more difficult than PRK.