The aim is to change the curvature of the cornea and thus affect its focusing power, allowing the patient to see in the distance without spectacles. It is used more often to correct short sight than long sight.
There are many different forms of laser refractive surgery:
Photorefractive Keratectomy (PRK): The superficial corneal epithelium is scraped off and the laser applied to modify the curvature of the cornea. The corneal epithelium then heals over by itself. This procedure can be painful in the early postoperative period, as the patient effectively has a total corneal abrasion. Vision will not improve until the cornea has healed completely.
LASIK (laser-assisted in situ keratomileusis): This is the most common form of laser refractive surgery. The surgeon uses a special, fine automated blade to cut a flap half through the thickness of the cornea. This flap is then lifted up and the laser used under the surface to change the shape of the cornea. The flap is then laid down and adheres by itself without the need for stitches. Patient comfort is not usually a problem, and the vision is often much improved by the following morning.
LASEK (laser epithelial keratomile): This is similar to LASIK, but rather than making a cut in the cornea, the whole sheet of epithelium is lifted off using alcohol, and laser applied to the underside to alter the shape. The above procedures are carried out under topical anaesthesia.
Dry eye: This is quite common, and usually self-limiting.
Flap dislocation: Because the LASIK flap is not sutured into place, this will always be a weak area, although the flap usually sticks down well. Injury, such as being poked in the eye, may cause the flap to lift off and wrinkle. The flap can often be ‘floated’ back into place.
Haze: After laser treatment, the cornea may heal but not retain total clarity. The patient might be left with some residual haze and, therefore, reduced vision.
Infection: Infection can be disastrous. It usually occurs in the interface beneath the flap, and can be caused by organisms of different virulence. The condition is commonly called diffuse lamellar keratitis (DLK). If the organism is of low virulence, the infection may be treated successfully but may leave the vision hazy.
Per-operative button holing: In the LASIK procedure, the cut may go too deep and into the eye, or may be too superficial, not forming a complete flap. If this is recognised, the procedure is usually abandoned. The situation is not usually disastrous however, and the procedure may still be done successfully at a later date.
Complications: These are effectively cosmetic procedures and so complications, particularly if sight-threatening, are particularly upsetting for the patient.