[The Excimer laser. An instrument for corneal surgery].

Photoablation of the cornea using excimer lasers (193 nm) results in keratectomies with very precise edges and minimal damage to the adjacent tissue. Deep keratectomies for relaxation incisions (astigmatic correction) and for trephination (lamellar or penetrating keratoplasty) are possible, but have not been applied routinely. Superficial keratectomies can induce corneal flattening--a promising approach for correction of myopia. This unique keratorefractive technique, called photorefractive keratectomy (PRK), has been studied worldwide with a follow-up time of up to 2 years. The success rate (+/- 1 D from the refraction aimed at) is approximately 90%, and vision-threatening complications are extremely rare. However, this is true only in corrections of up to -6.0 D. Corrections of more than this result in a significant decrease in the refractive success and a tremendous increase in complications. Therefore, we believe that corrections of more than -6.0 D are clinically not acceptable. Long-term stability is not yet proven, and consequently PRK must be used with strict indications. Superficial scars, corneal dystrophies, and degenerations of the outer cornea can be removed with the excimer laser much more gently than with conventional techniques.