[Refractive surgery].

The surgical correction of refractive errors has gained widespread acceptance in the past 20 years, mainly through the introduction of the excimer laser. The excimer is used to ablate the cornea, renoving stromal tissue in the center (to correct myopia through flattening of the surface), or in the midperiphery (to steepen the cornea to correct hyperopia). Although excimer procedures dominate the field of refractive surgery, other approaches are also available. In the cornea itself, ring segments can be implanted, heat-induced coagulation effects can produce steepening, and cross-linking of the collagen fibers can stiffen a weakened structure. While all corneal procedures are extraocular, refractive surgery can also be performed within the eye. Special intraocular lenses can be implanted in the anterior chamber angle, fixated onto the iris, or placed in the posterior chamber in front of the crystalline lens. These so-called phakic intraocular lenses are available in different optical magnitudes and act to correct the patient's refractive error. Prebyopic individuals can have the crystalline lens removed in a procedure identical to cataract surgery. In such cases the lens is extracted even though no cataract is present, and an intraocular lens is implanted in the now empty capsular bag of the crystalline lens. The implanted lens serves to correct the preoperative refractive error.