Other types of refractive surgery are available and may be more appropriate than LASIK for certain individuals. Advanced surface ablation: There are a variety of other techniques that utilize the excimer laser to reshape the cornea in much the same way as LASIK, but without the creation of a corneal flap. These are generically termed advanced surface ablation (ASA) and include photorefractive keratectomy (PRK), laser subepithelial keratomileusis (LASEK), and epipolis laser in situ keratomileusis (Epi-LASIK). All of these techniques involve first removing the most superficial corneal layer (epithelium) and then performing excimer laser ablation. Phakic intraocular lenses: For patients with extreme myopia, LASIK and advanced surface ablation are not reasonable options. In these cases, a phakic intraocular lens may be used. This lens is implanted inside the eye and can effectively treat nearsightedness up to -20 diopters. Conductive keratoplasty: Conductive keratoplasty (CK) is a technique that can be used for the temporary correction of hyperopia or presbyopia. CK involves using radiofrequency waves in the peripheral cornea to cause peripheral corneal shrinkage and central steepening. This procedure is very safe, but its effect is often not long-lasting, and regression is common after a few years. Intracorneal ring segments: Intacs (Addition Technology, Inc.) are approved for the correction of low myopia and for patients with keratoconus in the U.S. Intacs are micro-thin plastic segments that are implanted into the peripheral cornea in order to flatten the cornea centrally. Once implanted, the rings generally cannot be felt by the patient. These rings can be removed, and their effect is usually completely reversible. They are only able to correct up to -3 diopters of myopia, and visual recovery is generally slower and less predictable than LASIK.