Differences among the LASIK, PRK, LASEK, and Epi LASIK procedures

In laser-assisted in situ keratomileusis (LASIK, first column), a stromal flap is created mechanically with a microkeratome, or more recently using a femtosecond laser. Part of the stromal bed is then removed with an excimer laser to provide the refractive correction before repositioning the LASIK flap. In photorefractive keratotomy (PRK, second column), the central corneal epithelium is removed and stromal tissue is excised from the stromal surface with an excimer laser. In laser epithelial keratomileusis (LASEK, third column), an epithelial flap is formed with the help of dilute ethanol and special instruments, and stromal tissue is excised from the stromal bed with an excimer laser. The surgeon hopes to retain the epithelium in LASEK, but in some cases it is lost, and then the procedure is then similar to PRK. In epithelial laser-assisted in situ keratomileusis (Epi-LASIK, fourth column), an epikeratome, which is a mechanized blunt blade, is used to separate the epithelium from the underlying stroma.