Decentration after Laser in Situ Keratomileusis(LASIK) and Photorefractive Keratectomy(PRK)

ABSTRACT

LASIK procedure was introduced recently for the correction of high myopia because of many complications in high-myopic PRK. The characteristic procedures such as hinged flap formation and stromal ablation may increase decentration. We evaluated the amount of decentration relative to the pupil center in 80 eyes of LASIK and 52 eyes of PRK using corneal topography(Corneal Analysis System: EyeSys Laboratories). All treatments were performed using excimer laser, Aesculap-Meditec, MEL 60-94 and corneal light reflex was used for centering. The vacuum ring was used for globe fixation. Mean amount of decentration in LASIK(0.65+/-0.42mm) was statisticallysignificantly increased compared with 0.49+/-0.29mm in PRK(p=0.01). Under -12D of attempted correction, mean amount of decentration in LASIK was 0.54+/-0.38mm which was not significantly different from 0.49+/-0.29mm in PRK(p=0.07). No correlation was observed between the magnitude of decentration and the frequency of loss of best cerrected visual acuity and night glare(p>0.05). The decentration more than 1mm was associated with increased amount of attempted correction (p=0.003) and low preoperative best corrected visual acuity(p=0.01). We considered that the differencee of the magnitude of decentration was attributed to some difference in procedures between LASIK and PRK. When vaccum ring is not used in other reports with other device, the decentration of LASIK was approximately twice as much as in PRK. The use of vacuum ring for the maintenance of globe may be effective in LASIK in which patients self fixation during ablation is more difficult than in PRK because the ablation time is longer and the ablation is performed on the stroma after flap formation.