Factors influencing flap and INTACS decentration after femtosecond laser application in normal and keratoconic eyes

PURPOSE: To compare accuracy of LASIK flap and INTACS centration following femtosecond laser application in normal and keratoconic eyes. METHODS: This is a retrospective case series comprising 133 eyes of 128 patients referred for refractive surgery. All eyes were divided into two groups according to preoperative diagnosis: group 1 (LASIK group) comprised 74 normal eyes of 72 patients undergoing LASIK with a femtosecond laser (IntraLase), and group 2 (INTACS group) consisted of 59 eyes of 39 patients with keratoconus for whom INTACS were implanted using a femtosecond laser (IntraLase). Decentration of the LASIK flap and INTACS was analyzed using Pentacam. RESULTS: Temporal decentration was 612.56±384.24 μm (range: 30 to 2120 μm) in the LASIK group and 788.33±500.34 μm (range: 30 to 2450 μm) in the INTACS group. A statistically significant difference was noted between the groups in terms of decentration (P<.05). Regression analysis showed that the amount of decentration of the LASIK flap and INTACS correlated with the central corneal thickness in the LASIK group and preoperative sphere and cylinder in the INTACS group, respectively. CONCLUSIONS: Decentration with the IntraLase occurred in most cases, especially in keratoconic eyes. The applanation performed for centralization during IntraLase application may flatten and shift the pupil center, and thus cause decentralization of the LASIK flap and INTACS. Central corneal thickness in the LASIK group and preoperative sphere and cylinder in the INTACS group proved to be statistically significant parameters associated with decentration.