A Comparison Study Of The Centration Of The Treatment Zoneand Postoperative Visual Results Between Small Incision Lenticule Extraction(SMILE) And Wavefront-guided Femtosecond Laser-Assisted LASIK(FS-WASCA)

Objectives To investigate the centration of the treatment zone and compare postoperative visual results after Small Incision Lenticule Extraction(SMILE)and wavefront-guided Femtosecond Laser-Assisted LASIK(FS-WASCA).Methods In this prospective,non-randomized observational study,31 patients(55 eyes)received SMILE procedures,and 25 patients(45 eyes)received FS-WASCA procedures to correct myopia with astigmatism.Centration offset was measured with Orbscan II topography.Uncorrected and corrected distance visual acuity,manifest refraction,and higher order aberrations were analyzed at 1 and 6 months after the procedures.Results(1)In SMILE cases,the mean centration offset of the optical zone with reference to the corneal vertex was 0.218±0.162mm(range:0.001-0.879mm);In FS-WASCA cases,the mean centration offset of the optical zone with reference to the corneal vertex was 0.438±0.208 mm,(range: 0.021-1.022mm).The centration offset from the corneal vertex was larger in the FS-WASCA group(P <0.05).(2)The distribution pattern of the optical zone was more dispersed in FS-WASCA groups.The center of the optical zone of SMLE group located significantly nearer to the direction of the angle kappa(P=0.008).(3)There was no significant difference at 1 and 6 months postoperatively in uncorrected(P=0.239,0.738)or corrected distance visual acuity(CDVA)(P=0.164,P=0.256)between two surgical techniques.(4)No eyes lost 2 lines or more of CDVA after either procedure.(5)The mean achieved refraction was-0.08±0.39 D from the attempted refraction after SMILE and 0.09±0.28 D after FS-WASCA.After both procedures,90% of eyes were within ±0.50 D of target.(6)In terms of high order aberrations,the change in spherical aberration after SMILE was significantly smaller than that after FS-WASCA(P<0.001).On the other hand,there was no significant difference in the change of coma(P =0.089)and total HOAs(P=0.067).Conclusion(1)The centration of the treatment zone measured by Orbscan II topography was better in SMILE which was centered on the corneal vertex of the coaxially fixating eye,than FS-WASCA which was assisted by active eye trackers(2)Both of SMILE and FS-WASCA are safe,effective,predictable and stable surgical procedures to treat myopia and astigmatism.(3)SMILE induces significantly lower ocular spherical aberration than FS-WASCA,but no significant difference was found in coma and total HOAs.