| Purpose:To assess the repeatability of the Visante Omni system in measuring posterior corneal surface in myopic eyes and evaluate and compare the accuracy, reproducibility and regularity of corneal flap created with femtosecond laser(FS-LASIK) and Sub-Bowman’s Keratomileusis(SBK) refractive surgery. To assess early change in posterior corneal elevation after FS-LASIK, and compare it with Epipolis Laser in Situ Keratomileusis (Epi-LASIK), SBK.Methods:The elevation for thirteen points in different location, the corneal dioptric power in the flattest and steepest meridian, the flat axis, and Q value in the posterior corneal surface were chosen to evaluate the repeatability of Visante Omni system in measuring the posterior corneal surface. Visante OCT was used to measure the corneal flap thickness1day postoperatively. The thickness of thirteen measuring points across each flap was evaluated. Visante OMNI was used to collect the posterior corneal elevation data preoperatively and1day,1week,1month postoperatively, respectively. The elevation of thirteen measuring points across the posterior cornea were evaluated.Results:1. For the posterior corneal elevation, within-subject SD showed a trend of increase from the vertex to the periphery and was no more than3.95, the CVw ranged from0.16%to2.13%, the ICC of all the13points was no less than0.844. As for the posterior corneal dioptric power and Q value, all the Sw was no more than0.1except6.66for the flat axis, the CVw was from0.01%to1.47%, all the ICC was no less than0.90.2. The average thickness of flap on the vertex of cornea in femtosecond group was (97.49±7.34)μm; for the SBK group, this value was (112.93±9.99) μm. The average of absolute difference between actual and average thickness was (5.74±3.98)μm and (8.11±5.75)μm in the FS-LASIK and SBK group respectively, with statistical significant difference between these two groups(t=2.83, P=0.005). Flap morphology:The flap thickness showed good uniformity for different location away from the vertex in FS-LASIK group (F=1.206, P=0.303,) while flap thickness in the central area was thinner than peripheral area for the SBK group.3. For the FS-LASIK group, in the vertex, the posterior corneal elevation was2.03μm,2.26μm、2.16μm、2.06μm preoperatively and1day,1week,1month postoperatively, respectively; in the lmm and2mm district, the trend was the same with the vertex postoperatively; in the3mm district, the data was-4.64μm、-5.39μm、-4.73μm、-4.71μm at the four different times. For the SBK group, in the vertex, the posterior corneal elevation was1.44μm,1.74μm、1.66μm、1.53μm preoperatively and1day,1week,1month postoperatively; in the3mm district, this data was-5.09μm,-5.48μm、-5.27μm、-5.19μm at the four different times, there was a tiny backward displacement. For the Epi-LASIK group, in the vertex, the posterior corneal elevation was2.47μm,1.55μm、1.55μm、2.37μm preoperatively and1day,1week,1month postoperatively, there was a tiny backward displacement; in the1mm and2mm district, the trend was different from the vertex; in the3mm district, the trend was the same with the vertex postoperatively. FS-LASIK had bigger change than SBK1day postoperatively. Statistical analysis showed no statistical difference among the three surgical techniques and4times.Conclusions:Visante Omni system may provide a reasonably good repeatability in measuring posterior corneal surface for both the central and periphery area. Compared to SBK, the cornea flap of FS-LASIK shows more advantage in the accuracy and reproducibility, and the cornea flap is more regular from central to peripheral area. In the early stage after FS-LASIK, the posterior corneal elevation of both central and paracentral area had tiny changes and then returned to preoperative level with time, FS-LASIK is a relative safe surgical technique. |
PDF Full Text Request