Effects Of LASIK With The Flap Created By Femtosecond Laser, SBK And Common LASIK On Corneal Biomechanics

Objective:Measure the curvature radius of backsurface of cornea pre- and post- LASIK with the flap created by femtosecond laser, SBK and common LASIK. And then compare the different curvature radius changes of backsurface of cornea in the three groups.Find out which surgery can keep more biomechanical properties.It is very helpful for patients who have thin corner and high myopia to select the right surgery. It also provides theoretical support for the development of the LASIK.Methods: (1) Select 60 eyes of LASIK with the flap created by femtosecond laser and 60 eyes of SBK, which could be referred to as femtosecond group and SBK group, to do prospective analyses. Measure the preoperation central corneal thinkness and the residual bed thickness of all cases using A ultrasound, then calculate the flap thinkness and compare the flap thinkness, accuracy and repeatability of the two groups. (2) Select 760 eyes of LASIK cases to analyze retrospectively. Divide these cases into low myopia group (SE≤3.0D), moderate myopia group (3.0D6.0D) based on the spherical equivalent (SE). Each diopter group is further divided into LAISK with the flap created by femtosecond laser group, SBK group and common LASIK group. By comparing the pre-operational central and supreme curvature radiuses of backsurface of cornea with those 1 month, 3 months and 6 months after each kind of operation in each diopter group to reflect the stability of post-operational backsurface of cornea in each group.By comparing the postoperative residual bed thicknesses,changes of postoperative central and highest curvature radiuses of backsurface of cornea in the three kinds of operation to reflect the effects of the three surgeries on corneal biomechanics.Results:(1) The flap thickness in femtosecond group is (89.2±9.1) um, significantly lower than that in SBK group of (100.4±10.3) um (P<0.05). The range in femtosecond group is 44um, which is also lower than the range in SBK group of 56 um. This demonstrates that the flap created by femtosecond laser is thinner, and has better accuracy and repeatability. All the post-operative residual bed thicknesses of the three sugeries in each diopter group are greater than 280um, and the values tend to be femtosecond group > SBK group > common LASIK group. All the postoperative central and highest curvature radiuses of backsurface of cornea of the three surgeries in each diopter group show good stability (P>0.05), except the SBK group in high myopia group. Only the highest curvature radiuses of backsurface of cornea 1 month after the operation of the three surgeries in moderate myopia group show significant difference (SBK group (+0.018±0.108)mm, femtosecond group (-0.012±0.128)mm, common LASIK group (-0.018±0.094)mm). The differences of postoperative central and highest curvature radiuses of backsurface of cornea in other time period of the three surgeries in all diopter group are not statistically insignificant (P>0.05).Conclusions :On the condition that it has enough corneal bed thickness, the postoperative curvature radiuses of backsurface of cornea in FS-LASIK, SBK and common LASIK are all of good stability. They do not have significantly different effects on corneal biomechanical properties. This may be related to the following factors: Bowman layer is distroyed, the curvature radius of backsurface of cornea is not sensetive to the decrease of corneal biomechanics and the Pentacam anterior eye segment analysis system can provide more accurate measuring results.