| Objective: To investigate changes in the posterior corneal surface after laser in situ keratomileusis (LASIK). And to analyze factors relevant to these changes, especially the relationship of E (scleral rigidity coefficient) and forward shift of posterior corneal surface after LASIK through measuring IOP (intraocular pressure) and E preoperatively.Method: 288 eyes of 144 patients who had LASIK were examined. Corrected IOP and E were measured before surgery. Corneal topography of the posterior corneal surface (diff) was obtained with OrbscanⅡ(a scanning slit topography system) before and one week, one month after surgery. Multiple regression analysis was used to assess the factors that affect the forward shift of the posterior corneal surfaces.Result: After surgery, the posterior corneal surface had forward shift in any group, which was statistically significant. E had no relationship with forward shift of posterior corneal surface after LASIK. The regression equations of possible factors relevant to the forward shift of the posterior corneal surface were: Forward shift 1 week after LASIK(μm) = (0.284×ablation percentage per total corneal thickness)＋(0.368×forward shift before LASIK)＋(-0.197×residual thickness of corneal matrix bed); Forward shift 1 month after LASIK(μm) = (0.343×ablation percentage per total corneal thickness)＋(0.191×forward shift before LASIK).Conclusion: LASIK induces the forward shift of the posterior corneal surface. Eyes with thinner corneas and residual corneal matrix beds, larger ablation percentage, and larger forward shift of posterior corneal surface before LASIK are more predisposed to the forward shift of the cornea. E or corneal rigidity possibly has no relationship with forward shift of posterior corneal surface after LASIK. Corneal rigidity is just one small part of the biomechanic characteristics of cornea, other indexes are needed for researching their relationship. The change trend of forward shift of posterior corneal surface is not obvious in a short time, further observation is needed for a long time. |
