Experimental study of the influence of cornea flap and residual cornea bed on cornea intensity after LASIK

Objective To study the influence of cornea flap and residual cornea bed on cornea intensity after laser in situ keratomileusis (LASIK). Methods The established mature cats animal model of LASIK was used. In Group A, a 160 μm cornea flap was made, followed by performing ablation on the stroma by excimer laser to preserve the residual bed for 300 μm, and then the cornea flap was repositioned. The cornea flap was removed with the residual bed 300 μm remaining in Group B, while in Group C, a 160 μm cornea flap was made with the residual bed 180 μm, and followed reposition of the cornea flap. In Group D, the cornea flap was cut off and a 180 μm the residual bed was remained. Measurements included central cornea pachymetry, anterior chamber depth (ACD) and analysis of the posterior best fit sphere in cornea Topography before operation and 1 week, 1 month, 2 months and 3 months after operation. The results were analyzed statistically. 3 months after operation, the changes of cornea structures were observed by histopathological analysis and transmission electron microscope. Results Increase of ACD 3 months after operation: Group A, (0.16±0.08) mm; group B, (0.21±0.16) mm; group C, (0.33±0.09) mm; group D, (0.41±0.10) mm. There was no statistical difference between group A and group B (t=0.685,P0.05)and between group C and group D (t=1.457,P0.05).There was a statistical difference between group A and group C (t=3.458, P0.05) and between group B and group D (t=2.597, P0.05). Increase of posterior cornea prominence 3 months after operation: Group A, (27.78 ±9.52) μm; group B, (39.57±7.68) μm; group C, (58.57±8.66) μm; group D, (68.14±19.69) μm. No statistical difference was found between group A and group B (t=2.361,P0.05) and group C and group D (t=1.090,P0.05).There was a statistical difference between group A and group C (t=5.860, P0.05) and between group B and group D (t=3.310, P0.05). Light microscopy and transmission electronic microscopy showed that the arrangements of collagen fiber in the interface were disordered with no apparent cross arrangement. There was no significant increase of rough endoplasmic reticulum in fibroblast. Conclusions Theresidual cornea bed is the main factor to influence corneal intensity. After LASIK, the wound healing of the interface is different from scar. This may be the main reason for cornea flap′s no apparent influence on cornea intensity.