Corneal interlayer reaction is lighter after laser in situ keratomileusis(LASIK).It does not form scar tissue between corneal flap and posterior stromal bed.Corneal healing may keep clear visual area,but corneal structure has changed which is the main reason for the cornea intensity change.Forward shift of the posterior corneal surface curvature after LASIK is common.It correlates with the central corneal thickness,the residual corneal bed thickness,the corrective dioptre,preoperative IOP,corneal flap thickness,the ablation ratio per total corneal thickness,the ablation diameter,age and so on.Our study is to evaluate the forward shift of the posterior corneal surface curvature after LASIK and the correlative factors.