Early spatial changes in the posterior corneal surface after laser in situ keratomileusis

Abstract Purpose To evaluate the forward shift of the posterior corneal surface after myopic laser in situ keratomileusis (LASIK) relative to the residual stromal bed thickness and the ablation percentage of the total corneal thickness. Setting Department of Ophthalmology, Ilsan Paik Hospital, Inje University, Ilsan, Korea. Methods Three hundred sixty-three eyes of 182 consecutive patients who had LASIK were examined retrospectively. The range of the refractive errors was −1.5 to −12.0 diopters. Corneal topography using Orbscan ® II (Bausch & Lomb) and pachymetry were obtained preoperatively and 1 week and 1, 2, and 3 months postoperatively. The patients were divided into 4 groups based on the residual stromal bed thickness: Group 1, 145 eyes with less than 250 μm; Group 2, 129 eyes with 250 to 300 μm; Group 3, 76 eyes with 300 to 350 μm; and Group 4, 13 eyes with more than 350 μm. They were also grouped by the ablation percentage per total corneal thickness: Group A, 16 eyes with less than 10%; Group B, 166 eyes with 10% to 20%; Group C, 146 eyes with 20% to 30%; and Group D, 35 eyes with more than 30%. Results The increase in the forward shift of the posterior corneal surface postoperatively correlated with the residual corneal bed thickness and the ablation ratio per total corneal thickness. There were no statistically significant changes in the postsurgical forward shift of the posterior corneal surface if the residual corneal thickness remained greater than 350 μm or the ablation percentage was less than 10%. Conclusions Increased forward shift of the posterior corneal surface is common after myopic LASIK and correlates with the residual corneal thickness and the ablation percentage per total corneal thickness. An excessively thin residual corneal bed or a large ablation percentage may increase the risk of iatrogenic complications.