RESUMO
PURPOSE: To evaluate posterior corneal surface elevation after LASIK in relation to the residual stromal bed thickness and the ablation percentage. METHODS: 363 eyes that underwent LASIK were examined retrospectively. The range of their refractive error was from -1.5 to -10.0 D. We obtained their corneal topography with Orbscan II and pachymetry preoperatively, and at one week, one month, two months, and three months postoperatively. The patients were divided into four groups based on the residual stromal bed thickness: Group I; 145 eyes with less than 250 micrometer, Group II; 129 eyes with 250~300 micrometer, Group III; 79 eyes with 300~350 micrometer, and Group IV; 13 eyes with more than 350 micrometer. We also grouped them based on the ablation percentage per total corneal thickness: Group A; 16 eyes with less than 10%, Group B; 166 eyes with 10~15%, Group C; 149 eyes with 15~25%, and Group D; 35 eyes with more than 25%. RESULTS: The extent of increase in the post-LASIK posterior corneal surface elevation correlates with residual corneal bed thickness and the ablation ratio per total cornea. In contrast, posterior corneal elevation values for Group IV were 0.025+/-0.005 mm preoperatively, 0.038+/-0.007 mm at 1 weeks, 0.037+/-0.010 mm at 1 month, 0.03+/-6 0.012 mm at 2 months, 0.036+/-0.009 mm at 3 months. In Group A, the values at the same times were 0.029+/-0.009 mm, 0.043+/-0.012 mm, 0.039+/-0.013 mm, 0.040+/-0.013 mm, 0.038+/-0.010 mm. CONCLUSIONS: The extent of increase in the post-LASIK posterior corneal surface elevation correlates with residual corneal bed thickness and the ablation ratio. There were no statistically significant changes in postsurgical posterior corneal surface elevation, however, if the residual corneal thickness remained more than 350 micrometer or the ablation percentage was lower than 10%.