Influence of Different Surgery Types and Ablation Ratios on the Change of Corneal Topography After Excimer Laser Refractive Surgery

  Objective  To analyze the change of corneal topography after excimer laser photorefractive keratectomy and the influence of surgery types and ablation ratios.

  Methods  A total of 52 myopic patients (103 eyes) underwent excimer laser refractive surgery in our hospital from August 2008 to February 2009. The patients were grouped by the type of surgery:laser in situ keratomileusis (LASIK) group (27 patients, 53 eyes) and advanced surface ablation (ASA) group (25 cases, 50 eyes). In both groups, the patients were subgrouped by ablation depth/corneal thickness ratio (AD/CT):subgroup 1 (AD/CT ≤ 0.15) and subgroup 2 (AD/CT > 0.15). Routine ophthalmological examinations and corneal topography were performed before operation and 1 week, 1 month, and 3 months after operation. The main outcome measures included surface asymmetry index (SAI), surface regularity index (SRI), Δsimulated keratoscopy reading (ΔSimK), and simulated keratoscopy reading (SimK).

  Results  In subgroups L2 and A2, all the three postoperative SAI values improved significantly compared with preoperative values (P=0.000), but not in subgroups L1 and A1 (P>0.05). In subgroup L2, the SRI value improved significantly 1 week after surgery (P=0.010), but not after 1 month and 3 months (P > 0.05). In subgroup A2, the SRI values improved significantly 1 week and 1 month after surgery (P=0.000, P=0.005), but not after 3 months (P > 0.05). The SRI showed no significant difference among different time points in both subgroup L1 and A1 (P > 0.05). In all patients, both ΔSimK and SimK equivalent value decreased significantly after the operation (P=0.000). The changes of SAI and ΔSimK were influenced by both surgery type and the ablation ratio (P < 0.05), while the changes of SRI and SimK equivalent only by ablation ratio (P < 0.05).

  Conclusions  The postoperative corneal topographic parameters change after excimer laser refractive surgery. The changes after LASIK are larger than those after advanced surface ablation, and the changes increase with the ablation ratio.