准分子激光原位角膜磨镶术后角膜后表面Diff值的变化

目的 探讨近视患者准分子激光原位角膜磨镶术（LASIK）术后角膜后表面Diff值变化规律及其对术后视力的影响.方法 对62例（123眼）近视患者于LASIK术前、术后1 d、1周、1个月行角膜地形图检查.分别按照残余基质床厚度、残余基质床厚度占术前角膜厚度的比例及术前屈光度的不同分组,分析各组间及同一组不同时期角膜地形图后表面Diff值的改变及其与术后视力的关系.结果 术后后表面Diff值较术前增大,且随原屈光度增大而增加,随基质床厚度增大而减小.当残余基质床厚度〉300μm或残余基质床厚度占术前角膜厚度的比例≥55%时,后表面Diff值明显减小.术后后表面Diff值与视力呈一定程度负相关.结论 LASIK术后角膜后表面前凸是影响术后视力的原因之一.后表面前凸的主要影响因素包括术前屈光度的高低、残余基质床厚度等,残余基质床厚度在300 μm以上或残余基质床厚度占术前角膜厚度的比例≥55%也许更安全.

Change in posterior Diff value after LASIK for myopia

Objective To investigate the change in the posterior Diff value (distance from the top point of the posterior surface of the cornea to the perfect spherical surface) after laser in situ keratomileusis (LASIK) for myopia, and its relationship to visual acuity. Methods Comeal topography was performed on 62 myopic patients (123 eyes) before LASIK surgery and 1 day, 1 week, and 1 month after surgery. Subjects were divided into groups according to the thickness of the residual stromal bed, the ratio of the thickness of the residual stromal bed to that of the preoperative cornea or preoperative degree of myopia. The posterior Diff value and its relationship to visual acuity was analyzed. The posterior Diff value was compared between groups and interviews postoperation. Results The posterior Diff value was higher after LASIK surgery than before surgery. The value increased as the thickness of the residual stromal bed decreased, and it increased with an increase in the preoperative degree of myopia. When the thickness of the residual stromal bed was more than 300 μm or the ratio of the thickness of the residual stromal bed to that of the preoperative cornea was above 55%, the posterior Diff value clearly decreased. The posterior Diff value was related to visual acuity to some extent. Conclusion The posterior surface protrudes forward is elevated after LASIK. A change in the posterior surface is one of the factors that affect visual acuity. The changes are related to the thickness of the residual stromal bed and preoperative degree of myopia. LASIK may be safer if the thickness of the residual stromal bed is more than 300 μm or the ratio of the thickness of the residual stromal bed to that of the preoperative cornea is above 55%.