近视患者准分子激光原位角膜磨镶术前后OrbscanⅡ观察

目的探讨近视眼准分子激光原位角膜磨镶术（LASIK）后OrbscanⅡ的动态变化及影响角膜后表面前突出度的主要因素。方法216例（230只眼）近视患者,根据等效球镜屈光度分为4组,Ⅰ组：-1．25～-3．00D;Ⅱ组：-3．13～-5．75D;Ⅱ组：-6．00～-8．88D;Ⅳ组：-9．00～-15．75D,采用OrbscanⅡ角膜地形图系统分别于术前、术后1个月、3个月进行检测,取角膜厚度图、角膜后表面地形图进行动态对比分析。结果预留角膜最薄处厚度,角膜后表面屈光力及角膜后表面顶点距理想球面的距离（Diff值）,术后较术前明显改变,术前与术后1个月相比,差异有统计学意义（t=22．79,-20．63,-15.90;P〈0．05）。术前与术后3个月相比,差异有统计学意义（t=17．87,-17．98,-27．26;P〈0．05）,表现为角膜变薄,后表面屈光力及Diff值增加,术后同一时间段不同组间比较差异有统计学意义（术后1个月F=61．92,4．74,7．28;P〈0．05。术后3个月F=64．16,5．12,21．83;P〈0．05）,不同时间段同一组间比较差异无统计学意义（P〉0．05）。术后角膜最薄处厚度较术前预留最薄角膜厚度在不同组间比较差异有统计学意义（P〈0．01）,术前角膜后表面Diff值（Y）与术前角膜最薄处厚度（X1）、角膜中央厚度（X2）、角膜横径（X3）、眼轴长度（X4）建立多元线性回归方程为Y=0．0941-0．00053X1-0．000471X2-0．0063X3＋0．00122以（F=13．48,P〈0．01）。术后3个月与1个月角膜后表面Diff值的差值（Y）与术后3个月与1个月角膜最薄处厚度差值（X1）、术前眼压（X2）、术后3个月与1个月角膜后表面屈光力差值（X3）建立多元线性回归方程为Y=-0．027-0．00078X1＋0．00201X2-0．0055X3（F=21．81,P〈0．01）。结论OrbscanⅡ对近视眼LASIK术前患者的筛选及术后监测评估具有重要的临床意义,但角膜测厚功能在高度近视眼LASIK术后准确性差,不宜作为再次手术的筛选标准;影响近视眼术前角膜后表面前突出度变化的主要因素为角膜厚度、角膜横径与眼轴长度;影响术后3个月与1个月前突出度变化值的主要因素为术后3个月与1个月角膜最薄处厚度差值,角膜后表面屈光力差值及术前眼压。这些影响因素应作为术前筛选病例的参考指标。

Analysis of the dynamic changes of cornea after myopic excimer laser in situ keratomileusis using an Orbscan II topography system

OBJECTIVE: To study the changes and influence factors of an Orbscan II topography system in myopia after excimer laser in situ keratomileusis (LASIK). METHODS: Two hundred and sixteen myopia patients (230 eyes) were treated by LASIK, their corneal thickness and curve of corneal posterior surface was measured with an Orbscan II topography system before and after surgery. The results of measurement in different time points were compared. RESULTS: The thinnest point of cornea, the mean keratometry of the posterior best fit surface (BFS) and the distance from the apex to the BFS were significant difference before and after operation (P < 0.05). There were significant difference among those groups in different degree of myopia in the same time point (P < 0.05) after surgery, but there were no significant difference in the same group in difference time (P > 0.05). A significant difference in the area of the thinnest cornea before surgery and after surgery was detected among those groups (P < 0.01). The regression equation for preoperative Diff value was established as Y = 0.0941 - 0.000,53X(1) - 0.000,471X(2) - 0.0063X(3) + 0.001,22X(4) (P < 0.01), X(1) = corneal thickness of the thinnest point (microm), X(2) = central corneal thickness (microm), X(3) = corneal diameter (mm), X(4) = length of ocular axis (mm). The regression equation for postoperative decrease Diff value between the third month and the first month was produced as Y = - 0.027 - 0.000,78X(1) + 0.002,01X(2) - 0.0055X(3) (P < 0.01). X(1) = decrease in corneal thickness of the thinnest point (microm), X(2) = intraocular pressure pre-surgery (mmHg), X(3) = decrease in curvature of posterior corneal surface (D). CONCLUSIONS: The application of Orbscan II has an important clinical significance before and after LASIK. The Diff value measured before LASIK for myopia is influenced by the corneal thickness, corneal diameter and ocular axis. The postoperative decrease in Diff value between the third and first month is influenced by the postoperative decrease of corneal thinnest point and curvature of posterior corneal surface, and preoperative intraocular pressure.