准分子激光原位角膜磨镶术后角膜后表面改变的特点及其影响因素

Characteristics and correlative factors of posterior corneal surface changes after laser in situ keratomileusis

目的探讨准分子激光原位角膜磨镶术(LASIK)后角膜后表面的改变的特点和影响因素。方法对61例行LASIK术的近视患者分别于术前、术后1周、1个月、3个月采用OrbscanⅡ观察角膜后表面的曲率半径、不规则系数、前房深度,并利用多元回归分析术后1周角膜后表面的前膨与影响因素的关系,以最佳适合球面(PBFS)曲率半径的差值和角膜后表面高度差(PED)作为角膜后表面的前膨的指标。结果LASIK术前、术后1周、1个月、3个月前房深度分别为(3.2448±0.2806)、(3.2770±0.2810)、(3.2579±0.2932)、(3.2651±0.2875)mm;PBFS曲率半径分别为(6.5095±0.2177)、(6.3731±0.2127)、(6.4257±0.2358)、(6.4354±0.2266)mm;角膜后表面5.0mm范围的不规则系数分别为0.622±0.142、0.978±0.244、0.884±0.207、0.881±0.174,术后各期较术前明显增大(P<0.01),术后1个月和3个月的差异无统计学意义(P>0.05)。多元回归分析显示术后1周角膜后表面的前膨与术前屈光度数呈正相关(r=0.0173,P=0.005),与术后1周角膜厚度呈负相关(r=-1.495,P=0.001)。结论LASIK矫正近视直接改变了角膜前表面,也相应引起了角膜后表面的变化,术后角膜后表面变陡且不规则性增加,但3个月内不会渐进性发展。其改变与术前屈光度数呈正相关,与术后1周角膜厚度呈负相关。

Objective To assess the changes of the posterior corneal surface and the factors influencing these changes after laser in situ keratomileusis (LASIK). These factors included the preoperative refraction, preoperative intraocular pressure (IOP), preoperative corneal thickness, spherical equivalent correction and one-week postoperative corneal thickness. Methods The posterior corneal radius of curvature for the posterior best fit sphere (PBFS), irregularity of posterior surface, and anterior chamber depth (ACD) were obtained with the scanning slit topography system before and 1 week, 1 month and 3 months after LASIK in 64 eyes of 34 patients with myopic refractive errors of -2.25 to -12.5 diopters. Multiple regression analysis was used to assess the factors that affecting these changes of posterior corneal surface. The difference of radius PBFS and posterior elevation difference (PED) was used as an indicator for the forward shift of posterior corneal surface. Results The ACD before the surgery and 1 week, 1 month and 3 months after the surgery was (3.2448±0.2806),(3.2770±0.2810),(3.2579±0.2932) and (3.2651±0.2875)mm, respectively. The PBFS at that time was (6.5095±0.2177), (6.3731±0.2127), (6.4257±0.2358)and (6.4354±0.2266)mm, respectively. The posterior corneal irregularity at 5 diameters zone was 0.622±0.142, 0.978±0.244, 0.884±0.207 and 0.881±0.174, respectively The preoperative posterior corneal radius of curvature for PBFS, the irregularity of the posterior surface and the ACD were significantly different from that of postoperative data at each time point (P<0.01). There was no significant difference in these indexes between 1 month and 3 months postoperatively. Multiple regression analysis showed that factors relevant to the changes of posterior corneal surface were the corrected preoperative refraction (regression coefficient r=0.0173, P=0.005) and 1 week postoperative corneal thickness (mm) (regression coefficient r=-1.495, P=0.001). Conclusions The posterior corneal surface after LASIK become steeper and more irregular and remains stable in three months after the surgery. Eyes with thinner corneas and higher myopia requiring more ablation are more predisposed to the changes of posterior corneal surface. The results of the present study should not be used in extremely high degree myopia. A study using a larger group of patients with a longer observation period is required.