准分子激光原位角膜磨镶术术后早期角膜空间变化

Early spatial changes in the cornea after laser in situ keratomileusis for myopia

目的研究和分析近视性准分子激光原位角膜磨镶术(laser in stitu keratomileusis,LASIK)术后角膜空间变化规律.方法采用眼前节扫描系统(ORBSCAN Ⅱ)观察48例(89眼)LASIK术前及术后1～3 d、第1周、第1个月、第3个月、第6个月的角膜前后表面高度和角膜最薄厚度的变化.结果术后角膜前表面高度迅速变平,到第1周时达最大量,此后至术后第6个月缓慢回升;术前等效球面镜度数和角膜基质床厚度与术后第3个月的角膜前表面高度变化呈直线正相关,切削比百分数(切削厚度占最薄角膜厚度比)与之呈直线负相关.LASIK术后角膜后表面即前凸,并达最大量,术后第1周时较快回落,此后至术后第6个月缓慢回落;术前等效球面镜度数、术前最薄角膜厚度、角膜基质床厚度与术后第3个月角膜后表面高度变化呈直线负相关,切削比百分数与之呈直线正相关.术后1～3 d角膜最薄,厚度最小,随着时间延长至术后第6个月均逐渐增厚,但速度逐渐减慢; 术后 1～3 d 的实际角膜最薄厚度平均为 (424 ±65.0)μm,比预计角膜最薄厚度平均值(463.9±42.1)μm低,差异有显著性(t=3.218,0.001<P<0.002),角膜基质床厚度与术后第3个月角膜最薄厚度呈直线正相关.结论 LASIK术后1周内角膜后表面高度前凸、最薄厚度变薄和前表面变平量最大,此后至术后第6个月均缓慢回退.术前近视等效球面镜屈光度越高、激光切削量越大、角膜基质床厚度越薄,术后角膜前表面变平、后表面前凸越明显.术前角膜越薄,术后角膜后表面前凸越明显.角膜基质床厚度越薄,术后角膜最薄厚度越薄.术前后表面高度40 μm以上者应该根据所需矫正屈光度、角膜厚度、切削比、角膜基质床厚度和术前角膜后表面高度推算术后第3个月后表面高度,不超过80 μm较安全,角膜基质床厚度大于250 μm是安全的.

Objective To study the pattern of early spatial changes in the cornea afar laser in situ keratornileusis therapy for myopia. Methods Eighty-nine eyes of 48 consecutive patients who received LASIK therapy for myopia were included in the study. Anterior and posterior corneal surface elevation and thickness pachyrnetry were, obtained preoperatively and 1～3 days, 1 week, 1 month, 3 months, and 6 months postoperatively using an Orbscan Ⅱ （Bausch ＆ Lornb）.Results The posterior corneal bulge was greatest on postoperative days 1～3. The. anterior cornea was the. flattest 1 week postoperatively. Pachymetry was the thinnest 1 ～ 3 days postoperatively. There was a correlation between spherieal equivalent, residual stromal bed thickness, percentage of ablation per total corneal thickness and anterior corneal flattening 3 months postoperatively （ r = 0.772, 0.389, -0.629, respectively; P 〈 0.0005）. There was a correlation between spberical equivalent, pachymetry thiekness, residual stromal bed thickness, ablation percentage per total corneal thickness and posterior comeal bulge 3 months postoperatively （ r = -0.412, -0.276, -0.487, 0.489, respectively; P〈0.0005, 0.0025 〈P〈0.005, P〈0.0005, P〈0.0005）. The thinness of the. actual pachymetry （424 ± 65.0）μm was significantly less than the expected value （463.9 ± 42.1）μm 1 ～3 days postoperatively （ t = 3.218,0.001 〈 P〈 0. 002）. The thinnest pachymetry 3 months postperatively was correlated with residual stromal bed thichness （r = 0. 902, P 〈 0. 0005）. Conclusion An increased forward shift of the. posterior comeal surface is common after LASIK for myopia and correlates with the spherical equivalent, pachymetry, residual stromal bed thick, and the percentage of ablation per total corneal thickness. Anterior corneal flattening is common after LASIK for myopia and correlates with the. spherical equivalent, the. residual stromal bed thickness, and the percentage of the ablation per total corneal thickness. An excessively thin residual corneal bed or a large ablation percentage may increase the risk of iatrogenic comlications.