准分子激光角膜原位磨镶术后角膜后表面的高度变化

背景准分子激光角膜原位磨镶术（LASIK）术后发生的角膜扩张是一种严重影响视力的并发症，角膜后表面高度的测量有助于术后早期发现角膜的这种变化。目的探讨近视散光患者在LASIK术后角膜后表面高度变化规律及影响角膜后表面高度变化的因素。方法采用系列病例观察研究设计。对2008年5月至2010年1月在北京同仁医院眼科中心接受LASIK的66例近视散光患者127眼的角膜后表面高度变化进行回顾性分析。分别于术前和术后3个月、6个月及1年用Ocuyzer眼前节分析系统对术眼角膜后表面高度进行测量及统计分析。结果术前角膜后表面最高点、最低点和角膜顶点的高度值分别为（12．20±3．39）、（-19．02±7．38）和（1．05±3．25）μm；术后3个月时分别为（14．38±3．80）、（-18．55±7．11）和（2．83±4．81）μm；6个月时分别为（13．99±3．38）、（-17．57±6．54）和（2．45±4．61）μm；1年时分别为（14．40±3．85）、（-17．76±6．00）和（2．16±5．00）μm，术后角膜后表面最高点和角膜顶点的高度值较术前均明显增加，差异均有统计学意义（表面最高点：q：6．813、5．594、6．875，均P〈0．001；角膜顶点：q=4．488，P：0．002；q=3．530，P=0．013；q=2．799，P=0．047）；术后不同时间点各项高度值差异均无统计学意义（P〉0．05）。术后1年角膜后表面顶点高度与等效球镜度、切削深度和切削比呈正相关（r=0．295、0．297、0．295，均P=0．001），与残留基质厚度呈负相关（r=-0．208，P=0．019）。术前非接触眼压计测量值为（14．24±3．33）mmHg（1mmHg=0．133kPa），术后3个月、6个月、1年分别为（8．42±1．90）、（8．61±1．64）、（8．76±1．64）mmHg，术后各个时间点的眼压值均明显低于术前眼压，差异均有统计学意义（q=29．851、28．317、26．337，均P〈0．001），而术后各时间点差异无统计学意义（P〉0．05）。Ehlers法校正后术后眼压值与术前眼压值的差异无统计学意义（P〉0．05）。术前眼压值与术后1年角膜后表面顶点高度值呈正相关（r=0．258，P=0．003）。结论LASIK术后早期角膜后表面较术前轻度膨隆，随时间的延长逐渐稳定，屈光度是影响LASIK术后角膜后表面形态的主要因素，手术时应注意保留安全的残留角膜基质厚度并尽量减小切削偏心程度，从而降低术后角膜扩张的风险。

Change of cornea posterior elevation after laser in situ keratomileusis

Background Keratectasia after laser in situ keratomileusis （LASIK） is one of the serious complications which affect the vision. The measurement of cornea posterior elevation is an important way helping to find this change. Objective The aim of this study was to investigate the change of cornea posterior elevation after LASIK in myopic eyes with astigmatism and affecting factors. Methods A series case-observational study was adopted. One hundred and twenty-seven myopic eyes with astigmatism of 66 patients who received LASIK in 2008 May through 2010 January in Beijing Tongren Hospital were retrospectively analyzed to evaluate the change of cornea posterior elevation following the LASIK. The parameters related to cornea posterior elevation were measured and compared before and 3 months ,6 months and 1 year after surgery, respectively, with Oculyzer anterial segment analysis system. Results The height values from posterior cornea highest point, the lowest point and central vertex central elevation zone were （ 12.20±3.39 ） , （ - 19.02 ± 7.38 ） and （ 1.05 -± 3.25 ） μm respectively before LASIK and were （14.38±3.80）, （-18.55±7. 11）, （2.83±4. 81） Ixm in 3 months and （13.99±3.38）, （-17.57-±6.54）, （2.45±4.61 ）μm in 6 months after LASIK. They were （ 14.4±3.85 ） , （ -17.76± 6.00 ） , （2.16± 5.00 ）μmin 1 year after surgery. Significant increases were found in the vertex height and central elevation after LASIK compared with before surgery（highest point：q=6. 813,5. 594,6. 875 ,all at P〈0. 001. central vertex： q=4. 488,P=0. 002;q=3. 530,P= 0. 013 ;q=2. 799,P= 0. 047）. However, no significant difference was seen in various time points after LASIK （P〉 0.05）. A positive correlation was obtained between the height value of the posterior cornea central vertex with the spherical equivalent （SE） , maximum cutting depth or cutting proportion 1 year after LASIK （ r = 0. 295,0. 297, 0. 295, all at P=0. 001 ）, and there was a negative correlation between it with residual stroma （r=-0. 208,P = 0. 019）. The intraocular pressure （lOP） measured with noncontact tonometry （NCT） was （ 14.24：t：3.33 ） mmHg before LASIK,and those of 3 months,6 months and 1 year were （8.42±1.90）,（8.61±1.64） and （8.76±1.64） mmHg after LASIK,showing a significant lowing in lOP after LASIK in comparison with before LASIK （q = 29. 851, 28. 317,26. 337 ,all at P〈0. 001 ）. But no significant change was found in the different time points after LASIK （ P〉 0. 05）. There was significant difference in the IOP corrected by Ehlers after LASIK （P〉0. 05 ）. The IOP before LASIK had positive correlation with the central elevation of posterior cornea surface 1 year after LASIK（ r = 0. 258,P = 0. 003）. Conclusions The cornea posterior elevation increases slightly early stage after LASIK but retains stable level with lapse of time. The refraction diopter before LASIK is the main factor affecting the posterior corneal shape. To reduce the risk of corneal ectasia,more attention should be paid to the reserving of appropriate corneal residual stroma and smallest degree of eccentricity during the ablation procedure. Key words] Laser in situ keratomileusis; Cornea posterior elevation; Cornea thickness; Keratectasia