不同角膜测厚法对LASIK术后中央及旁中央角膜厚度测量值的影响及比较分析

Comparison of different methods for the measurement of central and paracentral corneal thickness in post-LASIK eyes

背景 准确的角膜厚度测量对准分子激光角膜屈光手术的术前设计及术后随访非常重要,对屈光欠矫及屈光回退的患者能否行二次激光加强手术更是不可或缺的重要检查. 目的 比较OrbscanⅡ眼前节分析仪（OrbscanⅡ）、非接触角膜内皮显微镜、眼前节光学相干断层扫描仪（AS-OCT）和A型超声角膜测厚仪对准分子激光角膜原位磨镶术（LASIK）术后角膜中央和旁中央厚度测量结果的差异. 方法 收集2011年3-6月在河南省眼科研究所＆河南省立眼科医院接受LASIK手术的患者64例64眼（均纳入右眼）,受检者术前平均等效球镜屈光度为（-4.75±2.38）D,平均水平角膜直径为（11.36±0.32）mm,采用OrbscanⅡ、非接触角膜内皮显微镜、AS-OCT和A型超声角膜测厚仪（超声法）分别测量受检眼的中央角膜厚度（CCT）,同时采用OrbscanⅡ、非接触角膜内皮显微镜、AS-OCT 3种非接触角膜厚度测量法测量距角膜中心3 mm区角膜上方（12：00）、下方（6：00）、鼻上方（2：00）和颞上方（10：00）的旁中央角膜厚度,比较不同角膜测厚仪测量结果的差异,评价检测仪器间测量结果的一致性. 结果 CCT测量结果显示,AS-OCT、A型超声角膜测厚仪、非接触角膜内皮显微镜和OrbsanⅡ的测量值分别为（467.12±31.10）、（466.67±30.99）、（441.84±33.65） μm和（422.51±44.09）μm,总体比较差异有统计学意义（F=23.730,P=0.000）;A型超声角膜测厚仪测得的CCT值明显高于OrbsanⅡ和非接触角膜内皮显微镜的结果,差异均有统计学意义（q=6.940、6.720,均P=0.000）;与OrbscanⅡ测量方法比较,非接触角膜内皮显微镜和AS-OCT测量的CCT值明显较高,差异均有统计学意义（q=-5.540、6.940,均P=0.000）,而AS-OCT测量的CCT值明显高于非接触角膜内皮显微镜的测量值,差异有统计学意义（q=6.800,P=0.000）.Bland-Ahman一致性分析结果显示,A型超声角膜测厚仪与AS-OCT测量值的最大绝对差值为25.3 μm,二者的一致性最好.旁中央角膜厚度测量结果显示,OrbsanⅡ测量的角膜厚度值最大,其次为AS-OCT,非接触角膜内皮显微镜测得值最小,3种测厚仪在12：00、2：00、10：00、6：00子午线测得的旁中央角膜厚度值的总体比较差异均有统计学意义（F=5.020、22.950、67.890、18.850,P＜0.01）.结论 在分析LASIK术后眼角膜厚度测量值时应考虑到不同检测仪器测量结果的差异,Orbscan Ⅱ对CCT的测量值偏薄,而对旁中央角膜厚度测量值偏厚,非接触角膜内皮显微镜对CCT和旁中央角膜厚度的测量值均偏薄,而AS-OCT与A型超声角膜测厚仪测得的CCT值非常接近,两种仪器可相互替代使用.

Background Accurate measurement of corneal thickness is very important during the pre-and post-operative management of corneal surgical procedures,especially laser-assisted in-situ keratomileusis （LASIK）,which is the most popular approach to the correction of refractive errors currently.This may be particularly important for the patients who have undergone previous laser refractive surgery with suboptimal outcomes and are being considered for an enhancement procedure.Objective This study was to compare the measuring outcomes of corneal thickness by slit-scanning pachymetry,non-contact specular microscope,anterior segment optical coherence tomography （AS-OCT）and ultrasound pachymetry,with a focus on central and midperipheral （from the central 3.0 mm） region of cornea in post-LASIK eyes.Methods Sixty-four right eyes of 64 patients who received LASIK were collected in Henan Eye Institute,Henan Eye Hospital from March to June 2011 with the equivalent spherical diopter of （-4.75±2.38）D and horizontal corneal diameter of （11.36±0.32）mm.Central corneal thickness was measured on each eye by using non-contact specular microscope （Topcon SP-3000P）,slit-scanning pachymetry （Orbscan Ⅱ）,AS-OCT and A-type ultrasound pachymetry,respectively,and the paracentral corneal thickness including 12：00,2：00,6：00 and 10：00 meridian was measured using Orbscan Ⅱ,non-contact specular microscope and AS-OCT.The measuring values and the agreement from different instruments were compared and evaluated.Results The mean central corneal thickness was （467.12±31.10）tμm for AS-OCT,（466.67±30.99）μm for ultrasound pachymetry,（441.84 ± 33.65） μm for specular microscopy and （422.51 ± 44.09） μm for Orbsan Ⅱ,respectively,showing a significant difference among the four methods （F =23.730,P =0.000）.The central thickness value of the A-type ultrasound pachymetry was significantly higher than that of Orbsan Ⅱ or non-contact specular microscope （q =6.940,6.720,both at P =0.000）.Compared with Orbscan Ⅱ,the measuring values of non-contact specular microscope and AS-OCT were significantly higher （q =-5.54,6.940,both at P =0.000）,and the measuring value of AS-OCT was significantly higher that of non-contact specular microscope （q =6.800,P =0.000）.The lowest difference value （25.3 μm）and the best agreement was found between the ultrasound pachymetry and AS-OCT.The paracentral corneal thickness values in 12：00,2：00,10：00,6：00 meridians were highest for Orbsan Ⅱ and the next for AS-OCT,and non-contact specular microscope had the lowest values,with significantly differences among them （F =5.020,22.950,67.890,18.850,all at P ＜ 0.01）.Conclusions The corneal thickness values vary with the different instruments.Orbsan Ⅱ underestimates the central corneal thickness and overestimates the midperipheral corneal thickness,and non-contact specular microscope underestimates both the central and midperipheral corneal thickness.The measuring outcome from AS-OCT has a good agreement with ultrasound pachymetry and therefore they can be used interchangeably.