准分子激光原位角膜磨镶术后Orbscan II估算术前角膜屈光力

Estimation of preoperative corneal power in patients with myopic LASIK based on postoperative corneal data measured from Orbscan II

目的比较Orbscan II测量准分子激光原位角膜磨镶术（LASIK）前后周边角膜后表面曲率半径改变，初步确立新的角膜前后表面曲率半径比率R，利用术后周边后表面角膜曲率半径和比率R估算术前角膜总屈光力。方法回顾分析OrbscanⅡ测量151只眼术前及术后3个月角膜7—10mm区后表面曲率半径值的变化，计算角膜0～7mm区前表面曲率半径与角膜7—10mm区后表面曲率半径比率R，利用比率R推算30只眼术前角膜总屈光力，并验证计算性角膜总屈光值与测量性角膜总屈光值的一致性。LASIK手术前后角膜7～10mm后表面曲率半径变化和计算性角膜总屈光力与术前Orbscan 1I测得角膜总屈光力比较采用配对t检验。结果LASIK术前后角膜7～10mm区后表面曲率半径差值为（-0．005±0．154）mm（t=0．417，P=0．677），术前角膜0～7mm区前表面曲率半径与角膜7-10mm区后表面曲率半径比率R为1．167±0．030，利用比率R推算的角膜总屈光力均值为（43．49±1．79）D，OrbscanⅡ测得实际角膜总屈光力均值为（43．77±1．53）D，两者差值均值为（-0．28±1．oo）D（t=-1．523，P=0．139）。结论LASIK手术前后周边区域角膜后表面曲率半径改变无实际临床意义，计算所得新角膜前后表面曲率半径比率R可准确的推算LASIK术者术前角膜总屈光力，为LASIK术后丢失术前资料患者双K法计算人工晶状体度数提供重要条件。（中华眼科杂志，2011，47：151-155）

Objective Compare the change of pre- and post-operative posterior corneal curvature measurements in peripheral fitting zones using the Orbscan II topographer in patients undergoing myopic laser in situ keratomileusis （LASIK）. To establish a new ratio of the anterior and posterior corneal curvature for the calculation of preoperative total corneal power using postoperative corneal data alone in patients after LASIK. Methods Retrospectively analyzed the changes of posterior corneal curvature in peripheral 7 to 10 mm fitting zones in 151 right eyes （ 151 individuals） 3 month after LASIK as measured by Orbscan Ⅱ. The new ratio between the anterior and posterior corneal curvature was measured. The new ratio was used to estimate pre-operative total corneal refractive power in 30 eyes. The estimated total corneal refractive power was compared with the value measured from Orbscan lI preoperatively. The accuracy of intraocular lens power estimated in 2 cases underwent cataract surgery after corneal refractive surgery was studied. Results The mean difference in estimated pre- and post-operative power of the posterior cornea was （ - 0. 005± 0. 154）mm （t =0. 417, P =0. 677）. The ratio between the preoperative anterior central （0-7 mm） corneal curvature and the posterior peripheral （7 to 10 mm） corneal curvature was 1. 167 ＋0. 030. Estimated mean pre-operative total corneal power was （43.49 ±1.79 ） D, whereas the value measuring from Orbscan 1I preoperatively was （43. 77± 1.53 ）D. The mean difference between these two measurements was （ -0. 28 ± 1.00）D （t = - 1. 523, P =0. 139）. The spherical equivalent refraction after cataract extraction of the two cases undertaken cataract surgery after corneal refractive surgery was 0. 54 D and 0. 69 D, respectively.Conclusions The difference in posterior corneal curvature measurement following myopic LASIK using the peripheral fitting zone with the Orbscan II, as compared to the preoperative values, is clinically insignificant. The pre-LASIK corneal power can be estimated using post-LASIK data together with the new calculated ratio. This will be useful in post-LASIK patients requiring cataract surgery but without the availability of pre-LASIK corneal data for the estimation of the intraocular lens power. （Chin J Ophthalmol, 2011,47：151-155 ）