后曲率实测法计算准分子激光角膜原位磨镶术后角膜屈光力的准确性

摘要

目的 探讨后曲率实测法计算准分子激光原位角膜磨镶术(LASIK)后角膜屈光力的准确性.方法 多种测量角膜屈光力方法的比较性研究.回顾性分析按后曲率实测法计算人工晶状体度数的LASIK术后人工晶状体植入眼8例(11只眼,10只为超声乳化白内障吸除及人工晶状体植入术,1只为人工晶状体置换术),计算术后稳定屈光状态与目标屈光度的差异,并据此推导实际角膜屈光力.分析其他角膜曲率法(自动曲率计、角膜地形图、球镜当量法、前曲率法、Pentacam提供的EKR曲率)计算人工晶状体度数可能造成的届光偏差.对LASIK术后6个月随访眼23例行详细屈光检查,根据术前角膜屈光力及手术前后眼屈光度改变推导术后理论角膜屈光力.分析后曲率实测法计算所得角膜屈光力与理论角膜屈光力的差异,并与其他角膜曲率法作比较.结果 采用后曲率实测法计算的人工晶状体植入眼术后平均裸眼视力0.8±0.2,与目标屈光度绝对偏差平均为(0.36±0.36)D(-0.63～+0.85 D),绝对偏差≤0.25 D、≤0.50 D、≤1.00 D的眼比例数分别为55%、73%和91%.其屈光偏差显著低于自动曲率计[(2.50±1.08)D]、角膜地形图[(1.90±0.88)D]、球镜当量法[(2.09±1.62)D](P<0.01)及前曲率法[(1.45±1.10)D](P<0.05)的预期结果;与EKR曲率法比较差异无统计学意义,但其偏差范围(-1.13～0.85 D)小于后者(-1.10～1.80 D).23例单纯LASIK术后眼的角膜屈光力测算同样显示后曲率实测法计算所得角膜屈光力与理论角膜屈光力偏离程度最小,绝对偏差为(0.67±0.45)D.结论 后曲率实测法计算LASIK术后角膜屈光力,可行性准确性俱佳.%Objective To estimate the accuracy of posterior curvature method in corneal power calculation after LASIK surgery.Methods Corneal power calculation in 11 eyes that underwent Intraccular Lens (IOL) implantation after LASIK surgery (10 cases of Phaco + IOL, 1 case of IOL displacement), all of which used posterior curvature method, was analyzed retrospectively.The differences between post-operative stable refraction and target refraction were calculated, the actual corneal powers were deduced, and the expected refractive errors using other corneal power evaluation methods (auto-keratometry, corneal topography, spherical equivalent method, anterior curvature method, Equivalent K Reading method provided by Pentacam) were analyzed.In addition, refraction of 23 eyes underwent LASIK surgery were done on their 6 months follow-up.The theoretical corneal powers were deduced by subtracting the change of refraction before and after LASIK surgery from the pre-operative corneal powers.The differences between calculated corneal powers using posterior curvature method and the theoretical corneal powers were analyzed, and were compared with other corneal power evaluation methods.Results The mean uncorrected post-operative visual acuity of IOL implantation eyes using posterior curvature method was 0.8±0.2, with mean absolute refractive error from target of (0.36±0.36) D(-0.63 to +0.85 D).The ratio of eyes with absolute error within 0.25 D, 0.50 D, and 1.00 D was 55%, 73%, and 91% respectively.This result was significantly lower than that of the auto-keratometry (2.50±1.08) D, corneal topography (1.90±0.88) D, and those obtained from spherical equivalent method(2.09±1.62)D(P<0.01 ) or anterior curvature method (1.45±1.10) D(P<0.05).It also showed less bias(-1.13 to 0.85 D) when compared to the Equivalent K Reading (-1.10 to 1.80 D), but the difference was not significant (P > 0.05 ).For the 23 post LASIK eyes, the absolute difference between the corrected corneal power using posterior curvature method and theoretical power was (0.67±0.45)D, also showed least bias compared with other methods.Conclusion It is a practical and accurate way to calculate the corneal power after LASIK surgery using posterior curvature method.