角膜后表面散光对Toric人工晶状体矫正效果的影响

The influence of posterior corneal astigmatism on the outcomes of toric intraocular lenses

目的 评价角膜后表面散光对临床Toric人工晶状体（IOL）矫正效果的影响.方法 回顾性系列病例研究.选择天津医科大学眼科医院准备行白内障超声乳化摘除术患者36例（36眼）,角膜散光为1.0～3.0 D,其中顺规散光（顺规组）18眼,逆规散光（逆规组）18眼.根据角膜模拟散光值（SimK,未考虑角膜后表面散光）计算植入相应型号的Toric IOL.术前使用Lenstar进行眼部生物测量,手动角膜曲率计与Pentacam分别测量3.0 mm直径范围内SimK及全角膜散光（TCA,考虑了角膜后表面散光）,并使用SimK与TCA进行全眼目标散光（TRA）的计算.术后3个月使用i-Trace进行3.0 mm直径范围验光,并检查Toric IOL轴位.采用矢量分析方法将TRA与术后i-Trace验光得到的残余散光（RA）进行比较.根据两者差值即散光矫正误差（ERA）（其中SimK方法为ERA1,TCA方法为ERA2）,定量分析角膜后表面散光对Toric IOL矫正效果的影响.将2种计算方法获得的TRA按照矢量进行分解,与RA进行相应矢量方向上的配对t检验分析.结果 36眼总体角膜后表面散光为（0.39±0.30）D,其中顺规组为（0.51 ±0.32）D,逆规组为（0.26±0.19）D.36眼中ERAl=0.38×（φ＋96）°,ERA2=0.12×（φ＋93）°,两者相差0.26 D.其中顺规组ERAl =0.65×（φ＋87）°,ERA2=0.13×（φ＋92）°,两者相差0.52 D;逆规组ERAl=0.28×（φ＋3）°,ERA2=0.05×（φ＋4）°,两者相差0.23 D.将总体、顺规组、逆规组SimK得到的TRA与RA进行比较,其K（φ）成分差异均有统计学意义（t=2.28、3.51、1.92,P＜0.05）,K（φ＋45）成分差异均无统计学意义;TCA得到的TRA与RA进行比较,其K（φ）、K（φ＋45）成分差异均无统计学意义.此外,顺规组角膜散光普遍过矫,逆规组角膜散光普遍欠矫.结论 忽略角膜后表面散光会导致Toric IOL矫正误差增加,术后RA增大.顺规散光容易出现散光过矫,逆规散光容易出现散光欠矫.采用TCA计算选择Toric IOL可以减小ERA,提高Toric IOL矫正效果.

Objective To evaluate the influence of posterior corneal astigmatism （PCA） on the outcomes of toric intraocular lenses （IOLs）.Methods This was a retrospective case series study.Thirty-six eyes of 36 patients in Tianjin Medical University Eye Hospital were enrolled.The magnitude of anterior corneal astigmatism for all patients was between 1.0 and 3.0 diopters （D）.Two groups of astigmatic eyes were established：＂with the rule＂ （WTR,n=18） and ＂against the rule＂ （ATR,n=18）.Each patient was implanted with a toric IOL according to the magnitude of the simulated keratometry （SimK）.Preoperatively,SimK and total corneal astigmatism （TCA） were measured by manual keratometry and Pentacam through the area with diameter of 3.0 mm respectively.Postoperatively,optometry was performed by i-Trace within a diameter of 3-mm area and toric IOL alignment was detected by slit-lamp examination.The target refractive astigmatism （TRA） was calculated with SimK or TCA.Afterward,the error of refractive astigmatism （ERA） was determined as the difference between TRA and refractive astigmatism （RA） from the i-Trace.The ERA1 （SimK） and ERA2 （TCA） were compared to evaluate the influence of PCA on the correction outcome of toric lOLs.Vector analysis was performed for astigmatism calculation.Paired t-tests were conducted between the relative orientation of TRA and RA in each group.Results The mean PCA magnitudes of all eyes and of eyes in the WTR and ATR groups were 0.39±0.30 D,0.51±0.32 D,and 0.26±0.19 D respectively.For all eyes,ERAl=0.38×（φ＋96）° and ERA2=0.12×（φ＋93）°.In the WTR group,ERAl=0.65×（φ＋87）° and ERA2=0.13×（φ＋92）°.In the ATR group,ERA1=0.28×（φ＋3）° and ERA2=0.05×（φ＋4）°.The differences between ERA1 and ERA2 in each group were 0.26 D,0.52 D,and 0.23 D respectively.For all eyes and for the WTR and the ATR groups,there was a significance difference between TRA and RA in K（φ） calculated with SimK （t=2.28,3.51,1.92,P〈0.01）.There was no significance difference for the TCA group.Moreover,there was overcorrection in most of the WTR cases and undercorrection in most of the ATR cases.Conclusion Ignoring posterior corneal astigmatism can result in more residual astigmatism and lower predictability of toric IOLs in the forms of overcorrection in WTR and undercorrection in ATR astigmatism.Instead of SimK,TCA can decrease the residual astigmatism and improve the outcomes of toric IOLs.