Adjustment of Anterior Corneal Astigmatism Values to Incorporate the Likely Effect of Posterior Corneal Curvature for Toric Intraocular Lens Calculation
Adjustment of Anterior Corneal Astigmatism Values to Incorporate the Likely Effect of Posterior Corneal Curvature for Toric Intraocular Lens Calculation
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DOI：
10.3928/1081597x-20150122-04
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发表时间：
2015-02-01
影响因子：
2.4
通讯作者：
van Zyl, Lourens
中科院分区：
文献类型：
--
作者：
Goggin, Michael;Zamora-Alejo, Katherine;van Zyl, Lourens
目的：探讨环状人工晶状体在角膜前部测量的基础上，根据散光规律计算角膜散光是否发生平均屈光过正或欠矫正，并计算个体眼的调节以避免这种系统性误差。方法：对115例143只眼连续行超声乳化术，人工晶状体屈光度仅用角膜前曲率计算。根据角膜前部的陡峭子午线，将眼睛分为“遵守规则”和“违反规则”。比较目标散光效果与已实现散光效果。主要测量结果是由于后方角膜散光的可能影响，植入环形人工晶状体后的残余屈光散光。结果：只有当人工晶状体的屈光度小于或等于2度时，散光结果才会出现显著的预测误差。结论：在角膜散光度数中，规则眼的调节系数为0.75，违规眼的调节系数为1.41，由此计算出的人工晶状体柱面屈光度比未调整的角膜前屈光度计算的IOL柱度数更合适。这些调整系数只适用于那些接受了2个或更少屈光度的人工晶状体，并用这种未调整的测量计算出来的眼睛。使用未调整的值可以足够准确地计算出更大的人工晶状体钢笔功率。
PURPOSE: To establish if average refractive overcorrection or undercorrection of corneal astigmatism based on the "rule" of the astigmatism occurs if toric intraocular lenses (IOLs) are calculated on the basis of anterior corneal measurements, and to calculate an adjustment for individual eyes to avoid this systematic error.METHODS: One hundred forty-three consecutive eyes of 115 patients underwent phacoemulsification with IOL powers calculated using anterior corneal curvature data alone. Eyes were grouped as either "with-the-rule" or "against-the-rule" on the basis of the steep anterior corneal meridian. Targeted versus achieved astigmatic outcomes were compared. Main outcome measure was residual refractive astigmatism following the insertion of a toric IOL due to the likely effect of posterior corneal astigmatism.RESULTS: Significant prediction errors in astigmatic outcome occurred only with IOL cylinders of 2 diopters or less. Overcorrection occurred by a factor of 1.38 in with-the-rule eyes and undercorrection occurred by a factor of 0.65 in against-the-rule eyes.CONCLUSIONS: A coefficient of adjustment of 0.75 for with-the-rule eyes and 1.41 for against-the-rule eyes can be applied to the corneal astigmatism power value to calculate a more appropriate IOL cylinder power than that calculated by using unadjusted anterior corneal curvature measurements. These adjustment coefficients apply only to those eyes that would have received IOLs with 2 diopters of cylinder or less and calculated with such unadjusted measurements. Greater IOL cylinder powers are sufficiently accurately calculated using unadjusted values.