Department of Ophthalmology, Korea University College of Medicine, Seoul, South Korea.
Department of Ophthalmology, Korea University College of Medicine, Seoul, South Korea.
Ophthalmology. 2013 Mar;120(3):477-481. doi: 10.1016/j.ophtha.2012.09.008. Epub 2013 Jan 23.
To evaluate the effect of average corneal power (K) and axial length (AL) in a data-adjusted A-constant for improving the refractive outcome in the Sanders-Retzlaff-Kraff (SRK)/T formula.
Retrospective, consecutive, case series.
A total of 637 patients (637 eyes) who underwent uncomplicated phacoemulsification with implantation of the Acrysof IQ (IQ; Alcon, Fort Worth, TX; 314 eyes) or Akreos AO (AO; Bausch & Lomb, Rochester, NY; 323 eyes) intraocular lens (IOL) by a single surgeon.
The correlation among the K, AL, and predicted refractive error in the SRK/T formula was analyzed. Patients were divided into 2 subgroups, the first to calculate the different data-adjusted A-constants based on the K and the second to compare the median absolute error (MedAE) based on different A-constants with the traditional A-constant in the SRK/T formula.
The data-adjusted A-constant and the MedAE (diopters [D]).
The data-adjusted A-constant showed a decreasing trend as K increased. The data-adjusted A-constant was 119.04 in the IQ group and 118.27 in the AO group. The calculated A-constant was 119.33 in the IQ group and 118.57 in the AO group when the cornea was flatter than 43.0 D and 43.2 D, respectively. The A-constant was 118.71 in the IQ group and 117.96 in the AO group when the cornea was steeper than or equal to 44.7 D and 45.0 D, respectively. The MedAE decreased from 0.29 D to 0.23 D in the IQ group (P = 0.001) and from 0.44 D to 0.38 D in the AO group (P < 0.001) when different A-constants were used. The MedAE further decreased from 0.36 D to 0.24 D in the IQ group (P = 0.005) and from 0.58 D to 0.37 D in the AO group (P < 0.001) when subjects with K 1.00 D or more above or 1.00 D below the most accurate K in each group were compared.
For a steep cornea, the calculated A-constant was smaller than that of the entire K, but for a flat cornea, a larger A-constant was calculated. Using different A-constants based on the K improved the refraction outcomes relying on the SRK/T formula.
评估平均角膜屈光力（K）和眼轴（AL）在数据调整的 A 常数中的作用，以改善 Sanders-Retzlaff-Kraff（SRK）/T 公式中的屈光结果。
回顾性、连续、病例系列。
共 637 名患者（637 只眼），由一名外科医生进行了单纯的超声乳化白内障吸除术，并植入了 Acrysof IQ（IQ；Alcon，沃斯堡，德克萨斯州；314 只眼）或 Akreos AO（AO；Bausch & Lomb，罗彻斯特，纽约州；323 只眼）人工晶状体（IOL）。
分析了 SRK/T 公式中 K、AL 和预测屈光误差之间的相关性。患者被分为 2 个亚组，第一组根据 K 计算不同的数据调整 A 常数，第二组比较不同 A 常数的中位数绝对误差（MedAE）与 SRK/T 公式中的传统 A 常数。
数据调整的 A 常数和中位数绝对误差（屈光度 [D]）。
数据调整的 A 常数随着 K 的增加呈现下降趋势。在 IQ 组中，数据调整的 A 常数为 119.04，在 AO 组中为 118.27。当角膜平坦度分别小于 43.0 D 和 43.2 D 时，计算出的 A 常数分别为 119.33 和 118.57。当角膜平坦度分别大于或等于 44.7 D 和 45.0 D 时，A 常数分别为 118.71 和 117.96。在 IQ 组中，MedAE 从 0.29 D 降至 0.23 D（P = 0.001），在 AO 组中，MedAE 从 0.44 D 降至 0.38 D（P < 0.001）。当在 IQ 组中比较 K 值高于或低于每组最准确 K 值 1.00 D 的患者时，MedAE 进一步从 0.36 D 降至 0.24 D（P = 0.005），在 AO 组中，MedAE 从 0.58 D 降至 0.37 D（P < 0.001）。
对于陡峭的角膜，计算出的 A 常数小于整个 K，但对于平坦的角膜，计算出的 A 常数较大。基于 K 使用不同的 A 常数可以改善基于 SRK/T 公式的屈光结果。
