Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations
Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations
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DOI：
10.1016/s0886-3350(97)80115-0
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发表时间：
1997-11-01
影响因子：
2.8
通讯作者：
Holladay, JT
中科院分区：
文献类型：
--
作者：
Holladay, JT
目的：提供一种方法和数值，促进超声生物测量、角膜曲率测量和人工晶状体 (IOL) 屈光度计算常数的标准化。地点：美国德克萨斯州休斯顿德克萨斯大学医学院，方法：角膜曲率测量和超声生物测量为六个可变聚散方程提供两个测量输入变量，用于计算特定白内障患者的适当 IOL 屈光度。对反映过去 156 年研究和开发的文献的回顾揭示了角膜曲率计用于净角膜屈光力的适当折射率、角膜主平面的位置、视网膜厚度的标称值以及眼轴长度超声测量的适当速度。厚 IOL 与薄 IOL 的关系是根据厚晶状体的物理位置推导出来的。描述了两种方法，它们提供了制造商使用的最佳 IOL 常数，以最大限度地减少首次使用晶状体的外科医生的预测误差。还导出了有晶状体眼 IOL 和二次背负式 IOL 的公式，并将其应用于上述标准 IOL 的方法。结果：使用角膜的标准化净折射率 4/3 消除了预测屈光度 (D) 中 0.56 屈光度 (D) 的变异性。使用标准化的 1532 m/s 速度进行轴向长度测量并添加 0.28 mm 的值，可将任何长度眼的轴向长度测量的公差降低至 +/-0.03 mm。厚IOL的次主平面的物理位置必须位于薄晶状体之前，相当于厚晶状体的主平面的大约间隔。对于双凸聚（甲基丙烯酸甲酯）IOL，主平面的间距约为 0.10 mm。利用这些关系，厚晶状体在眼睛内的物理位置可用于确认任何 IOL 样式的晶状体常数。结论：标准化角膜曲率测量、超声生物测量和 IOL 度数计算的常数可以显着提高屈光结果的可预测性。反向计算和物理测量晶状体在眼睛内的位置可以为外科医生提供已知的初始晶状体常数，其平均值的标准误差为+/-0.05毫米（+/-0.10D）。其他参数，例如晶状体的基点、形状因子、晶状体触觉平面和中心晶状体厚度，将允许进一步细化 IOL 屈光度计算。
Purpose: To provide a method and values that facilitate standardization of constants for ultrasonic biometry, keratometry, and intraocular lens (IOL) power calculations.Setting: University of Texas Medical School, Houston, Texas, USA,Methods: Keratometry and ultrasonic biometry provide the two measured input variables for the six variable vergence equations used to calculate the appropriate IOL power for a specific patient with a cataract. A review of the literature reflecting the past 156 years of research and development reveals the appropriate index of refraction to be used with the keratometer for net optical corneal power, the location of the principal planes of the cornea, the nominal value for retinal thickness, and the appropriate velocities for ultrasonic measurement of the axial length. The relationship of the thick IOL to the thin IOL is derived along with the physical location of the thick lens. Two methods are described that provide the best IOL constant to be used by a manufacturer to minimize the prediction error for a surgeon using the lens for the first time. The formulas for phakic IOLs and secondary piggyback IOLs are also derived and applied to methods described above for standard IOLs.Results: Using a standardized net index of refraction of 4/3 for the cornea eliminates a variability of 0.56 diopter (D) in the predicted refraction. Using a standardized 1532 m/s velocity for axial length measurements and adding a value of 0.28 mm reduces the tolerance of axial length measurements to +/-0.03 mm for any length eye. The physical location of the thick IOL's secondary principal plane must be anterior to the thin lens equivalent by approximately the separation of the principal planes of the thick lens. For biconvex poly(methyl methacrylate) IOLs, the separation in the principal planes is approximately 0.10 mm, Using these relationships, the physical position of the thick lens within the eye can be used to confirm the lens constant for any IOL style,Conclusions: Standardizing the constants for keratometry, ultrasonic biometry, and IOL power calculations can significantly improve the predictability of refractive outcomes. Back-calculating and physically measuring the position of the lens within the eye can provide surgeons with an initial lens constant known to have a standard error of the mean of +/-0.05 mm (+/-0.10 D). Other parameters such as the cardinal points of a lens, the shape factor, the lens-haptic plane, and the center lens thickness would allow further refinement of IOL power calculations.