Anterior Surface-Based Keratometry Compared With Scheimpflug Tomography-Based Total Corneal Astigmatism
Anterior Surface-Based Keratometry Compared With Scheimpflug Tomography-Based Total Corneal Astigmatism
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DOI：
10.1167/iovs.14-15659
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发表时间：
2015-01-01
影响因子：
4.4
通讯作者：
Kohnen, Thomas
中科院分区：
文献类型：
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作者：
Tonn, Bastian;Klaproth, Oliver Klaus;Kohnen, Thomas
目的。使用Scheimpflug断层扫描仪通过光线跟踪描述总角膜屈光度(TCRP)散光。方法：分析Scheimpflug断层扫描测量结果，通过光线跟踪计算确定3 mm区域TCRP散光(CA(TCRP))、模拟角膜曲率计15度区域的散光(CA(Sim-K))、前表面散光(CA(ANT))和后表面散光(CA(POST))。对随年龄的变化进行分析。通过向量分析计算了用CA(Sim-K)估计CA(TCRP)所产生的误差。结果：共分析了3818只健康未做过手术的眼的垂直、倾斜和水平垂直、倾斜和水平排列的子午线百分比。屈光度(D)为-0.33。CA(ANT)组和CA(POST)组分别有71.2%和88.8%的眼出现垂直排列的陡峭子午线(60°~120°)。随着年龄的增长，CA(ANT)陡经水平排列的发生率从9.1%(20~29岁)增加到31.8%(70~79岁)，垂直排列的发生率从77.4%下降到48.1%。CA(桩)对齐以垂直为主(90.9%~80.7%)。当CA(ANT)垂直时，CA(POST)有97%是垂直的，CA(Sim-K)高估了角膜总散光(平均0.11+/-0.22D)。当CA(ANT)为水平时，18%的CA(POST)为水平，CA(Sim-K)低估了(平均0.26+/-0.31D)总的角膜散光。CA(TCRP)和CA(Sim-K)在178度时的平均向量差为0.18，超过0.50D的占9%。结论：对于有规则性散光的眼，CA(Sim-K)高估了总的角膜散光，而对于没有规则性散光的眼，仅靠正视测量是不安全的。
PURPOSE. Description of total corneal refractive power (TCRP) astigmatism by ray tracing using a Scheimpflug tomographer.METHODS. Analysis of Scheimpflug tomography measurements to determine 3-mm-zone TCRP astigmatism (CA(TCRP)) by ray tracing calculations, astigmatism in 15 degrees-zone from simulated keratometry (CA(Sim-K)), anterior-surface astigmatism (CA(ant)), and posterior-surface astigmatism (CA(post)). An analysis of changes with age was performed. The error produced by estimating CA(TCRP) using CA(Sim-K) was calculated through vector analyses. The percentages of steep meridian aligned vertically, obliquely, and horizontally of CA(ant) and CA(post) were calculated.RESULTS. A total of 3818 healthy, previously unoperated eyes were analyzed. The mean magnitude of CA(post) was -0.33 diopter (D). A vertically aligned steep meridian (60 degrees to 120 degrees) was found in 71.2% of eyes for CA(ant) and in 88.8% for CA(post). With increasing age, the occurrence of steep meridian aligned horizontally in CA(ant) increased from 9.1% (age 20-29 years) to 31.8% (70-79 years), while vertical alignment decreased from 77.4% to 48.1%. Alignment of CA(post) mostly remained vertical (90.9%-80.7%). When CA(ant) is vertical, CA(post) is vertical in 97% and CA(Sim-K) overestimates total corneal astigmatism (mean 0.11 +/- 0.22 D). When CA(ant) is horizontal, 18% of CA(post) is horizontal and CA(Sim-K) underestimates (mean 0.26 +/- 0.31 D) total corneal astigmatism. The mean vector difference between CA(TCRP) and CA(Sim-K) was 0.18 at 178 degrees and exceeded 0.50 D in 9% of eyes.CONCLUSIONS. Total corneal astigmatism is overestimated by CA(Sim-K) in eyes with with-the-rule astigmatism and cannot be predicted safely in eyes that do not have with-the-rule astigmatism by anterior measurements only.