Li Yan, Meisler David M, Tang Maolong, Lu Ake T H, Thakrar Vishakha, Reiser Bibiana J, Huang David
Center for Ophthalmic Optics and Lasers, Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California 99033, USA.
Ophthalmology. 2008 Dec;115(12):2159-66. doi: 10.1016/j.ophtha.2008.08.004. Epub 2008 Nov 5.
To detect abnormal corneal thinning in keratoconus using pachymetry maps measured by high-speed anterior segment optical coherence tomography (OCT).
Cross-sectional observational study.
Thirty-seven keratoconic eyes from 21 subjects and 36 eyes from 18 normal subjects.
The OCT system operated at a 1.3 microm wavelength with a scan rate of 2000 axial scans per second. A pachymetry scan pattern (8 radials, 128 axial scans each; 10 mm diameter) centered at the corneal vertex was used to map the corneal thickness. The pachymetry map was divided into zones by octants and annular rings. Five pachymetric parameters were calculated from the region inside the 5 mm diameter: minimum, minimum-median, inferior-superior (I-S), inferotemporal-superonasal (IT-SN), and the vertical location of the thinnest cornea. The 1-percentile value of the normal group was used to define the diagnostic cutoff. Placido-ring-based corneal topography was obtained for comparison.
The OCT pachymetric parameters and a quantitative topographic keratoconus index (keratometry, I-S, astigmatism, and skew percentage [KISA%]) were used for keratoconus diagnosis. Diagnostic performance was assessed by the area under the receiver operating characteristic (AROC) curve.
Keratoconic corneas were thinner. The pachymetric minimum averaged 452.6+/-60.9 microm in keratoconic eyes versus 546+/-23.7 microm in normal eyes. The 1-percentile cutoff was 491.6 microm. The thinnest location was inferiorly displaced in keratoconus (-805+/-749 microm vs -118+/-260 microm; cutoff, -716 microm). The thinning was focal (minimum-median: -95.2+/-41.1 microm vs -45+/-7.7 microm; cutoff, -62.6 microm). Keratoconic maps were more asymmetric (I-S, -44.8+/-28.7 microm vs -9.9+/-9.3 microm; cutoff, -31.3 microm; and IT-SN, -63+/-35.7 microm vs -22+/-11.4 microm; cutoff, -48.2 microm). Keratoconic eyes had a higher KISA% index (2641+/-5024 vs 21+/-19). All differences were statistically significant (t test, P<0.0001). Applying the diagnostic criteria of any 1 OCT pachymetric parameter below the keratoconus cutoff yielded an AROC of 0.99, which was marginally better (P = .09) than the KISA% topographic index (AROC, 0.91).
Optical coherence tomography pachymetry maps accurately detected the characteristic abnormal corneal thinning in keratoconic eyes. This method was at least as sensitive and specific as the topographic KISA.
FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.
使用高速眼前节光学相干断层扫描（OCT）测量的角膜厚度图检测圆锥角膜中的异常角膜变薄。
横断面观察性研究。
21名受试者的37只圆锥角膜眼和18名正常受试者的36只眼睛。
OCT系统在1.3微米波长下运行，扫描速率为每秒2000次轴向扫描。以角膜顶点为中心的角膜厚度扫描模式（8条径向线，每条128次轴向扫描；直径10毫米）用于绘制角膜厚度图。角膜厚度图按八分法和环形环分为多个区域。从直径5毫米范围内的区域计算五个角膜厚度参数：最小值、最小中位数、下-上（I-S）、颞下-鼻上（IT-SN）以及最薄角膜的垂直位置。正常组的第1百分位数用于定义诊断临界值。获取基于Placido环的角膜地形图以进行比较。
OCT角膜厚度参数和定量地形学圆锥角膜指数（角膜曲率、I-S、散光和偏斜百分比[KISA%]）用于圆锥角膜诊断。通过受试者操作特征（AROC）曲线下面积评估诊断性能。
圆锥角膜更薄。圆锥角膜眼的角膜厚度最小值平均为452.6±60.9微米，而正常眼为546±23.7微米。第1百分位数临界值为491.6微米。圆锥角膜中最薄位置向下移位（-805±749微米对-118±260微米；临界值，-716微米）。变薄是局灶性的（最小-中位数：-95.2±41.1微米对-45±7.7微米；临界值，-62.6微米）。圆锥角膜图更不对称（I-S，-44.8±28.7微米对-9.9±9.3微米；临界值，-31.3微米；IT-SN，-63±35.7微米对-22±11.4微米；临界值，-48.2微米）。圆锥角膜眼的KISA%指数更高（2641±5024对21±19）。所有差异均具有统计学意义（t检验，P<0.0001）。应用任何1个OCT角膜厚度参数低于圆锥角膜临界值的诊断标准得出的AROC为0.99，略优于（P = 0.09）KISA%地形学指数（AROC，0.91）。
光学相干断层扫描角膜厚度图准确检测到圆锥角膜眼中特征性的异常角膜变薄。该方法至少与地形学KISA一样敏感和特异。
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