Department of Ophthalmology, Peking University Third Hospital, Beijing, China.
Beijing Key Laboratory of Restoration of Damaged Ocular Nerves, Peking University Third Hospital, 49 North Garden Road, Haidian District, 100191, Beijing, China.
BMC Ophthalmol. 2021 Sep 20;21(1):339. doi: 10.1186/s12886-021-02102-2.
In vivo corneal biomechanics evaluation has been used to help screen early keratoconus in recent years. This study is to evaluate the value of a Scheimpflug-based biomechanical analyser combined with tomography in detecting subclinical keratoconus by distinguishing normal eyes from frank keratoconus (KC) and forme frusta keratoconus (FFKC) eyes in Chinese patients.
Study design: diagnostic test. This study included 31 bilateral frank keratoconus patients, 27 unilateral clinically manifesting keratoconus patients with very asymmetric eyes, and 79 control subjects with normal corneas. Corneal morphological and biomechanical parameters were measured using a Pentacam HR and a Corvis ST (OCULUS, Wetzlar, Germany). The diagnostic ability of computed parameters reflecting corneal biomechanical and morphological traits [including the Belin-Ambrósio deviation index (BAD_D), the Corvis biomechanical index (CBI) and the tomographic and biomechanical index (TBI)] was determined using receiver operating characteristic (ROC) curve analysis and compared by the DeLong test. Additionally, the area under the curve (AUC), the best cut-off values, and the Youden index for each parameter were reported. A novel corneal stiffness parameter, the stress-strain index (SSI), was also compared between KC, FFKC and normal eyes.
Every morphological and biomechanical index analysed in this study was significantly different among KC, FFKC and normal eyes (P = 0.000). The TBI was most valuable in detecting subclinical keratoconus (FFKC eyes), with an AUC of 0.928 (P = 0.000), and both forms of corneal ectasia (FFKC and frank KC eyes), with an AUC of 0.966 (P = 0.000). The sensitivity and specificity of the TBI was 97.5 and 77.8 % in detecting FFKC and 97.5 and 89.7 % in detecting any KC, respectively, with a cut-off value of 0.375. The morphological index BAD_D and the biomechanical index CBI were also very useful in distinguishing eyes with any KC from normal eyes, with AUCs of 0.965 and 0.934, respectively. The SSI was significantly different between KC, FFKC and normal eyes (P = 0.000), indicating an independent decrease in corneal stiffness in KC eyes.
The combination of a Scheimpflug-based biomechanical analyser and tomography could increase the accuracy in detecting subclinical keratoconus in Chinese patients. The TBI was the most valuable index for detecting subclinical keratoconus, with a high sensitivity and specificity. Evaluation of corneal biomechanical properties in refractive surgery candidates could be helpful for recognizing potential keratoconic eyes and increasing surgical safety.
近年来，活体角膜生物力学评估已被用于帮助筛选早期圆锥角膜。本研究旨在评估基于 Scheimpflug 的生物力学分析仪与断层扫描相结合，通过区分正常眼与真性圆锥角膜（KC）和亚临床圆锥角膜（FFKC），在中国人中检测亚临床圆锥角膜的价值。
研究设计：诊断性试验。本研究纳入了 31 例双侧真性 KC 患者、27 例单侧临床表现为 KC 且双眼非常不对称的患者和 79 例正常角膜的对照者。使用 Pentacam HR 和 Corvis ST（OCULUS，德国威茨拉尔）测量角膜形态学和生物力学参数。使用受试者工作特征（ROC）曲线分析评估反映角膜生物力学和形态特征的计算参数[包括 Belin-Ambrósio 离差指数（BAD_D）、角膜生物力学指数（CBI）和断层扫描与生物力学指数（TBI）]的诊断能力，并通过 DeLong 检验进行比较。此外，报告了每个参数的曲线下面积（AUC）、最佳截断值和 Youden 指数。还比较了 KC、FFKC 和正常眼中的一种新型角膜硬度参数-应变-应力指数（SSI）。
本研究分析的每一个形态学和生物力学指标在 KC、FFKC 和正常眼中均有显著差异（P=0.000）。TBI 在检测亚临床圆锥角膜（FFKC 眼）中最有价值，AUC 为 0.928（P=0.000），在检测两种形式的角膜扩张（FFKC 和真性 KC 眼）中也最有价值，AUC 为 0.966（P=0.000）。TBI 检测 FFKC 的敏感性和特异性分别为 97.5%和 77.8%，检测任何 KC 的敏感性和特异性分别为 97.5%和 89.7%，截断值为 0.375。形态学指标 BAD_D 和生物力学指标 CBI 也非常有助于区分任何 KC 眼与正常眼，AUC 分别为 0.965 和 0.934。SSI 在 KC、FFKC 和正常眼中有显著差异（P=0.000），表明 KC 眼中角膜硬度独立降低。
基于 Scheimpflug 的生物力学分析仪与断层扫描相结合可提高中国人亚临床圆锥角膜检测的准确性。TBI 是检测亚临床圆锥角膜最有价值的指标，具有较高的敏感性和特异性。评估屈光手术候选者的角膜生物力学特性有助于识别潜在的圆锥角膜眼并提高手术安全性。
