Liu Jun, He Xiaoyin, Pan Xueliang, Roberts Cynthia J
Biomedical Engineering Department, The Ohio State University, 270 Bevis Hall, 1080 Carmack Rd., Columbus, OH 43210, USA.
J Biomech. 2007;40(5):1177-82. doi: 10.1016/j.jbiomech.2006.04.017. Epub 2006 Jun 22.
Non-invasive measurement of biomechanical properties of corneas may provide important information for ocular disease management and therapeutic procedures. An ultrasonic non-destructive evaluation method with a wave propagation model was developed to determine corneal biomechanical properties in vivo. In this study, we tested the feasibility of the approach in differentiating the mechanical properties of soft contact lenses as corneal phantoms. Three material types of soft contact lenses (six samples in each group) were measured using a broadband ultrasound transducer. The ultrasonic reflections from the contact lenses were recorded by a 500MHz/8-bit digitizer, and displayed and processed by a PC. A reference signal was recorded to compute the normalized power spectra using Fast Fourier Transformation. An inverse algorithm based on least-squares minimization was used to reconstruct three parameters of the contact lenses: density, thickness, and elastic constants lambda+2micro. The thickness of each sample was verified using an electronic thickness gauge, and the averaged density for each type of lenses was verified using Archimedes' principle and manufacturer's report. Our results demonstrated that the ultrasonic system was able to differentiate the elastic properties of the three types of the soft contact lenses with statistical significance (P-value<0.001). The reconstructed thicknesses and densities agreed well with the independent measurements. Our studies on corneal phantoms indicated that the ultrasonic system was sensitive and accurate in measuring the material properties of cornea-like structures. It is important to optimize the system for in vivo measurements.
角膜生物力学特性的非侵入性测量可为眼部疾病管理和治疗程序提供重要信息。开发了一种具有波传播模型的超声无损评估方法，以在体内确定角膜生物力学特性。在本研究中，我们测试了该方法区分作为角膜模型的软性隐形眼镜力学特性的可行性。使用宽带超声换能器对三种材料类型的软性隐形眼镜（每组六个样品）进行测量。隐形眼镜的超声反射由一个500MHz/8位数字化仪记录，并由一台个人计算机进行显示和处理。记录一个参考信号，以便使用快速傅里叶变换计算归一化功率谱。使用基于最小二乘最小化的逆算法重建隐形眼镜的三个参数：密度、厚度和弹性常数lambda+2micro。使用电子厚度计验证每个样品的厚度，并使用阿基米德原理和制造商报告验证每种类型镜片的平均密度。我们的结果表明，该超声系统能够在统计学上显著地区分三种类型软性隐形眼镜的弹性特性（P值<0.001）。重建的厚度和密度与独立测量结果吻合良好。我们对角膜模型的研究表明，该超声系统在测量类角膜结构的材料特性方面灵敏且准确。优化该系统以进行体内测量很重要。
