Kasprzak H T, Iskander D R
Faculty of Health, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia.
Eye (Lond). 2007 Sep;21(9):1212-9. doi: 10.1038/sj.eye.6702578. Epub 2006 Aug 25.
To study the naturally occurring kinetic characteristics of corneal surface.
The right eyes of three subjects (young, early presbyope, and presbyope) were examined. Cardiac signal and longitudinal corneal apex movements were simultaneously measured with electrocardiography (ECG) and a high-speed videokeratoscope, respectively. Time, frequency, and combined time-frequency representations of the acquired signals were derived to establish their temporal and spectral contents. Coherence analysis was used to assess the correlation between the corneal apex velocities and the cardiopulmonary system.
In all measurements, longitudinal corneal apex velocity signals showed close correlation with the corresponding ECG signals. The signatures of the pulse frequency, which was inferred from the ECG spectra and their variations in time, were clearly visible in the spectral content of corneal apex velocities. For the young subject, the correlation was the strongest and all of the spectral content of the pulse signal including the harmonics was propagating to the corneal apex velocities. For the other two subjects, there was a clear propagation of the pulse signal itself but not of all pulse harmonics.
Longitudinal movements of the corneal apex are closely related to the cardiopulmonary system. The differences in propagation of pulse harmonics to the corneal apex velocities for different subjects suggest that the frequency characteristics of apex velocity could be related to pulsative variations in the intraocular pressure and biomechanical properties of the eye. These findings could potentially be used in noninvasive assessment of the hemodynamic status of the eye with high-speed videokeratoscopy.
研究角膜表面的自然动力学特征。
对三名受试者（年轻人、早期老花眼患者和老花眼患者）的右眼进行检查。分别使用心电图（ECG）和高速角膜地形图仪同时测量心脏信号和角膜顶点的纵向运动。对采集到的信号进行时间、频率和联合时频分析，以确定其时间和频谱内容。采用相干分析评估角膜顶点速度与心肺系统之间的相关性。
在所有测量中，角膜顶点纵向速度信号与相应的心电图信号显示出密切的相关性。从心电图频谱及其随时间的变化推断出的脉搏频率特征，在角膜顶点速度的频谱内容中清晰可见。对于年轻受试者，相关性最强，脉搏信号的所有频谱内容（包括谐波）都传播到角膜顶点速度。对于其他两名受试者，脉搏信号本身有明显传播，但并非所有脉搏谐波都如此。
角膜顶点的纵向运动与心肺系统密切相关。不同受试者脉搏谐波向角膜顶点速度传播的差异表明，顶点速度的频率特征可能与眼内压的脉动变化和眼睛的生物力学特性有关。这些发现可能潜在地用于通过高速角膜地形图仪对眼睛的血流动力学状态进行无创评估。
