Osmers Jan, Sorg Michael, Fischer Andreas
University of Bremen, Bremen Institute for Metrology, Automation and Quality Science (BIMAQ), 28359 Bremen, Germany.
Biomed Tech (Berl). 2019 Aug 27;64(4):471-480. doi: 10.1515/bmt-2018-0093.
Motivation Glaucoma is currently the most common irreversible cause of blindness worldwide. A significant risk factor is an individually increased intraocular pressure (IOP). A precise measurement method is needed to determine the IOP in order to support the diagnosis of the disease and to monitor the outcome of the IOP reduction as a medical intervention. A handheld device is under development with which the patient can perform self-measurements outside the clinical environment. Method For the measurement principle of the self-tonometer the eye is acoustically excited to oscillate, which is analyzed and attributed to the present IOP. In order to detect the corneal oscillation, an optical sensor is required which meets the demands of a compact, battery driven self-tonometer. A combination of an infrared diode and a phototransistor provides a high-resolution measurement of the corneal oscillation in the range of 10 μm-150 μm, which is compared to a reference sensor in the context of this study. By means of an angular arrangement of the emitter and the detector, the degree of reflected radiation of the cornea can be increased, allowing a measurement with a high signal-to-noise ratio. Results By adjusting the angle of incidence between the detector and the emitter, the signal-to-noise ratio was improved by 40 dB which now allows reasonable measurements of the corneal oscillation. For low amplitudes (10 μm) the signal-to-noise ratio is 10% higher than that of the commercial reference sensor. On the basis of amplitude variations at different IOP levels, the estimated standard uncertainty amounts to <0.5 mm Hg in the physiological pressure range with the proposed measuring approach. Conclusion With a compact and cost-effective approach, that suits the requirements for a handheld self-tonometer, the corneal oscillation can be detected with high temporal resolution. The cross-sensitivity of the sensor concept concerning a distance variation can be reduced by adding a distance sensor. Existing systematic influences of corneal biomechanics will be integrated in the sensor concept as a consecutive step.
青光眼是目前全球最常见的不可逆性失明原因。一个重要的风险因素是个体眼压（IOP）升高。需要一种精确的测量方法来测定眼压，以辅助疾病诊断并监测作为医学干预手段的眼压降低效果。目前正在研发一种手持设备，患者可借助该设备在临床环境之外自行测量眼压。
对于自眼压计的测量原理，通过对眼睛进行声学激发使其振荡，然后对该振荡进行分析并与当前眼压相关联。为了检测角膜振荡，需要一个光学传感器，该传感器要满足紧凑型、电池供电的自眼压计的要求。红外二极管和光电晶体管的组合可在10μm - 150μm范围内对角膜振荡进行高分辨率测量，在本研究中，该测量结果会与参考传感器进行比较。通过发射器和探测器的角度布置，可以提高角膜反射辐射的程度，从而实现高信噪比的测量。
通过调整探测器与发射器之间的入射角，信噪比提高了40dB，现在可以对角膜振荡进行合理测量。对于低振幅（10μm），信噪比比商用参考传感器高10%。基于不同眼压水平下的振幅变化，采用所提出的测量方法，在生理压力范围内估计的标准不确定度小于0.5mmHg。
采用一种紧凑且经济高效的方法，该方法符合手持自眼压计的要求，可以高时间分辨率检测角膜振荡。通过增加一个距离传感器，可以降低传感器概念中关于距离变化的交叉敏感性。作为后续步骤，角膜生物力学的现有系统影响将被纳入传感器概念中。
