KEYWORDS: Glucose, Absorption, Eye, In vivo imaging, Optical testing, Sensors, Spectroscopy, Dielectric polarization, Near infrared, Near infrared spectroscopy
Continuous monitoring of the glucose level is a key technology for improved diagnosis and therapy of Diabetes Mellitus patients. Non-invasive optical measurement techniques at the Anterior Chamber of the eye suffer from the lack of intensity of reflected light and the very small magnitudes of the optical effects. Hence using higher magnitude physical and/or chemical effects as primary effects and using non-contact optical readout increases feasibility for in-vivo
measurement systems substantially. Hence this article proposes a miniaturized micro structured measurement cell covered by a semi permeable diaphragm to be implanted micro invasively into the anterior chamber of the eye. Osmotic pressure within this cell depends on the intraocular glucose concentration and is translated into deformation of the diaphragm which is measured using white light interferometry. A bio-compatible micro structured interference filter has to be added on parts of the diaphragm to ensure high reflection properties crucial for optical deformation measurement. The article also discusses the special requirements of in-vivo measurements for the optical measurement system.
Non-invasive monitoring of the glucose level is a key technology for improved diagnosis and therapy for Diabetes patients. Optical measurement techniques like polarimetry measuring at the human eye offer promising properties for non-invasive and painless application. This article presents a polarimetric measurement system utilizing the polarizing properties of the Aqueous Humour (AH) for quantative glucose measurements. In particular the special requirements of in-vivo measurements for such a system are discussed.
To allow measurements of the intraocular pressure (IOP) by glaucoma patients themselves (self-tonometry) a handheld-interferometer system for non-contact in vivo measurements of microvibrations of the human eye was realized. The measurement principle is based on the dependence of the resonance frequencies of the human eye on the IOP. To analyze this, the human eye is stimulated by ultrasonic waves and the induced microvibrations are measured with a vibrometer and processed by a DSP unit. Beside a stabilized diode laser and a low noise photodetector an exact three-dimensional positioning system had to be developed to guarantee reliable measurements. To investigate the corresponding requirements a camera-based system for the detection of human eye movements was developed and test series with several persons were made. Based on these results an adjustment unit was integrated in a miniaturized interferometer system: After a short self-adjusting procedure lateral to the setup by overlaying two targets of a highly sensitive optical system the correct measuring distance between the cornea and the vibrometer parallel to the optical axis is determined automatically by an astigmatic auto-focus system. With this handheld-vibrometer in vivo measurements with several test persons were made with very good results concerning the reliability and handling capability.
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