Wilhelm Stork

Implantable osmotic-pressure-based glucose sensor with non-invasive optical readout

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.

Micro-optical imaging concepts for an intraocular vision aid

About 10 million people around the world are suffering from blindness, where the path of light is disturbed due to an opaque, irreversible damaged, and inoperable cornea. Although vision is not given to this group of population, the retina is still intact. To date, there is no artificial implant which is able to replace the natural cornea. The work presented here describes an approach to build and implant a micro-optical and microelectronic system to be used as an intraocular vision aid. By overcoming the disturbed light path, it yields to an improved visual acuity of the patient. The main aspect of this bio-mimetic system is to transfer information representing the patients field of view to the retina. An image of the field of view is captured in real-time outside the eye. After employing data processing, it is wireless transferred to the implanted part of the vision aid. From there, the information emerging from a micro display is imaged to the retina via a micro-optical system. The limited display resolution available inside the eye and the limited dimensions of the eyeball build the constrains of the optical system. A combination of a spatial light modulator together with an imaging lens system realizes intelligent spatial information distribution schemes onto the retina. This ensures a high outcome of visual acuity in the central region of the retina. Various retinal acuities can be realized. The employment of in-vivo adjustment mechanisms of the focal plane is discussed.

Optical noninvasive calculation of hemoglobin components concentrations and fractional oxygen saturation using a ring-scattering pulse oximeter

The deficiencies of the currently used pulse oximeter are discussed in diverse literature. A hazardous pitfalls of this method is that the pulse oximeter will not detect carboxyhemoglobin (COHb) and methemoglobin (metHb) concentrations. This leads to incorrect measurement of oxygen saturation by carbon monoxide poisoning and methemoglobinemia. Also the total hemoglobin concentration will not be considered and can only be measured in-vitro up to now. A second pitfall of the standard pulse oximetry is that it will not be able to show a result by low perfusion of tissues. This case is available inter alia when the patient is under shock or has a low blood pressure. The new non-invasive system we designed measures the actual (fractional) oxygen saturation and hemoglobin concentration. It will enable us also to measure COHb and metHb. The measurement can be applied at better perfused body central parts. Four or more light emitting diodes (LEDs) or laser diodes (LDs) and five photodiodes (PDs) are used. The reflected light signal detected by photodiodes is processed using a modified Lambert-Beer law (I=I0•e-α.d ). According to this law, when a non scattering probe is irradiated with light having the incident intensity I0, the intensity of transmitted light I decays exponentially with the absorption coefficient a of that probe and its thickness d. Modifications of this law have been performed following the theoretical developed models in literature, Monte Carlo simulation and experimental measurement.