Osmers, Jan
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Osmers, Jan
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Osmers, Jan
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Item-typ:Veröffentlichung, Optical measurement of the corneal oscillation for the determination of the intraocular pressureMotivation: 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.Wissenschaftlicher ArtikelBand:64Heft:42651 2633 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Adaptive finite element eye model for the compensation of biometric influences on acoustic tonometryBackground and objective: Glaucoma is currently a major cause for irreversible blindness worldwide. A risk factor and the only therapeutic control parameter is the intraocular pressure (IOP). The IOP is determined with tonometers, whose measurements are inevitably influenced by the geometry of the eye. Even though the corneal mechanics have been investigated to improve accuracy of Goldmann and air pulse tonometry, influences of geometric properties of the eye on an acoustic self-tonometer approach are still unresolved. Methods: In order to understand and compensate for measurement deviations resulting from the geometric uniqueness of eyes, a finite element eye model is designed that considers all relevant eye components and is adjustable to all physiological shapes of the human eye. Results: The general IOP-dependent behavior of the eye model is validated by laboratory measurements on porcine eyes. The difference between simulation and measurement is below 8 µm for IOP levels from 5 to 40 mmHg. The adaptive eye model is then used to quantify systematic uncertainty contributions of a variation of eye length and central corneal thickness based on input statistics of a clinical trial series. The adaptive eye model provides the required relation between biometric eye parameters and the corneal deflection amplitude, which here is the measured quantity to trace back to the IOP. Implementing the relations provided by the eye model in a Gaussian uncertainty propagation calculation now allows the quantification of the uncertainty contributions of the biometric parameters on the overall measurement uncertainty of the acoustic self-tonometer. As a result, a systematic uncertainty contribution resulting from deviations in eye length dominate stochastic deviations of the sensor equipment by a factor of 3.5. Conclusion: As perspective, the proposed adaptive eye model provides the basis to compensate for systematic deviations of (but not only) the acoustic self-tonometer.Wissenschaftlicher ArtikelBand:20091 137 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Die Biometrie des Auges als Ursache für systematische Messabweichungen bei der akustischen TonometrieZur Glaukomtherapie ist eine Überwachung des Augeninnendrucks erforderlich, wofür ein akustisches Selbsttonometer entwickelt worden ist. Die Laborversuche an Schweineaugen und die Patientenmessungen in einer klinischen Versuchsreihe belegen jedoch signifikante Querempfindlichkeiten von den biometrischen Parametern des Auges auf den gemessenen Augeninnendruck. Um die Individualität der Augen in der Auswertung der Messdaten zu berücksichtigen, werden Finite-Elemente-Simulationen des Auges für unterschiedliche geometrische Ausprägungen durchgeführt. Anhand der Simulationsergebnisse wird der Einfluss der Augengeometrie auf die Messunsicherheit des zu messenden Augeninnendrucks quantifiziert. Dadurch lässt sich bei Kenntnis der individuellen Augengeometrie des Patienten die systematische Messabweichung des Augeninnendrucks signifikant reduzieren und für das akustische Selbsttonometer eine Messunsicherheit in der Größenordnung aktueller klinischer Tonometer erzielen.Wissenschaftlicher ArtikelBand:86Heft:481 52