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Merhof, Dorit

Biomedical Engineering / Biomedizinische Technik

Joint Journal of the German Society for Biomedical Engineering in VDE and the Austrian and Swiss Societies for Biomedical Engineering and the German Society of Biomaterials

Editor-in-Chief: Dössel, Olaf

Editorial Board: Augat, Peter / Habibović, Pamela / Haueisen, Jens / Jahnen-Dechent, Wilhelm / Jockenhoevel, Stefan / Knaup-Gregori, Petra / Leonhardt, Steffen / Plank, Gernot / Radermacher, Klaus M. / Schkommodau, Erik / Stieglitz, Thomas / Boenick, Ulrich / Jaramaz, Branislav / Kraft, Marc / Lenarz, Thomas / Lenthe, Harry / Lo, Benny / Mainardi, Luca / Micera, Silvestro / Penzel, Thomas / Robitzki, Andrea A. / Schaeffter, Tobias / Snedeker, Jess G. / Sörnmo, Leif / Sugano, Nobuhiko / Werner, Jürgen /

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Volume 64, Issue 4


Volume 57 (2012)

Optical measurement of the corneal oscillation for the determination of the intraocular pressure

Jan Osmers
  • Corresponding author
  • University of Bremen, Bremen Institute for Metrology, Automation and Quality Science (BIMAQ), 28359 Bremen, Germany
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  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Michael Sorg
  • University of Bremen, Bremen Institute for Metrology, Automation and Quality Science (BIMAQ), 28359 Bremen, Germany
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Andreas Fischer
  • University of Bremen, Bremen Institute for Metrology, Automation and Quality Science (BIMAQ), 28359 Bremen, Germany
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
Published Online: 2018-09-19 | DOI: https://doi.org/10.1515/bmt-2018-0093



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.


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.


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.


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.

Keywords: corneal vibration; glaucoma; intensity based sensor; IOP; noncontact; self-tonometer


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About the article

Received: 2018-05-28

Accepted: 2018-08-21

Published Online: 2018-09-19

Published in Print: 2019-08-27

Author Statement

Research funding: The project was funded by the German Federal Ministry of Education and Research (BMBF, reference number 13GW0054, Funder Id: 10.13039/501100002347).

Conflict of interest: Authors state no conflict of interest.

Informed consent: Informed consent is not applicable.

Ethical approval: The conducted research is not related to either human or animals use.

Citation Information: Biomedical Engineering / Biomedizinische Technik, Volume 64, Issue 4, Pages 471–480, ISSN (Online) 1862-278X, ISSN (Print) 0013-5585, DOI: https://doi.org/10.1515/bmt-2018-0093.

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