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Measurement of vibration induced by diagnostical ultrasound in an eye model with simulted retina

 
: Brand, U.; Mengedoht, K.; Pessel, M.; Paul, M.; Trier, H.

Fercher, A.F. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.; Biomedical Optics Society -BiOS-; European Optical Society -EOS-:
Microscopy, holography, and interferometry in biomedicine 1993. Proceedings : 1 - 3 September 1993, Budapest, Hungary
Bellingham/Wash.: SPIE, 1994 (SPIE Proceedings Series 2083)
ISBN: 0-8194-1350-X
pp.347-355
Conference "Microscopy, Holography, and Interferometry in Biomedicine" <1993, Budapest>
English
Conference Paper
Fraunhofer IZFP ()
ultrasound; interferometry

Abstract
The aim of the experiments is the development of a non-invasive technique for determining the location of an ultrasonic focus in the wall of the human eye. This would enable improvements in ultrasonic biometry and in ultrasonic tissue characterisation in the eye.
Ultrasonic biometry is today generally accepted for clinical measurements of axial length in the human eye. Ultrasonic radio frequency signal analysis is used for the tissue-characterisation of small regions of interest in the ocular wall. Up to now in both applications the precise location of the area examined ultrasonically in an individual eye is not exactly known, because the acoustical beam undergoes refraction and diffraction by the components of the eye.
For the study, an eye model, consisting of an artificial cornea, a typical intraocular implant lens and a thein polyethylene pellicle simulating the retinal membrane was built. The model was irradiated in water by ultrasonic pulses from a medical A-mode transducer for biometry of the eye (single element, piston type, 8 MHz nominal center frequency, 1 kHz pulse repetition rate) and by a laser beam simultaneously.
The slight vibration of the simulated retina induced by the ultrasonic pulses caused a phase modulation of the light beam proportional to the amplitude of motion. The modulation was analysed in a MACH-ZENDER type interferometer, using heterodyne technique. We succeeded in detecting ultrasound induced vibrations of the pellicle with a high spatial resolution, resulting in amplitudes of about 10 nm in the centre and below 1nm at the margins of the ultrasonic focus. Averaging of many transients enhanced the resolution up to the sub-nm regime. The results encourage further experiments to detect the location of an ultrasonic beam in the eye wall, passing both the acoustical and optical beam through the cornea and lens of an eye.
This study is part of the project: "Opto-acoustical biometry of the eye" supported by Deutsche Forschungsgemeinschaft, Bonn.

: http://publica.fraunhofer.de/documents/N-19925.html