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Proceedings Paper

Speckle interferometric sensor to measure low-amplitude high frequency Ocular Microtremor (OMT)
Author(s): James P. Ryle; Mohammed Al-Kalbani; Unnikrishnan Gopinathan; Gerard Boyle; Davis Coakley; John T. Sheridan
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Paper Abstract

Ocular microtremor (OMT) is a physiological high frequency (up to 150Hz) low amplitude (150-2500nm) involuntary tremor of the human eye. It is one of the three fixational ocular motions described by Adler and Fliegelman in 1934 as well as microsaccades and drift. Clinical OMT investigations to date have used eye-contacting piezoelectric probes or piezoelectric strain gauges. Before contact can be made, the eye must first be anaesthetised. In some cases, this induces eyelid spasms (blepharospasm) making it impossible to measure OMT. Using the contact probe method, the eye motion is mechanically damped. In addition to this, it is not possible to obtain exact information about the displacement. Results from clinical studies to date have given electrical signal amplitudes from the probe. Recent studies suggest a number of clinical applications for OMT, these include monitoring the depth of anaesthesia of a patient in surgery, prediction of outcome in coma, diagnosis of brainstem death. In addition to this, abnormal OMT frequency content is present in patients with neurological disorders such as Multiple sclerosis and Parkinson's disease. However for ongoing clinical investigations the contact probe method falls short of a non-contact accurate measurement solution. In this paper, we design a compact non contact phase modulating optical fiber speckle interferometer to measure eye motions. We present our calibration results using a calibrated piezoelectric vibration simulator. Digital signal processing is then performed to extract the low amplitude high frequency displacement information.

Paper Details

Date Published: 22 August 2009
PDF: 12 pages
Proc. SPIE 7429, Novel Optical Systems Design and Optimization XII, 74290J (22 August 2009); doi: 10.1117/12.826891
Show Author Affiliations
James P. Ryle, Univ. College Dublin (Ireland)
SFI Strategic Research Ctr. in Solar Energy Conversion (Ireland)
Mohammed Al-Kalbani, Mercer's Institute for Research on Ageing (Ireland)
St. James's Hospital (Ireland)
Unnikrishnan Gopinathan, Instrument Research and Development Establishment (India)
Gerard Boyle, Mercer's Institute for Research on Ageing (Ireland)
St. James's Hospital (Ireland)
Davis Coakley, Mercer's Institute for Research on Ageing (Ireland)
St. James's Hospital (Ireland)
John T. Sheridan, Univ. College Dublin (Ireland)
SFI Strategic Research Ctr. in Solar Energy Conversion (Ireland)


Published in SPIE Proceedings Vol. 7429:
Novel Optical Systems Design and Optimization XII
R. John Koshel; G. Groot Gregory, Editor(s)

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