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Proceedings Paper

Ocular microtremor laser speckle metrology
Author(s): M. Al-Kalbani; E. Mihaylova; N. Collins; V. Toal; D. Coakley; G. Boyle
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Paper Abstract

Ocular Microtremor (OMT) is a continual, high frequency physiological tremor of the eye present in all subjects even when the eye is apparently at rest. OMT causes a peak to peak displacement of around 150nm-2500nm with a broadband frequency spectrum between 30Hz to 120Hz; with a peak at about 83Hz. OMT carries useful clinical information on depth of consciousness and on some neurological disorders. Nearly all quantitative clinical investigations have been based on OMT measurements using an eye contacting piezoelectric probe which has low clinical acceptability. Laser speckle metrology is a candidate for a high resolution, non-contacting, compact, portable OMT measurement technique. However, tear flow and biospeckle might be expected to interfere with the displacement information carried by the speckle. The paper investigates the properties of the scattered speckle of laser light (λ = 632.8nm) from the eye sclera to assess the feasibility of using speckle techniques to measure OMT such as the speckle correlation. The investigation is carried using a high speed CMOS video camera adequate to capture the high frequency of the tremor. The investigation is supported by studies using an eye movement simulator (a bovine sclera driven by piezoelectric bimorphs). The speckle contrast and the frame to frame spatiotemporal variations are analyzed to determine if the OMT characteristics are detectable within speckle changes induced by the biospeckle or other movements.

Paper Details

Date Published: 24 February 2009
PDF: 12 pages
Proc. SPIE 7176, Dynamics and Fluctuations in Biomedical Photonics VI, 717606 (24 February 2009); doi: 10.1117/12.808855
Show Author Affiliations
M. Al-Kalbani, St. James's Hospital (Ireland)
E. Mihaylova, Dublin Institute of Technology (Ireland)
N. Collins, St. James's Hospital Dublin (United States)
Royal Victoria Eye and Ear Hospital (Ireland)
V. Toal, Dublin Institute of Technology (Ireland)
D. Coakley, St. James's Hospital (Ireland)
G. Boyle, St. James's Hospital (Ireland)

Published in SPIE Proceedings Vol. 7176:
Dynamics and Fluctuations in Biomedical Photonics VI
Valery Viktorovich Tuchin; Lihong V. Wang; Donald D. Duncan, Editor(s)

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