We describe a novel, noninvasive measurement approach for recording a small involuntary tremor of the eye known as ocular microtremor. The method is based on measuring out-of-plane angular displacements of a target by using laser-speckle correlation of images recorded in the Fourier plane of a lens. The system has a dynamic range of 4 to 5000 μrad, resolution of 4 μrad, and a bandwidth of 250 Hz. The design and optimization of the system is presented with an in vitro validation of the system against its specification.

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Ocular microtremor (OMT) is a small involuntary eye movement present in all subjects. In this paper we present the results of in vivo OMT measurement using a novel non-contact laser speckle technique. OMT signals have not previously been measured from the sclera using this laser speckle correlation technique. To verify the system's ability to record eye movements, it is first tested using a large angle eye rotation. Next, the system is tested with a group of 20 subjects and OMT parameters are extracted. The results of OMT measurements gave a mean frequency of 78 ± 3.86 Hz and peak-to-peak amplitude of 21.42 ± 7.01 µrad, these values are consistent with known values from eye-contacting methods.

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Ocular microtremor (OMT) is an involuntary fixational eye movement. We identify the implications of biospeckle for a noninvasive, laser speckle correlation technique to measure OMT. Biospeckle from the in-vivo eye is characterized and, using the resulting characteristics, a mathematical model to describe the biospeckle from the eye is designed and tested. Through in-vivo measurements, biospeckle is shown to disrupt the temporal stability of the speckle images over time. However, provided each speckle image is cross correlated with the previous image within a sufficiently short time, the stability of speckle images captured from the eye is shown to be adequate to measure OMT-like displacements.

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