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.
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.
The human eye moves continuously even while it appears to be at rest. The involuntary eye movements causing this
motion are called fixational eye movements. Ocular Microtremor (OMT) is the smallest (150 - 2500nm amplitude) and
fastest (~ 80Hz) of these eye movements. OMT has been proven to provide useful clinical information regarding depth
of consciousness and neurological disorders.
Most quantitative clinical investigations of OMT have been carried out using an eye-contacting piezoelectric probe.
However, this measurement procedure suffers from a number of disadvantages which limit the potential of the technique
in the clinical environment. The need for eye contact requires the eye to be anaesthetised and not all subjects can tolerate
A promising alternative to the piezoelectric technique is speckle metrology. A speckle correlation instrument for
measuring OMT was first described by Al-Kalbani et al. The approach presented in this paper is a non contact
measurement technique implementing laser speckle correlation and using a highly light sensitive video camera operating
The OMT measurement technique in this paper was investigated using a human subject and an eye movement simulator.
Using this system, measurement of speckle on the eye takes only a few minutes, no eye drops are necessary and no
discomfort is caused to the subject. The paper describes the preliminary results of capturing speckle from the simulator
and from the human eye in-vivo at eye safe laser powers. The effects of tear flow, biospeckle and speckle shifting by
larger eye movements on the displacement information carried by the speckle are also discussed.
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.
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.
Ocular microtremor (OMT) is a physiological high-frequency (up to 150 Hz) low-amplitude (25-2500 nm peak-to-peak) involuntary motion of the human eye. Recent studies suggest a number of clinical applications for OMT that include monitoring the depth of anesthesia of a patient in surgery, prediction of outcome in coma, and diagnosis of brain stem death. Clinical OMT investigations to date have used mechanical piezoelectric probes or piezoelectric strain gauges that have many drawbacks which arise from the fact that the probe is in contact with the eye. We describe the design of a compact noncontact sensing device to measure OMT that addresses some of the above drawbacks. We evaluate the system performance using a calibrated piezoelectric vibrator that simulates OMT signals under conditions that can occur in practice, i.e., wet eye conditions. We also test the device at low light levels well within the eye safety range.
Ocular microtremor (OMT) is a biological high frequency (up to 150Hz) low amplitude (25-2500nm peak to peak)
involuntary motion of the human eye. Clinical OMT investigations to date have used eye-contacting mechanical
piezoelectric probes or piezoelectric strain gauges. Before contact can be made, the eye must first be anaesthetized. In
some cases, this eyelid spasms occur making it impossible to measure OMT. Using the contact probe method, the eye
motion is mechanically loaded. Results from clinical studies with this method to date have given electrical signal
amplitudes from the probe proportional to the displacement, but not the exact displacement information. Recent studies
suggest a number of clinical applications for OMT, these include monitoring the depth of anesthesia of a patient in
surgery, prediction of outcome in coma, diagnosis of brain stem death. In addition to this, in patients with neurological
disorders such as Multiple Sclerosis and Parkinson's disease, abnormal OMT frequency content is present. In this paper,
we design a compact non-contact phase modulating optical fiber speckle interferometer to measure eye motions. We
simulate OMT motion using a calibrated piezoelectric vibration simulator and compare results produced using a contact
method with those using our optical non-contact method.
Contact techniques exist to measure low amplitude low frequency mechanical vibration, however, by mechanically
loading the system of interest, they affect the measured results. In this paper, we design a compact non-contact optical
fiber speckle interferometer to measure inplane displacements. We implement this under laboratory conditions, and
present our calibration results, measuring low-amplitude microvibrations from 0.34 nm to 1.5 μm over a frequency range
from 10 Hz to 150 Hz.
Endoscopes are imaging devices routinely used for the diagnosis of disease within the human digestive tract. Light is transmitted into the body cavity via incoherent fibreoptic bundles and is controlled by a light feedback system. Fibreoptic endoscopes use coherent fibreoptic bundles to provide the clinician with an image. It is also possible to couple fibreoptic endoscopes to a clip-on video camera. Video endoscopes consist of a small CCD camera, which is inserted into gastrointestinal tract, and associated image processor to convert the signal to analogue RGB video signals. Images from both types of endoscope are displayed on standard video monitors. Diagnosis is dependent upon being able to determine changes in the structure and colour of tissues and biological fluids, and therefore is dependent upon the ability of the endoscope to reproduce the colour of these tissues and fluids with fidelity. This study investigates the colour reproduction of flexible optical and video endoscopes. Fibreoptic and video endoscopes alter image colour characteristics in different ways. The colour rendition of fibreoptic endoscopes was assessed by coupling them to a video camera and applying video colorimetric techniques. These techniques were then used on video endoscopes to assess how the colour rendition of video endoscopes compared with that of optical endoscopes. In both cases results were obtained at fixed illumination settings. Video endoscopes were then assessed with varying levels of illumination. Initial results show that at constant luminance endoscopy systems introduce non-linear shifts in colour. Techniques for examining how this colour shift varies with illumination intensity were developed and both methodology and results will be presented. We conclude that more rigorous quality assurance is required to reduce colour error and are developing calibration procedures applicable to medical endoscopes.