Oculomotor Tests of Otolith Function Using Human Centrifugation

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The effects of dysfunction of the balance system of the inner ear (the vestibular system) can range from mild brief episodes of dizziness to almost complete incapacitation: where the patient feels unstable, their posture is unstable, their vision is unstable. In order to guide appropriate treatment and rehabilitation, diagnostic tests are needed to identify whether the dysfunction is due to a brain problem or a problem in the inner ear, and if an ear problem - which part of the inner ear system is affected. By combining basic research with clinically feasible methods my colleagues and I have, with NH and MRC support, developed some of the most widely used clinical tests of balance function available today (see Halmagyi, Cremer and Curthoys 2003 for a review). In this Project I seek to continue the development of a test of part of the balance system (the utricular macula) for which there are few acceptable tests. I will do that by using the unique facilities available at Sydney University and RPA Hospital, presenting controlled stimuli (linear accelerations) to healthy human subjects and patients with known vestibular losses, and measuring precisely their eye movement responses to these stimuli using computerized image processing techniques. The experiments will test an hypothesis about how part of the vestibular system, the utricular macula, works and controls eye movements. One eye movement response, rolling of the eye around the line of sight (called ocular torsion) during maintained roll head-tilts (to the patients left or right) may be due to the joint activation of two regions of the balance receptors: the utricular and saccular maculae. As a result of a recent direct test we have managed to conduct on two normal subjects, we think that hypothesis should be thoroughly re-tested on subjects and patients with known vestibular losses and in doing so provide new understanding of otolith function which may lead to new clinical tests.