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The Human Eye Position Control System in a Rehabilitation Setting

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Author(s): Yvonne Nolan | Edward Burke | Clare Boylan | Annraoi de Paor

Journal: Advances in Electrical and Electronic Engineering
ISSN 1336-1376

Volume: 4;
Issue: 3;
Start page: 118;
Date: 2005;
Original page

Keywords: Eye position | rehabilitation | control system.

ABSTRACT
Our work at Ireland’s National Rehabilitation Hospital involves designing communication systems for people suffering from profound physical disabilities. One such system uses the electro-oculogram, which is an (x,y) system of voltages picked up by pairs of electrodes placed, respectively, above and below and on either side of the eyes. The eyeball has a dc polarisation between cornea and back, arising from the photoreceptor rods and cones in the retina. As the eye rotates, the varying voltages projected onto the electrodes drive a cursor over a mimic keyboard on a computer screen. Symbols are selected with a switching action derived, for example, from a blink. Experience in using this mode of communication has given us limited facilities to study the eye position control system. We present here a resulting new feedback model for rotation in either the vertical or the horizontal plane, which involves the eyeball controlled by an agonist-antagonist muscle pair, modelled by a single equivalent bidirectional muscle with torque falling off linearly with angular velocity. We have incorporated muscle spindles and have tuned them by pole assignment associated with an optimum stability criterion.

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