Eye tracking brings greater freedom for severely disabled

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Industrial vision technology is improving the quality of life of those with debilitating illnesses such as cerebral palsy and muscular dystrophy, as well as traumatic brain injuries, through an eye tracking system. LC Technologies (Fairfax, Virginia, USA), a provider of eye tracking technology, has developed its Eyegaze Edge system allowing people who are unable to control their body movement or speech to speak, write, operate a computer, play video games and control appliances, all through monitoring their eye movements.

Eyegaze Edge is a non-intrusive monocular system based on a single machine vision camera. It tracks one of the patient’s eyes to determine the gaze point. The system consists of a 13.3-inch tablet PC, a Guppy F-038 NIR industrial camera by Allied Vision Technologies mounted just below the screen, and an adjustable table mount.

Users operate the system by looking at rectangular keys that are displayed on the control screen and are able to ‘press’ a key by looking at it for a specified period of time. The system features an array of menus and options that allow them to navigate the system and perform a multitude of tasks from synthesising speech, controlling their environment (lights, call bells, etc.), typing, running computer software, operating a computer mouse and accessing e-mail.

A 15 second calibration procedure is required to set up the system. To calibrate, the user fixes their gaze on a sequence of small circles displayed on Eyegaze Edge‘s screen. This allows the system to learn several physiological properties of the person’s eye, such as the curvature of the eye’s cornea, in order to be able to project their gaze point accurately. The system can be adjusted to accommodate users with very large and very small pupils, drooping eyelids, and irregularly shaped pupils. It can also be operated in any position (sitting, lying down or head tipped to the side).

The Guppy F-038 NIR camera is a very small camera featuring an interlaced CCD sensor with enhanced near-infrared sensitivity that makes it ideal for imaging in low-light conditions. The camera system features LC Technologies’ patent aperture technology, which incorporates a small, low-power infrared LED light at the centre of the camera lens. The infrared light is used to illuminate the eye to generate a corneal reflection that causes a bright pupil effect. The camera frames the user’s pupil and images at 60fps to capture the user’s eye movements.

Sophisticated image processing software continually analyses the video image of the eye in real time and determines where the user is looking on the screen. It does this thanks to trigonometric calculations based on the position of the user’s pupil centre and corneal reflection within the image. Gaze point measurements are made with ¼ inch accuracy or less.

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