Oculometer
[1][2] The oculometer computes eye movement by tracking corneal reflection relative to the center of the pupil.
[3] An oculometer, which can provide continuous measurements in real time, can be a research tool to understand gaze as well as cognitive function.
[4] The first improvement on this occurred in 1738, when an observer would feel the outside of closed eyelids to track eye movement.
[4] Though rudimentary, these early techniques show repeated need throughout history to track eye movements.
[4] Due to the many applications of an eye tracking device to aviators and pilots, NASA and the United States Air Force carried out extensive studies on this technology, propelling the field forward.
This implies minimal parallax error between the corneal reflection and the center of the pupil, thus making the oculometer insensitive to changes in the head position during measurements.
It also negates the need for extensive equipment like bite plates or rigid skull clamping for measurements.
[4] This can be overcome by either rigidly fixing the head to prevent any movements, however this is intrusive and uncomfortable for the user and not broadly applicable for human research studies.
[8] The optical design of the oculometer allows normal vision, directs light from a fixed internal source onto the eye of the user, and forms the image of the pupil on a detector.
In order to attenuate the light from the source through reflections in the eyepiece, a linear polarizer in the V direction is placed in the optical path.
This arrangement does not include the traditional eye-piece and user sees through a transparent, curved visor placed in front of his eyes.
[3] When the user first sees through the eye piece, a rough raster scan captures the black pupil and bright reflections from the cornea.
[3] Then, the device automatically switches to tracking mode where time-division-multiplex-scans acquires continuous measurements of eye direction.
[3] In recent designs, the acquisition mode has been automated to ensure that the pupil/iris boundary was instantly captures once the user sees through the eye piece.
[3] The automation also led to automatic switch to tracking mode after initial acquisition was obtained or after the user blinks.
Further, flight programs can use the oculometer to inform cockpit design in terms of instrumentation panels, by studying the gaze of pilots as they fly.
[9] Using those eye movement patterns both as a diagnostic tool and for monitoring disease progression has therefore been of scientific interest.
[5] Patients with Parkinson's disease displayed high inabilities in performing antisaccadic tasks (eye movement in the opposite direction from the onset trigger).
[6] The use of multiple detectors not only enables oculometers to be used as lightweight wearables but also ensures that signals detected by the sensors are not dependent on external illumination.
[6] Other potential application of oculometers that are still currently under development include in air traffic control for operators to designate aircraft through eye movement;[10] in laser communication in dynamic situations where operators can transmit signals by looking at the signal; in television systems to monitor the eye direction as it views the television display such that sensory requirements of the eye can be met with lower bandwidths; and in psychological tests to analyze pattern of images that patients tend to avoid.
