The eye tracker consists of an eye tracking computer, a small camera and several infrared illuminators.
Image processing software inside the computer “recognizes” the pupil and the reflections from the infrared illuminators on the surface of the eye (cornea).
By analyzing the spacial relationships between these benchmarks the location of the eye in 3d space and the direction the eye is pointed can be computed.
The exact point of gaze as it falls on a computer screen can be determined by a rapid calibration procedure where a person is asked to look at a series of dots as they appear in known positions on the computer screen.
The point of gaze is tracked in real time and can be superimposed on an image of the object being studied.