Sensors measure the reflected light. Eye movements cause a different amount of light to be reflected on the sensors. These systems are low cost, portable, and are great for measuring horizontal saccade latency. Inexpensive, portable and offer good temporal resolution. However, these designs have a poor vertical signal and requires chin rest.
Remote video imaging The eye is illuminated with infrared lights.
These landmarks to compute the point of gaze. A good, general purpose technique. The Applied Science Laboratories 210 system is a head mounted infrared reflection eye tracker. Typically, horizontal position is sampled from one eye, and vertical position is sampled from the other eye. The 504 is a remote video eye movement monitor, which samples the eye position at 60 Hz.