The Model 310 is a limbus (iris-sclera boundary) and eyelid tracker capable of measuring horizontal and vertical eye movements. The basic system consists of control unit and sensor assembly mounted on spectacle frames or an optional headband. Both analog and digital outputs are available directly from the control unit. When used with the optional PC-DARS software package, data can be recorded and analysed on a PC. Recorded data include vertical and horizontal eye position, event marks, 16 bits of user generated data and elapsed time.