A new system for the measurement of ocular motility using a personal computer

A new system (automated Hess screen, AHS) for the measurement of ocular motility using a personal computer is described. The subject is seated with his/her head restrained at a fixed distance from a colour monitor and views the screen through red/green goggles. A red target is displayed on the screen and the subject is instructed to move a green stimulus (using a joystick control) until the stimulus appears to be centred on the target. A button on the joystick is pressed and the computer registers the relative position of the target and stimulus. This procedure is repeated for a range of target locations (positions of gaze) and the entire routine is then repeated with the other eye fixing, by reversing the colour of the target and stimulus. The oculomotor fields may be displayed on the screen, printed, plotted or saved on a magnetic disc. A prototype system (based on an IBM AT with a 20 in monitor viewed from 25 cm) has been evaluated in a clinical environment on a sample of patients with a wide range of oculomotor problems, and compared with the electronic Hess screen (EHS). In general, the shapes of the oculomotor fields obtained using the two instruments were similar, but the AHS tended to measure a slightly converged displacement of the plots relative to the EHS and to record larger deviations, particularly in patients with incomitant fields. However, the test-retest reliability and the diagnostic value of the charts obtained were similar for both instruments. There was no significant difference between the durations of the examinations with the EHS and AHS. The AHS is a viable alternative to the EHS.