1. A system for testing visual fields comprising: a display for presenting a visual stimulus; an eye tracker for tracking movement of at least one of a patient's eyes to determine its position in three dimensions without requiring the patient to wear any tracking equipment; means for changing the position of the stimulus on the display by an amount that is a function of the tracked three dimensional position of the patient's eye and a visual field position that is to be tested, and means for using the change to the position of the stimulus and any tracked eye movement to assess the patient's visual field.