Figure 3.

The zone of clear single binocular vision (ZCSBV). Focal and vergence distances are plotted in diopters on the ordinate and abscissa, respectively. The dashed diagonal line represents the vergence and focal stimuli associated with natural viewing. The line labeled “Minimum relative vergence” represents the smallest vergence distance for which the viewer can maintain a single, well-focused image of the stimulus target at each focal distance. The line labeled “Maximum relative vergence” represents the largest vergence distance for which the viewer can maintain single, well-focused vision.