binocular vision single zone of clear

zone of clear, single, binocular vision 

In Donders' diagram it is the region determined by the extremes of accommodation and convergence that can be evoked while retaining a clear, single image. Clinically, this is determined by measuring the limits of negative and positive relative convergence by using base-in and base-out prisms to blur, or by measuring relative accommodation by binocularly adding concave or convex lenses, for various binocularly fixated distances (Fig. Z1). See relative amplitude of accommodation; relative convergence; Donders' diagram; rotary prism; binocular vision." >Fig. Z1 Zone of clear, single, binocular vision (NRC, negative relative convergence; PRC, positive relative convergence; NRA, negative relative accommodation; PRA, positive relative accommodation; BI, base-in prism; BO, base-out prism)