Vergence Prism With Stainless Steel StickVergence Facility Prismis used for a quick test of binocular vision capability. Vergence Prism test is used to assess the ability of the fusional vergence system to respond rapidly and accurately to changing vergence demands over time. This is measured in number of cycles per minute (cpm) that a stimulus can be fused through, alternating base in (BI) and base out (BO) prisms. Vergence facility response can be tested over a 1 or 2 minute period at 40