vergence facility

A measure of how quickly and accurately the fast fusional vergence system responds to rapidly changing vergence demands. Typically tested using prism flippers, the patient alternates fusion through 3Δ base-in and 12Δ base-out prisms at near, and the cycles per minute (cpm) are recorded. Reduced vergence facility (<15 cpm) can indicate binocular vision disorders. This dynamic test reflects vergence automaticity, as opposed to slow fusional vergence ranges.