An instrument designed to present separate images to each eye. Each eye can see independently. Two plane mirrors are joined at one edge at a 90-degree angle and two target holders, one opposite one mirror and the other, mounted on a screw base which, when turned, synchronously moves the targets toward or away from each other. The Amblyoscope, Troposcope, Synoptophore, and the Bernell Mirror Stereoscope are examples of this design.
A wedge-shaped lens which is thicker on one edge than the other. The prism bases (thicker end) are in the same direction for both eyes (up, down, left, or right). Yoked prisms are used to train or compensate for a binocular dysfunction (eye teaming problem) or a visual field loss. Sometimes used in optometric vision therapy programs.