Monocular Maddox Phoria Measure

A Maddox designed to measure Anisophoria which is the change in the phoria away from the primary position.

This phoria measure combines a large 25mm aperture, and a red Maddox mounted perpendicular to the handle with a 10PD prism in a rotating disc with knurled edge. The small indicator in the periphery of the disc indicates the effective prism power from 0PD to 10PD.