My wife (Dana) tells me I need to do this in English
Phorias are conditions when you look at a target, one eye is dominant and looks directly at the target while the other eye will look slightly to the left or right of the target. The Maddox rod test helps identify this condition. One then places a prism (or several prisms) in front of the eye to bring the objects together so they are one. This prism measured in diopters is the way we report the phoria. Many AME's use a vision testing machine with this function built into the machine. The FAA has no hard standards for the values but they want to know that with 6 diopters or more there is no evidence of diplopia or serious eye pathology and all other aspects of the examination are favorable.