NBEO Ocular Motility Practice Test

Noncomitant deviations are when the amount of misalignment changes as the gaze direction changes. Clinically, if the difference in the deviation between gaze positions exceeds 5 prism diopters, it’s considered noncomitant. This threshold helps separate true changes in alignment due to a restricted or palsied muscle from small measurement variances that can occur with exam technique. For example, you might find a large angle in one gaze and a noticeably smaller angle in another, with the difference over 5 PD, indicating noncomitance. If the variation is only a couple of prism diopters, it could be within normal measurement fluctuation and doesn’t necessarily indicate a noncomitant deviation. So, the standard criterion is a difference greater than 5 prism diopters between gaze positions. Differences larger than this (such as greater than 10 PD) still fall under noncomitance, but 5 PD is the defining threshold.