In a non-comitant deviation, will the primary or secondary deviation always be greater?

• A. Primary deviation
• B. Secondary deviation
• C. They are equal
• D. It varies with gaze

Answer: (B)

Incomitant (noncomitant) deviations change with where you look, so the amount of misalignment isn’t the same in all gaze positions. The primary deviation is the amount of misalignment when the normal eye is fixing in the primary position. The secondary deviation is the misalignment of the other eye when the deviating eye becomes the fixing eye (or, put another way, when role-reversal testing reveals the deviation).

Because the underlying problem is a muscle weakness or restriction that isn’t the same in every gaze, the full effect of that limitation tends to show up more clearly when the nonfixating eye is tested. This makes the secondary deviation larger than the primary deviation on average. So the best answer is that the secondary deviation is greater.