Paradoxical fixation disparity occurs when the associated and disassociated phorias are in which relationship?

• A. Opposite directions
• B. Same direction
• C. Zero difference
• D. Random directions

Answer: (A)

Fixation disparity shows how the eyes’ alignment behaves when fusion is intact versus when it is broken. The associated phoria is the vergence posture the eyes adopt to maintain single binocular vision when fusion is active, while the disassociated (latent) phoria reveals what the eyes would do to re-align if fusion were disrupted. Paradoxical fixation disparity arises when these two phorias pull in opposite directions. In other words, the direction suggested by the cue to fuse and the direction revealed when fusion is broken clash, so the residual misalignment (the fixation disparity) ends up appearing in the opposite sense to what either measurement alone would predict. If the two phorias pointed the same way, no paradox would occur; zero difference or random directions don’t produce this specific conflicting scenario.