Which fixation disparity curve is seen in an exo deviation?

• A. Type 1
• B. Type 2
• C. Type 3
• D. Type 4

Answer: (C)

Fixation disparity curves show how a small, misalignment under binocular viewing changes as you change vergence demand with prisms. In an outward (exo) deviation, the eyes tend to sit in an exo alignment at zero prism and the fusion system has to work to converge to compensate. The pattern that reflects this common compensatory behavior is the Type 3 curve: the fixation disparity remains in the exo direction across the range of prism adjustments, with a relatively steep response to changes in vergence demand. This is why an exodeviation is associated with the Type 3 curve.