Which statement about fixation disparity curve types is correct?

• A. Type 1 is sigmoidal and asymptomatic
• B. Type 2 is seen in an exo deviation
• C. Type 3 is seen in an eso deviation
• D. Type 4 is typically seen in asymptomatic individuals

Answer: (A)

Fixation disparity curves show how a small misalignment between the eyes (fixation disparity) changes as you apply more prism. A Type 1 pattern is an S-shaped (sigmoidal) curve that centers near zero prism and, importantly, the person remains asymptomatic. This combination—sigmoidal shape with no symptoms—fits best with normal, comfortable binocular vision. The other statements assign fixed associations to the remaining curve types that aren’t as consistently described, so they don’t match the standard description as neatly.