Which vergence measure describes the amount of convergence that must be stimulated from the resting position to fuse?

Which vergence measure describes the amount of convergence that must be stimulated from the resting position to fuse?

• A. Positive relative vergence
• B. Negative fusional vergence
• C. Negative relative vergence
• D. Positive fusional vergence

Answer: (D)

The idea here is fusional vergence—the amount the eyes must generate to maintain single vision when there’s a disparity. If fusion requires the eyes to move inwards (converge) from their resting position, that is positive fusional vergence. It reflects how much convergence you need to stimulate starting from rest to fuse a stereoscopic disparity. Negative fusional vergence would be the opposite—divergence from rest to fuse. Relative vergences describe how vergence changes with changes in accommodation or viewing distance, not the starting amount needed to fuse from rest.

The idea here is fusional vergence—the amount the eyes must generate to maintain single vision when there’s a disparity. If fusion requires the eyes to move inwards (converge) from their resting position, that is positive fusional vergence. It reflects how much convergence you need to stimulate starting from rest to fuse a stereoscopic disparity. Negative fusional vergence would be the opposite—divergence from rest to fuse. Relative vergences describe how vergence changes with changes in accommodation or viewing distance, not the starting amount needed to fuse from rest.