Which statement defines Positive Fusional Vergence (PFV)?

Which statement defines Positive Fusional Vergence (PFV)?

• A. The amount of convergence that can be stimulated relative to the target position
• B. The amount of convergence that can be stimulated from the resting position
• C. The amount of divergence that can be stimulated from the resting position
• D. The amount of convergence that can be simulated from the resting position to fuse

Answer: (D)

Positive fusional vergence is the convergence that the eyes can generate starting from their resting, relaxed position in order to keep a single image when the dissociating stimulus tries to separate the images. In practice, you introduce a base-out dissociating cue (like a prism) that would push the images apart, and then the person must converge to fuse them. The key idea is that PFV measures the amount of convergence available from the resting position specifically to fuse a target that has been displaced outward. That’s why the best statement is that PFV is the amount of convergence that can be simulated from the resting position to fuse. The other descriptions either omit the fusion goal, or refer to convergence from the rest position without tying it to maintaining single vision, or describe divergence instead of convergence.

Positive fusional vergence is the convergence that the eyes can generate starting from their resting, relaxed position in order to keep a single image when the dissociating stimulus tries to separate the images. In practice, you introduce a base-out dissociating cue (like a prism) that would push the images apart, and then the person must converge to fuse them. The key idea is that PFV measures the amount of convergence available from the resting position specifically to fuse a target that has been displaced outward.

That’s why the best statement is that PFV is the amount of convergence that can be simulated from the resting position to fuse. The other descriptions either omit the fusion goal, or refer to convergence from the rest position without tying it to maintaining single vision, or describe divergence instead of convergence.