What is the difference between PFV and PRV?

What is the difference between PFV and PRV?

• A. PFV is the amount that can be simulated from the resting position; PRV is the amount relative to the target position
• B. PFV and PRV are the same
• C. PFV measures accommodation; PRV measures vergence
• D. PFV is the amount of convergence from the true target location

Answer: (A)

This item tests how PFV and PRV are defined and measured in vergence testing, specifically where the measurement starts and what drives the response. Positive fusional vergence (PFV) is the amount of vergence you can generate starting from the eyes’ resting, neutral posture to compensate for disparity. It tracks how much additional convergence (or divergence) you can achieve beyond the baseline when prisms push the images apart, so it’s about simulating from the resting position. Proximal vergence (PRV), on the other hand, reflects the vergence response driven by the target’s perceived distance. It’s the amount of vergence change relative to where the target actually is, not from the resting state. So PFV = how much you can simulate from rest; PRV = how much vergence you produce as the target’s position changes. The other options misstate either the starting point or what drives the response.

This item tests how PFV and PRV are defined and measured in vergence testing, specifically where the measurement starts and what drives the response. Positive fusional vergence (PFV) is the amount of vergence you can generate starting from the eyes’ resting, neutral posture to compensate for disparity. It tracks how much additional convergence (or divergence) you can achieve beyond the baseline when prisms push the images apart, so it’s about simulating from the resting position. Proximal vergence (PRV), on the other hand, reflects the vergence response driven by the target’s perceived distance. It’s the amount of vergence change relative to where the target actually is, not from the resting state. So PFV = how much you can simulate from rest; PRV = how much vergence you produce as the target’s position changes. The other options misstate either the starting point or what drives the response.