In Convergence Excess, which ranges are primarily reduced?

In Convergence Excess, which ranges are primarily reduced?

• A. PFV ranges
• B. NFV ranges
• C. Both PFV and NFV
• D. Neither PFV nor NFV

Answer: (B)

In convergence excess, the problem is an over-strong convergence response at near, so the ability to diverge back out (base-in movement) becomes the limiting factor. Negative fusional vergence (divergence) is what helps offset excessive convergence, and when it’s reduced, the eyes can’t diverge enough to maintain single vision as demand changes. Positive fusional vergence (convergence beyond the basic demand) tends to be relatively preserved because the system is already biased toward convergence; there isn’t a need for greater divergence to a large extent, so PFV is not the primary limiter. The net effect is a reduced NFV range, especially at near, which explains why NFV is the main deficit in convergence excess.

In convergence excess, the problem is an over-strong convergence response at near, so the ability to diverge back out (base-in movement) becomes the limiting factor. Negative fusional vergence (divergence) is what helps offset excessive convergence, and when it’s reduced, the eyes can’t diverge enough to maintain single vision as demand changes. Positive fusional vergence (convergence beyond the basic demand) tends to be relatively preserved because the system is already biased toward convergence; there isn’t a need for greater divergence to a large extent, so PFV is not the primary limiter. The net effect is a reduced NFV range, especially at near, which explains why NFV is the main deficit in convergence excess.