Which combination of findings would best indicate Fusional Vergence Dysfunction?

• A. Reduced NFV Ranges Alone
• B. Reduced PFV Ranges Alone
• C. Reduced NFV Ranges and Reduced PFV Ranges with Normal Distance/Near Phoria
• D. Normal NFV and PFV Ranges with Abnormal Phoria

Answer: (C)

Fusional vergence dysfunction shows up when the eyes can’t recruit enough fusional vergence to maintain single vision as demands change, even though there isn’t a constant misalignment at rest. The hallmark is reduced range in both directions of fusional vergence—negative fusional vergence (divergence) and positive fusional vergence (convergence)—while the static phoria at distance and near stays within normal limits. That combination means the motor system for fusion is globally limited, not merely carrying a misalignment.

If both NFV and PFV ranges are reduced and phorias are normal, you’re seeing a bilateral limitation of fusional reserves that underlies symptoms like eyestrain or blurred/binocular vision during near tasks. If only one direction were reduced, it would point to a directional issue (divergence insufficiency or convergence insufficiency) rather than a general fusional dysfunction. If phorias were abnormal, the pattern would reflect a static misalignment rather than a primary fusional reserve problem. In this question, the pattern of reduced NFV and reduced PFV ranges with normal distance/near phoria best indicates Fusional Vergence Dysfunction.