PFV testing typically involves which method?

PFV testing typically involves which method?

• A. Base-in prism testing
• B. Vergence range testing with glare
• C. Base-out prism testing
• D. Assessment of ocular motility only

Answer: (C)

PFV measures how much inward turning (convergence) the eyes can do to keep two images fused when the image shifts outward. To test this, we use base-out prisms. Placing a base-out prism before the eye makes the image appear to move outward, so the eyes must converge more to maintain single vision. We gradually increase the prism until fusion breaks or becomes blur, and the prism strength at that break point reflects the PFV range. This is distinct from base-in prisms, which probe divergence (negative fusional vergence). Using prisms with glare or relying on ocular motility alone doesn’t directly assess the convergence limit that PFV measures.

PFV measures how much inward turning (convergence) the eyes can do to keep two images fused when the image shifts outward. To test this, we use base-out prisms. Placing a base-out prism before the eye makes the image appear to move outward, so the eyes must converge more to maintain single vision. We gradually increase the prism until fusion breaks or becomes blur, and the prism strength at that break point reflects the PFV range. This is distinct from base-in prisms, which probe divergence (negative fusional vergence). Using prisms with glare or relying on ocular motility alone doesn’t directly assess the convergence limit that PFV measures.