NFV is the vergence response that diverges to overcome which demand?

NFV is the vergence response that diverges to overcome which demand?

• A. Base-out prism testing
• B. Base-out demand
• C. Accommodative testing
• D. Base-in prism testing

Answer: (D)

Negative fusional vergence is the divergent eye movement used to maintain single vision when the visual input produces an inward shift that would otherwise blur or double vision. When a base-in prism is placed in front of the eye, it shifts the image toward the nose, creating an inward demand. To fuse the images, the eyes must diverge, and that divergent response is what NFV measures. So the test that elicits this divergence to overcome the inward (base-in) demand is base-in prism testing. By contrast, base-out prisms create a demand that is typically overcome by convergence (positive fusional vergence) to maintain fusion. Accommodative testing relates to focusing, not vergence.

Negative fusional vergence is the divergent eye movement used to maintain single vision when the visual input produces an inward shift that would otherwise blur or double vision. When a base-in prism is placed in front of the eye, it shifts the image toward the nose, creating an inward demand. To fuse the images, the eyes must diverge, and that divergent response is what NFV measures. So the test that elicits this divergence to overcome the inward (base-in) demand is base-in prism testing.

By contrast, base-out prisms create a demand that is typically overcome by convergence (positive fusional vergence) to maintain fusion. Accommodative testing relates to focusing, not vergence.