Base-in prisms produce what impact on near tasks?

Base-in prisms produce what impact on near tasks?

• A. Increase convergence demand (PFV)
• B. Increase divergence demand (NFV)
• C. No effect on vergence
• D. Decrease accommodation

Answer: (B)

Base-in prisms shift the image toward the nose for each eye. To keep both eyes fused on a near target, the visual system must compensate by diverging the eyes more than usual, increasing negative fusional vergence. So, the presence of base-in prisms raises the divergence demand at near tasks. Accommodation isn’t directly changed by prisms, so they don’t decrease or increase accommodation themselves; they mainly alter vergence requirements.

Base-in prisms shift the image toward the nose for each eye. To keep both eyes fused on a near target, the visual system must compensate by diverging the eyes more than usual, increasing negative fusional vergence. So, the presence of base-in prisms raises the divergence demand at near tasks. Accommodation isn’t directly changed by prisms, so they don’t decrease or increase accommodation themselves; they mainly alter vergence requirements.