Low vision patients that require a high ADD power will often utilize which prism to reduce the demand on convergence?

Low vision patients that require a high ADD power will often utilize which prism to reduce the demand on convergence?

• A. BI prism
• B. BO prism
• C. Fresnel prism
• D. No prism

Answer: (A)

When a prism is used, it shifts the image you’re fusing, changing how much vergence the eyes must exert. For near tasks with a large near add, the eyes would normally have to converge quite a bit. Placing a prism with the base toward the nose (base-in) shifts the image inward, so the eyes can fuse with less inward turning. That reduces the convergence demand. A base-out prism would push the image outward and would increase convergence (or divergence) requirements, which isn’t helpful here. Fresnel is just a way to apply a prism; the critical factor is the base direction, which in this case is base-in.

When a prism is used, it shifts the image you’re fusing, changing how much vergence the eyes must exert. For near tasks with a large near add, the eyes would normally have to converge quite a bit. Placing a prism with the base toward the nose (base-in) shifts the image inward, so the eyes can fuse with less inward turning. That reduces the convergence demand. A base-out prism would push the image outward and would increase convergence (or divergence) requirements, which isn’t helpful here. Fresnel is just a way to apply a prism; the critical factor is the base direction, which in this case is base-in.