Periballasting is a technique similar to prism ballasting except it incorporates what?

• A. A Prism into the optic zone
• B. BD prism into the bottom outside of the optic zone
• C. Slab off
• D. Truncation

Answer: (B)

The idea being tested is how periballasting uses prism, but in a peripheral way. In periballasting, a base-down prism is incorporated into the bottom outside of the optic zone. Placing the prism in the peripheral area stabilizes and orientates the lens without introducing prism into the central optical zone, so visual acuity remains unaffected while improving lens centration and lid/lid-tear interaction. This distinguishes it from methods that place prism within the optic zone or use other edge modifications, which would alter the vision through the central area.