American Board of Opticianry (ABO) Practice Test 2025 - Free ABO Practice Questions and Study Guide

In the context of prisms, compounding refers to the combination of two prisms where the bases are oriented in the same direction, thereby adding their effects together. For instance, when two prisms with the same base direction are combined, their power increases.

The option that describes Base Out and Base In presents a situation where the effects of the prisms oppose each other. Base Out has a direction that diverges, while Base In converges. This opposition results in the two prisms essentially negating each other's effects rather than compounding them. Thus, this scenario exemplifies non-compounding behavior, as the total prism power can either reduce the overall effect or might even nullify it completely.

In contrast, combinations like Base Out and Base Out, Base Up and Base Up, as well as Base Down and Base Down all contribute to compounding situations, where the powers of the prisms add together because they are aligned in the same direction. Hence, the choice that reflects a non-compounding scenario is indeed the combination of Base Out and Base In.