ABO NOCE Practice Test

Which prism combinations will compound together?

1. BU/BD

2. BI/BI

3. BO/BO

4. BU/BO

The correct answer is: BI/BI

When considering prism combinations that will compound together, it is essential to understand the orientation and type of the prisms involved. Prisms are described based on their base direction: base up (BU), base down (BD), base inward (BI), base outward (BO), etc. The choice of two prisms with the same base direction, such as base inward (BI) with base inward (BI), will indeed compound together effectively. When two prisms have the same base orientation, their optical effects can add together directly. This means that the total prism effect is simply the sum of the two individual prisms, allowing for a straightforward calculation of the resulting prism power. In contrast, combinations featuring different base orientations (like base up and base down or base outward and base outward) would not yield a simple additive effect, as their opposing directions can cancel each other out or alter the resultant angle in a more complex manner. Therefore, the choice of two base inward prisms compounding together correctly exemplifies how prisms of like orientation work in synergy to produce a cumulative effect. This understanding is crucial for opticians and eyecare professionals when determining the appropriate prism adjustments needed for a patient's prescription.