When checking for prism at the PRPs on a PAL, the values you obtain for the right and left lenses occur at the same time; therefore you should use the paired prism rules to determine the total amount of prism.

• A. True
• B. False
• C. Not applicable
• D. It depends

Answer: (A)

The key idea is binocular prism interaction. When you check prism at the PRP on a PAL, both eyes are involved in binocular viewing at the same time, so you must combine the prismatic effects from both eyes using the paired prism approach. This means you determine the total prism by considering both prisms together—add them if their bases point in the same direction, or subtract if they point in opposite directions—rather than looking at one eye in isolation. Since the prisms from the right and left eye occur concurrently, applying the paired prism rules gives the correct total amount of prism.