Are prism values for the right and left lens on a PAL measured at the same time, allowing use of paired prism rules?

• A. True
• B. False
• C. Not sure
• D. It depends on the frame

Answer: (A)

When dealing with prism in PALs, you assess binocularly—the eyes are evaluated together against the same viewing direction and frame reference. That means the prism values for the right and left lenses are determined with respect to a common gaze, using the same target and frame position. Because both eyes share that reference point, you can apply paired prism rules, which relate the prisms in corresponding directions across the two eyes, to understand the overall prismatic effect and how it will function when the wearer looks through the lenses. The frame fit and the progressive zones don’t prevent measuring prisms simultaneously; in practice, measuring prisms for both eyes together reflects how the lenses will behave in binocular vision.