Where is the prismatic effect verified on a P.A.L.?

The prismatic effect of a progressive addition lens (P.A.L.) is verified at the dot directly below the fitting cross. This location is significant because it is where the optical alignment is typically assessed for optimal visual function. The fitting cross indicates the center of the distance portion of the lens, where the prescription is calibrated for distance vision. Below this point, the lens transitions into the near vision zone, and the prismatic effect can be most clearly evaluated.

This assessment is critical for ensuring that the wearer’s visual experience is comfortable and that the lens is correctly tailored to their specific needs. If the prismatic effect is not verified correctly at this point, it could lead to visual disturbances, such as double vision or discomfort, particularly when shifting between distances. The lower area where the near power is verified, while important for determining the optical power for reading and near activities, does not provide the same level of reference for the desired vertical alignment and prismatic effect as the dot below the fitting cross does.

Understanding the role of the fitting cross and associated points on a P.A.L. lens is essential for precise dispensing and ensuring customer satisfaction with their eyewear.