What Is Prism Reference Point

Prism Reference Point, or PRP, is the point on a progressive lens that you will use in order to determine if any prism is present within the lens. You can find it on verification masks for all of your progressive lenses, or you can determine by the semi-visible markings on a PAL.

Where is the prism reference point?

The prism reference point is centered directly between the two horizontal alignment engravings (or ink markings), usually about 2 to 4 mm below the fitting cross of the lens. Next, note the amount of vertical prism in the lens.

What is PRP in glasses?

The PRP is a control point in a progressive lens used to verify thickness, prism and mounting. This reference point is required by ANSI and used to verify the accurate manufacture of a completed pair of prescription eyeglasses.