PAL Lensometry
A reference point 2-4mm above the PRP
What is the fitting cross?
The lateral distance from the major reference point to the geometrical center of the segment
What is the segment inset?
The point on a lens where, according to the manufacturer, the power of the near addition is to be measured.
What is the near reference point?
A lens having optics that vary in power gradually from the distance to near zones
What is a progressive addition lens?
This measurement ensures proper horizontal placement of a PAL
What is monocular PDs?
This calculation is used to determine the near power of a multifocal
What is the distance sphere power minus the near sphere power?
The point on a lens where prism power is to be verified.
What is the prism reference point?
A multifocal lens with a flat-top bifocal-style segment in the lower portion of the lens and an inverted flat-top bifocal-style segment in the upper portion of the lens
What is a double-D lens?
When no prism is prescribed, the optical center and the ____ are one and the same
What is the MRP?
This value is located temporally on a progressive lens
What is the lens add power?
This PAL centration method uses the distance from the PRP to the fitting cross instead of the fitting cross itself
What is hidden circles?
The ability to change the power of the eye's inner crystalline lens
What is accommodation?
Vertical prism of equal value ground on both right and left lenses of a progressive lens for the purpose of reducing lens thickness
What is yoked prism?
These multifocal lenses are invisible to the observer but are not progressive addition lenses
What are blended bifocals?
This tool helps verify manufacturer-specific PAL designs
What is the progressive identifier?
The reciprocal of the distance in air from the rear surface of the lens to the second principle focus, which serves as a specific measure of the power of a lens
What is back vertex power?