FREE ABO-NOCE Verification of Progressive Lenses Questions and Answers

Question 1

What is the very first step an optician should take when placing a progressive addition lens (PAL) in a lensometer for verification?

Accepted Answer

Locate the semi-visible markings and engravings

Answer

Before taking any measurements, the optician must locate the semi-visible markings, which include the alignment circles, engravings, and fitting cross. These markings are essential for correctly orienting the lens to find the distance reference point, prism reference point, and near reference point.

Question 2

To verify the distance prescription of a PAL, the lens should be positioned in the lensometer so that the mires are centered on the:

Accepted Answer

Distance reference point (DRP)

Answer

The distance reference point (DRP) is the specific location on the lens where the prescribed distance power should be verified. It is typically located a few millimeters above the fitting cross.

Question 3

How is the full add power of a progressive lens accurately measured with a lensometer?

Accepted Answer

By subtracting the distance sphere power from the near sphere power

Answer

The add power is the difference in spherical power between the near reference point (NRP) and the distance reference point (DRP). The optician must first measure the distance power, then move the lens up to the NRP and measure the new spherical power, with the difference being the add.

Question 4

While verifying a PAL, you notice that the reticle is displaced vertically at the prism reference point (PRP), even when the lens is correctly oriented. This indicates the presence of:

Accepted Answer

Prism-thinning (yoked prism)

Answer

Prism-thinning, also known as yoked or equalized prism, is vertical prism deliberately ground into a pair of PALs to reduce thickness differences between the top and bottom edges. It is measured at the prism reference point and should be equal in magnitude and direction for both lenses.

Question 5

The permanent markings engraved on a PAL, typically found nasally and temporally, are used to identify the:

Accepted Answer

Lens manufacturer and add power

Answer

The engraved markings are permanent and contain crucial information. They typically include the lens manufacturer's logo or symbol and the numerical add power, allowing for identification even after the semi-visible markings are removed.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

FREE ABO-NOCE Verification of Progressive Lenses Questions and Answers