Free ABO-NOCE Verification of Progressive Lenses Questions and Answers — 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?
- Measure the add power immediately
- Locate the semi-visible markings and engravings (Correct answer)
- Center the lens and check for prism
- Focus the eyepiece of the lensometer
Correct answer: Locate the semi-visible markings and engravings
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:
- Fitting cross
- Near reference point (NRP)
- Geometric center of the lens
- Distance reference point (DRP) (Correct answer)
Correct answer: Distance reference point (DRP)
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?
- By measuring the power at the fitting cross
- By subtracting the distance sphere power from the near sphere power (Correct answer)
- By reading the temporal engraving on the lens
- By measuring the power difference between the top and bottom edge of the lens
Correct answer: By subtracting the distance sphere power from the near sphere power
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:
- An incorrect prescription
- Unwanted horizontal prism
- Prism-thinning (yoked prism) (Correct answer)
- A warped lens
Correct answer: Prism-thinning (yoked prism)
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:
- Patient's pupillary distance
- Lens manufacturer and add power (Correct answer)
- Optical center and fitting cross location
- Recommended segment height
Correct answer: Lens manufacturer and add power
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.
Question 6: What is the primary purpose of the fitting cross on a progressive lens?
- To verify the distance power
- To measure the add power
- To align the lens with the patient's pupil center (Correct answer)
- To indicate the location of prescribed prism
Correct answer: To align the lens with the patient's pupil center
The fitting cross is the primary reference point for positioning the lens in front of the patient's eye. It should be centered directly in front of the pupil when the patient is looking straight ahead in their primary gaze position.
Question 7: When neutralizing the near reference point (NRP) of a PAL, what is the correct procedure after measuring the distance power?
- Rotate the axis wheel 90 degrees
- Move the lens up to center the NRP and re-focus the sphere mires (Correct answer)
- Move the lens down to the bottom edge
- Add prism to the lensometer reading
Correct answer: Move the lens up to center the NRP and re-focus the sphere mires
After neutralizing the distance power at the DRP, the lens is moved vertically upwards in the lensometer until the NRP is centered. The power wheel is then adjusted (typically by adding plus power) to bring the spherical mires back into focus, without changing the axis wheel.
Free ABO-NOCE Verification of Progressive Lenses Questions and Answers
What is the very first step an optician should take when placing a progressive addition lens (PAL) in a lensometer for verification?