ABO NOCE Basic Opticianry Verification of Progressive Lenses 2 — Questions and Answers
Question 1: When using a lensometer to verify a progressive lens, where should the distance power be measured?
- At the geometric center of the lens
- Through the distance reference point (DRP) or distance zone (Correct answer)
- At the prism reference point (PRP)
- At the fitting cross
Correct answer: Through the distance reference point (DRP) or distance zone
Distance power is verified through the distance reference point (DRP) or the distance zone of a progressive lens, not the geometric center.
Question 2: According to ANSI Z80.1 standards, what is the allowable tolerance for the add power of a progressive lens up to +4.00 D add?
- +/- 0.12 D
- +/- 0.25 D (Correct answer)
- +/- 0.50 D
- +/- 0.18 D
Correct answer: +/- 0.25 D
ANSI Z80.1 allows a +/- 0.25 D tolerance for the add power on progressive lenses with adds up to +4.00 D.
Question 3: A patient complains of swimming or swaying when wearing new progressives. Which verification step should the optician prioritize?
- Checking the pantoscopic tilt of the frame
- Verifying the corridor length matches the prescribed design
- Measuring the monocular PD at the fitting cross (Correct answer)
- Confirming the seg height is marked correctly
Correct answer: Measuring the monocular PD at the fitting cross
Swimming or swaying is often caused by incorrect monocular PD placement; verifying the monocular PD at the fitting cross is the critical first check.
Question 4: What is the purpose of the prism reference point (PRP) on a progressive lens?
- It indicates where to measure the near addition power
- It is the point used to verify prescribed prism or confirm zero prism (Correct answer)
- It marks the optical center of the distance zone
- It identifies the start of the corridor
Correct answer: It is the point used to verify prescribed prism or confirm zero prism
The PRP is the standardized point on a progressive lens used to verify any prescribed prism or to confirm that unwanted prism is within tolerance.
Question 5: When verifying a progressive lens on a lensometer, the mire appears blurry or broken. What does this most likely indicate?
- The lens has too much cylinder power
- The lens is positioned in the intermediate or near zone rather than the distance zone (Correct answer)
- The add power exceeds the prescription
- The lens has a scratch affecting the reading
Correct answer: The lens is positioned in the intermediate or near zone rather than the distance zone
A broken or blurry mire in a lensometer usually indicates the lens is not positioned at the distance reference point and is instead in the progressive corridor or near zone.
Question 6: A progressive lens is ordered with 2Δ base-in prism OD. During verification, no prism is detected at the PRP. What should the optician do?
- Accept the lens because prism in progressives is difficult to verify
- Reject the lens and reorder with the correct prism (Correct answer)
- Grind additional prism into the lens in-office
- Move the measurement point and re-read
Correct answer: Reject the lens and reorder with the correct prism
If prescribed prism is absent when measured at the PRP, the lens does not meet the prescription and must be rejected and reordered.
Question 7: Which tool is commonly used to physically locate and mark the fitting cross and reference points on a progressive lens before verification?
- Geneva lens clock
- Vertexometer
- Progressive lens identifier/decoding kit or felt-tip marker with the lens chart (Correct answer)
- Distometer
Correct answer: Progressive lens identifier/decoding kit or felt-tip marker with the lens chart
A progressive lens identifier or decoding kit is used to locate hidden engravings and plot the fitting cross, PRP, DRP, and NRP on the lens surface.
ABO NOCE Basic Opticianry Verification of Progressive Lenses 2
When using a lensometer to verify a progressive lens, where should the distance power be measured?