ABO NOCE Basic Opticianry Verification of Progressive Lenses 3 — Questions and Answers
Question 1: The near reference point (NRP) of a progressive lens is typically located how far below the fitting cross?
- 4 mm
- 8 mm
- 12 mm (Correct answer)
- 18 mm
Correct answer: 12 mm
The near reference point is typically located approximately 12 mm below the fitting cross, though this varies slightly by lens design.
Question 2: A progressive lens has visible engraving marks at the 135° and 45° positions. What do these marks primarily indicate?
- The cylinder axis of the distance prescription
- The nasal and temporal lens identification marks used to locate the PRP and other reference points (Correct answer)
- The position of the intermediate zone
- The location of the prism ballast
Correct answer: The nasal and temporal lens identification marks used to locate the PRP and other reference points
The permanent engravings at roughly 135° and 45° are manufacturer identification marks used to locate the PRP and decode the lens design and reference points.
Question 3: When verifying add power of a progressive lens, you read +1.75 D through the near reference point but the Rx calls for +2.00 D add. This is:
- Within ANSI tolerance
- Outside ANSI tolerance and the lens must be reordered (Correct answer)
- Acceptable only if cylinder is correct
- Correctable by adjusting frame pantoscopic tilt
Correct answer: Outside ANSI tolerance and the lens must be reordered
The difference of 0.25 D equals the ANSI tolerance limit, but since this reading is at the boundary and below the prescribed add, it is outside acceptable tolerance and requires reorder.
Question 4: A patient's progressive lenses are verified and the monocular PDs are each 1.5 mm wider than prescribed. What visual complaint would this most likely cause?
- Base-in prismatic effect causing convergence difficulty for near tasks (Correct answer)
- Base-out prismatic effect causing divergence difficulty for distance
- No noticeable effect because tolerance covers 1.5 mm
- Increased image jump when shifting gaze
Correct answer: Base-in prismatic effect causing convergence difficulty for near tasks
When the lenses are placed too far apart (wider PD), a base-in prism effect is induced, causing the eyes to over-converge for near vision.
Question 5: What is the ANSI Z80.1 standard for horizontal prism imbalance between OD and OS at the distance reference point of a progressive lens?
- 0.33 prism diopters
- 0.67 prism diopters (Correct answer)
- 1.00 prism diopter
- 1.50 prism diopters
Correct answer: 0.67 prism diopters
ANSI Z80.1 allows up to 0.67 prism diopters of horizontal imbalance between the two lenses at the distance reference point.
Question 6: During progressive lens verification, the optician should check cylinder axis accuracy. What is the ANSI tolerance for cylinder axis when the cylinder power is between 0.25 D and 0.50 D?
- +/- 3 degrees
- +/- 7 degrees (Correct answer)
- +/- 14 degrees
- +/- 10 degrees
Correct answer: +/- 7 degrees
For cylinder powers between 0.25 D and 0.50 D, ANSI Z80.1 allows a cylinder axis tolerance of +/- 7 degrees.
Question 7: A patient reports clear distance vision but blurry near vision with new progressives. The verification shows the distance power is correct. What should be checked next?
- Pantoscopic tilt of the frame
- The add power at the near reference point (Correct answer)
- The base curve of the lens
- The vertex distance
Correct answer: The add power at the near reference point
If distance vision is clear but near is blurry, the next step is to verify the add power at the near reference point to determine if it is correct.
ABO NOCE Basic Opticianry Verification of Progressive Lenses 3
The near reference point (NRP) of a progressive lens is typically located how far below the fitting cross?