ABO NOCE Basic Opticianry Verification of Progressive Lenses 4 — Questions and Answers
Question 1: Which measurement is used to determine if a progressive lens has been correctly positioned for the correct seg height after dispensing?
- Measuring from the lower rim to the fitting cross with the patient wearing the frame (Correct answer)
- Measuring the distance from the optical center to the bottom of the lens blank
- Verifying the near reference point against the lower pupil margin
- Checking the prism reference point location relative to the pupil
Correct answer: Measuring from the lower rim to the fitting cross with the patient wearing the frame
Seg height for progressives is confirmed by measuring from the lower rim (or lowest point of the frame) to the center of the pupil while the patient wears the frame in its adjusted position.
Question 2: A short-corridor progressive lens design has which of the following characteristics compared to a long-corridor design?
- Wider reading zones and less peripheral distortion
- A shorter distance from the fitting cross to the full near power zone (Correct answer)
- Greater total lens diameter required
- A lower add power capability
Correct answer: A shorter distance from the fitting cross to the full near power zone
Short-corridor designs have a shorter distance from the fitting cross to where full near power is reached, making them suitable for smaller frames.
Question 3: When verifying progressive lenses with a lensometer, which zone should be used to verify the cylinder power and axis?
- The near reference point
- The intermediate zone
- The distance reference point (DRP) (Correct answer)
- The corridor midpoint
Correct answer: The distance reference point (DRP)
Cylinder power and axis are verified at the distance reference point (DRP) because the distance zone contains the full prescribed cylinder.
Question 4: According to ANSI Z80.1, what is the maximum allowable vertical prismatic imbalance between the two progressive lenses at the distance reference point?
- 0.25 prism diopters
- 0.33 prism diopters (Correct answer)
- 0.67 prism diopters
- 1.00 prism diopter
Correct answer: 0.33 prism diopters
ANSI Z80.1 allows a maximum vertical prismatic imbalance of 0.33 prism diopters between the two lenses at the distance reference point.
Question 5: A progressive lens is ordered with no prescribed prism, but during verification, 0.5Δ base-down is measured at the PRP of the right lens. This finding is:
- Acceptable because progressive lenses inherently have prism
- Outside ANSI tolerance and the lens should be remade (Correct answer)
- Acceptable if the left lens also has 0.5Δ base-down
- Normal for all progressive lens designs
Correct answer: Outside ANSI tolerance and the lens should be remade
When no prism is prescribed, 0.5Δ at the PRP exceeds the ANSI Z80.1 tolerance of 0.33Δ vertical or 0.67Δ horizontal, so the lens must be remade.
Question 6: What effect does excessive pantoscopic tilt have on the functional performance of a progressive lens?
- It narrows the distance zone only
- It shifts the effective near zone upward, potentially causing the patient to miss the near zone when looking down
- It shifts the effective near zone downward, requiring the patient to tilt their head further down (Correct answer)
- It has no clinically significant effect
Correct answer: It shifts the effective near zone downward, requiring the patient to tilt their head further down
Excessive pantoscopic tilt shifts the effective optical zones downward, causing the patient to need to tilt their head further down to access the near zone.
Question 7: When checking a progressive lens blank before cutting, which reference marks must be clearly visible to ensure correct orientation during fabrication?
- The distance zone engravings only
- The prism reference point, fitting cross, and manufacturer's permanent engravings (Correct answer)
- The near zone boundary markers
- The corridor width indicators
Correct answer: The prism reference point, fitting cross, and manufacturer's permanent engravings
The PRP, fitting cross, and permanent manufacturer engravings must be visible to ensure the progressive lens is correctly oriented before surfacing or cutting.
ABO NOCE Basic Opticianry Verification of Progressive Lenses 4
Which measurement is used to determine if a progressive lens has been correctly positioned for the correct seg height after dispensing?