Verification of Progressive Lenses Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Verification of Progressive Lenses flashcards as text
Which measurement is used to determine if a progressive lens has been correctly positioned for the correct seg height after dispensing?
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.
A short-corridor progressive lens design has which of the following characteristics compared to a long-corridor design?
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.
When verifying progressive lenses with a lensometer, which zone should be used to verify the cylinder power and axis?
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.
According to ANSI Z80.1, what is the maximum allowable vertical prismatic imbalance between the two progressive lenses at the distance reference point?
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.
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:
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.
What effect does excessive pantoscopic tilt have on the functional performance of a progressive lens?
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.
When checking a progressive lens blank before cutting, which reference marks must be clearly visible to ensure correct orientation during fabrication?
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.