ABO NOCE Basic Opticianry Spectacle Dispensing Procedures Questions and Answers 5 — Questions and Answers
Question 1: What is the purpose of 'blocking' a lens during the fabrication process?
- To apply the anti-reflective coating
- To secure the lens to a chuck for surfacing or edging at the correct optical center (Correct answer)
- To cut the lens blank to the correct diameter
- To apply the scratch-resistant hard coat
Correct answer: To secure the lens to a chuck for surfacing or edging at the correct optical center
Blocking attaches the lens blank to a holding device (block) so it can be processed with the optical center precisely positioned for surfacing or edging.
Question 2: A patient's old glasses have a base curve of 4.00 D. Their new prescription is filled on a 6.00 D base curve. The patient complains of distortion. The MOST likely cause is:
- Incorrect PD on the new lenses
- Adaptation difficulty due to change in lens form (Correct answer)
- Incorrect seg height
- Vertex distance change
Correct answer: Adaptation difficulty due to change in lens form
A significant change in base curve alters the lens form, changing peripheral aberrations and causing adaptation issues for some patients.
Question 3: Which ANSI standard governs the tolerances for finished prescription spectacle lenses in the US?
- ANSI Z80.1 (Correct answer)
- ANSI Z87.1
- ANSI Z80.3
- ANSI Z80.5
Correct answer: ANSI Z80.1
ANSI Z80.1 establishes the prescription tolerances and optical requirements for finished ophthalmic lenses dispensed in the United States.
Question 4: When dispensing lenses with significant prism, the optical center placement is replaced by which reference point?
- The boxing center
- The fitting cross
- The prism reference point (PRP) (Correct answer)
- The geometric center
Correct answer: The prism reference point (PRP)
The prism reference point (PRP) is the location where prescribed prism is verified and placed relative to the pupil for lenses containing prism.
Question 5: A patient's frame has a B measurement of 32 mm and they require a flat-top 28 bifocal. The seg height is ordered at 17 mm. This placement positions the seg top:
- Above the lower lid margin
- At the lower lid margin
- At the geometric center of the lens
- Below the lower lid margin (Correct answer)
Correct answer: Below the lower lid margin
With a 32 mm B measurement and 17 mm seg height, the segment top is 15 mm from the bottom, which typically falls at or just below the lower lid margin.
Question 6: In spectacle dispensing, 'decentration' refers to:
- The amount the optical center is moved from the geometric center of the cut lens (Correct answer)
- The distance from the pupil to the frame edge
- The angle of the lens relative to the frame front
- The difference between the lens power and prescribed power
Correct answer: The amount the optical center is moved from the geometric center of the cut lens
Decentration is the horizontal (and sometimes vertical) displacement of the optical center from the geometric center of the edged lens to align with the patient's pupil.
Question 7: A patient receives new glasses and reports that straight lines appear curved or wavy when looking through the periphery. This is MOST consistent with:
- Incorrect axis on an astigmatic prescription
- Oblique aberrations due to high base curve or large frame (Correct answer)
- Incorrect add power in a progressive lens
- Prism imbalance between the two lenses
Correct answer: Oblique aberrations due to high base curve or large frame
Peripheral distortion causing straight lines to appear curved is characteristic of oblique (marginal) aberrations, which increase with steeper base curves and larger lens diameters.
ABO NOCE Basic Opticianry Spectacle Dispensing Procedures Questions and Answers 5
What is the purpose of 'blocking' a lens during the fabrication process?