ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 5 — Questions and Answers
Question 1: Which lens form is said to be in 'best form' (corrected curve) configuration?
- Any plano-convex or plano-concave lens
- A lens where the base curve is chosen to minimize oblique astigmatism for the given power (Correct answer)
- A lens where front and back curves are equal
- A bifocal with matched segment curves
Correct answer: A lens where the base curve is chosen to minimize oblique astigmatism for the given power
Best form (corrected curve) lenses use a specific base curve for each power to minimize peripheral aberrations such as oblique astigmatism.
Question 2: In a toric lens, the two principal meridians are always:
- Parallel to each other
- Perpendicular to each other (Correct answer)
- At 45° to each other
- Determined by the pantoscopic tilt
Correct answer: Perpendicular to each other
A toric surface has two principal meridians of maximum and minimum curvature that are always 90° apart.
Question 3: What is the purpose of an 'edging allowance' when ordering a lens blank?
- Extra power added for the reading zone
- Additional blank diameter to ensure the prescription can be cut to fit the frame shape (Correct answer)
- UV coating applied to the edge of the lens
- Prism added to account for frame wrap
Correct answer: Additional blank diameter to ensure the prescription can be cut to fit the frame shape
The edging allowance ensures the blank is large enough so the prescription area extends fully to all edges of the traced frame shape.
Question 4: Minus lenses are thicker at the:
- Center
- Top edge only
- Edge (periphery) (Correct answer)
- Optical center when decentered
Correct answer: Edge (periphery)
Minus (concave) lenses are thinnest at the center and increase in thickness toward the edges.
Question 5: What is 'lens clock' (lens measure) used to measure?
- The optical center height
- The surface curvature (base curve) of a lens surface (Correct answer)
- The lens diameter
- The segment height on a bifocal
Correct answer: The surface curvature (base curve) of a lens surface
A lens clock (lens measure) measures the surface power/curvature of a lens by sensing the sagittal depth across a fixed chord.
Question 6: Which of the following best describes 'wraparound' or high-wrap frame considerations for lens power?
- No compensation is needed for wrap frames
- Vertex distance increases, requiring a power adjustment
- The lens must be compensated for pantoscopic tilt and face-form angle to maintain intended prescription (Correct answer)
- Only the cylinder axis must be adjusted
Correct answer: The lens must be compensated for pantoscopic tilt and face-form angle to maintain intended prescription
High-wrap frames introduce both pantoscopic tilt and face-form angle, requiring compensated power calculations so the wearer experiences the correct prescription.
Question 7: When neutralizing a lens using loose trial lenses, the lens is considered neutralized when:
- The image through the lens appears magnified
- The 'against' motion of the test lens is observed
- No movement (scissors motion) is seen through the combined lens system (Correct answer)
- The lens and trial lens create equal and opposite prism
Correct answer: No movement (scissors motion) is seen through the combined lens system
Neutralization is complete when the combined lens and trial lens produce no movement of the observed target—indicating equal and opposite powers.
ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 5
Which lens form is said to be in 'best form' (corrected curve) configuration?