Ophthalmic Lenses and Materials Questions and Answers 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 Ophthalmic Lenses and Materials Questions and Answers flashcards as text
Which lens form is said to be in 'best form' (corrected curve) configuration?
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.
In a toric lens, the two principal meridians are always:
Answer: Perpendicular to each other
A toric surface has two principal meridians of maximum and minimum curvature that are always 90° apart.
What is the purpose of an 'edging allowance' when ordering a lens blank?
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.
Minus lenses are thicker at the:
Answer: Edge (periphery)
Minus (concave) lenses are thinnest at the center and increase in thickness toward the edges.
What is 'lens clock' (lens measure) used to measure?
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.
Which of the following best describes 'wraparound' or high-wrap frame considerations for lens power?
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.
When neutralizing a lens using loose trial lenses, the lens is considered neutralized when:
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.