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
In ophthalmic lens terminology, what is the 'optical center' of a lens?
Answer: The point through which light passes without prismatic deviation
The optical center is the point on a lens through which a ray passes without being deviated by prism.
Prentice's Rule states that prismatic effect equals:
Answer: Decentration (cm) multiplied by Power (D)
Prentice's Rule: Prism (Δ) = Decentration (cm) × Power (D), where decentration is in centimeters.
What distinguishes a 'fused' bifocal segment from a 'solid' bifocal?
Answer: Fused bifocals use a different plastic for the segment; solid bifocals are ground from one piece
Fused bifocals embed a higher-index glass segment into the main lens blank, while solid (one-piece) bifocals are ground entirely from a single blank.
What is the effect of increasing the pantoscopic tilt of a frame on the effective optical power experienced by the wearer?
Answer: It increases effective sphere power and induces cylinder at the horizontal meridian
Pantoscopic tilt tilts the optical axis downward, effectively increasing sphere power and inducing oblique cylinder.
Which lens treatment absorbs UV radiation up to 400 nm and is considered full UV protection?
Answer: UV400 coating
UV400 coatings block all ultraviolet radiation up to 400 nm, encompassing both UVA and UVB wavelengths.
A 'slab-off' grind on a lens is used to correct which problem in anisometropic patients?
Answer: Vertical prismatic imbalance at the reading level
Slab-off (bicentric grinding) compensates for vertical prismatic imbalance that occurs when anisometropic patients look down to read.
What does 'specific gravity' indicate when comparing lens materials?
Answer: The material's weight relative to an equal volume of water
Specific gravity is the ratio of a material's density to that of water; lower specific gravity means a lighter lens.