Ophthalmic Lenses and Materials 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 flashcards as text
Which lens material has the highest Abbe value among commonly used ophthalmic plastics?
Answer: CR-39 (Allyl diglycol carbonate)
CR-39 has an Abbe value of approximately 58, the highest among common ophthalmic plastic materials, meaning it produces the least chromatic aberration.
A patient's prescription is -8.00 DS. Which lens material would BEST minimize edge thickness?
Answer: High-index 1.74
High-index 1.74 has the highest index of refraction among common ophthalmic materials, bending light most efficiently and producing the thinnest lenses for high minus prescriptions.
What is the primary optical disadvantage of polycarbonate lenses compared to CR-39?
Answer: Lower Abbe value causing chromatic aberration
Polycarbonate has an Abbe value of about 30, significantly lower than CR-39's 58, meaning it disperses light into its spectral components more, causing chromatic aberration (color fringing).
An aspheric lens design primarily reduces which aberration compared to a spheric lens?
Answer: Marginal astigmatic error (oblique astigmatism)
Aspheric lens designs flatten the peripheral curves to reduce oblique astigmatic error (marginal astigmatic error), improving peripheral vision quality.
What does the term 'specific gravity' indicate about a lens material?
Answer: Its density relative to water, affecting lens weight
Specific gravity is the ratio of a material's density to that of water; materials with lower specific gravity produce lighter lenses for greater patient comfort.
Which coating is applied FIRST directly to the lens substrate during the manufacturing process?
Answer: Hard coat (scratch-resistant coating)
Hard coat (scratch-resistant coating) is applied directly to the lens substrate first, providing a durable base layer before any anti-reflective or other coatings are applied.
Which lens type would you recommend for a patient who needs both distance and near correction but refuses bifocals for cosmetic reasons?
Answer: Progressive addition lenses (PALs)
Progressive addition lenses (PALs) provide a seamless transition from distance to near correction without visible lines, making them the cosmetically preferred alternative to bifocals.