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 material has the highest Abbe value among commonly used ophthalmic plastics?
Answer: CR-39
CR-39 has the highest Abbe value (~58) among common plastics, meaning it produces the least chromatic aberration.
A lens with a base curve of +6.00 D and a front surface power of +6.00 D has what back surface power if the lens is -2.00 D?
Answer: -8.00 D
Back surface power = total power − front power = -2.00 − (+6.00) = -8.00 D.
What is the primary advantage of Trivex over polycarbonate for ophthalmic use?
Answer: Greater optical clarity (higher Abbe value)
Trivex has an Abbe value around 45 compared to polycarbonate's ~30, resulting in better optical clarity.
In a progressive addition lens, the 'corridor' refers to which region?
Answer: The channel of usable power between distance and near zones
The corridor (or progressive zone) is the narrow channel connecting the distance and near portions where power gradually increases.
Which coating reduces glare from light sources at night and is especially beneficial for driving?
Answer: Anti-reflective (AR) coating
AR coatings eliminate surface reflections, significantly reducing glare and halos around lights during nighttime driving.
What does 'sagitta' (sag) describe in ophthalmic lens geometry?
Answer: The depth of a curved surface measured from its chord
Sagitta is the perpendicular distance from the midpoint of a chord to the curved surface, used to calculate lens thickness.
A patient requires +3.00 DS lenses. Which material would produce the thinnest lens for a typical frame?
Answer: High-index 1.74
Higher refractive index materials bend light more per unit thickness, so n=1.74 produces the thinnest plus lenses.