ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 2 — Questions and Answers
Question 1: Which lens material has the highest Abbe value among commonly used ophthalmic plastics?
- Polycarbonate
- CR-39 (Correct answer)
- Trivex
- High-index 1.74
Correct answer: CR-39
CR-39 has the highest Abbe value (~58) among common plastics, meaning it produces the least chromatic aberration.
Question 2: 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?
- -8.00 D (Correct answer)
- +4.00 D
- -6.00 D
- +8.00 D
Correct answer: -8.00 D
Back surface power = total power − front power = -2.00 − (+6.00) = -8.00 D.
Question 3: What is the primary advantage of Trivex over polycarbonate for ophthalmic use?
- Higher refractive index
- Greater optical clarity (higher Abbe value) (Correct answer)
- Lower cost
- Greater thickness reduction
Correct answer: Greater optical clarity (higher Abbe value)
Trivex has an Abbe value around 45 compared to polycarbonate's ~30, resulting in better optical clarity.
Question 4: In a progressive addition lens, the 'corridor' refers to which region?
- The reading zone at the bottom
- The distance zone at the top
- The channel of usable power between distance and near zones (Correct answer)
- The peripheral blending area
Correct 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.
Question 5: Which coating reduces glare from light sources at night and is especially beneficial for driving?
- UV-absorbing coating
- Anti-reflective (AR) coating (Correct answer)
- Mirror coating
- Photochromic tint
Correct answer: Anti-reflective (AR) coating
AR coatings eliminate surface reflections, significantly reducing glare and halos around lights during nighttime driving.
Question 6: What does 'sagitta' (sag) describe in ophthalmic lens geometry?
- The lens diameter
- The depth of a curved surface measured from its chord (Correct answer)
- The optical center location
- The edge thickness of the lens
Correct 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.
Question 7: A patient requires +3.00 DS lenses. Which material would produce the thinnest lens for a typical frame?
- CR-39 (n=1.50)
- Polycarbonate (n=1.586)
- High-index 1.67
- High-index 1.74 (Correct answer)
Correct answer: High-index 1.74
Higher refractive index materials bend light more per unit thickness, so n=1.74 produces the thinnest plus lenses.
ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 2
Which lens material has the highest Abbe value among commonly used ophthalmic plastics?