NOCE Ophthalmic Products and Materials 2 — Questions and Answers
Question 1: Which lens material has the highest Abbe value, indicating the least chromatic aberration?
- Polycarbonate
- Trivex
- Crown glass (Correct answer)
- High-index 1.74
Correct answer: Crown glass
Crown glass has an Abbe value of approximately 59, the highest among common ophthalmic materials, meaning it produces the least chromatic aberration.
Question 2: A patient needs lenses with maximum impact resistance for safety eyewear. Which material is the BEST choice?
- CR-39
- Crown glass
- Polycarbonate (Correct answer)
- High-index 1.67
Correct answer: Polycarbonate
Polycarbonate is the most impact-resistant ophthalmic lens material and is the standard for safety eyewear and ANSI Z87.1 compliance.
Question 3: What is the primary advantage of Trivex over polycarbonate for ophthalmic lenses?
- Higher impact resistance
- Greater thinness at high prescriptions
- Higher Abbe value and better optical clarity (Correct answer)
- Lower cost
Correct answer: Higher Abbe value and better optical clarity
Trivex has an Abbe value of about 45 compared to polycarbonate's 30, providing significantly better optical clarity and less chromatic aberration.
Question 4: Which anti-reflective coating layer is responsible for bonding the AR stack to the lens surface?
- Top coat
- Hard coat
- Adhesion layer (Correct answer)
- Multi-layer stack
Correct answer: Adhesion layer
The adhesion layer (base layer) chemically bonds the AR coating stack to the lens substrate, ensuring durability of the entire coating system.
Question 5: A photochromic lens that does not darken adequately in a car is most likely because:
- The lens is defective
- UV light is blocked by the windshield (Correct answer)
- The temperature is too high
- The lens material is too thin
Correct answer: UV light is blocked by the windshield
Modern automotive windshields block UV radiation, which is required to activate photochromic dye molecules, preventing the lenses from darkening inside a vehicle.
Question 6: Which lens treatment is MOST effective at reducing glare from wet roads for a driver?
- Anti-reflective coating
- Polarized lenses (Correct answer)
- Photochromic lenses
- UV 400 coating
Correct answer: Polarized lenses
Polarized lenses eliminate horizontally polarized light that creates glare from flat reflective surfaces like wet roads, water, and snow.
Question 7: A scratch-resistant coating on a CR-39 lens primarily increases the lens's resistance to scratching by:
- Increasing lens thickness
- Applying a hard silicone-based layer (Correct answer)
- Chemically bonding metal oxides
- Increasing the refractive index
Correct answer: Applying a hard silicone-based layer
Scratch-resistant (hard) coatings typically use silicone-based compounds applied via dip or spin coating to create a harder surface layer on plastic lenses.
NOCE Ophthalmic Products and Materials 2
Which lens material has the highest Abbe value, indicating the least chromatic aberration?