ABO NOCE Basic Opticianry Ophthalmic Products and Materials Questions and Answers 3 — Questions and Answers
Question 1: Which lens treatment blocks the highest percentage of UV radiation for uncoated lenses without additional coating?
- Polycarbonate lenses (Correct answer)
- CR-39 lenses
- Crown glass lenses
- High-index 1.67 lenses
Correct answer: Polycarbonate lenses
Polycarbonate inherently blocks nearly 100% of UV radiation up to 380nm without any additional UV coating.
Question 2: A scratch-resistant coating on a plastic lens primarily adds hardness by:
- Depositing a thin layer of silica-based compound (Correct answer)
- Increasing the lens base curve
- Adding a metallic oxide layer
- Fusing glass to the plastic surface
Correct answer: Depositing a thin layer of silica-based compound
Scratch-resistant (hard) coatings use silica-based or similar inorganic compounds applied in thin layers to harden the plastic surface.
Question 3: What is the main advantage of Trivex over polycarbonate for ophthalmic use?
- Higher Abbe value (less chromatic aberration) (Correct answer)
- Greater impact resistance
- Lower cost
- Higher refractive index
Correct answer: Higher Abbe value (less chromatic aberration)
Trivex has an Abbe value of approximately 45 compared to polycarbonate's 30, resulting in better optical clarity with less chromatic aberration.
Question 4: A hydrophobic coating on an ophthalmic lens is designed to:
- Repel water and make the lens easier to clean (Correct answer)
- Absorb UV radiation
- Prevent lens fogging
- Increase lens hardness
Correct answer: Repel water and make the lens easier to clean
Hydrophobic (water-repellent) coatings cause water to bead up and roll off, making the lens surface easier to clean and maintain.
Question 5: Which frame material is known for its shape memory properties and returns to its original shape after bending?
- Memory metal (Flexon/titanium alloy) (Correct answer)
- Monel
- Zyl acetate
- Stainless steel
Correct answer: Memory metal (Flexon/titanium alloy)
Memory metal frames (such as Flexon) are made from titanium-nickel alloys that spring back to their original shape after bending.
Question 6: A high-index lens with an index of 1.74 compared to 1.50 CR-39 will be:
- Thinner but heavier per unit volume (Correct answer)
- Thicker and heavier
- Thinner and lighter in all cases
- The same weight but thinner
Correct answer: Thinner but heavier per unit volume
High-index 1.74 lenses are thinner due to higher refractive index but have greater specific gravity, so they are denser per unit volume even though the finished lens may still be lighter due to reduced thickness.
Question 7: What is the purpose of a mirror coating on sunwear lenses?
- Reflect additional light away from the eyes reducing glare (Correct answer)
- Increase UV absorption
- Strengthen lens surface
- Block blue light
Correct answer: Reflect additional light away from the eyes reducing glare
Mirror coatings reflect a portion of visible light away from the lens surface, reducing the amount of light reaching the eye and decreasing glare.
ABO NOCE Basic Opticianry Ophthalmic Products and Materials Questions and Answers 3
Which lens treatment blocks the highest percentage of UV radiation for uncoated lenses without additional coating?