ABO NOCE Basic Opticianry Lens Coatings and Treatments 4 — Questions and Answers
Question 1: A patient reports that their anti-reflective coated lenses look smudged almost immediately after cleaning. What is the most likely cause?
- The AR coating has delaminated
- The patient is using a silicone-based cleaner incompatible with AR coating (Correct answer)
- The lens substrate is too hydrophilic
- The patient has an oily skin condition causing abnormal sebum transfer
Correct answer: The patient is using a silicone-based cleaner incompatible with AR coating
Silicone-based or alcohol-based cleaners can break down the hydrophobic top coat on AR lenses, making them attract oils and smear more easily.
Question 2: Which property of a photochromic lens determines how dark it becomes in sunlight?
- The index of refraction of the lens material
- The concentration and type of photochromic molecules embedded in the lens (Correct answer)
- The thickness of the anti-reflective coating applied over the photochromic layer
- The base curve of the lens
Correct answer: The concentration and type of photochromic molecules embedded in the lens
The darkening depth of photochromic lenses depends on the density and chemical nature of the silver halide or organic photochromic molecules within the lens.
Question 3: A scratch-resistant coating is best described as:
- A coating that makes lenses completely scratchproof
- A hard surface treatment that reduces but does not eliminate lens scratching (Correct answer)
- A UV-absorbing polymer layer applied to the front surface only
- A chemical treatment that restores scratched lenses to their original clarity
Correct answer: A hard surface treatment that reduces but does not eliminate lens scratching
Scratch-resistant coatings increase surface hardness to reduce scratching but cannot make a lens completely impervious to abrasion.
Question 4: What is the primary purpose of a hydrophobic (water-repellent) top coat applied over an AR coating?
- To increase the UV protection of the lens
- To improve impact resistance of the lens
- To make the lens surface easier to clean by causing water to bead and roll off (Correct answer)
- To darken the lens in UV light like a photochromic treatment
Correct answer: To make the lens surface easier to clean by causing water to bead and roll off
Hydrophobic top coats reduce the surface energy of the lens so water beads up and rolls off rather than spreading, keeping the lens cleaner.
Question 5: When dispensing AR-coated lenses to a patient who works in a kitchen, which additional coating property is most important to recommend?
- High UV protection factor
- Oleophobic (oil-repellent) properties (Correct answer)
- Polarization
- Blue light filtering
Correct answer: Oleophobic (oil-repellent) properties
Kitchen workers are frequently exposed to cooking oils and grease, making an oleophobic coating critical to maintaining lens cleanliness.
Question 6: A patient's photochromic lenses do not darken adequately when driving. What is the most likely explanation?
- The lenses are outdated and the photochromic molecules have degraded
- Automotive windshields block most UV light, which is required to activate photochromic lenses (Correct answer)
- The lenses were manufactured with insufficient photochromic dye concentration
- Cold temperatures inhibit the photochromic reaction
Correct answer: Automotive windshields block most UV light, which is required to activate photochromic lenses
Standard automotive windshields are laminated with UV-blocking interlayers, preventing the UV light needed to trigger photochromic darkening from reaching the lenses.
Question 7: Which statement about mirror coatings on sunglass lenses is TRUE?
- Mirror coatings replace the need for a tinted lens substrate
- Mirror coatings are applied to the back surface of the lens to reduce reflections
- Mirror coatings are thin metallic films vacuum-deposited on the front lens surface (Correct answer)
- Mirror coatings increase the UV protection beyond 100%
Correct answer: Mirror coatings are thin metallic films vacuum-deposited on the front lens surface
Mirror coatings are applied via vacuum deposition (sputtering) as a thin metallic or dielectric film on the front surface of the lens to reflect light away.
ABO NOCE Basic Opticianry Lens Coatings and Treatments 4
A patient reports that their anti-reflective coated lenses look smudged almost immediately after cleaning.
What is the most likely cause?