ABO NOCE Basic Opticianry Lens Coatings and Treatments 1 — Questions and Answers
Question 1: What is the primary purpose of an anti-reflective (AR) coating on ophthalmic lenses?
- To eliminate surface reflections, improve light transmission, and reduce glare (Correct answer)
- To protect lenses from scratches and surface abrasions
- To block ultraviolet radiation from reaching the eye
- To darken the lens automatically in bright sunlight
Correct answer: To eliminate surface reflections, improve light transmission, and reduce glare
AR coating uses destructive interference to cancel surface reflections, allowing more light to pass through the lens and significantly reducing glare for the wearer.
Question 2: Which type of lens treatment darkens when exposed to ultraviolet (UV) radiation and returns to clear when indoors?
- Polarized
- Photochromic (Correct answer)
- Mirror-coated
- Anti-reflective
Correct answer: Photochromic
Photochromic lenses contain photochromic molecules that change shape when activated by UV light, causing the lens to darken, and revert to clear when UV exposure is removed.
Question 3: What is the approximate percentage of light lost due to reflection on each uncoated CR-39 lens surface?
- 1%
- 4% (Correct answer)
- 8%
- 12%
Correct answer: 4%
Each uncoated CR-39 lens surface reflects approximately 4% of incoming light due to the refractive index difference at the air-lens interface, totaling about 8% across both surfaces.
Question 4: Which lens coating is applied primarily to repel water, smudges, and fingerprints from the lens surface?
- Anti-reflective coating
- Hard coat
- Hydrophobic/oleophobic coating (Correct answer)
- UV absorbing coating
Correct answer: Hydrophobic/oleophobic coating
Hydrophobic coatings repel water while oleophobic coatings repel oils; applied as the outermost layer on AR-coated lenses, they resist smudges, fingerprints, and water spots.
Question 5: What is the function of a scratch-resistant hard coat applied to plastic ophthalmic lenses?
- Blocks UV radiation from reaching the eye
- Increases the refractive index of the lens material
- Provides a more durable surface to resist surface abrasions (Correct answer)
- Changes tint density based on ambient light conditions
Correct answer: Provides a more durable surface to resist surface abrasions
Hard coats are thin, chemically bonded layers applied to plastic lenses to increase surface hardness and resistance to scratching, significantly extending the usable life of the lens.
Question 6: According to ANSI Z80.3, UV-absorbing ophthalmic lenses should block radiation up to which wavelength to provide complete UV protection?
- 280 nm
- 315 nm
- 380 nm
- 400 nm (Correct answer)
Correct answer: 400 nm
ANSI Z80.3 specifies that ophthalmic lenses should block UV radiation up to 400 nm to protect against both UV-B (280–315 nm) and UV-A (315–400 nm) radiation.
Question 7: Which statement best describes how a polarized lens reduces glare?
- It darkens automatically when exposed to bright light
- It filters out light waves vibrating in the horizontal plane to reduce reflected glare (Correct answer)
- It applies multiple thin layers to eliminate surface reflections
- It has a gradient tint that is darker at the top than the bottom
Correct answer: It filters out light waves vibrating in the horizontal plane to reduce reflected glare
Polarized lenses contain a chemical film oriented to block horizontally polarized light, which is the primary component of glare reflected from flat surfaces like water, roads, and snow.
ABO NOCE Basic Opticianry Lens Coatings and Treatments 1
What is the primary purpose of an anti-reflective (AR) coating on ophthalmic lenses?