Free NOCE Ophthalmic Products and Materials Questions and Answers — Questions and Answers
Question 1: A patient who works in a manufacturing plant requires safety glasses. According to the ANSI Z87.1 standard for high-velocity impact, the lens must resist an impact from a 1/4-inch steel ball traveling at what minimum speed?
- 100 feet per second
- 150 feet per second (Correct answer)
- 200 feet per second
- 250 feet per second
Correct answer: 150 feet per second
The ANSI Z87.1 high-velocity impact test, a requirement for the Z87+ marking, specifies that a safety lens must withstand the impact of a 1/4-inch (6.35mm) steel ball fired at a speed of 150 feet per second (45.7 m/s) without fracturing or allowing the ball to penetrate.
Question 2: An optician is explaining the benefits of Trivex lenses to a parent for their child's new glasses. Which of the following sets of properties best describes the advantages of Trivex material?
- Highest scratch resistance, lowest specific gravity, and highest Abbe value.
- Highest index of refraction, superior tintability, and moderate impact resistance.
- High impact resistance, low specific gravity, and excellent optical clarity (high Abbe value). (Correct answer)
- Lowest cost, moderate optical clarity, and highest index of refraction.
Correct answer: High impact resistance, low specific gravity, and excellent optical clarity (high Abbe value).
Trivex material is renowned for its 'trio' of performance properties: high impact resistance (comparable to polycarbonate), very low specific gravity (making it the lightest common lens material), and excellent optical clarity due to a high Abbe value (around 43-45), which minimizes chromatic aberration.
Question 3: A patient complains about annoying reflections on their lenses, especially during video calls and when driving at night. Which lens treatment is specifically designed to minimize these reflections and increase the amount of light passing through the lens?
- Photochromic treatment
- Scratch-resistant coating
- UV coating
- Anti-reflective coating (Correct answer)
Correct answer: Anti-reflective coating
Anti-reflective (AR) coating consists of multiple microscopic layers of metallic oxides applied to the lens surfaces. These layers use the principle of destructive interference to cancel out reflected light waves, allowing more light (up to 99%) to transmit through the lens, which enhances visual acuity and reduces distracting glare and reflections.
Question 4: Photochromic lenses darken when exposed to sunlight. What is the primary trigger for this change in modern plastic photochromic lenses?
- Exposure to infrared (IR) radiation
- A change in ambient temperature
- Exposure to ultraviolet (UV) radiation (Correct answer)
- Reaction to visible light intensity
Correct answer: Exposure to ultraviolet (UV) radiation
Modern plastic photochromic lenses contain proprietary dyes with molecules that undergo a reversible chemical reaction when exposed to ultraviolet (UV) radiation. This reaction causes the molecules to change shape, allowing them to absorb visible light and making the lenses darken. The process reverses when UV light is no longer present.
Question 5: When comparing two finished lenses of the exact same power and size, which material property is the primary determinant of the lens's final weight?
- Abbe value
- Specific gravity (Correct answer)
- Index of refraction
- ANSI impact rating
Correct answer: Specific gravity
Specific gravity is the measure of a material's density relative to the density of water. For a given volume, a material with a lower specific gravity will be lighter. Therefore, when comparing two lenses of identical dimensions, the one made from the material with the lower specific gravity (e.g., Trivex at 1.11 g/cm³) will weigh less than one made from a material with a higher specific gravity (e.g., Crown Glass at 2.54 g/cm³).
Question 6: A patient with a high plus prescription complains that their current spherical lenses make their eyes look magnified and cause visual distortions at the edges of the glasses. Which lens design would be most effective at reducing these effects?
- Aspheric design (Correct answer)
- Slab-off design
- Atoric design
- Spherical design
Correct answer: Aspheric design
Aspheric lenses have a more complex surface profile that gradually flattens from the center to the edge. This design reduces spherical aberrations, providing sharper peripheral vision. For high plus lenses, it also significantly reduces the magnification effect that makes the wearer's eyes appear larger, resulting in a better cosmetic appearance and improved visual quality.
Free NOCE Ophthalmic Products and Materials Questions and Answers
A patient who works in a manufacturing plant requires safety glasses.
According to the ANSI Z87.1 standard for high-velocity impact, the lens must resist an impact from a 1/4-inch steel ball traveling at what minimum speed?