FREE NOCE Ophthalmic Products and Materials 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?

Accepted Answer

150 feet per second

Answer

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?

Accepted Answer

High impact resistance, low specific gravity, and excellent optical clarity (high Abbe value).

Answer

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?

Accepted Answer

Anti-reflective coating

Answer

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?

Accepted Answer

Exposure to ultraviolet (UV) radiation

Answer

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?

Accepted Answer

Specific gravity

Answer

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).

NOCE - National Opticianry Competency Examination Practice Test

NOCE - National Opticianry Competency Examination Practice Test

FREE NOCE Ophthalmic Products and Materials Questions and Answers