ABO NOCE Basic Opticianry Ophthalmic Products and Materials 2 — Questions and Answers
Question 1: Which lens material has the highest Abbe value among commonly used ophthalmic plastics?
- CR-39 (Allyl diglycol carbonate) (Correct answer)
- Polycarbonate
- Trivex
- High-index 1.74
Correct answer: CR-39 (Allyl diglycol carbonate)
CR-39 has an Abbe value of approximately 58, the highest among common ophthalmic plastic materials, indicating the least chromatic aberration.
Question 2: A patient reports their anti-reflective coated lenses show a persistent colored sheen even after cleaning. This most likely indicates:
- Normal thin-film interference from the AR coating
- A delaminating or deteriorating AR coating (Correct answer)
- Excessive UV absorption
- Incorrect lens material for the coating
Correct answer: A delaminating or deteriorating AR coating
A persistent or irregular colored sheen after cleaning suggests the AR coating is delaminating or degrading and the lenses should be replaced.
Question 3: What is the primary purpose of a hard coat applied to plastic ophthalmic lenses?
- Reduce ultraviolet light transmission
- Improve scratch resistance (Correct answer)
- Enhance anti-reflective properties
- Increase impact resistance
Correct answer: Improve scratch resistance
Hard coats are applied to plastic lenses to improve scratch resistance, since most plastics are inherently softer than glass.
Question 4: Which frame material is most commonly associated with nickel allergy reactions in patients?
- Titanium
- Monel (Correct answer)
- Beta titanium
- Aluminum
Correct answer: Monel
Monel, a nickel-copper alloy widely used in eyewear frames, is the most common source of nickel contact dermatitis in optical patients.
Question 5: High-index lenses with an index of 1.74 compared to CR-39 (1.50) will produce lenses that are:
- Thicker and lighter
- Thinner but heavier (Correct answer)
- Thinner and lighter
- Same thickness but more impact resistant
Correct answer: Thinner but heavier
While high-index 1.74 lenses are significantly thinner, the denser material makes them heavier than CR-39 lenses of equivalent prescription.
Question 6: A progressive addition lens (PAL) is ordered with a +2.00 add. What is the purpose of the 'corridor' in a PAL?
- To provide the distance prescription zone
- To create a gradual transition zone between distance and near powers (Correct answer)
- To increase the width of the reading area
- To reduce peripheral distortion
Correct answer: To create a gradual transition zone between distance and near powers
The corridor in a PAL is the progressive zone through which power gradually increases from the distance prescription to the full near addition power.
Question 7: Which lens treatment blocks wavelengths below approximately 380nm to protect against UV radiation?
- Anti-reflective coating
- Mirror coating
- UV400 treatment (Correct answer)
- Photochromic treatment
Correct answer: UV400 treatment
UV400 treatment blocks all ultraviolet light up to 400nm wavelength, providing comprehensive UV protection for the eye.
ABO NOCE Basic Opticianry Ophthalmic Products and Materials 2
Which lens material has the highest Abbe value among commonly used ophthalmic plastics?