ABO NOCE Basic Opticianry Lens Coatings and Treatments 5 — Questions and Answers
Question 1: A patient asks why their new AR-coated lenses show a faint green or purple reflection. How should you respond?
- The coating is defective and the lenses should be remade
- This residual reflection is normal and indicates the AR coating is functioning correctly (Correct answer)
- The lenses need an additional UV coating to eliminate the color
- The reflection indicates the lens index is too high for AR coating
Correct answer: This residual reflection is normal and indicates the AR coating is functioning correctly
A slight residual green or purple reflection is characteristic of a properly applied AR coating and results from the specific wavelengths of light that the multi-layer stack does not fully cancel.
Question 2: What does the Bayer abrasion test measure in the context of lens coatings?
- The UV transmittance through the coating stack
- The relative scratch resistance of a coated lens compared to a standard reference (Correct answer)
- The adhesion strength of the anti-reflective coating to the substrate
- The impact resistance of the coated lens under drop-ball conditions
Correct answer: The relative scratch resistance of a coated lens compared to a standard reference
The Bayer abrasion test tumbles sand or abrasive particles against a lens and measures how much haze develops compared to a reference lens to quantify scratch resistance.
Question 3: Which type of coating is most appropriate for a patient who spends significant time under fluorescent office lighting and reports eyestrain from screens?
- Photochromic treatment
- Blue light filtering (HEV) coating (Correct answer)
- Mirror coating
- Polarized treatment
Correct answer: Blue light filtering (HEV) coating
Blue light (HEV) filtering coatings or treatments selectively reduce high-energy visible light from screens and fluorescent lighting, potentially reducing digital eyestrain.
Question 4: A patient's AR-coated polycarbonate lenses develop a network of fine surface cracks (crazing). What is the most likely cause?
- The patient exposed the lenses to excessive cold temperatures
- The lens was cleaned with a solvent incompatible with the coating, causing differential expansion (Correct answer)
- The AR coating was applied too thickly during manufacturing
- Polarization was added after the AR coating, causing adhesion failure
Correct answer: The lens was cleaned with a solvent incompatible with the coating, causing differential expansion
Solvents such as acetone or certain household cleaners dissolve or swell the coating or substrate differently, creating stress cracks known as crazing.
Question 5: Which standard is commonly referenced in the US for classifying the level of UV protection provided by ophthalmic lenses?
- ISO 8980-3
- ANSI Z87.1
- ANSI Z80.3 (Correct answer)
- FDA 21 CFR Part 801
Correct answer: ANSI Z80.3
ANSI Z80.3 is the US standard for non-prescription sunglasses and covers UV transmittance requirements, while ISO 8980-3 is the international equivalent for ophthalmic lenses.
Question 6: A patient with a high minus prescription is concerned about the thick edge appearance of their lenses. Which coating decision would have NO direct effect on reducing edge thickness?
- Choosing a higher-index lens material
- Applying an anti-reflective coating (Correct answer)
- Using aspheric lens design
- Reducing the frame eye size
Correct answer: Applying an anti-reflective coating
AR coating improves the cosmetic appearance of lens edges optically by reducing reflections but does not change the physical thickness or geometry of the lens.
Question 7: What is the main advantage of a multi-layer AR coating compared to a single-layer AR coating?
- Multi-layer coatings provide 100% elimination of all surface reflections
- Multi-layer coatings reduce reflections across a broader range of wavelengths more effectively (Correct answer)
- Multi-layer coatings are more resistant to UV degradation over time
- Multi-layer coatings can be applied to any lens without adhesion primers
Correct answer: Multi-layer coatings reduce reflections across a broader range of wavelengths more effectively
Each layer in a multi-layer AR stack is optimized for different wavelengths, allowing destructive interference to cancel reflections across a wider visible spectrum than a single layer can achieve.
ABO NOCE Basic Opticianry Lens Coatings and Treatments 5
A patient asks why their new AR-coated lenses show a faint green or purple reflection.
How should you respond?