NBEO Optics & Lens Design 2 — Questions and Answers
Question 1: What is anti-reflective (AR) coating on lenses?
- A multi-layer thin-film coating that reduces light reflection from lens surfaces, improving visual clarity, reducing glare, and enhancing cosmetic appearance (Correct answer)
- A scratch-resistant coating
- A UV-blocking tint
- A water-repellent treatment
Correct answer: A multi-layer thin-film coating that reduces light reflection from lens surfaces, improving visual clarity, reducing glare, and enhancing cosmetic appearance
AR coatings use thin layers of metal oxides that cause destructive interference of reflected light, increasing light transmission through the lens from ~92% to ~99%, reducing ghost images and improving night driving vision.
Question 2: What is high-index lens material?
- Lens material with a higher refractive index that bends light more efficiently, allowing thinner and lighter lenses for strong prescriptions (Correct answer)
- A lens material for children only
- The cheapest lens option
- A lens that blocks blue light
Correct answer: Lens material with a higher refractive index that bends light more efficiently, allowing thinner and lighter lenses for strong prescriptions
High-index materials (1.67, 1.74) bend light more per unit of thickness than standard materials (1.50 CR-39), allowing significantly thinner and lighter lenses for high prescriptions, improving comfort and cosmetics.
Question 3: What is vertex distance and why does it matter?
- The distance from the back surface of a spectacle lens to the front of the cornea, which affects the effective power of the lens (Correct answer)
- The distance between a patient's two eyes
- The thickness of the lens at its center
- The focal length of the lens
Correct answer: The distance from the back surface of a spectacle lens to the front of the cornea, which affects the effective power of the lens
Vertex distance (typically 12-14mm) affects effective lens power. For prescriptions over ±4.00D, changes in vertex distance require power adjustment. Contact lens prescriptions must be adjusted from spectacle prescriptions for this reason.
Question 4: What is a photochromic lens?
- A lens containing molecules that darken when exposed to UV light and return to clear indoors (Correct answer)
- A lens that permanently changes color
- A prescription for nearsightedness
- A type of progressive lens
Correct answer: A lens containing molecules that darken when exposed to UV light and return to clear indoors
Photochromic lenses (like Transitions) contain silver halide or organic photochromic molecules that reversibly darken in response to UV radiation, providing convenient sun protection that adapts to lighting conditions.
Question 5: What is the optical center of a lens?
- The point on the lens through which light passes without being deviated by prismatic effect, which must align with the patient's pupil (Correct answer)
- The physical center of the lens
- The thickest part of the lens
- The point where the lens is mounted in the frame
Correct answer: The point on the lens through which light passes without being deviated by prismatic effect, which must align with the patient's pupil
The optical center must be positioned precisely at the patient's pupillary distance (PD) and height. Misalignment induces unwanted prismatic effect, causing eyestrain, headaches, and potentially diplopia.
Question 6: What is blue light filtering in ophthalmic lenses?
- Lens treatments or materials that selectively filter high-energy visible (blue) light from digital screens and sunlight (Correct answer)
- A coating that makes lenses appear blue
- A type of UV protection
- A test for color blindness
Correct answer: Lens treatments or materials that selectively filter high-energy visible (blue) light from digital screens and sunlight
Blue light filtering lenses reduce transmission of 400-450nm wavelength light, which is emitted by digital devices and LED lighting. They may reduce digital eye strain, though research on their effectiveness continues to evolve.
NBEO Optics & Lens Design 2
What is anti-reflective (AR) coating on lenses?