NBEO Optics & Lens Design 2

Question 1

What is anti-reflective (AR) coating on lenses?

Accepted Answer

A multi-layer thin-film coating that reduces light reflection from lens surfaces, improving visual clarity, reducing glare, and enhancing cosmetic appearance

Answer

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?

Accepted Answer

Lens material with a higher refractive index that bends light more efficiently, allowing thinner and lighter lenses for strong prescriptions

Answer

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?

Accepted 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

Answer

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?

Accepted Answer

A lens containing molecules that darken when exposed to UV light and return to clear indoors

Answer

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?

Accepted Answer

The point on the lens through which light passes without being deviated by prismatic effect, which must align with the patient's pupil

Answer

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.

NBEO - National Board of Examiners in Optometry Practice Test

NBEO - National Board of Examiners in Optometry Practice Test

NBEO Optics & Lens Design 2