ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 4

Question 1

In ophthalmic lens terminology, what is the 'optical center' of a lens?

Accepted Answer

The point through which light passes without prismatic deviation

Answer

The optical center is the point on a lens through which a ray passes without being deviated by prism.

Question 2

Prentice's Rule states that prismatic effect equals:

Accepted Answer

Decentration (cm) multiplied by Power (D)

Answer

Prentice's Rule: Prism (Δ) = Decentration (cm) × Power (D), where decentration is in centimeters.

Question 3

What distinguishes a 'fused' bifocal segment from a 'solid' bifocal?

Accepted Answer

Fused bifocals use a different plastic for the segment; solid bifocals are ground from one piece

Answer

Fused bifocals embed a higher-index glass segment into the main lens blank, while solid (one-piece) bifocals are ground entirely from a single blank.

Question 4

What is the effect of increasing the pantoscopic tilt of a frame on the effective optical power experienced by the wearer?

Accepted Answer

It increases effective sphere power and induces cylinder at the horizontal meridian

Answer

Pantoscopic tilt tilts the optical axis downward, effectively increasing sphere power and inducing oblique cylinder.

Question 5

Which lens treatment absorbs UV radiation up to 400 nm and is considered full UV protection?

Accepted Answer

UV400 coating

Answer

UV400 coatings block all ultraviolet radiation up to 400 nm, encompassing both UVA and UVB wavelengths.

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