ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials 2

Question 1

Which lens material has the highest Abbe value among commonly used ophthalmic plastics?

Accepted Answer

CR-39 (Allyl diglycol carbonate)

Answer

CR-39 has an Abbe value of approximately 58, the highest among common ophthalmic plastic materials, meaning it produces the least chromatic aberration.

Question 2

A patient's prescription is -8.00 DS. Which lens material would BEST minimize edge thickness?

Accepted Answer

High-index 1.74

Answer

High-index 1.74 has the highest index of refraction among common ophthalmic materials, bending light most efficiently and producing the thinnest lenses for high minus prescriptions.

Question 3

What is the primary optical disadvantage of polycarbonate lenses compared to CR-39?

Accepted Answer

Lower Abbe value causing chromatic aberration

Answer

Polycarbonate has an Abbe value of about 30, significantly lower than CR-39's 58, meaning it disperses light into its spectral components more, causing chromatic aberration (color fringing).

Question 4

An aspheric lens design primarily reduces which aberration compared to a spheric lens?

Accepted Answer

Marginal astigmatic error (oblique astigmatism)

Answer

Aspheric lens designs flatten the peripheral curves to reduce oblique astigmatic error (marginal astigmatic error), improving peripheral vision quality.

Question 5

What does the term 'specific gravity' indicate about a lens material?

Accepted Answer

Its density relative to water, affecting lens weight

Answer

Specific gravity is the ratio of a material's density to that of water; materials with lower specific gravity produce lighter lenses for greater patient comfort.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials 2