Lens Material and Design

Question 1

What does an Abbe value measure?

Answer 1

An Abbe value is a measure of the amount of aberration in a material. The higher the abbe value, the lower the aberration.

Question 2

Which is a better product, a lens with a low Abbe value or a lens with a high Abbe value?

Answer 2

A lens with a high Abbe value will be clearer and have less aberrations, so it will be better.

Question 3

What is the name of the instrument used to check to see if a glass lens has been heat treated?

Answer 3

It is called both a colmascope and a polariscope.

Question 4

True or false: Crown glass lenses have UV protection inherent in the material and don’t need additional UV coatings.

Answer 4

False

Question 5

Arrange the following materials from most UV protection to least UV protection: Crown glass, CR-39 with trans, Poly, Clear CR-39

Answer 5

Poly, CR-39 with trans, CR-39, Crown glass

Question 6

True or false: Listing a lens material as part of the script is inappropriate.

Answer 6

False

Question 7

What do you look for when you are trying to determine which lens material would be the thinnest?

Answer 7

Index of refraction - the higher the index of refraction, the thinner the lens

Question 8

Which lens characteristic will tell you how much chromatic aberration a lens will have?

Answer 8

Abbe Value

Question 9

What is chromatic aberration?

Answer 9

Color distortion due to the material when light passes through it; dispersion of light

Question 10

True or false: Polycarbonate is the softest spectacle material.

Answer 10

True - Because it’s soft, it’s used for safety and sports lenses, but it also scratches easier

Question 11

How are glass lenses hardened?

Answer 11

Heat treating is done in two to three minutes in a small furnace. Chemical treating is done by immersing lenses in a molten salt.

Question 12

What does product liability mean for eyewear types? Be specific for eyewear types.

Answer 12

Product liability is when the product was not up to accepted standards. Dress eyewear must pass the drop ball test. Safety eyewear must past Z87 requirements and thickness standards. Sports eyewear must past impact resistance and specific requirements for the sport in question.

Question 13

How long does the FDA require that you keep a patient’s file?

Answer 13

3 years

Question 14

True or False: Since the lab takes full responsibility for the accuracy of safety and sports eyewear, verification of lens thickness by the dispenser is unnecessary.

Answer 14

False

Question 15

The FTC established Eyeglass I in 1978 and Eyeglass II in 1989. What is the difference between them?

Answer 15

Eyeglass I is the rx release rule and lists minimum info to be included in the rx. Eyeglass II no longer lists minimum info needed to make spectacle rx’s.

Question 16

What does the FDA regulate for opticianry (excluding contact lenses) and when did they start doing it?

Answer 16

Impact resistance in 1971.

Question 17

True or false: Both scratch resistant and AR coatings are harder than the plastic lens material they are adhered to.

Answer 17

True

Question 18

True or false: the harder the material the more impact resistant it will be.

Answer 18

False

Question 19

Which of the following glass lenses is exempt from the drop ball test? Slab-off lenses, cataract lenses, or custom laminate lenses.

Answer 19

All of the above are exempt.

Question 20

If the following four materials were used to make lenses with the exact same curves and thickness, which lens would be the heaviest? Poly, CR-39, Hi Index Resin 1.60, Crown glass

Answer 20

Crown glass

Question 21

True or false: A lens for safety glasses must be 3.0 mm thick if it is CR-39 or glass, but if it is poly the thickness must be at least 2.0mm.

Answer 21

False - Poly is the only lens material used for safety glasses