Lens material and design Flashcards
Crown glass
Index of refraction:
Specific gravity (density):
Abbe Value:
1.523
2.54
59
CR-39
Index of refraction:
Specific gravity (density):
Abbe Value:
1.498(1.50)
1.32
58
Polycarbonate
Index of refraction:
Specific gravity (density):
Abbe Value:
1.586
1.22
29-32
TRIVEX
Index of refraction:
Specific gravity (density):
Abbe Value:
1.53
1.11
43-46
NXT
Index of refraction:
Specific gravity (density):
Abbe Value:
1.53
1.11
43-46
Hard Resin 1.67
Index of refraction:
Specific gravity (density):
Abbe Value:
1.67
1.35
32
Which is a better product, a lens with a low Abbe value or a high Abbe value?
High Abbe value
What is the name of the instrument used to check to see if a glass lens has been heat treated?
Colmascope and Polariscope
Crown glass lenses have UV protection inherent in the material and do not need additional UV coatings.
True or false
False
Arrange these lens materials in order starting with the one that has the most UV protection and ending with the one that has the least protection. 1 being the most and 4 being the least.
Crown glass
CR-39 with transitions
Polycarbonate
Clear CR-39
1 polycarbonate
2 CR-39 with transitions
3 Clear CR-39
4 Crown glass
Listing a lens material as part of the eyeglass prescription is inappropriate.
True or false
False
What do you look for when you are trying to determine which lens material would be the thinnest?
Highest index of refraction
Which lens characteristic will tell you how much chromatic aberration a lens will have?
Abbe value
What is chromatic aberration?
Color distortion due to the material when light passes through it, dispersion of light.
Polycarbonate is the softest spectacle lens material.
True or false
True
How are glass lenses hardened? Briefly describe the methods.
Heat treating is done in two to three minutes in a small furnace and chemical treating is done by immersing lenses in molten salt.
How long does the FDA require that you keep a patients file?
3 years
What does product liability mean for opticians? Be specific for eyewear types.
The product was not up to accepted standards.
Dress eyewear: Drop ball test
Safety eyewear: Z87 meets and thickness standards
Sports eyewear: Faulty design, impact resistance, ASTM 803 met when needed.
Since the fabricating laboratory takes full responsibility for the accuracy of safety and sports eyewear, verification of lens thickness by the dispenser is unnecessary.
True or false
False
The Federal Trade Commission established Eyeglasses 1 in 1978 and Eyeglass 2 in 1989. What’s the difference between them?
Eyeglass 1 is the prescription release rule and lists minimum information to be included in the Rx. Eyeglass 2 no longer lists minimum information needed to make spectacle Rxs.
What does the FDA regulate for opticianry (excluding contact lenses) and when did they start doing it?
Impact resistance in 1971
Both scratch-resistance and anti-reflective coatings are harder than the plastic lens material they are adhered to.
True or false
True
The harder the material the more impact resistant it will be.
True or false
False
Which glass lenses is exempt from the drop ball test?
Slab-off lenses
Cataract lenses
Custom laminate lenses
If four lenses were made with the exact same curves and thickness, which lens would be the heaviest?
Crown glass
A lens for safety glasses must be 3.0mm thick if it is CR-39 or glass, but if it is polycarbonate the thickness must be at least 2.0mm.
True or false
False
