lens material

Question 1

CR39 properties

Answer 1

1.498 RI - moderate
v value- 58 high
specific gravity- 1.32
CVF- 1.05
reflectance- 3.97%
UV cut off- 355nm

Question 2

benefits of cr39

Answer 2

cheap
easy to tint
lowest reflectance so doesn’t need MAR

Question 3

disadvantages

Answer 3

thick due to low n value
shatters under high impact
not scratch resistant

Question 4

trivet properties

Answer 4

n= 1.53
v value= 45
specific gravity= 1.11
CVF= 0.99
reflectance= 4.39%
uv cut off= 400nm

Question 5

benefits of trivex

Answer 5

high impact resistance
blocks 100% of uva and uvb
higher v value than polycarbonate
light lens material

Question 6

disadvantages of trivex

Answer 6

thicker than polycarbonate
scratches easily
not easy to tint
difficult to glaze

Question 7

polycarbonate features

Answer 7

n= 1.59
v value=30
specific gravity= 1.21
cvf= 0.89
reflectance= 5.19%
uv cut off= 385nm

Question 8

benefits of polycarbonate

Answer 8

high impact resistance
lighter than high index plastic lenses
thinner than trivex
good uv protection
thermoplastic- can be remoulded
good for supra and rimless- drill into it

Question 9

disadvantages of polycarbonate

Answer 9

low v value- more dispersion
not chemical resistant
difficult to tint

Question 10

1.6 plastic features

Answer 10

n= 1.6
v value= 42
sg=1.36
cvf= 0.78
reflectance= 5.33%
uv cut off= 395nm

Question 11

1.6 plastic benefits

Answer 11

thin and lightweight
cheaper than 1.74
good uv protection

Question 12

1.6 plastic disadvantages

Answer 12

low v value
difficult to tint
flatter so more reflections

Question 13

1.67 plastic features

Answer 13

n= 1.67
v value= 32
SG= 1.36
CVF=0.78
reflectance= 6.29%
uv cut off= 395nm

Question 14

1.67 benefits

Answer 14

thin
cheaper than 1.74
good uv protection

Question 15

1.67 disadvantages

Answer 15

low v value
difficult to tint
flatter so more reflections

Question 16

1.74 plastic features

Answer 16

n=1.74
v value= 32
sg= 1.46
cvf= 0.71
reflectance= 7.29%
uv cut off= 395nm

Question 17

1.74 plastic benefits

Answer 17

thinnest lens

good uv protection

Question 18

1.74 plastic disadvantages

Answer 18

low v value
difficult to tint
highest sg out of all plastics

Question 19

crown glass features

Answer 19

n=1.523
v value= 59
sg= 2.54
cvf= 1
reflectance= 4.3%
uv cut off= 320nm

Question 20

crown glass benefits

Answer 20

cheap
doesn’t scratch easily
chemical resistant

Question 21

crown glass disadvantages

Answer 21

heavy
brittle
thick for high rx
not impact resistance unless toughened

Question 22

1.7 heavy flint glass

Answer 22

n= 1.706
v value= 39.3
sg=2.93
cvf= 0.74
reflectance= 6.81%
100% uva

Question 23

1.8 heavy flint glass

Answer 23

n= 1.8
v value= 35.4
sg= 3.62
cvf= 0.65
rf= 8.16%
100% uva

Question 24

1.9 heavy flint glass features

Answer 24

n= 1.893
v value= 30.4
sg= 4.0
cvf= 0.59
rf= 9.53%
100% uva