Plastic Lens Materials

Question 1

CR39 (Essilor Orma)

Answer 1

N Value = 1.498
V Value = 58
Specific Gravity = 1.32
CVF = 1.05
Reflectance = 3.97%
UV cut off = 355nm

Question 2

Key features and benefits of CR39

Answer 2

• Excellent Optics
• Low cost
• Easy to tint
• Lowest reflectance so doesnt need MAR

Question 3

Disadvantages of CR39

Answer 3

• Thickness
• Shatters under high impact into hooked shards
• Not very scratch resistant

Question 4

Trivex

Answer 4

N value = 1.53
V value = 45
Specific Gravity = 1.11
CVF = 0.99
Reflectance = 4.39%
UV Cut off = 400nm

Question 5

Key features and Benefits of Trivex

Answer 5

• High impact resistance
• Blocks 100% of UVA & UVB
• Higher V value than polycarbonate
• Lightest lens material available
• Good chem resistance

Question 6

Disadvantages of Trivex

Answer 6

• Tinting not possible
• Slightly thicker than polycarbonate
• Scratches easily
• Difficult to glaze

Question 7

Polycarbonate (Essilor airwear)

Answer 7

N = 1.59
V Value = 30
Specific Gravity = 1.21
CVF = 0.89
Reflectance - 5.19% 
UV Cut off = 385nm

Question 8

Key features and 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 as you can drill into it and cut grooves

Question 9

Disavantages of Polycarbonate

Answer 9

• Not good for chem resistance - if used with acetone, lens goes milky
• Low V value means more dispersion
• Not very scratch resistant
• Difficult to tint

Question 10

1.6 Plastic (Essilor Ormix)

Answer 10

N = 1.60
V Value = 42
Specific Gravity = 1.30
CVF = 0.87 
Reflectance = 5.33% 
UV Cut off = 395nm

Question 11

Key features and Benefits of 1.6 Plastic

Answer 11

• Thin and lightweight
• Less costly than 1.74 plastic
• Good UV protection

Question 12

Disadvantages of 1.6 Plastic

Answer 12

• Low V value
• Difficult to tint
• Flatter so more reflections (MAR coated)

Question 13

1.67 Plastic (Essilor Stylis)

Answer 13

N = 1.67
V Value = 32
Specific Gravity = 1.36
CVF = 0.78
Reflectance = 6.29%
UV Cut off = 395nm

Question 14

Key features and Benefits of 1.67 Plastic

Answer 14

• Cheaper than 1.74
• Good UV protection
• Thin

Question 15

Disadvantages of 1.67 Plastic

Answer 15

• Low V value
• Diff to tint
• Flatter so more reflections (MAR coated)

Question 16

1.74 Plastic (Essilor Lineis)

Answer 16

N = 1.74
V Value = 32
Specific Gravity = 1.46
CVF = 0.71
Reflectance = 7.29% 
UV Cut off = 395nm

Question 17

Key features and Benefits of 1.74 Plastic

Answer 17

Thinnest readily available plastic lens (1.76 lenses are available)

Question 18

Disadvantages of 1.74 Plastic

Answer 18

• Diff to tint

- Low V value causes increased dispersion and TCA