lens materials Flashcards Preview

optitcian > lens materials > Flashcards

Flashcards in lens materials Deck (45)
Loading flashcards...
1

index of refraction

index of refraction is, the more it bends (refracts) light—and the thinner the lens can be. That’s why high-index lenses are so thin and lightweight.

2

Refractive Indices of Common Lens Materials


Refractive Indices of Common Lens Materials

Plastic (regular—CR-39)

1.498

Crown glass

1.523

Trivex

1.53

Polycarbonate

1.586

High-index plastic

1.74

3

You’ll often hear people refer to plastic lens materials as what?

CR-39

4

the name of the formula originally used for plastic lenses.
was what?

CR-39

5

plastic advantages

On the plus side, plastic is lighter than glass, and it can be tinted.

Lenses made from high-index plastic are significantly thinner than regular plastic lenses. This makes high-index plastic an excellent choice for rimless frames and semi-rimless frames.

High minus-powered lenses are extremely thick at the edge, so it’s smart to recommend high-index plastic for these prescriptions. The thinner you can make these lenses, the more comfortable they’ll be for your client—and the better they’ll look.

6

Plastic drawbacks.

On the minus side, plastic lenses are a little thicker than glass lenses, and they scratch easily.

7

crown glass

Optical labs use a special type of glass called crown glass to make eyeglass lenses. Crown glass is very hard and clear, and it’s denser than plastic.

Crown glass is the heaviest material we can use for glasses. Like plastic, it has its pros and cons. It provides excellent optics, so it does a great job of correcting vision. It doesn’t scratch easily, and it’s not affected very much by changes in temperature. However, in addition to its weight, it breaks easily.

As you learned in today’s reading, manufacturers in the United States need to make sure their lenses, including glass lenses, pass a drop ball test (which we’ll talk more about later). This guarantees that the material is hard enough to meet certain standards. But even though glass lenses have to pass this test, they can still shatter! For this reason, we don’t recommend glass lenses in our practice. Anything hitting the glasses may cause glass to shatter into a person’s eye.

8

the heaviest material we can use for glasses.

Crown glass

9

pros of crown glass

It provides excellent optics, so it does a great job of correcting vision. It doesn’t scratch easily, and it’s not affected very much by changes in temperature.

10

cons of crown glass

However, in addition to its weight, it breaks easily.


11


manufacturers in the United States need to make sure their lenses, including glass lenses, pass what?

a drop ball test (which we’ll talk more about later). This guarantees that the material is hard enough to meet certain standards. But even though glass lenses have to pass this test, they can still shatter! For this reason, we don’t recommend glass lenses in our practice. Anything hitting the glasses may cause glass to shatter into a person’s eye.

12



The refractive index of polycarbonate


1.586, which is much higher than plastic.

13

Because the refractive index of polycarbonate is higher than plastic, labs can make polycarbonate lenses that are
what?


polycarbonate lenses that are much thinner than any plastic lens—as thin as 1 millimeter!

14

polycarbonate blocks what?

100% of UV light.

15

Better yet, polycarbonate is what?

impact-resistant. (That’s why engineers used it for the windows in the space shuttles.) Obviously, this makes polycarbonate an ideal lens for all children’s glasses as well as safety and sports glasses.

16

Why is polycarbonate so impact-resistant?

Because it’s fairly soft. However that same softness makes it extremely easy to scratch. That’s why polycarbonate lenses today are manufactured with a scratch-resistant coating.

17

Polycarbonate is extremely easy to

scratch

18

polycarbonate lenses today are manufactured with what?

a scratch-resistant coating.

19

The tri in the name Trivex stands for what?

its three primary benefits: superior optics, impact resistance, and UV blocking.

20


The optics of Trivex are better than those of polycarbonate because of what?

Trivex has a higher Abbe Value. this means that it creates less chromatic aberration as a person’s vision moves away from the optical center of the lens. Thus Trivex is an excellent choice for people who need good peripheral vision for work or sports. It is also a great lens material for children’s glasses, just like polycarbonate.

21

The index of refraction for Trivex

1.53.

22

trivex is less likely to split or crack than what?

it’s less likely to split or crack than polycarbonate.

23

Trivex is a good material for

Trivex is a good material for high-prescription lenses in drilled rimless frames because it’s less likely to split or crack than polycarbonate. Its UV-blocking properties are also a big asset.

24

Optyl is used primarily in

sunglasses.

25

Optyl, is

hypoallergenic.

26

when optyl is heated,

it can be bent to fit and stays in its new shape.

27

optyl cons

if the lenses become too hot, they can pop out of the frame. Also Optyl isn’t impact-resistant, and it’s not very thin.

28

the thinnest portion of a safety lens should not be less than what?

3.0 mm. This applies to all lens materials except for polycarbonate and Trivex, since these materials are already impact-resistant!

29

for any children’s, safety, or sports eyewear, what are the only materials to consider.

Trivex and polycarbonate

30

Trivex and polycarbonate are available in

single-vision, bifocal, and progressive designs.