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O Optics B11 > Lens Material And Design > Flashcards

Lens Material And Design Flashcards

1
Q

Does glass have a low or high abbe number?, what does this mean regarding chromatic aberrations

A

High abbe number=low chromatic aberrations

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2
Q

What are 4 advantages of glass?

A
  • highly transparent and colorless
  • resistant to heat and chemicals
  • high scratch resistant
  • high abbe number= low aberrations
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3
Q

What are 5 disadvantages of glass?

A
  • weight
  • poor impact resistance
  • poor UV protection
  • cant be tinted after manufacturing
  • lengthy processing time
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4
Q

What are the 2 types of plastics?

A
  • thermoplastic (polycarbonate)

- thermosetting (CR-39)

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5
Q

This plastic can be softened when heated?

A

Polycarbonate

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6
Q

This plastic when hardened cant be softened even at high temps?

A

CR-39

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7
Q

Does CR-39 have a love or high abbe number?

A

High

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8
Q

What are the 5 advantages of CR-39?

A
  • lighter weight than glass
  • high abbe number
  • inexpensive
  • tintable
  • many designs
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9
Q

What are 4 disadvantages of CR-39?

A
  • scratches and chips easily
  • thicker than hi index plastic
  • warpage
  • not for children
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10
Q

T/F: the higher the index, the thinner a lens can be and still produce the same power

A

True

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11
Q

This is type of lens material is good for high prescriptions

A

Hi-index plastic

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12
Q

Does hi index plastic have a low or high abbe number?

A

Low

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13
Q

Since hi-index plastic has a low abbe number=more aberrations, what type of coating does it need?

A

A/R coating

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14
Q

What is the refractive index of glass/crown glass?

A

1.523

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15
Q

What is the refractive index of CR-39?

A

1.498

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16
Q

What is the refractive index of polycarbonate?

A

1.586

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17
Q

What are the 3 advantages of polycarbonate?

A
  • excellent impact resistant
  • UV protection
  • many designs
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18
Q

What are 4 disadvantages of polycarbonate?

A
  • not great for optics
  • not great for tinting
  • soft surfaces, scratches easily if not treated
  • must avoid exposure to heat
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19
Q

This type of lens material is used in children’s glasses or sportswear

A

Polycarbonate

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20
Q

What is the refractive index of trivex?

A

1.53

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21
Q

What is the order of refractive indexes from low to high?

A
  1. ) CR39
  2. ) glass
  3. ) trivex
  4. )polycarbonate
  5. ) hi index plastic
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22
Q

What are 5 advantages of trivex?

A
  • tintable
  • good UV protection
  • very lightweight
  • extremely high impact resistant
  • fewer heat issues that polycarb
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23
Q

This lens material is low cost and has excellent optics

A

CR-39

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24
Q

This lens material is chemically resistant and not commonly used

A

Glass

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25
Q

This lens material is expensive, has chromatic dispersions, scratches easily, and is used for strong rx’

A

Hi-index plastic

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26
Q

These lens materials are used for children, sports, hazardous jobs, and thinner/light lenses

A

Polycarbonate and trivex

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27
Q

A point on the datum line halfway between the 2 vertical lines which are tangent to the edges

A

Geometrical center

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28
Q

Horizontal length of the box when referring to the frame or lens

A

Eye size or lens size (A)

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29
Q

The vertical length of the box

A

B distance (B)

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30
Q

Shortest horizontal distance between the lenses

A

Bridge size (DBL)

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31
Q

Horizontal distance between the geometrical centers of the 2 lenses

A

Frame PD

32
Q

The longest diameter of a lens

A

Effective diameter (ED)

33
Q

Point on the lens through which the line of sight passes (this would correspond to the optical axis if no prism power were needed)

A

Major reference point (MRP)

34
Q

The plus power in a multifocal lens segment that is added to the power in the distance portion of the lens

A

Near addition

35
Q

Distance is measured at ~___ft or ~____m

A

20ft or 6m

36
Q

Computer/intermediate is measured at ____

A

Arms length

37
Q

Reading is measured at ___cm

A

40cm

38
Q

If asphericity is applied to the front surface of a plus lens, the surface will become ___ away from the center.

A

Flatter

39
Q

If asphericity is applied to the back surface of a plus lens, the surface will become ___ away from the center.

A

Steeper

40
Q

If asphericity is applied to the front surface of a minus lens, the surface will become ___ away from the center.

A

Steeper

41
Q

If asphericity is applied to the back surface of a minus lens, the surface will become ___ away from the center.

A

Flatter

42
Q

Designed for one rx correction

A

Single vision lenses

43
Q

A lens where blurring in parts around the periphery results in a lack of clarity

A

Spherical lens

44
Q

A lens with peripheral blurring improves, resulting in enhanced clarity

A

Aspheric lens

45
Q

Longest horizontal dimension of the segment

A

Seg width

46
Q

Longest vertical dimension of the segment

A

Seg depth

47
Q

Distance from the lowest point on the lens to the top of the segment

A

Seg height

48
Q

Vertical distance between the MRP and the top of the seg

A

Seg drop

49
Q

T/F: the distance portion of the lens is decentered from the GC to correspond to the wearers PD

A

True

50
Q

the distance from the Geometric Center (GC) to the Major Reference Point (MRP)

A

Distance decentration

51
Q

the inset accounting for the near PD (because PD is different for near vision). The distance from the MRP to the center or the seg

A

Seg Inset

52
Q

The inset of the seg as measured from the Optical Center of the lens. Distance from the GC to the center of the seg

A

total inset

53
Q

First one-piece bifocal. Designed by starting with required near power and adding a second curvature to upper portion and back of surface.

A

Solid upcurve

54
Q

Small segment cemented to back surface of lens. Segment could be replaced as add changed.

A

Cement

55
Q

components fused together by heat instead of cement.

A

Fused kryptok

56
Q

One-piece back surface bifocal

A

Ultex

57
Q

What are the 7 types of bifocals

A
  • straight top/flat top
  • rounded
  • blended
  • executive
  • curved top
  • B or ribbon
  • ultex
58
Q

What are the 2 advantages of a round segment?

A
  • least visible

- light

59
Q

What are the 2 disadvantages of a round segment?

A
  • takes a while to get down to a useful width

- most jump, especially in larger segs

60
Q

What are the 3 advantages of a flat top?

A
  • Immediate broad field
  • minimal jump
  • no prism
  • light
61
Q

What an disadvantage of a flat top bifocal?

A

Visible ledge in larger segs

62
Q

What is an advantage of an executive bifocal?

A

Widest field

63
Q

What are 6 disadvantages of an executive bifocal?

A
  • thick
  • heavy
  • ugly
  • collects debris
  • chips
  • no jump
64
Q

has a smooth continuous building of power from the distance to the near through a “corridor”.

A

PAL

65
Q

Do PAL have an image jump?

A

NO

66
Q

process by which a PAL can be made thinner by removing some base up prism. This leaves residual BD prism and a substantially thinner lens

A

Prism thinning

67
Q

the cylindrical power lateral to the umbilic of a progressive surface increases twice as rapidly as the addition power

A

Minkwitzs theorem

68
Q

Vertical meridian of a PAL that is spherical at every point

A

Umbilic

69
Q

T/F: lens designs with shorter corridors produce more unwanted cylinder power in the periphery or narrower viewing zones.

A

True

70
Q

Design characterized by wider area of stable optics at distance and near along with a shorter, narrower corridor (steeper gradients); Better for sustained viewing tasks

A

Hard designs

71
Q

Designs have narrower areas of optimal power at distance and near, but offer a longer, wider intermediate zone (shallower gradients); Better for dynamic viewing tasks

A

Soft designs

72
Q

Many lenses today are multi-design meaning what?

A

Softer with decreasing add power and harder with increasing add power

73
Q

PALS with small B measurements

A

Short corridor PALs

74
Q

uses computer- aided design and processing to create high-level, customized lenses unique to your prescription; makes you see better and across more of your lens

A

Free-form processing

75
Q

What are 4 advantages of PALs?

A
  • no image jump
  • cosmetically appealing
  • more youthful and fashionable
  • uninterrupted vision from distance to near
76
Q

What are 3 disadvantages of PALs?

A
  • expensive
  • adaptation time
  • unwanted Astigmatism is periphery

O Optics B11 (4 decks)

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