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Opthalmic Optics > Review > Flashcards

Review Flashcards

1
Q

What are the characteristics of an ideal lens?(6)

A
  • High index of refraction
  • High ABBE
  • low specific gravity
  • Low UV transmittance
  • high light transmittance
  • high impact resistance
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2
Q

What type of lens materials are available to recommend to patients?

A
  • glass
  • plastic
  • high index
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3
Q

Different type of plastic lenses include:

A

Thermosetting
Thermoplastic
Trivex

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4
Q

Different kinds of high index lenses include

A

Plastic and glass

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5
Q

Physical requirements that lenses must meet before they are able to be worn?

A

-meet standard impact resistance requirements

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6
Q

Physical requirements for dress eyewear:

A

No minimum thickness requirement

Lens must not fracture on resistance test

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7
Q

Who supplies the standards that ophthalmic products should follow?

A

ANSI: American national standards institute

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8
Q

n for CR39

A

1.50

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9
Q

n for crown

A

1.523

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10
Q

n for poly

A

1.586

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11
Q

n for 1.7 index

A

1.701

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12
Q

Specific gravity for 1.7 index

A

2.99

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13
Q

Specific gravity for crown

A

2.54

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14
Q

Specific gravity for cr39

A

1.32

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15
Q

Specific gravity for poly

A

1.20

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16
Q

Abbe value for crown

A

58.9

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17
Q

Abbe value for CR39

A

57.8

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18
Q

Abbe value for 1.7 index

A

30.8

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19
Q

Abbe value for poly

A

30

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20
Q

Has exceptional impact resistance

A

Polycarbonate

21
Q

How does the reflectance of a lens material vary with its index of refraction?

A

Based on the equation: higher index means higher reflection

22
Q

Why do optometrist care about the light reflected from ophthalmic lenses?

A

The reflection can cause ghost images, it can be aesthetically frustrating in photos, cause haze or decrease contrast

23
Q

Which lens materials are/is thermosetting?

A

CR39

24
Q

Which material is/are thermoplastic

A

Polycarbonate

25
Q

What is the difference between thermosetting and thermoplastic?

A
  • Thermosetting cannot be melted back while melting and cooling are the cycles used in thermoplastic lenses
  • thermosetting uses cross linking while thermoplastic so dont
26
Q

Compare and contrast trivex and polycarbonate

A
  • trivex abbe value = 43-45 far better than poly carb = 30
  • trivex rivals poly in terms of impact resistance
  • trivex is very lightweight just like poly
  • 2x more scratch resistance over poly
27
Q

What is a lens blank

A

Circular ophthalmic lenses at any stage (unfinished, semi, or finished) prior to being edged

28
Q

What is lens surfacing?

A

When a prescription is ground onto the surface of a lens blank

29
Q

What is lens edging

A

Cutting a lens blank to fit an ophthalmic spectacle frame

30
Q

Compare semi-unfinished with finished lenses

A
  • semi-finished: unfinished back surface, typically used for multi focal and high-powered single vision lenses
  • finished: finished optical surfaces on both the front and back -> ready for edging
31
Q

What lenses would you recommend to patients with high prescriptions and/or requesting thin/ner lenses

A

High index

32
Q

What ophthalmic lens material is a patient likely viewing through if they “see rainbows”?

A

Some type of low ABBE value meaning there is more chromatic aberration (poly)

33
Q

How does curvature relate to the radius of a surface

A

The curve has an inverse relationship to the radius

34
Q

Compare minus cylinder and plus cylinder form lenses

A

Plus cyl= toric portion on the front of the lens

Minus cyl= toric portion on the back of the lens

35
Q

Tsercherning ellipse

A

The locus of points showing the relationship between the power of a surface and the power of the lens for which oblique astigmatism is eliminated

36
Q

WTR

A

150-180 and 180-030

37
Q

ATR

A

060-120

38
Q

Oblique

A

030-060 and 120-150

39
Q

What is the optical axis

A

Line going through the center of the lens

40
Q

Optic center

A

Literally a point of the center of the lens

41
Q

Refract light ray to meet at one common point

A

Spherical

42
Q

Refract rays to a focal line

A

Cylindrical

43
Q

Refract light rays to form 2 line images perpendicular to each other

A

Spherocylindrical

44
Q

For a cyl lens the axis meridian has most___ power and power meridian has most ___ power

A

Plus

Minus

45
Q

How do we determine the power of a obliquely crossed toric lenses

A

The sin squares law of curvature

If alpha is 30 degrees make sure to go 30 degrees from the axis meridian

46
Q

Generalizations about the resultant power of obliquely crossed toric lenses

A
  • both cyl with same sign= axis is between the original axes
  • 2 cyl are of equal power = axis is between the 2
  • if the 2 cyl are of unequal power= axis is shifter toward the stronger of the 2 cylinders
47
Q

Pantoscopic tilt

A

180 degree axis

48
Q

Face form tilt

A

090 axis

49
Q

How is the optic center adjusted for purposely pantoscopic lens tilt

A

Optical center must be lowered from the pupillary level an amount in mm - equal to one half the pantoscopic tilt in degrees

Opthalmic Optics (5 decks)

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