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II. Ophthalmic Optics > Midterm I > Flashcards

Midterm I Flashcards

1
Q

Where were corrective lens first developed?

A

China and Europe simultaneously

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2
Q

What were the two critical factors that lead to the development of corrective lenses?

A
  1. Increase visual demands with inc age

2. Development of glass

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3
Q

What type of correction were the first glasses made for?

A

presbyopia

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4
Q

What type of correction were the second glasses made for?

A

myopia

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5
Q

Who invented the biofocals? 1. Who assisted him?2

A
  1. Ben Franklin

2. John McAllister

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6
Q

What was the last type of correction that was corrected with glasses?

A

astigmatism

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7
Q

What is the amorphous solid material that is obtain by an inorganic mixture fused at high temperatures used to make spectacles?

A

glass

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8
Q

What are the natural types of glass?

A
  1. obsidian

2. fulgarites

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9
Q

What do flint glasses contain in them that is not like crown glass?

A

lead oxide

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10
Q

What does high index glass contain in it that is not like crown glass?

A

titanium oxide

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11
Q

What is how light behaves differently based on the wavelength? 1. How is it measured? 2

A
  1. Dispersion

2. Abbe Value

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12
Q

What is the distortion of a point because a lens will behave differently based on the wavelength?

A

chromatic aberration

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13
Q

What is the ratio of the density of a substance to the density of water?

A

specific gravity

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14
Q

How is the Abbe value calculated? 1. Is a high value or low value better? 2

A
  1. reciprocal of relative dispersion

2. high

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15
Q

What are the advantages of glass?

A
  1. inert
  2. scratch resistant
  3. high optical quality
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16
Q

What are the disadvantages of glass?

A
  1. heavy (high specific gravity)
  2. lower impact resistance
  3. potential for liability
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17
Q

What is an organic polymeric material of high molecular weight that can be shaped by flow?

A

plastic

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18
Q

What kind of plastic softens when heated and can be remodeled? 1. What kind cannot be softened once hardened? 2

A
  1. thermoplastic (Zial)

2. thermosetting

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19
Q

Why did people start preferring plastic to glass?

A
  1. impact resistance requirement
  2. light weight, reduced scratching
  3. larger frames can be used
  4. tints available
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20
Q

What is the allyl diglycol carbonate monomer that is a thermosetting plastic and has UV absorbers?

A

CR-39

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21
Q

What are the desirable properties of CR-39?

A
  1. lightweight
  2. impact resistant
  3. chemically inert
  4. resistant to pitting
  5. resistant to fogging
  6. tintable
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22
Q

What type of plastic is polycarbonate?

A

thermoplastic

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23
Q

What are the advantages of polycarbonate lenses?

A
  1. superior to glass and CR-39 for impact resistance
  2. lighter than CR-39
  3. UV absorption
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24
Q

What are the disadvantages of polycarbonate lenses?

A
  1. more easily scratched
  2. low Abbe Value (high dispersion)
  3. more reflections
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25
Q

What is the relatively new lens material that is similar to polycarbonate but higher Abbe Value?

A

Trivex

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26
Q

How does index of refraction affect the thickness of the lens?

A

high the index, thinner the lens

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27
Q

Is weight more of a concern in plus or minus lenses?

A

plus

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28
Q

What does the durability and safety of a lens depend on?

A
  1. resistance to scratching
  2. tensile strength
  3. impact resistance
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29
Q

What is the order from most to least scratch resistant lens type?

A

glass>CR-39 (should coat) >polycarbonate (need coat)

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30
Q

What is the order from most to least expensive lens type?

A
  1. trivex
  2. glass
  3. polycarb
  4. CR-39
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31
Q

What is the most common lens type in the U.S.? 1. Second? 2

A
  1. Polycarb

2. CR-39

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32
Q

Are the standards set by ANSI voluntary or involuntary?

A

voluntary

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33
Q

What does the drop ball test consist of for the impact resistance test?

A
  1. 5/8 inch steel ball
  2. weight=0.56 ounces
  3. drop height = 50 inches
  4. dropped on front surface geometric center of lens
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34
Q

What are the exceptions for the drop ball test?

A
  1. test for stats. significant
  2. plastic lenses
  3. non-prescription lenses
  4. special use lenses
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35
Q

What is the regulatory body of the government that prevents unfair business practices?

A

Federal Trade Commission (FTC)

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36
Q

What did the Eyeglasses II (1989) change as far as regulations from Eyeglasses I?

A
  1. remove minimum info on Rx

2. suggest expiration

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37
Q

What is the regulatory agency to protect the workers?

A

Occupational Safety & Health Administration (OSHA)

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38
Q

What did ANSI Z80.1 set a standard for?

A
  1. Standards for ophthalmic lens tolerances

2. lens quality criteria

39
Q

What did ANSI Z80.3 set a standard for?

A
  1. nonprescription sunglasses

2. minimum UV protection

40
Q

What did ANSI Z80.5 set a standard for?

A

Standards for dress eyewear frames

41
Q

What did ANSI Z87.1 set a standard for?

A

Standards for safety eyewear

42
Q

What is the minimum thickness for safety glasses?

A

3.0 mm

43
Q

What is the minimum thickness for dress eyewear?

A

none

44
Q

What is the procedure of heating a lens to near softening point and then rapidly cooling called? 1. What are the restrictions after this? 2

A
  1. thermal tempering

2. cannot be resurfaced or re-edged

45
Q

What is the procedure that uses ion exchange to meet impact resistance standard? 1. What are the restrictions after this? 2

A
  1. chemical tempering

2. none

46
Q

Does CR-39 or chem tempered glass have better impact resistance for large slow objects? 1. Slow fast moving? 2

A
  1. chem tempered glass

2. CR-39

47
Q

What is the most impact resistant material?

A

polycarb (or Trivex)

48
Q

What is the equation for the curvature of a lens?

A

(R) = C = 1/r

49
Q

What is the distance between a point on the circle and the midpoint of a chord of the circle?

A

sagitta

50
Q

What does a lens clock directly measure? 1 What does it indirectly measure? 2

A
  1. sag

2. power

51
Q

What is the index of refraction for most lens clocks?

A

1.53

52
Q

If n(c)>n(T), then P(c) is an overestimate, an underestimate, or an exact measurement of P(T)?

A

overestimate

53
Q

What is the only lens form that is still currently made?

A

meniscus

54
Q

What refers to the relationship between the front and back surface curvatures of a lens?

A

lens form

55
Q

What is the lens form of meniscus lenses?

A

convex front surface (+) and concave back surface (-)

56
Q

On most modern single vision lenses, where is the toricity?

A

plus sphere on front and minus cylinder on back

57
Q

What is the name for a blank that has neither side ground or polished?

A

rough blank

58
Q

What is the name for a blank that has one surface ground and polished?

A

semi-finished blank

59
Q

What is the name for a blank that has both surfaces ground and polished but not edged to fit the frame?

A

uncut lens

60
Q

What side of the lens is the base curve usually referring to?

A

the front (flattest surface)

61
Q

What are selected to minimize the lens aberrations and is a compromise between lens thickness and image quality?

A

base curve

62
Q

Are flatter lens thicker or thinner?

A

thinner

63
Q

What are lenses designed to minimize lens aberrations called?

A

“best form” or “corrected curve”

64
Q

What is the most important factor in aberrations?

A

oblique astigmatism

65
Q

What is the line connecting the centers of curvature of the two lens surfaces?

A

optic axis

66
Q

What are the points on the front and back surface of a lens which intersect the optic axis

A

lens poles

67
Q

What does the spherical equivalent determine?

A

location of the circle of least confusion

68
Q

What are the three methods of determining the resultant power of obliquely crossed cylinders?

A
  1. vector analysis
  2. mathematical
  3. polar coordinates
69
Q

When is finding the result of obliquely crossed cylinders used? 1. What is it used with? 2

A
  1. fitting toric contact lenses

2. SCOR (sphero cylinder over refraction)

70
Q

What is a tilt of the bottom of a lens towards the face called?

A

pantoscopic tilt

71
Q

What is a tilt of the bottom of a lens away the face called?

A

retroscopic tilt

72
Q

What is a tilt of the temples of a lens toward the patient?

A

positive faceform

73
Q

What is the axis of added cylinder in pantoscopic tilt?

A

180

74
Q

What is the axis of added cylinder in faceform?

A

90

75
Q

What is the power found using the lens clock?

A

nominal power

76
Q

What is the algebraic sum of the lens surfaces?

A

nominal power

77
Q

What is the power that is equal to the power of a single, thin lens placed at the secondary principal plane? 1. What is it used for? 2

A
  1. equivalent power

2. low vision devices

78
Q

What is another name for the front vertex power? 1. How is it found? 2

A
  1. neutralizing power

2. hand neutralization or lensometer

79
Q

What is the power that ophthalmic prescriptions are specified with? 1. What is it usually measured with? 2

A
  1. back vertex power

2. lensometer

80
Q

What is refractive behavior of the lens when moved to a different distance?

A

effective power

81
Q

What is the power that provides the lens required when the vertex distance is changed?

A

compensated power

82
Q

Will a contact lens or a glasses prescription have more plus power?

A

CL prescription

83
Q

If there is a “with” motion when doing hand neutralization what is the net power?

A

minus

84
Q

If there is a “against” motion when doing hand neutralization what is the net power?

A

plus

85
Q

What kind of telescope is a lensometer?

A

Keplerian telescope

86
Q

Where is the lens stop located in lensometery?

A

secondary focal plane of standard lens in lensometer

87
Q

For a plus lens measurement does the target move toward or away from the standard lens?

A

toward

88
Q

For a minus lens measurement does the target move toward or away from the standard lens?

A

away

89
Q

Does higher index make a lens thicker or thinner?

A

thinner

90
Q

Around what amount does lens thickness usually become important?

A

+- 4.00 D

91
Q

Do stronger surface powers produce shorter or longer radii of curvature?

A

shorter

92
Q

If: front surface (D) > back surface (D), what is the result? 1. If: front surface (D)

A
  1. plus lens

2. minus lens

93
Q

What are the center thicknesses required for minus lens safety glasses?

A

between 1.0 and 2.2 mm

94
Q

What are the edge thicknesses required for plus lens safety glasses?

A

between 1.0 and 2.0 mm

II. Ophthalmic Optics (3 decks)

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