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Final Review > Lens II Review > Flashcards

Lens II Review Flashcards

1
Q

Vertical Imbalance Steps.

A
  1. find power @ 90
  2. find optical difference. same signs subtract, opp add.
  3. use formula Dd/10=^
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2
Q

Segments
Rd 22

Location?

A

11mm

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3
Q

Segments
Rd 25

Location?

A

12.5mm

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4
Q

Segments
Rd28

Location?

A

14mm

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5
Q

Segments
Ft25, Ft28, Ft35

Location?

A

all 5mm.

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6
Q

Segments
Ultex

Location

A

19mm

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7
Q

Segments
Exec

Location

A

0mm

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8
Q

Calculating IJ

ex. 22Rd w/ +2.00ADD

A

To solve, use Dd/10=^

where D = near oc, d=ADD, and 10 is constant.
(11)(22)/10=22/10=2.2^IJ

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9
Q

Power at 90

if the axis is 0 away from 90, how much cyl is felt?

A

0%

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10
Q

Power at 90

if the axis is 30 away from 90, how much cyl is felt?

A

25% felt

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11
Q

Power at 90

if the axis is 45 away from 90, how much cyl is felt?

A

50% felt

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12
Q

Power at 90

if the axis is 60 away from 90, how much cyl is felt?

A

75% felt

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13
Q

Power at 90

if the axis is 90 away from 90, how much cyl is felt?

A

100% felt

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14
Q

Calc. power at 90

ex. +1.00-4.00x060

A

axis is 30 away from 90, so 25% of cyl felt. (-4.00x25%=-1.00)
take 1.00 and combine with sph. (-1.00 + 1.00 = PL)
PLANO=power at 90

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15
Q

t/f
A FT BF has its near optical center 5mm below the segment line regardless of the width and regardless whether its a BF or TF.

A

True,

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16
Q

The wearer can opt for two pairs of glasses to correct for VI at near.

A

true

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17
Q

Fused MF construction methods are only used with glass?

t/f

A

true

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18
Q

Reverse Slab Off

reverse is ALWAYS BD

A

find power at 90
find optical difference, same sub, opp add
calc VI with ^= Dd/10
^ goes in lens with LEAST - or MOST +

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19
Q

Reverse Slab off goes in the lens with the least minus, most plus.

t/f

A

true

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20
Q

Slab off is always ground BU on the lens with the MOST minus, LEAST plus.

t/f

A

True

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21
Q

Calc. Slab Off

A

find power at 90
find optical diff. (same signs sub, diff add)
Calc VI using ^= Dd/10
BU on lens w/ MOST minus & Least plus

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22
Q

Cosmetic appearance is a factor when using dissimilar segments to correct for VI @ near.

t/f

A

true

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23
Q

Prism segments are widely used to correct VI

true/false

A

false

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24
Q

Vertical imbalance of more than 2D should always be considered.

t/f

A

true

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25
Q

Reverse slab off is available in fused FT-28 BF

t/f

A

false.

reverse= front molding

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26
Q

Reverse slab off is placed in the most _____ lens.

minus
plus

A

plus

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27
Q

Conventional slab off is available in PAL

t/f

A

true

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28
Q

A client has VI of 2.5D BD OD, what should we do to compensate?

A

Slab off 2.5 BU OD.

If VI is BD, give BU to neutralize.
BU= slab off BUMM

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29
Q

Reverse slab off is molded not ground.

t/f

A

true

reverse= molded on front lens
slab off= ground on back lens

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30
Q

A client has VI 2.00BU OD, what should we do to compensate?

A

REVERSE slab off 2.00BD OD

give BD to neutralize.
BD = Reverse slab off. BDMP

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31
Q

VI compensation at near is required when there is a VI of 1.00D or less between two eyes.

t/f

A

false. 1.5VI or more.

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32
Q

Conventional slab off is available in a one-piece FT-28 BF

t/f

A

true

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33
Q

Conventional slab off is placed in the most _____ lens.

minus
plus

A

minus

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34
Q

Reverse slab off is base _____ prism.

up
down

A

down

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35
Q

Conventional slab off is base ____ prism.

up
down

A

up, BUMM

36
Q

AR coatings help eliminate specular reflections

t/f

A

true, higher the index of refraction, more light reflected.

37
Q

The pupil of the wearer reduces the effect of spherical abberation.

t/f

A

true, not a problem in lower power lenses because of the small limiting size of the pupil.

38
Q

In curvature of field, the image is curved.

t/f

A

true

39
Q

Reverse slab off is available in half diopter steps.

t/f

A

true

40
Q

Chromatic aberration is a result of the nature of the material of the lens.

t/f

A

true

41
Q

The higher the index of refraction of the lens, the greater amount of specular reflection will occur.

t/f

A

true

42
Q

An aspheric front surface of a plus lens steepens towards the periphery

t/f.

A

false, flattens is periphery.

43
Q

Most ophthalmic lenses have no aberrations.

t/f

A

false

44
Q

1 surface of percent of intensity

  1. 3%
  2. 94%
A

4.3%

45
Q

2 surfaces for percent of intensity.

  1. 3%
  2. 94%
A

3.94%

46
Q

In coma, the abberation is a result of the rays of light oblique to the lens surface.

t/f

A

true

47
Q

Spherical aberration results from the lens having different powers in different areas.

t/f

A

true

48
Q

Conventional slab off is available in quarter diopter steps

t/f

A

true

49
Q

In coma, the aberration is a result of rays of light parallel to the lens surface.

t/f

A

false, coma is oblique.

50
Q

In distortion, the object will appear to have a pincushion look when viewed through a minus lens.

t/f

A

false. Pincushion is plus, Barrel is minus

51
Q

In coma, the pupil of the wearer has no effect on the aberration.

t/f

A

false. The pupil acts as a small aperture which limits the light rays at periphery of lens.

52
Q

The refracting power of a lens decreases toward the periphery

t/f

A

false, it increases, decreases at near OC

53
Q

All lenses moved farther away from the eye will gain in plus power, we compensate for this by adding minus power.

t/f

A

true

54
Q

The law of reflection states that the angle of incidence is always greater than the angle of reflection.

t/f

A

false, its equal to.

55
Q

A high plus lens will show _____ distortion

pin
barrel
radio wave

A

pin. PLUS

56
Q

A convex surface has ____ dioptric power

plus
minus
plano

A

plus = convex, minus = concave

57
Q

As a ray of light passes from a more dense to a less dense material at an oblique angle, the refracted ray will be deviated _____ the normal.
away
toward
parallel

A

away, more to less dense.

58
Q

Vertex distance compensation should be considered when the total power of the lens, in any meridian, is +/-7.00 or greater.

t/f

A

true

59
Q

A high minus lens will show ____ distortion.

pin
barrel
radio

A

Barrel

60
Q

A surface with a flatter curve will have less dioptric power.

t/f

A

true.

61
Q

In the surface power formula, we must be sure that “r” (radius) is in meters, not mm, or cm.

t/f

A

true

62
Q

When light strikes an object, 3 things occur. They include: refraction, absorption, and reflection.

t/f

A

true

63
Q

As light strikes a lens with a spherical front surface, it refracts more at the periphery than near the center.

t/f

A

true

64
Q

A surface with a shorter radius will have a flatter curve

t/f

A

false, steeper=shorter, flatter=longer.

65
Q

As a ray of light passes through from a LESS dense to a MORE dense material at an oblique angle, the ray will be more deviated ___ the normal.
toward
away

A

less->more dense, toward the normal.

66
Q

In coma, the aberration is a result of rays of light parallel to the lens surface.

t/f

A

false, coma=oblique

67
Q

A plano surface has____ power

zero
minus
plus

A

zero

68
Q

A concave surface has ____ power

minus
plus
plano

A

minus, convex = plus

69
Q

In curvature of field, the image is curved convex towards the object.

t/f

A

False. Curvature=concave

70
Q

Convex surfaces: t/f

covex surface bulging
converges light rays
plus power

A

true

71
Q

Concave surfaces: t/f

minus
diverges light
concave surface is hollow

A

true

72
Q

Radius of Curvature: t/f

Curve on a smaller circle is steeper than the curve of a larger circle.

A

true

73
Q

Radius of curvature: t/f

the steeper the curve, the more power

A

true

74
Q

Surface Power Formula

D=n-1/r

A

where D= power
nr=index of refractive material
ni=index of the incident material
r=radius of curves of meters

75
Q

Vertical Imbalance of less than 2D is never noticeable to the wearer.

t/f

A

false, anything 1.5^ or more is noticeable.

76
Q

Example of Surface Power Formula.

A concave surface with a radius of 50cm and an index of 1.6. What is the surface power? Convert 50cm to meters = .5

A

D=n-1/r
1.6-1=.6/.5
D=1.2
rounded to the nearest 1/8D, 1.2=1.25

77
Q

Index of poly?

  1. 498
  2. 586
  3. 523
A

1.586

78
Q

Index of cr-39?

  1. 498
  2. 586
  3. 523
A

1.498

79
Q

Index of crown glass?

  1. 586
  2. 523
  3. 530
A

1.523

80
Q

Index of trivex?

  1. 530
  2. 523
  3. 498
A

1.530

81
Q

Angle of incidence is the angle formed between the refracted ray and the normal.

t/f

A

true

82
Q

The angle of refraction is the angle formed between the refracted ray and the normal.

t/f

A

true

83
Q

The angle of deviation is the angle formed between the refracted ray and the path the incident ray would have taken had it not been refracted.

t/f

A

true

84
Q

Compensating for Vertex Power

CAP, FAM

t/f

A

True

85
Q

Compensating Vertex Distance formula

power x power x distance moved/1000=amount of compensation

A

CAP, FAM

Final Review (3 decks)

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