Test 1 Review Flashcards

1
Q

What is the formula for mm to diopter conversion?

A

D = 337.5 / mm

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2
Q

What is the average HVID?

A

11.7mm

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3
Q

What is the average VVID?

A

10.6mm

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4
Q

What is average CCT?

A

0.52mm

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5
Q

What is average limbal corneal thickness?

A

0.67mm

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6
Q

What is the average central radius of the cornea?

A

7.8mm

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7
Q

What is the average sagittal depth of the cornea?

A

2.6mm

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8
Q

What is the average index of refraction of the cornea?

A

n = 1.376

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9
Q

What percentage of the cornea is made up of water?

A

78%

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10
Q

How thick is the corneal epithelium?

A

50 microns

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11
Q

What ensures the transparency of the stroma?

A

The lamellar arrangement

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12
Q

Which lenses are made via lathing or molding?

A

GP

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13
Q

Which lenses are made via cast-molding or spin casting?

A

SCL

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14
Q

What are some advantages to lathing GP lenses?

A

Almost unlimited designs

Good for custom lenses

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15
Q

What is the GP manufacturing method of choice?

A

Lathing

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16
Q

What are some disadvantages to lathing GP lenses?

A

Slow production
High cost per lens
Labor intensive

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17
Q

What is plasma treatment?

A

A “super cleaning” using room temperature, ionized oxygen and UV energy to break organic bonds

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18
Q

Which lenses can be plasma treated?

A

GP

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19
Q

How long does plasma treatment last?

A

Few days, to months

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20
Q

What is the purpose of plasma treatment?

A

To increase wettability

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21
Q

What is Dk?

A

Oxygen permeability

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22
Q

What is the “D” in Dk

A

Diffusion coefficient

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23
Q

What is “k” in Dk?

A

Solubility of the gas in the material

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24
Q

What is Dk/t?

A

Dk value / thickness

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25
Q

What is the necessary Dk/t for DW lenses under open eye conditions?

A

24

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26
Q

What is the necessary Dk/t for EW lenses under open eye conditions?

A

87

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27
Q

What is the necessary Dk/t for DW lenses under closed eye conditions?

A

35

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28
Q

What is the necessary Dk/t for EW lenses under closed eye conditions?

A

125

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29
Q

What is the required EOP for DW lenses?

A

9.9%

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30
Q

What is the required EOP for EW lenses?

A

17.9%

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31
Q

What removes lipids from CLs?

A

Isopropyl alcohol

Surfactants

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32
Q

What removes proteins from CLs?

A

Proteolytic enzymes

Surfactants

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33
Q

Proteins are attracted to which type of CL?

A

Ionic lenses

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34
Q

Lipids are attracted to which type of CL?

A

Non-ionic lenses

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35
Q

What is the usual percentage of Hydrogen Peroxide in peroxide based cleaners?

A

3%

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36
Q

How long do lenses need to be left in peroxide to kill acanthomoeba?

A

3-6 hours

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37
Q

Do multipurpose solutions sterilize lenses?

A

No - they disinfect and preserve

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38
Q

What is the main difference between the Andrasko and IER staining studies?

A

Andrasko was measured after 2 hours of exposure

IER was 3 months worth of data

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39
Q

Which type of soft CL is prone to lipid deposits?

A

Si-Hy

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40
Q

Si-hy lenses are prone to lipid deposits, and what else?

A

Mucin balls

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41
Q

What damage do mucin balls do to the cornea?

A

Epithelial dimples, causing NaFl pooling, but not staining

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42
Q

What is PMMA, and some of it’s properties?

A

Hard lens materia
No Oxygen transmission
Old material

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43
Q

What are the two old, traditional Hard lens materials?

A

PMMA

CAB

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44
Q

What are the 4 common hard lens materials?

A

PMMA
CAB
SA
FSA

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45
Q

What is the “standard” soft lens material?

A

HEMA

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46
Q

What is EGDMA and its properties??

A

A crosslinking agent for soft lenses that stiffens material and lowers the water content

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47
Q

What does GMA do?

A

Increases wettability and deposit resistance in SCLs

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48
Q

Why does GMA increase deposit resistance?

A

Smaller pore size

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49
Q

What does MMA do?

A

Decreases water content
Increases strength of lens
No Oxygen transmission

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50
Q

What does PVA do?

A

Increases water content
Increases resistance to deposits
Increases Dk
Increases Strength

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51
Q

What are the characteristics of MAA and NVP?

A

Increase water content
Very hydrophilic
Ionic

52
Q

What is the water content of hydrogel lenses?

A

80%

53
Q

What is the water content of Si-hy lenses?

A

24%

54
Q

Higher water content usually means ___Dk value.

A

Lower

55
Q

What is the “stem” for the hydrogel family?

A

Filcon

56
Q

What group are Si-Hy lenses in?

A

Group V

57
Q

What group are hydrogel lenses in?

A

Group IV

58
Q

What is the “stem” of non hydrogel lenses?

A

Focon

59
Q

What is the average lens diameter of a soft lens?

A

12-14.5

60
Q

What is the average diameter of a GP lens?

A

9-10mm

61
Q

How do you calculate the optic zone diameter of a GP lens?

A

OAD - (2 x peripheral curve widths)

62
Q

If you have a high plus lens, and you make the diameter bigger, what happens to the center of gravity?

A

It pushes forward

63
Q

If you have a high plus lens, and you make the diameter smaller, what happens to the center of gravity?

A

It moves backward

64
Q

If you have a high minus lens, and you increase the diameter, what happens to the center of gravity?

A

It moves backward

65
Q

Why is a minus carrier used?

A

To reduce center thickness in a high plus lens

66
Q

Why is a plus carrier used?

A

To reduce edge thickness of high minus lenses

67
Q

Describe Lipcof grade 1

A

1 small conj fold, smaller than the tear meniscus

Mild dry eye

68
Q

Describe Lipcof grade 2

A

Conj fold up to the height of the tear meniscus

Moderate dry eye

69
Q

Describe Lipcof grade 3

A

Fold of greater height than the tear meniscus, or multiple folds
Severe dry eye

70
Q

What is normal for Phenol Red Thread test?

A

Greater than 20mm in 15 seconds

71
Q

When a GP is placed on a toric cornea, how much astigmatism is left?

A

10%

72
Q

A flat fitting GP gives what lacrimal lens?

A

minus

73
Q

A steep fitting GP gives what lacrimal lens?

A

Plus

74
Q

If your SCL is decentered, what should you do to make it fit better?

A

Use a steeper BCR

75
Q

How long does a SCL need to “settle” in the eye?

A

5 minutes

76
Q

What is the average HVID?

A

11.7mm

77
Q

What is the average VVID?

A

10.6

78
Q

What is the approximate water content of the cornea?

A

78%

79
Q

Your patient wears +2.00D SCLs. The Va is decreased. In over the lens keratometry, the mires are irregular. What is the most likely reason?

A

Lenses are inside out

80
Q

Why do we use n=1.3375 for the cornea in calculations?

A

We consider the cornea to be a single surface for calculations

81
Q

According to Holden and Mertz, a dialy wear contact lens should have at least what Dk/t value?

A

24

82
Q

According to Holden and Mertz, an extended wear contact lenst should have at least what Dk/t value?

A

87

83
Q

What do sessile drop and captive bubble measure?

A

Wetting angle

84
Q

Which is a way to in-vivo test CL wettability?

A

Break-up time

85
Q

What is the role of an enzymatic cleaner?

A

Removes proteinaceous layer from a CL surface

86
Q

What material is added to a CL material to improve oxygen permeability?

A

Silicone

87
Q

What is a component added to a GP lens to improve wettability?

A

Fluroine

88
Q

Which study is critical for MPS products made by Bausch and Lomb?

A

Andrasko

89
Q

What is the key difference between the methodologies of the Andrasko and IER studies?

A

Duration of time preceding assessment

90
Q

What sequesters contaminants through formation of micelles?

A

Surfactant

91
Q

What has a main role of inhibiting microbial growth?

A

Preservative

92
Q

Which MPS additive contains mercury and is known to be toxic?

A

Thimerosal

93
Q

The killing and/or the removal of some or all resident pathogenic organisms is called___.

A

Disinfection

94
Q

What is the typical GP lens diameter?

A

9-10mm

95
Q

A GP lens fitted steeper than the flat K will result in what power lacrimal lens?

A

Positive

96
Q

What is the purpose of prism in a CL?

A

Stabilize cyl power

97
Q

What are Bennet’s classification of CL Dk values?

A

Low: 25-50
High: 51-99
Hyper: 100+

98
Q

What was the first SCL material?

A

HEMA

99
Q

What is the water content of a HEMA polymer?

A

38%

100
Q

What is the water content of a Si-Hy lens?

A

24%

101
Q

What does PVA do as a CL material?

A

Increases water content
Increases resistance to deposits
Increases Dk
Increases hardness and strength

102
Q

What does MMA do as a CL material?

A

Lowers water content
Increases hardness and strength
Has NO oxygen permeability

103
Q

What are the two core components of modern Silcone hydrogel lenses?

A

Si-O

MMA

104
Q

In hydrogel lenses, water content and Dk are usually ___ related.

A

Directly

105
Q

Most silicone hydrogel lenses are ___ water content, ___Dk.

A

Low water

High Dk

106
Q

CAB, FSA and PMMA are all materials for which type of CL?

A

GP

107
Q

What is the maximum acceptable corneal swelling induced by a CL?

A

4%

108
Q

What is the approximate atmospheric percentage present at the anterior cornea in an open eye condition?

A

21%

109
Q

What is the approximate atmospheric pressure present at the anterior cornea in an open eye situation?

A

747mmHg

110
Q

What is the approximate partial oxygen pressure present at the anterior cornea in an open eye situation?

A

155mmHg

111
Q

What is the approximate partial oxygen pressure present at the posterior cornea in an open eye situation?

A

55mmHg

112
Q

What is the approximate partial oxygen pressure present at the anterior cornea in a closed eye condition?

A

55mmHg

113
Q

What is the primary source of oxygen for the corneal epithelium in a closed eye condition?

A

Palpebral Conjunctiva

114
Q

A modern GP lens from FSA is most commonly made how?

A

Lathing

115
Q

The power of a lens stated on the packaging is mostly likely stated as what?

A

Back vertex power

116
Q

A GP lens change of 0.1mm equal how many diopters?

A

0.50

117
Q

Which curve is the steepest in a tetra-curve GP lens?

A

BCR

118
Q

What is the typical center thickness of GP lenses?

A

0.2mm

119
Q

Decreasing OAD in a minus power GP lens will do what to the center of gravity?

A

Move it forward

120
Q

Evaluating the amount of fluorescein under the edge of a GP lens is called what?

A

Edge clearance

121
Q

Decreasing OAD in a high minus power GP lens will do what?

A

Reduce edge thickness

122
Q

What kind of lag is expected with SCLs?

A

1mm

123
Q

According to Young, which test is most predictive in assessing a hydrogel lens fit?

A

Lower lid push up test

124
Q

When a hydrogel lens undergoes dehydration on the eye, what happens to the fit?

A

The lens tightens and moves less

125
Q

How much corneal astigmatism does a spherical soft lens compensate?

A

0%