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III. Contact Lenses I > Midterm I > Flashcards

Midterm I Flashcards

1
Q

In order to steepen a GP lens, what must be done (with numbers)?

A
  1. increase BCR by 0.50D
    OR
  2. increase OZD by 0.3mm
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2
Q

What type of lenticular should be used for lower plus lenses or tighter lids?

A

regular carrier

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3
Q

What is the upper lid position in normal lid position? 1. Lower lid? 2. What is the required GP lens fit? 3

A
  1. 1/3 to 1/6 over cornea (10:00 and 2:00)
  2. at limbus
  3. lid attachment fit
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4
Q

What is the distance from the extension of the case curve edge to the surface of the lens?

A

radial edge lift (REL) (less than AEL)

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5
Q

If a GP lens has too much fluorescein at the edges (excessive edge width), what are the options for changing the lenses (with numbers)?

A
  1. steepen SCR/PCR by at least 1.0mm

2. decrease SCW/PCW by at least 0.2mm

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6
Q

What are the key relationship changes to BCR and OZD to maintain the same fitting relationship (with numbers)?

A
  1. flatten BCR (dec) 0.25D for every 0.4 to 0.5mm increase in OZD
  2. steepen BCR (inc) 0.25D for every 0.4 to 0.5mm decrease in OZD
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7
Q

What is the measurement that represents the true curvature data?

A

tangential

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8
Q

What are sagittal depth calculations used for clinically?

A
  1. maintaining or changing the fitting relationship
  2. comparing two soft contact lenses
  3. calculating center thickness of a CL
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9
Q

What are the results of using plasma of GP lenses?

A
  1. cleaning contamination from substrates
  2. improved lubricity
  3. decrease in wetting angle measurements (good thing), thereby improveing on-eye wettability
  4. increased bond strength
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10
Q

How would you decrease the edge lift of a lens?

A

steepen the peripheral curve radii and/or decrease the peripheral width

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11
Q

When were rigid gas permeable lenses first used?

A

1979

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12
Q

In order to flatten a GP lens, what must be done (with numbers)?

A
  1. decrease BCR by 0.50D
    OR
  2. decrease OZD by 0.3mm
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13
Q

What is the typical edge thickness for unpolished lenses?

A

0.10 to 0.12mm

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14
Q

What are the best strategies to examine the fluorescein pattern of a GP lens?

A
  1. use 10x or less mag
  2. cobalt blue filter
  3. wratten yellow filter
  4. wide beam on slit lamp
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15
Q

Do myopes accommodate and converge more or less in spectacles?

A

less

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16
Q

What are the advantages to a lid attachment fit?

A
  1. less movement

2. more comfortable

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17
Q

What type of prism is not able to go into contact lenses?

A

lateral

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18
Q

What is the typical center thickness for plano lenses?

A

0.20 to 0.21mm

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19
Q

What are the benefits of PMMA’s?

A
  1. readily machined
  2. low cost
  3. fairly wettable
  4. easy to care for
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20
Q

What are the lens types that have a Dk of around 100?

A
  1. Optimum Extra
  2. Boston XO
  3. Fluoroperm 151
  4. HDS 100
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21
Q

What is the typical center thickness for +3.00 and up lenses?

A

0.30 to 0.60mm

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22
Q

What is selected to provide the appropriate power of a GP lens?

A

front/power curve (anterior optic zone)

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23
Q

What is the average range of horizontal visible iris diameter (HVID)?

A

10 to 13mm

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24
Q

What is the range of lenses that use a plano shape?

A

-2.00 to -3.00

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25
Q

What is the lenticular curve of a GP lens viewed with?

A

microscope

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26
Q

What do the peripheral curve designs provide?

A
  1. fit cornea better
  2. encourages tear exchange behind lens
  3. aids in lens removal
  4. assists in centration
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27
Q

What should the SCW be for a tetra-curve design? 1. ICW? 2. PCW? 3

A
  1. 0.3
  2. 0.2
  3. 0.2
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28
Q

What are the different types of monomers used in GPs?

A
  1. methacrylic acid (MA)
  2. methyl methacrylate (MMA)
  3. hydroxyethyl methacrylate (HEMA)
  4. glycerol methacrylate (GMA)
  5. vinyl pyrrolidone (VP)
  6. vinyl alcohol (VA)
  7. phosphorylcholine (PC)
  8. siloxane
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29
Q

What is the distance from the edge of lens to extension of base curve radius (parallel to optic axis)?

A

axial edge lift (AEL)

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30
Q

What is the care protocol for plasma treated lenses?

A
  1. non-abrasive cleaner

2. after 6 months can use Boston and other abrasives

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31
Q

What is the upper lid position in a high lower lid position? 1. Lower lid? 2. What is the required GP lens fit? 3

A
  1. 1/3 to 1/6 over cornea (10:00 and 2:00)
  2. above limbus
  3. smaller OAD
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32
Q

What determines the modulus of a GP lens? 1. What are the results of this? 2

A
  1. polymer chemistry cross-linking

2. more cross-linking means more durability but less O2 transmission

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33
Q

What should be considered when the patient has dry eye for the GP lens fit assessment?

A

fluorescein will dissipate quickly and lens will look flat

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34
Q

What are the types of surface wettability for GP lenses (are they advancing or receding)?

A
  1. contact angle in air (advancing and receding)
  2. captive bubble (more like receding)
  3. Wilhelmy plate (advancing and receding)
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35
Q

What is the optic zone diameter (OZD) of a GP lens used for? 1. What is it measured with? 2

A
  1. fitting central cornea

2. hand magnifier

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36
Q

What are the advantages of Menicon Z GP lenses?

A
  1. higher Dk (163)

2. approved for 30 nights use

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37
Q

What are the types of rigid thermoplastic contact lenses?

A
  1. PMMA
  2. CAB
  3. GP (silicone acrylates and fluorosilicone acrylates)
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38
Q

What is the pupil diameter that is considered small? 1. Medium? 2. Large? 3

A
  1. less than 5mm
  2. 5 to 7 mm
  3. over 7mm
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39
Q

Are contact lenses considered thin or thick lenses?

A

thick

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40
Q

What areas need special attention when performing the anterior segment evaluation for a possible GP lens wearer?

A
  1. dry eye assessment
  2. evert lower and upper lid
  3. corneal staining with strips
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41
Q

What is the Gp lens fit that has central pooling of fluorescein with mid-peripheral bearing? 1. What are other characteristics of the lens? 2

A
  1. apical clearance

2. minimal movement, uncomfortable, and will warp/steepen cornea

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42
Q

When moving from glasses Rx to contact lenses, does a minus Rx become more or lens minus in power?

A

less minus

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43
Q

What does the transmissibility of GP lenses depend on?

A

thickness (Dk/L or Dk/t)

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44
Q

If the corneal topography showed a small corneal cap, should the lens fit be flatter or steeper? 1. Larger corneal cap? 2

A
  1. steeper

2. flatter

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45
Q

What is the benefit of topographers to keratometers?

A

topographers allow assessment of peripheral corneal astigmatism (3 vs 6mm)

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46
Q

What systemic diseases lead to caution when fitting GP lenses?

A
  1. thyroid dysfunction
  2. diabetes
  3. immunocompromised
  4. severe allergies
  5. any disease that leads to dexterity disorder
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47
Q

What are the lens types that have a Dk of around 30?

A
  1. Optimum Classic
  2. Boston ES
  3. Fluoroperm 30
  4. Fluoroperm 60
  5. HDS
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48
Q

What is the lenticular where the edge thickness is greater than the junction thickness? 1. What is the benefit of this? 2

A
  1. minus carrier

2. more interaction with the lid

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49
Q

What is the normal blink rate range?

A

10 to 15 blinks per minute

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50
Q

What is the definition of a an ON-k GP lens?

A

base curve that is equal to flat K

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51
Q

What is the OAD required to create a lid attached fit? 1. BCR? 2

A
  1. medium/large OAD (over 9mm)

2. slightly flat or On-K

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52
Q

What is the corneal curvature used to determine relating to a GP lens?

A

1/ base curve selection

  1. assess corneal regularity
  2. predict residual astigmatism
  3. predict irregular astigmatism
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53
Q

What is the overall diameter (OAD) of a GP lens measured with?

A
  1. hand magnifier

2. various gauges

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54
Q

What are the consequences of too little edge lift?

A
  1. poor tear exchange

2. poor lid interaction, inferior centration

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55
Q

If a GP lens has almost no fluorescein at the edges (minimal edge width), what are the options for changing the lenses (with numbers)?

A
  1. flatten SCR/PCR by at least 1.0mm

2. increase SCW/PCW by at least 0.2mm

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56
Q

What are the effects of lenticulars on plus lenses?

A
  1. thinner lenses
  2. decrease lens mass
  3. improves DK/t
  4. improves sharp/thin edges to interact better with the lid
  5. move center of gravity backwards
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57
Q

What should the SCR be compared to the BCR in a tri-curve design? 1. PCR compared to SCR? 2

A
  1. BCR + 1.0 to 1.5

2. SCR + 1.5 or 2.0

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58
Q

What is the lenticular where the edge thickness equals the junction thickness?

A

regular carrier

59
Q

What should be used to view the fluorescein pattern in UV protected GPs?

60
Q

How would you increase the edge lift of a lens?

A

Flatten the peripheral curve radii and/or widen the peripheral width

61
Q

What is the factor that contributes to the durability of a lens that that accounts for the resistance of material to breakage? 1. What contributes to this? 2

A
  1. toughness

2. cross-linking and thickness

62
Q

What are the steps to polymer cutting and preparation of a GP lens?

A
  1. evaluate purity and quality of raw materials
  2. refrigerate material
  3. tested for impurities using distillation
  4. polymerization
63
Q

What is a GP lens fit between the lids and in the aperture?

A

interpalpebral

64
Q

What person first used PMMA lenses?

65
Q

When the OZD is increased with the same BCR, what happens to the sagittal depth?

A

increases (steeper)

66
Q

What are the possible descriptions used for the edge lift/peripheral pattern?

A
  1. adequate
  2. excessive
  3. minimal
67
Q

What are the lens types that have a Dk of around 60?

A
  1. Optimum Comfort
  2. Boston EO
  3. Fluoroperm 92
68
Q

What does the diameter and radius of curvature of a lens produce?

A

fitting relationship of the CL and cornea

69
Q

If the GP is too steep, what are the options for changing the lens (with numbers)?

A
  1. flatten BCR by at least 0.50D

2. decrease OZD by at least 0.3mm

70
Q

What is the range of lenses that use a plus shape?

A

around plano and up (more plus)

71
Q

What is the type of semi-rigid contact lens?

A

silicone elastomers

72
Q

What are the most important factors for a lid attached fit?

A
  1. lid position

2. lid tension

73
Q

What is the GP lens fit that has central touch with mid-peripheral clearance? 1. What are other characteristics of the lens? 2

A
  1. apical bearing

2. often decenters, excessive movement, warp/flatten cornea

74
Q

What is the base curve radius (BCR) of a GP lens measured with?

A

radiuscope

75
Q

What should the SCR be compared to the BCR in a tetra-curve design? 1. ICR compared to SCR? 2. PCR compared to ICR? 3

A
  1. BCR + 0.8
  2. SCR + 1.0
  3. ICR + 1.4
76
Q

What is the lens mass equal to?

A

volume x specific gravity

77
Q

What are the lens types that have a Dk of around 150?

A
  1. Optimum Extreme
  2. Boston XO2
  3. Menicon Z
78
Q

What does molding GPs like soft contact lenses provide?

A

eliminates inconsistencies

79
Q

What is the upper lid position in a large palpebral aperture? 1. Lower lid? 2. What is the required GP lens fit? 3

A
  1. above upper limbus
  2. below lower limbus
  3. interpalpebral
80
Q

What does adding the fluorine monomer to SA material like in fluorosilicone acrylates (FSA) change?

A
  1. lowers surface charge

2. higher Dk’s (40 to 100)

81
Q

What are the disadvantages of a interpalpebral GP lens fit?

A
  1. more movement

2. less comfortable

82
Q

What are the disadvantages of PMMA’s?

A

no O2 transmissability

83
Q

What are the secondary and peripheral curve widths measured with?

A

hand maginifier

84
Q

What is the minimum junction thickness required to have an anterior peripheral curve?

85
Q

Is a plus or minus lens more likely to drop due to center of mass?

86
Q

What is the major benefit of GP lenses over soft CLs?

A

more tear exchange in GPs

87
Q

What is the ideal range of edge lift? 1. What are ranges are considered unacceptable? 2

A
  1. 0.5 to 1.0mm

2. less than 0.30mm or more than 1.0mm

88
Q

What is the range of lenses that use a minus shape?

A

-4.00 and less (more minus)

89
Q

What is the most important factor that determines the center of mass of a GP lens?

A

lens diameter (4 to 7 times more)

90
Q

What is the factor that contributes to the durability of a lens that that accounts for the stiffness of a lens? 1. What is it important for? 2

A
  1. modulus

2. mask astigmatism

91
Q

What are the advantages of silicone acrylate GPs?

A
  1. higher Dk than previous lenses

2. reduced rigidity

92
Q

What is the OAD required to create a interpalpebral fit? 1. Relative BCR? 2

A
  1. small OAR (8 to 9mm)

2. steeper fit

93
Q

When the OZD is decreased with the same BCR, what happens to the sagittal depth?

A

decreases (flatter)

94
Q

What is the smoothing of junctions between curves called?

95
Q

What does too steep of peripheral curves lead to?

A

false apical clearance

96
Q

What should the SCW range be for a tri-curve design? 1. PCW? 2

A
  1. 0.3 to 0.4

2. 0.3 to 0.4

97
Q

Do hyperopes accommodate and converge more or less in spectacles?

98
Q

Why is the thickness of a GP lens important?

A
  1. influence O2 transmissibility
  2. influence flexibility
  3. influence lens mass
99
Q

What should be done to the specific gravity of a GP lens that drops low on the cornea?

A

lower (less mass)

100
Q

What are the possible indications of using Gp lenses?

A
  1. refractive error
  2. cosmesis
  3. presbyopia
  4. irregular astigmatism
  5. corneal disorders
  6. amblyopia
  7. nystagmus
  8. vertical prism correction
101
Q

What type of lenticular should be used for higher plus lenses or looser lids?

A

minus carrier

102
Q

What are the Dk values to limit overnight swelling of GP lenses?

103
Q

What is the force on a GP lens that suctions a lens to the eye and is an interaction of water molecules on lens and cornea?

A

surface tension

104
Q

What is the ratio of the mass of a solid to an equal volume of distilled water at 4 degC called?

A

specific gravity

105
Q

What is the typical edge thickness for polished lenses?

106
Q

What are the forces acting on a GP lens?

A
  1. surface tension
  2. lid interactions
  3. gravitational
107
Q

What are repeating short units of monomers joined to form long chains called? 1. What are they linked by? 2

A
  1. polymers

2. covalent bonds

108
Q

What is the comparison of open eye oxygen uptake of the cornea by electrode to oxygen uptake after contact lens exposure?

A

equivalent oxygen percentage (EOP)

109
Q

What are the differences in machining for high Dk lenses?

A
  1. slower speeds
  2. slower polishing
  3. reduce heat
110
Q

What does the D in Dk stand for?

A

inherent ability of the material to allow gas through

111
Q

When the vertical cornea is steeper than the horizontal is it considered with-the-rule or against-the-rule astigmatism?

A

with the rule

112
Q

What is the typical center thickness for -3.00 and other minus lenses?

A

0.15 to 0.18mm

113
Q

What is the factor that contributes to the durability of a lens that that accounts for the scratchability of a lens?

114
Q

When using a high Dk material and CT of 0.10 to 0.12mm how much flexure is expected?

A

up to 1/3 of corneal toricity

115
Q

How long should you wait for a lens to settle before assessing it?

A

10 to 15 minutes

116
Q

What is considered a large palpebral aperture height/lid position? 1. Small? 2

A
  1. over 12mm

2. under 9mm

117
Q

What is the minimum Dk required for daily wear GP lenses to avoid swelling?

118
Q

What are the disadvantages of fluorosilicone acrylates (FSA)?

A
  1. surface easily scratched

2. greater lens flexure than PMMA

119
Q

What are the effects of lenticulars on minus lenses?

A
  1. thinner lenses
  2. decrease lens mass
  3. improves DK/t
  4. improves thick edges to decrease lid awareness and improve comfort
120
Q

What is the clinical measurement that is the distance from the cornea to the lens edge?

A

edge lift/clearance (less than AEL)

121
Q

What does a anterior peripheral curve create?

A

anterior optic zone or optical cap (1.4 to 1.0mm smaller than OAD

122
Q

What is the balancing point of a GP lens called? 1. Is the lens more likely to drop with it closer or further away from the lens itself? 2

A
  1. center of mass

2. closer to back surface

123
Q

What is the central thickness of a GP lens measured with?

A

thickness gauge

124
Q

What ocular disorders lead to caution when fitting GP lenses?

A
  1. pinguecula and pterygium
  2. glaucoma
  3. dry eye and blepharitis
125
Q

When the BCR is steepened with the same OZD, what happens to the sagittal depth?

A

increases (steeper)

126
Q

What is the SCW range for an IP fit? 1. PCW? 2

A
  1. 0.25 to 0.35

2. 0.30 to 0.40

127
Q

How much corneal astigmatism must be present when WTR for clinically significant flexure to occur?

128
Q

If the GP is too flat, what are the options for changing the lens (with numbers)?

A
  1. steepen BCR by at least 0.50D

2. increase OZD by at least 0.3mm

129
Q

What is the machining of GP lenses usually done by?

A

lathe cutting

130
Q

What is the GP lens fit that has even fluorescein pattern over the entire cornea?

A

alignment fit

131
Q

When the BCR is flattened with the same OZD, what happens to the sagittal depth?

A

decreases (flatter)

132
Q

Is light transmission through GP lenses greater or less than that of spectacles?

133
Q

What are the factors that lead to a center of mass of a GP lens that is further back from the back surface?

A
  1. larger lenses
  2. more minus power
  3. thinner
134
Q

Which people first used glass scleral lenses mostly for keratoconus?

A

Muller, Fick, Kalt

135
Q

What are the disadvantages of silicone acrylate GPs?

A
  1. more lipid deposit prone
  2. surface easily scratched
  3. higher breakage rate
  4. flexure problems
  5. parameter instability
136
Q

What should be done to the specific gravity of a GP lens that rides high on the cornea?

A

higher (more mass)

137
Q

What should be done to the specific gravity of a GP lens that is a prism ballast lens?

138
Q

What are the consequences of too much edge lift?

A
  1. corneal desiccation
  2. lens awareness
  3. decentration
139
Q

What is the global view of the corneal curvature as a whole that is compared between corneas called?

140
Q

What are the GP lenses that a doctor should not modify in office?

A
  1. high Dk lenses

2. lenses with plasma or other coatings

141
Q

What are the three major factors that contribute to the durability of a GP lens?

A
  1. hardness
  2. modulus
  3. toughness
142
Q

What are the advantages of fluorosilicone acrylates (FSA)?

A

1, higher Dk’s

  1. fewer lipid deposits
  2. better wetting
143
Q

What does the k in DK stand for?

A

degree to which oxygen is solubilized

III. Contact Lenses I (2 decks)

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