Midterm I Flashcards
(143 cards)
1
Q
In order to steepen a GP lens, what must be done (with numbers)?
A
- increase BCR by 0.50D
OR - increase OZD by 0.3mm
2
Q
What type of lenticular should be used for lower plus lenses or tighter lids?
A
regular carrier
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
- 1/3 to 1/6 over cornea (10:00 and 2:00)
- at limbus
- lid attachment fit
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)
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
- steepen SCR/PCR by at least 1.0mm
2. decrease SCW/PCW by at least 0.2mm
6
Q
What are the key relationship changes to BCR and OZD to maintain the same fitting relationship (with numbers)?
A
- flatten BCR (dec) 0.25D for every 0.4 to 0.5mm increase in OZD
- steepen BCR (inc) 0.25D for every 0.4 to 0.5mm decrease in OZD
7
Q
What is the measurement that represents the true curvature data?
A
tangential
8
Q
What are sagittal depth calculations used for clinically?
A
- maintaining or changing the fitting relationship
- comparing two soft contact lenses
- calculating center thickness of a CL
9
Q
What are the results of using plasma of GP lenses?
A
- cleaning contamination from substrates
- improved lubricity
- decrease in wetting angle measurements (good thing), thereby improveing on-eye wettability
- increased bond strength
10
Q
How would you decrease the edge lift of a lens?
A
steepen the peripheral curve radii and/or decrease the peripheral width
11
Q
When were rigid gas permeable lenses first used?
A
1979
12
Q
In order to flatten a GP lens, what must be done (with numbers)?
A
- decrease BCR by 0.50D
OR - decrease OZD by 0.3mm
13
Q
What is the typical edge thickness for unpolished lenses?
A
0.10 to 0.12mm
14
Q
What are the best strategies to examine the fluorescein pattern of a GP lens?
A
- use 10x or less mag
- cobalt blue filter
- wratten yellow filter
- wide beam on slit lamp
15
Q
Do myopes accommodate and converge more or less in spectacles?
A
less
16
Q
What are the advantages to a lid attachment fit?
A
- less movement
2. more comfortable
17
Q
What type of prism is not able to go into contact lenses?
A
lateral
18
Q
What is the typical center thickness for plano lenses?
A
0.20 to 0.21mm
19
Q
What are the benefits of PMMA’s?
A
- readily machined
- low cost
- fairly wettable
- easy to care for
20
Q
What are the lens types that have a Dk of around 100?
A
- Optimum Extra
- Boston XO
- Fluoroperm 151
- HDS 100
21
Q
What is the typical center thickness for +3.00 and up lenses?
A
0.30 to 0.60mm
22
Q
What is selected to provide the appropriate power of a GP lens?
A
front/power curve (anterior optic zone)
23
Q
What is the average range of horizontal visible iris diameter (HVID)?
A
10 to 13mm
24
Q
What is the range of lenses that use a plano shape?
A
-2.00 to -3.00
25
What is the lenticular curve of a GP lens viewed with?
microscope
26
What do the peripheral curve designs provide?
1. fit cornea better
2. encourages tear exchange behind lens
3. aids in lens removal
4. assists in centration
27
What should the SCW be for a tetra-curve design? 1. ICW? 2. PCW? 3
1. 0.3
2. 0.2
3. 0.2
28
What are the different types of monomers used in GPs?
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
29
What is the distance from the edge of lens to extension of base curve radius (parallel to optic axis)?
axial edge lift (AEL)
30
What is the care protocol for plasma treated lenses?
1. non-abrasive cleaner
| 2. after 6 months can use Boston and other abrasives
31
What is the upper lid position in a high lower lid position? 1. Lower lid? 2. What is the required GP lens fit? 3
1. 1/3 to 1/6 over cornea (10:00 and 2:00)
2. above limbus
2. smaller OAD
32
What determines the modulus of a GP lens? 1. What are the results of this? 2
1. polymer chemistry cross-linking
| 2. more cross-linking means more durability but less O2 transmission
33
What should be considered when the patient has dry eye for the GP lens fit assessment?
fluorescein will dissipate quickly and lens will look flat
34
What are the types of surface wettability for GP lenses (are they advancing or receding)?
1. contact angle in air (advancing and receding)
2. captive bubble (more like receding)
3. Wilhelmy plate (advancing and receding)
35
What is the optic zone diameter (OZD) of a GP lens used for? 1. What is it measured with? 2
1. fitting central cornea
| 2. hand magnifier
36
What are the advantages of Menicon Z GP lenses?
1. higher Dk (163)
| 2. approved for 30 nights use
37
What are the types of rigid thermoplastic contact lenses?
1. PMMA
2. CAB
3. GP (silicone acrylates and fluorosilicone acrylates)
38
What is the pupil diameter that is considered small? 1. Medium? 2. Large? 3
1. less than 5mm
2. 5 to 7 mm
3. over 7mm
39
Are contact lenses considered thin or thick lenses?
thick
40
What areas need special attention when performing the anterior segment evaluation for a possible GP lens wearer?
1. dry eye assessment
2. evert lower and upper lid
3. corneal staining with strips
41
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
1. apical clearance
| 2. minimal movement, uncomfortable, and will warp/steepen cornea
42
When moving from glasses Rx to contact lenses, does a minus Rx become more or lens minus in power?
less minus
43
What does the transmissibility of GP lenses depend on?
thickness (Dk/L or Dk/t)
44
If the corneal topography showed a small corneal cap, should the lens fit be flatter or steeper? 1. Larger corneal cap? 2
1. steeper
| 2. flatter
45
What is the benefit of topographers to keratometers?
topographers allow assessment of peripheral corneal astigmatism (3 vs 6mm)
46
What systemic diseases lead to caution when fitting GP lenses?
1. thyroid dysfunction
2. diabetes
3. immunocompromised
4. severe allergies
5. any disease that leads to dexterity disorder
47
What are the lens types that have a Dk of around 30?
1. Optimum Classic
2. Boston ES
3. Fluoroperm 30
4. Fluoroperm 60
5. HDS
48
What is the lenticular where the edge thickness is greater than the junction thickness? 1. What is the benefit of this? 2
1. minus carrier
| 2. more interaction with the lid
49
What is the normal blink rate range?
10 to 15 blinks per minute
50
What is the definition of a an ON-k GP lens?
base curve that is equal to flat K
51
What is the OAD required to create a lid attached fit? 1. BCR? 2
1. medium/large OAD (over 9mm)
| 2. slightly flat or On-K
52
What is the corneal curvature used to determine relating to a GP lens?
1/ base curve selection
2. assess corneal regularity
3. predict residual astigmatism
4. predict irregular astigmatism
53
What is the overall diameter (OAD) of a GP lens measured with?
1. hand magnifier
| 2. various gauges
54
What are the consequences of too little edge lift?
1. poor tear exchange
| 2. poor lid interaction, inferior centration
55
If a GP lens has almost no fluorescein at the edges (minimal edge width), what are the options for changing the lenses (with numbers)?
1. flatten SCR/PCR by at least 1.0mm
| 2. increase SCW/PCW by at least 0.2mm
56
What are the effects of lenticulars on plus lenses?
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
57
What should the SCR be compared to the BCR in a tri-curve design? 1. PCR compared to SCR? 2
1. BCR + 1.0 to 1.5
| 2. SCR + 1.5 or 2.0
58
What is the lenticular where the edge thickness equals the junction thickness?
regular carrier
59
What should be used to view the fluorescein pattern in UV protected GPs?
a filter
60
How would you increase the edge lift of a lens?
Flatten the peripheral curve radii and/or widen the peripheral width
61
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
1. toughness
| 2. cross-linking and thickness
62
What are the steps to polymer cutting and preparation of a GP lens?
1. evaluate purity and quality of raw materials
2. refrigerate material
3. tested for impurities using distillation
4. polymerization
63
What is a GP lens fit between the lids and in the aperture?
interpalpebral
64
What person first used PMMA lenses?
Feinbloom
65
When the OZD is increased with the same BCR, what happens to the sagittal depth?
increases (steeper)
66
What are the possible descriptions used for the edge lift/peripheral pattern?
1. adequate
2. excessive
3. minimal
67
What are the lens types that have a Dk of around 60?
1. Optimum Comfort
2. Boston EO
3. Fluoroperm 92
68
What does the diameter and radius of curvature of a lens produce?
fitting relationship of the CL and cornea
69
If the GP is too steep, what are the options for changing the lens (with numbers)?
1. flatten BCR by at least 0.50D
| 2. decrease OZD by at least 0.3mm
70
What is the range of lenses that use a plus shape?
around plano and up (more plus)
71
What is the type of semi-rigid contact lens?
silicone elastomers
72
What are the most important factors for a lid attached fit?
1. lid position
| 2. lid tension
73
What is the GP lens fit that has central touch with mid-peripheral clearance? 1. What are other characteristics of the lens? 2
1. apical bearing
| 2. often decenters, excessive movement, warp/flatten cornea
74
What is the base curve radius (BCR) of a GP lens measured with?
radiuscope
75
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
1. BCR + 0.8
2. SCR + 1.0
3. ICR + 1.4
76
What is the lens mass equal to?
volume x specific gravity
77
What are the lens types that have a Dk of around 150?
1. Optimum Extreme
2. Boston XO2
3. Menicon Z
78
What does molding GPs like soft contact lenses provide?
eliminates inconsistencies
79
What is the upper lid position in a large palpebral aperture? 1. Lower lid? 2. What is the required GP lens fit? 3
1. above upper limbus
2. below lower limbus
3. interpalpebral
80
What does adding the fluorine monomer to SA material like in fluorosilicone acrylates (FSA) change?
1. lowers surface charge
| 2. higher Dk's (40 to 100)
81
What are the disadvantages of a interpalpebral GP lens fit?
1. more movement
| 2. less comfortable
82
What are the disadvantages of PMMA's?
no O2 transmissability
83
What are the secondary and peripheral curve widths measured with?
hand maginifier
84
What is the minimum junction thickness required to have an anterior peripheral curve?
0.13mm
85
Is a plus or minus lens more likely to drop due to center of mass?
plus lens
86
What is the major benefit of GP lenses over soft CLs?
more tear exchange in GPs
87
What is the ideal range of edge lift? 1. What are ranges are considered unacceptable? 2
1. 0.5 to 1.0mm
| 2. less than 0.30mm or more than 1.0mm
88
What is the range of lenses that use a minus shape?
-4.00 and less (more minus)
89
What is the most important factor that determines the center of mass of a GP lens?
lens diameter (4 to 7 times more)
90
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
1. modulus
| 2. mask astigmatism
91
What are the advantages of silicone acrylate GPs?
1. higher Dk than previous lenses
| 2. reduced rigidity
92
What is the OAD required to create a interpalpebral fit? 1. Relative BCR? 2
1. small OAR (8 to 9mm)
| 2. steeper fit
93
When the OZD is decreased with the same BCR, what happens to the sagittal depth?
decreases (flatter)
94
What is the smoothing of junctions between curves called?
blend
95
What does too steep of peripheral curves lead to?
false apical clearance
96
What should the SCW range be for a tri-curve design? 1. PCW? 2
1. 0.3 to 0.4
| 2. 0.3 to 0.4
97
Do hyperopes accommodate and converge more or less in spectacles?
more
98
Why is the thickness of a GP lens important?
1. influence O2 transmissibility
2. influence flexibility
3. influence lens mass
99
What should be done to the specific gravity of a GP lens that drops low on the cornea?
lower (less mass)
100
What are the possible indications of using Gp lenses?
1. refractive error
2. cosmesis
3. presbyopia
4. irregular astigmatism
5. corneal disorders
6. amblyopia
7. nystagmus
8. vertical prism correction
101
What type of lenticular should be used for higher plus lenses or looser lids?
minus carrier
102
What are the Dk values to limit overnight swelling of GP lenses?
85 to 135
103
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?
surface tension
104
What is the ratio of the mass of a solid to an equal volume of distilled water at 4 degC called?
specific gravity
105
What is the typical edge thickness for polished lenses?
0.08mm
106
What are the forces acting on a GP lens?
1. surface tension
2. lid interactions
3. gravitational
107
What are repeating short units of monomers joined to form long chains called? 1. What are they linked by? 2
1. polymers
| 2. covalent bonds
108
What is the comparison of open eye oxygen uptake of the cornea by electrode to oxygen uptake after contact lens exposure?
equivalent oxygen percentage (EOP)
109
What are the differences in machining for high Dk lenses?
1. slower speeds
2. slower polishing
3. reduce heat
110
What does the D in Dk stand for?
inherent ability of the material to allow gas through
111
When the vertical cornea is steeper than the horizontal is it considered with-the-rule or against-the-rule astigmatism?
with the rule
112
What is the typical center thickness for -3.00 and other minus lenses?
0.15 to 0.18mm
113
What is the factor that contributes to the durability of a lens that that accounts for the scratchability of a lens?
hardness
114
When using a high Dk material and CT of 0.10 to 0.12mm how much flexure is expected?
up to 1/3 of corneal toricity
115
How long should you wait for a lens to settle before assessing it?
10 to 15 minutes
116
What is considered a large palpebral aperture height/lid position? 1. Small? 2
1. over 12mm
| 2. under 9mm
117
What is the minimum Dk required for daily wear GP lenses to avoid swelling?
over 25
118
What are the disadvantages of fluorosilicone acrylates (FSA)?
1. surface easily scratched
| 2. greater lens flexure than PMMA
119
What are the effects of lenticulars on minus lenses?
1. thinner lenses
2. decrease lens mass
3. improves DK/t
4. improves thick edges to decrease lid awareness and improve comfort
120
What is the clinical measurement that is the distance from the cornea to the lens edge?
edge lift/clearance (less than AEL)
121
What does a anterior peripheral curve create?
anterior optic zone or optical cap (1.4 to 1.0mm smaller than OAD
122
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
1. center of mass
| 2. closer to back surface
123
What is the central thickness of a GP lens measured with?
thickness gauge
124
What ocular disorders lead to caution when fitting GP lenses?
1. pinguecula and pterygium
2. glaucoma
3. dry eye and blepharitis
125
When the BCR is steepened with the same OZD, what happens to the sagittal depth?
increases (steeper)
126
What is the SCW range for an IP fit? 1. PCW? 2
1. 0.25 to 0.35
| 2. 0.30 to 0.40
127
How much corneal astigmatism must be present when WTR for clinically significant flexure to occur?
1.00D
128
If the GP is too flat, what are the options for changing the lens (with numbers)?
1. steepen BCR by at least 0.50D
| 2. increase OZD by at least 0.3mm
129
What is the machining of GP lenses usually done by?
lathe cutting
130
What is the GP lens fit that has even fluorescein pattern over the entire cornea?
alignment fit
131
When the BCR is flattened with the same OZD, what happens to the sagittal depth?
decreases (flatter)
132
Is light transmission through GP lenses greater or less than that of spectacles?
greater
133
What are the factors that lead to a center of mass of a GP lens that is further back from the back surface?
1. larger lenses
2. more minus power
3. thinner
134
Which people first used glass scleral lenses mostly for keratoconus?
Muller, Fick, Kalt
135
What are the disadvantages of silicone acrylate GPs?
1. more lipid deposit prone
2. surface easily scratched
3. higher breakage rate
4. flexure problems
5. parameter instability
136
What should be done to the specific gravity of a GP lens that rides high on the cornea?
higher (more mass)
137
What should be done to the specific gravity of a GP lens that is a prism ballast lens?
higher
138
What are the consequences of too much edge lift?
1. corneal desiccation
2. lens awareness
3. decentration
139
What is the global view of the corneal curvature as a whole that is compared between corneas called?
sagittal
140
What are the GP lenses that a doctor should not modify in office?
1. high Dk lenses
| 2. lenses with plasma or other coatings
141
What are the three major factors that contribute to the durability of a GP lens?
1. hardness
2. modulus
3. toughness
142
What are the advantages of fluorosilicone acrylates (FSA)?
1, higher Dk's
2. fewer lipid deposits
3. better wetting
143
What does the k in DK stand for?
degree to which oxygen is solubilized
