Test 1 Review Flashcards
1
Q
What is the formula for mm to diopter conversion?
A
D = 337.5 / mm
2
Q
What is the average HVID?
A
11.7mm
3
Q
What is the average VVID?
A
10.6mm
4
Q
What is average CCT?
A
0.52mm
5
Q
What is average limbal corneal thickness?
A
0.67mm
6
Q
What is the average central radius of the cornea?
A
7.8mm
7
Q
What is the average sagittal depth of the cornea?
A
2.6mm
8
Q
What is the average index of refraction of the cornea?
A
n = 1.376
9
Q
What percentage of the cornea is made up of water?
A
78%
10
Q
How thick is the corneal epithelium?
A
50 microns
11
Q
What ensures the transparency of the stroma?
A
The lamellar arrangement
12
Q
Which lenses are made via lathing or molding?
A
GP
13
Q
Which lenses are made via cast-molding or spin casting?
A
SCL
14
Q
What are some advantages to lathing GP lenses?
A
Almost unlimited designs
Good for custom lenses
15
Q
What is the GP manufacturing method of choice?
A
Lathing
16
Q
What are some disadvantages to lathing GP lenses?
A
Slow production
High cost per lens
Labor intensive
17
Q
What is plasma treatment?
A
A “super cleaning” using room temperature, ionized oxygen and UV energy to break organic bonds
18
Q
Which lenses can be plasma treated?
A
GP
19
Q
How long does plasma treatment last?
A
Few days, to months
20
Q
What is the purpose of plasma treatment?
A
To increase wettability
21
Q
What is Dk?
A
Oxygen permeability
22
Q
What is the “D” in Dk
A
Diffusion coefficient
23
Q
What is “k” in Dk?
A
Solubility of the gas in the material
24
Q
What is Dk/t?
A
Dk value / thickness
25
What is the necessary Dk/t for DW lenses under open eye conditions?
24
26
What is the necessary Dk/t for EW lenses under open eye conditions?
87
27
What is the necessary Dk/t for DW lenses under closed eye conditions?
35
28
What is the necessary Dk/t for EW lenses under closed eye conditions?
125
29
What is the required EOP for DW lenses?
9.9%
30
What is the required EOP for EW lenses?
17.9%
31
What removes lipids from CLs?
Isopropyl alcohol
| Surfactants
32
What removes proteins from CLs?
Proteolytic enzymes
| Surfactants
33
Proteins are attracted to which type of CL?
Ionic lenses
34
Lipids are attracted to which type of CL?
Non-ionic lenses
35
What is the usual percentage of Hydrogen Peroxide in peroxide based cleaners?
3%
36
How long do lenses need to be left in peroxide to kill acanthomoeba?
3-6 hours
37
Do multipurpose solutions sterilize lenses?
No - they disinfect and preserve
38
What is the main difference between the Andrasko and IER staining studies?
Andrasko was measured after 2 hours of exposure
| IER was 3 months worth of data
39
Which type of soft CL is prone to lipid deposits?
Si-Hy
40
Si-hy lenses are prone to lipid deposits, and what else?
Mucin balls
41
What damage do mucin balls do to the cornea?
Epithelial dimples, causing NaFl pooling, but not staining
42
What is PMMA, and some of it's properties?
Hard lens materia
No Oxygen transmission
Old material
43
What are the two old, traditional Hard lens materials?
PMMA
| CAB
44
What are the 4 common hard lens materials?
PMMA
CAB
SA
FSA
45
What is the "standard" soft lens material?
HEMA
46
What is EGDMA and its properties??
A crosslinking agent for soft lenses that stiffens material and lowers the water content
47
What does GMA do?
Increases wettability and deposit resistance in SCLs
48
Why does GMA increase deposit resistance?
Smaller pore size
49
What does MMA do?
Decreases water content
Increases strength of lens
No Oxygen transmission
50
What does PVA do?
Increases water content
Increases resistance to deposits
Increases Dk
Increases Strength
51
What are the characteristics of MAA and NVP?
Increase water content
Very hydrophilic
Ionic
52
What is the water content of hydrogel lenses?
80%
53
What is the water content of Si-hy lenses?
24%
54
Higher water content usually means ___Dk value.
Lower
55
What is the "stem" for the hydrogel family?
Filcon
56
What group are Si-Hy lenses in?
Group V
57
What group are hydrogel lenses in?
Group IV
58
What is the "stem" of non hydrogel lenses?
Focon
59
What is the average lens diameter of a soft lens?
12-14.5
60
What is the average diameter of a GP lens?
9-10mm
61
How do you calculate the optic zone diameter of a GP lens?
OAD - (2 x peripheral curve widths)
62
If you have a high plus lens, and you make the diameter bigger, what happens to the center of gravity?
It pushes forward
63
If you have a high plus lens, and you make the diameter smaller, what happens to the center of gravity?
It moves backward
64
If you have a high minus lens, and you increase the diameter, what happens to the center of gravity?
It moves backward
65
Why is a minus carrier used?
To reduce center thickness in a high plus lens
66
Why is a plus carrier used?
To reduce edge thickness of high minus lenses
67
Describe Lipcof grade 1
1 small conj fold, smaller than the tear meniscus
| Mild dry eye
68
Describe Lipcof grade 2
Conj fold up to the height of the tear meniscus
| Moderate dry eye
69
Describe Lipcof grade 3
Fold of greater height than the tear meniscus, or multiple folds
Severe dry eye
70
What is normal for Phenol Red Thread test?
Greater than 20mm in 15 seconds
71
When a GP is placed on a toric cornea, how much astigmatism is left?
10%
72
A flat fitting GP gives what lacrimal lens?
minus
73
A steep fitting GP gives what lacrimal lens?
Plus
74
If your SCL is decentered, what should you do to make it fit better?
Use a steeper BCR
75
How long does a SCL need to "settle" in the eye?
5 minutes
76
What is the average HVID?
11.7mm
77
What is the average VVID?
10.6
78
What is the approximate water content of the cornea?
78%
79
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?
Lenses are inside out
80
Why do we use n=1.3375 for the cornea in calculations?
We consider the cornea to be a single surface for calculations
81
According to Holden and Mertz, a dialy wear contact lens should have at least what Dk/t value?
24
82
According to Holden and Mertz, an extended wear contact lenst should have at least what Dk/t value?
87
83
What do sessile drop and captive bubble measure?
Wetting angle
84
Which is a way to in-vivo test CL wettability?
Break-up time
85
What is the role of an enzymatic cleaner?
Removes proteinaceous layer from a CL surface
86
What material is added to a CL material to improve oxygen permeability?
Silicone
87
What is a component added to a GP lens to improve wettability?
Fluroine
88
Which study is critical for MPS products made by Bausch and Lomb?
Andrasko
89
What is the key difference between the methodologies of the Andrasko and IER studies?
Duration of time preceding assessment
90
What sequesters contaminants through formation of micelles?
Surfactant
91
What has a main role of inhibiting microbial growth?
Preservative
92
Which MPS additive contains mercury and is known to be toxic?
Thimerosal
93
The killing and/or the removal of some or all resident pathogenic organisms is called___.
Disinfection
94
What is the typical GP lens diameter?
9-10mm
95
A GP lens fitted steeper than the flat K will result in what power lacrimal lens?
Positive
96
What is the purpose of prism in a CL?
Stabilize cyl power
97
What are Bennet's classification of CL Dk values?
Low: 25-50
High: 51-99
Hyper: 100+
98
What was the first SCL material?
HEMA
99
What is the water content of a HEMA polymer?
38%
100
What is the water content of a Si-Hy lens?
24%
101
What does PVA do as a CL material?
Increases water content
Increases resistance to deposits
Increases Dk
Increases hardness and strength
102
What does MMA do as a CL material?
Lowers water content
Increases hardness and strength
Has NO oxygen permeability
103
What are the two core components of modern Silcone hydrogel lenses?
Si-O
| MMA
104
In hydrogel lenses, water content and Dk are usually ___ related.
Directly
105
Most silicone hydrogel lenses are ___ water content, ___Dk.
Low water
| High Dk
106
CAB, FSA and PMMA are all materials for which type of CL?
GP
107
What is the maximum acceptable corneal swelling induced by a CL?
4%
108
What is the approximate atmospheric percentage present at the anterior cornea in an open eye condition?
21%
109
What is the approximate atmospheric pressure present at the anterior cornea in an open eye situation?
747mmHg
110
What is the approximate partial oxygen pressure present at the anterior cornea in an open eye situation?
155mmHg
111
What is the approximate partial oxygen pressure present at the posterior cornea in an open eye situation?
55mmHg
112
What is the approximate partial oxygen pressure present at the anterior cornea in a closed eye condition?
55mmHg
113
What is the primary source of oxygen for the corneal epithelium in a closed eye condition?
Palpebral Conjunctiva
114
A modern GP lens from FSA is most commonly made how?
Lathing
115
The power of a lens stated on the packaging is mostly likely stated as what?
Back vertex power
116
A GP lens change of 0.1mm equal how many diopters?
0.50
117
Which curve is the steepest in a tetra-curve GP lens?
BCR
118
What is the typical center thickness of GP lenses?
0.2mm
119
Decreasing OAD in a minus power GP lens will do what to the center of gravity?
Move it forward
120
Evaluating the amount of fluorescein under the edge of a GP lens is called what?
Edge clearance
121
Decreasing OAD in a high minus power GP lens will do what?
Reduce edge thickness
122
What kind of lag is expected with SCLs?
1mm
123
According to Young, which test is most predictive in assessing a hydrogel lens fit?
Lower lid push up test
124
When a hydrogel lens undergoes dehydration on the eye, what happens to the fit?
The lens tightens and moves less
125
How much corneal astigmatism does a spherical soft lens compensate?
0%
