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Flashcards in Sem 1 Deck (147):
1

Full time wear of contact lenses is when the patient wants to wear the lenses how often?

5-7 days per week

2

Part time wear of CLs is when the Px wants to wear the lenses how often?

occasional wear or only a few times per week

3

Daily wear is?

wearing CLs during waking hours only

4

Extended wear is?

wearing CLs continuously including overnight use

5

Disposable CLs are?

replaced (or diposed of) at greater frequency - daily, fortnightly, monthly

6

Conventional CLs are replaced how often?

annually

7

Spherical RGPs fit what type of corneas?

near spherical cornea and any refractive error where the refractive astigmatism is mostly corneal

8

Spherical SCLs fit on what type of corneas?

most corneas and any refractive error with low refractive astigmatism

9

Front toric RGPs fit what type of corneas?

near spherical corneas and where there is significant refractive astigmatism

10

Toric SCLs fit what type of corneas?

most corneas and where there is significant refractive astigmatism

11

Bitoric/back toric RGPs fit on what type of corneas?

highly astigmatic corneas

12

Multifocal/Bifocal CLs have both RGP and SCL choices for patients requiring?

an ADD component

13

Other types of contact lenses? (6)

color SCL
prosthetic SCL
semi scleral RGPs
reverse geometry RGPs
OTK RGPs
post-surgical lenses

14

A positive spectacle lens becomes more or less positive when brought to the ocular plane?

more positive

15

ΔK is the?

amount of corneal astigmatism

16

With ΔK, which K value is flat and which one is steep?
K1 @ _____?
K2 @ _____?

K1 = flat
K2 = steep

17

ΔK = ?

K1 - K2 x flat axis

18

Refractive astigmatism that is significant and primary due to corneal astigmatism in origin is optically best managed with a?

RGP CL

19

The corneal diameter is also known as?

Horizontal visible iris diameter

20

Corneal diameter is relevant in determining what parameter of a contact lens?

overall diameter

21

Which keratometer can measure along two principle meridians with one measurement?

Bausch and Lomb

22

Which keratometer can only measure one principle meridian at a time?

Javal-Schiotz

23

Keratometers are limited to what three things?

restricted to spherocylindrical surfaces
3mm central area only
greatly affected by user and focusing error

24

The range of a keratometer can be extended. For steep corneas a _____ trial lens is used and for fat corneas a _____ trial lens is used

+1.25
-1.00

25

Videokeratoscopes measure how much area?

central 6-10mm

26

If the rings on a placido disc are spaced further apart this means that the cornea is?

flat

27

Normal axial patterns observed from topography maps? (5)

round
oval
symmetric bow tie
asymmetric bow tie
irregular

28

What does thhe tangential display of a topographer do?

shows more discrete changes

29

The following characteristics apply to which topography map type?
- measures radius of curvature to a comparable sphere
- centers of rotation fall on the axis defined by videokeratoscope
- reasonably represents refractive
- involves smoothening

axial map/sagittal map

30

The following characteristics apply to which topography map type?
- Is not constrained by centers of rotation falling on axis of videokeratoscope
- more accurately depicts the irregularity and location
- shows local irregularity

tangential maps/instantaneous local map

31

Keratometers can be used to? (5)

measure normal variations
look at pathology/abnormal corneas
identify irregular corneas
monitor corneal shape changes
simulate RGP lens on eye fitting relationship

32

On a topography map, would you expect the hotter colors to run vertically or horizontally for a WTR astigmatic cornea?

vertically

33

Astigmatic corneas can be categorised into irregular astigmatism and regular astigmatism. What angle α is the boundary between the two?

20
ie α greater than 20 degrees = irregular astigmatism
α smaller than 20 degrees = regular

34

What is the term given to a flat cornea?

keratoplana

35

Pellucid marginal degeneration is thinning of which part of the cornea?

inferior

36

Spherical RGPs are good for?
a) High corneal cyl and low refractive cyl
b) High corneal cyl and high refractive cyl
c) Low to medium corneal cyl and low to medium refractive cyl (same axis)
d) Low to medium corneal cyl and high refractive cyl

Low to medium corneal cyl and low to medium refractive cyl (same axis)

37

Why are spherical RGPs not good for fitting eyes with low corneal cyl and high refractive astigmatism?

because the tear layer formed is insufficient to correct the refractive astigmatism

38

Why are spherical RGPs not good for fitting eyes with high corneal cyl and high refractive cyl?

the tear layer power formed would correct the refractive astigmatism however the spherical RGP would not fit the toric corneal shape well

39

Why are spherical RGPs not good for fitting eyes with high corneal cyl and low refractive cyl?

the tear layer power formed would over-correct the refractive astigmatism and the spherical RGP would not fit the toric cornea shape well - this is the LEAST DESIRABLE OPTION

40

What RGP parameters MUST you have to order a spherical RGP?

diameter
optic zone diameter
BC
BVP
RGP design
material

41

The diameter of a RGP should be how many millimeters smaller than the cornea?

2-2.5mm

42

An RGP that fits within the lids is called?

intra-palpebral fitting (usually small diameter lenses)

43

An RGP that stays more or less in the middle of the cornea and between the lids is called?

inter-palpebral fitting (usually medium diameter lenses)

44

An RGP that stays tucked under the upper eyelid and moves with the upper lid during blinking is called?

lid attachment fitting (usually large diameter lenses with respect to aperture size)

45

For a steep cornea (>47D) what lens diameter size would you choose?

small/medium

46

For a flat cornea (<39D) what lens diameter size would you choose?

Med/large to large

47

A small diameter RGP is classified as?

<9.00mm (7.0 OZD)

48

A small/medium diameter RGP is classified as?

~9.0-9.3mm (7.5 OZD)

49

A medium/large diameter RGP is classified as?

~9.5-9.8mm (8.0 OZD)

50

A large diameter RGP is classified as?

>9.8mm (8.5 OZD)

51

When fitting a spherical RGP what are the parameters to select in order? (5)

1. Diameter of lens
2. Base curve
3. BVP
4. Lens design
5. Test lens on eye

52

How thick should the channel of tears be through the central portion of a RGP?

10-20um

53

a 0.1mm change in radius is equivalent to how much dioptric change?

0.5D

54

When there is moderate astigmatism what BC do you select for a spherical RGP?

slightly steeper than flat K

55

What is the ideal axial edge lift?

120um

56

What does this mean:
7.85:7.6/8.50:8.2/11.0:9.0

7.85BC and 7.6 OZD
8.50 secondary curve and 8.2 diameter
11.0 peripheral curve and 9.0 diameter

57

Peripheral curve design - tangent designs uses the tangent cone concept and involves?

landing of midperiphery to allow even distribution of pressure and limit lens lateral drift

58

Dynamic fitting characteristics looks at?

how the lens acts naturally on the eye

59

Static fitting characteristics shows the?

lens-to-cornea curvature relationship

60

What is the minimum threshold needed in order to judge the presence of fluoroscein?

20um

61

The optimum edge width is?

0.5mm

62

A RGP should decentre less than how many mm?

0.5mm

63

A RGP can be graded as flat and loose. The level of looseness is graded considering? The level of flatness is graded by the?

dynamic fitting characteristics
static fitting characteristics

64

Most loot fitting RGPs are caused by?

BOZR too much flatter than corneal curvature

65

Loose lenses can also be due to fitting ____ lenses without a ___ BC component

small
flat

66

A lens that shows excessive central pooling, heavy mid-peripheral contact , narrow edge lift and width is?

steep and tight fitting lens

67

a slightly loose or tight RGP should have its BC changed by?

0.15mm

68

A visibly loose/tight RGP should have its BC changed by?

0.2-0.3mm

69

Very loose/right RGP should have its BC changed by?

0.4mm

70

An excessively loose RGP should have its BC changed by?

0.5mm

71

tight fitting lenses are most commonly caused by?

BOZR too much steeper than corneal curvature

72

Tight fitting RGPs can also occur when a lens fitting is too _____ leading to lens vaulting

large

73

What is wrong with a RGP if you see the following characteristics?
- typically ride centrally or low
- move quickly on blink
- vault over the central cornea too much
- produce bubbles in the central zone
- impinge on the peripheral cornea

BC too steep

74

What is wrong with a RGP if you see the following?
- typically ride high but eventually slip off to the side or downward
- float around on the eye
- have large excursions or hang beneath the lid
- have too much edge lift

BC too flat

75

What is wrong with a RGP if you see the following?
- irregular pressure over the cornea
- movement shows the lens to rock up and down or rock left and right

cornea too astigmatic

76

a lens movement that rocks up and down is associated with what sort of astigmatism?

with the rule

77

What is wrong with a RGP if it has the following characteristics?
- typically move freely on the eye or decentre easily
- may dislodge onto conj or pop off the eye with quick lateral gazes

diameter too small

78

Bigger lenses are naturally looser/tighter because of lower/higher sagittal height

tighter
higher

79

Smaller lenses are naturally looser/tighter because of lower/higher sagittal height

looser
lower

80

What is wrong with a RGP with the following characteristics?
- excessive lens tightness
- restrict movement
- limit tear exchange
- can irritate limbal area = excessive tearing and lens awareness

lens too big

81

If a lens is made 0.5mm larger then the BC should be made how much flatter/steeper? (unless you want central clearance to change)

0.05mm flatter (0.25D)

82

What effect does increasing TD have on edge lift?

increases edge lift

83

What two things does a high edge lift cause?

causes lens to ride higher
produces more lid attachment

84

Reducing TD has what effect on edge lift?

decreases edge lift

85

What two things does a low edge lift cause?

causes lens to ride lower
less lid attachment

86

To increase edge lift, what parameters can you increase? (5)

SCR (most influential)
PCR
SCW (while reducing OZD)
PCW (while reducing OZD)
TD along with OZD

87

High plus powered RGPs have possible problems with inferior decentration. This can be managed through?

adding a minus carrier on the edge

88

High minus powered RGPs can have possible problems with lid interactions. This can be managed through?

adding a plus lenticular - resulting in wedge shape

89

What edge configuration has the best comfort level?

centre>posterior>anterior

90

Wettability is measured with what three methods

sessile drop
Wilhelmy plate
captive bubble

91

Dk denotes the ______ of contact lens materials

permeability

92

Dk/t denotes what?

the transmissibility through a lens of given thickness

93

What lens parameters can you change for a lens that is too tight? (4)

increase BC
increase peripheral curve (edge lift)
widen peripheral curve
decrease OZD

94

What lens parameters can you change for a lens that is too loose? (4)

decrease BC
decrease peripheral curve (edge left)
reduce peripheral curve width
increase OZD (with TD)

95

Dimple veiling is caused if the lens is? (2)

steep centrally
too much edge lift

96

Constant high or low riding RGPs can lead to?

mechanically induced corneal warpage/moulding

97

The underlying associated cause of corneal warpage is?

prolonged oedema

98

What is often the cause of staining at 3 and 9o'clock?

lens edge miniscus causing local tear film thinning

99

What is characterised by an opaque, elevated mass at the nasal and/or temporal cornea adjacent the limbus

vascularised limbal keratitis

100

What is the etiology of blink related problems with a RGP?

lens edge awareness
sensation of any surface irregularity
excessive lens movement

101

The upper lid being subjected to higher frictional forces of intrinsic or extrinsic nature causes what?

lid-wiper epitheliopathy

102

Toric RGPs are used in what two situations?

to improve fitting on regular astigmatic cornea
to correct residual astigmatism that occurs when fitting spherical RGP

103

Calculated residual astigmatism (CRA) = ?

spectacle cyl - corneal cyl

104

What makes residual astigmatism significant?

>0.75DC
Oblique when not corrected > ATR > WTR
large pupils with ATR astig
if the Px is habitually fully corrected with cyl

105

Bitoric and back-surface toric CLs are used to fit corneas with a minimum how many dioptres of regular astigmatism?

2D

106

How do you choose the BCs for a back toric RGP?

select BC equal to flat K for r1
select BC 0.1mm flatter than steep K for r2 (note -0.50 tear layer)

107

Bennet's tricurve design SCR and PCR parameters?

SCR add 1.0-1.5mm to BC/0.3 wide
PCR add 1.5-2.0mm to SC/0.4 wide

108

The induced over-correction is a minus cylinder at the same axis as the _______ principle meridian. The magnitude is proportional to the degree of ________ and reractive index of ________

flatter
CL toricity
CL material

109

Back surface torics work for a patient that has refractive cylinder that is _____ greater than the corneal cylinder

30-50%

110

Back surface toric ΔBVP (dioptres) =

ΔBC (dioptres) * material factor

111

What RGP works well with patients who have spectacle cyl = corneal cyl

SPE back toric RGP

112

Rotation of what toric RGP does NOT induce unwanted astigmatism?

SPE back toric

113

Sterilisation results in

all viable microbes to be eliminated; none can reproduce

114

Disinfection results in

substantial reduction in level of microbial contamination

115

The D-value of a solution is an index for what? Is a lower or higher D-value better?

index of disinfection rate
lower is better

116

Complete disinfection requires pressure of ____kPa applied to steam and temperature of _____ degrees and after _____ mins all bacteria, spores, fungi, and viruses killed

100
121
120

117

Name three buffers used in soft lens solutions

sod phosphate
sod borate
sod bicarbonate

118

Methyl cellulose is what kind of agent and what does it do?

viscosity agent
improve wetting time + comfort

119

Chelating agents e.g. sodium adetate have what function?

enhances actions of preservatives

120

You cannot use SCLs with what 3 eye drops?

Lomide
Naphcon-A
Latanoprost

121

Hydrogen peroxide systems aren't as good against which type of microbe?

acanthamoeba

122

PVA, PVP and PEG are all examples of what?

wetting agents

123

BAK, PHX, CHX are examples of what ind of agents?

RGP solution preservatives

124

What are the top RGP troubleshooting tips?

Polishing 6-12 monthly
Progent protein cleaner
AO Sept, omnicare

125

What lens is used when a normal spherical RGP gives good vision but uneven edge lift on a toric cornea

TSP

126

Adding what component to a lens makes it ionic?

methacrylic acid (MA)

127

An ionic lens causes what two things?

attracts more lysozyme but
makes material more wettable

128

FDA 1

low water + non-ionic

129

FDA 2

high water + non-ionic

130

FDA 3

low water + ionic

131

FDA 4

high water + ionic

132

higher water content of SCL usually correlates with

higher Dk/t (except SiHi)

133

How much O2 is needed to prevent oedema for DW and EW SCLs?

9.9% (Dk/t = 24) for DW
17.9% (Dk/t = 87) for EW

134

Thin or thick SCLs interact more with the lids and move more?

thick

135

What effect does increasing water content do to lens movement?

decreases lens movement

136

The Da Vinci Code helped understand what concept?

corneal neutralisation in a bowl of water

137

Rene Descartes is known for what concept?

elongated fluid-filled tube to enlarge retinal image size

138

1946 Kevin Tuohy did what?

discovered first corneal lens

139

Dry eye etiologies with contact lenses? (3)

1. Dessication secondary to pervaporation (SCL)
2. Dessication secondary to exposure/poor tear consistency over cornea (RGP)
3. Bioincompatibility leading to tear instability

140

The lipid layer of the tear film has two phases which are? (2)

non-polar phase
polar phase

141

What is the function of the outermost layer of the lipid layer?

regulate transmission water rate, CO2, O2, ions

142

What is the function of the inner layer of the lipid layer?

provide enhanced stability

143

Which lipid layer is abundant in short chain saturated fatty acids?

polar phase

144

Which FDA group material is the most lipid binding?
Which one has the least?

FDA group II materials (high water, non-ionic)
FDA group III

145

Local dry spots are caused by hydroph____ areas

hydrophobic

146

Proteins deposit on what FDA group material which makes surface less hydrophilic which then attracts lipids

FDA group IV

147

What is the first step of management for lipid deposition on CLs?

select different material for Px