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Contact Lens Part One > Exam one Material > Flashcards

Exam one Material Flashcards

1
Q

what was phase one of contact lenses

A

understanding corneal neutralization

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2
Q

what was phase two of contact lens

A

linking neutralization with on eye device

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3
Q

what was phase three of contact lens

A

clinical experiments

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4
Q

who were the three men credited for invention of Cls

A

Muller, Kalt, and Fick

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5
Q

this man is the “father of optics” ; came up with the idea of protective lens - corneal lens with lacrimal lens effects

A

August Muller

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6
Q

this man developed scleral lenses for keratoconus ; realized keratoconus had ectasia and could flatten the cornea

A

Eugene Kalt

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7
Q

this man developed Cls use in aphakia, prosthetic /cosmetic - blown glass, scleral lenses ; credited with using the term “contact lenses”

A

Adolf Fick

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8
Q

this guy recognized the adaptational process “FIcks Phenomenon” -

A

Adolf Fick

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9
Q

What is Ficks Phenomenon

A

less edema when air trapped behind lens on insertion

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10
Q

what was phase 4 of CLs

A

getting the lenses to fit, getting pts to adapt and working on materials and designs

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11
Q

phase 5 of Cls development

A

plastic Cls

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12
Q

phase 6 of Cls development

A

hydrogels

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13
Q

T or F: with GP lenses you have to take into account the tear film and the lens for total correction

A

T

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14
Q

Do we usually fit GP lenses off from K

A

yes: we usually fit the lens flatter/steeper than K

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15
Q

what is the index of the cornea

A

1.3375

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16
Q

what happens to the tear film when the Cls is the same curvature of the cornea

A

tear film will be plano

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17
Q

is a longer radius of curvature flatter or steeper power

A

flatter

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18
Q

T or F: for every 0.1 mm change in the radius of curvature -> 0.50 D change in tear film power

A

T ( flatter add -0.50 minus , and steeper add +0.50 plus )

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19
Q

What is the formula to find the BC

A

F= 337.5/ radius in mm

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20
Q

T or F: the BC in diopters is NOT the front surface of the tear lens

A

F : it is the front surface of the tear lens

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21
Q

TL = ?

A

front of tears + back of tears

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22
Q

T or F: the front of the tears is the same as the BC ( plus ) and the back of the tears is the same as K ( minus)

A

T

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23
Q

If BC is flatter than K what happens to tear film

A

it becomes negative

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24
Q

If bc is steeper than K what happens to the tear film

A

it becomes positive

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25
Q

If BC is on k what happens to the tear film

A

it becomes plano

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26
Q

will the tear lens have the same cyl as the cornea

A

Y ( CL can be spherical and still correct astigmatism ; HUGE advantage for GPs)

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27
Q

will the TL correct all of the patients astigmatism

A

Maybe: TL will match and correct for the corneal Astigmatism but it cant correct for the crystalline lens cyl

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28
Q

T or F: for a rigid lens, the RA is simply the amt of crystalline lens cyl

A

T

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29
Q

what amt of uncorrected RA do we have to worry about

A

> 0.75 D

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30
Q

what if the axes don’t match when trying to find RA on GP lenses

A

rule of thumb: 20 degrees or less we can consider them the same axis ; more than that and we cant work the problem

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31
Q

where does the cornea mostly get its oxygen from

A

the atmosphere ( endothelium oxygen comes from aqueous too )

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32
Q

oxygen Is what % of atmosphere

A

21% independent of elevation

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33
Q

what is total atm pressure at sea level

A

760 mm Hg ( so 21% x 760 = 159.6 mmHG actual value 155)

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34
Q

what are the routes of oxygen to the cornea while wearing a Cls

A

through the active tear pump or through the lens material

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35
Q

what is the tear pump

A

open eye, movement, waste, debris

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36
Q

is the tear pump more active in the GP lens

A

Y: they move more; they are non draping - 10-20% of tears are exchanged per blink a SCL has 1% tear exchange

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37
Q

what are the diff sources of oxygen to the cornea

A

tears, and aqueous from anterior chamber( major source for endothelium)

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38
Q

where does the OPEN eye get its oxygen from

A

atmosphere ( 21%), aqueous ( 7.4%) and 1 mm below the superior limbus ( 10.4%)

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39
Q

where does the CLOSED eye get its oxygen frmo

A

palpebral conjunctiva 7.5% ( this is not enough which is why you sometimes have corneal edema ) and limbal vasculature ( closed and open eye ) -> minor role ( insignificant unless eye is compromised)

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40
Q

how much oxygen is needed

A

12% needed or you get a reduction in mitosis and 8% needed or you get a decrease in corneal sensitivity

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41
Q

this is the rate of flow for a given material - rep by Dk numbers

A

permeability

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42
Q

what is the relationship between water content and permeability for standard hydrogels

A

more water content= more oxygen

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43
Q

What does D in Dk stand for

A

diffusion coefficient - the flow rate

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44
Q

What does k in Dk stand for

A

solubility coefficient of oxygen in material ; expressed as some number x 10^11

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45
Q

what affects permeability

A

initial gas pressure, ambient temp ( warmer = more oxygen transmitted), and surrounding pressure

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46
Q

what is permeability

A

how fast oxygen moves in a given material

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47
Q

what permeability number is a good range

A

50-60 is a good midrange ( for example Polycon II= 12 is not good but Boston EO = 58 which is good) - higher number is better

48
Q

what is the Dk for the Bostons

A

Boston ES 18-25
Boston EO 60
Boston XD 100

49
Q

Whats the Dk for the Paragons

A

Paragon HDS 60

Paragon HDS100 -100

50
Q

Whats the Dk for the Menicon Z

A

170

51
Q

what is transmissibility

A

this takes into account the distance traveled by oxygen ; rep as Dk/t; units are 10^-9

52
Q

What is the Equivalent Oxygen %

A

this looks at how fast the cornea is sucking up oxygen; this is in vivo ( on the cornea) whereas Dk/t is in vitro - the more oxygen depleted the cornea is the more oxygen it will take up

53
Q

what is the relationship of EOP to Dk/t

A

non linear; no matter how good the Dk/t value , the EOP eventually tapers off

54
Q

why do we suggest daily wear

A

to avoid swelling ; EOP of 10 % or DK/t of 24- these values are holden mertz criteria

55
Q

WHy do we suggest EW

A

to allow for overnight swelling of 4% but return to normal thickness during the day ; EOP 12% or Dk/t 34 ( side note: 4% is physiologic swelling) - these values are holden mertz criteria

56
Q

what is the emerging transmissibility number for overnight wear

A

125 Dk/t units

57
Q

T or F: Dk/t will be less in thicker areas

A

T

58
Q

what is the diff between an empirical fit and a diagnostic fit

A

an empirical fit is not trying anything on the pt ; a diagnostic fit is when you put the Cls on the eye and adjust from there

59
Q

what is an empirical fitting and why is it common

A

K’s and refraction; most common way of ordering GP lenses in the US bc most docs don’t feel comfortable fitting GP lenses

60
Q

what are some disadvantages of an empirical fit

A

you lose valuable information on lids/lens interaction, movement ( should move 2-3 mm per blink ) , and topography , you lose the warranty lens

61
Q

with GP lenses will you have looser or tighter fit with a flatter cornea

A

flatter /looser and steeper/ tighter

62
Q

which lenses should you never try empirically

A

MF and irregular corneal fits

63
Q

what are the advantages of a diagnostic fitting

A

evaluate on eye performance; first custom lens will be more accurate; can tweak parametes before buying the lens

64
Q

what are some disadvantages of diagnostic GPs fit

A

more chair time, first time pts tries its blurry and not really comfortable

65
Q

what is the first step in fitting steps for GPS

A

choose a fitting philosophy - is the lid attached or intrapalpebral ? a normal upper lid position is below the limbus which facilitates lid attachment; high upper lid position at or above the limbus is better for intrapalpebral fit

66
Q

T or F: normal lid tension facilitates lid attachment

A

T

67
Q

T or F: the lens will move in the direction of least resistance along the steep meridian

A

T; the lens will slide more on the steep meridian ( think about a slope, you move more on a steep slope)

68
Q

how will GP lenses move on specific corneal shapes of astigmatism

A

WTR: flatter horizontal meridian so it will slide up and down which is good
ATR: flatter vertical meridian so it will slide L and R which is not good
and oblique slides all over

69
Q

which lenses do we fit on the different astigmats

A

WTR : tend to do Lid attachment
ATR: tend to do intrapalpebral
oblique: coujld do either

70
Q

what is step 2 for fitting GP lenses

A

choose a diameter; based on lid position/ fitting philosophy, corneal diameter, and pupil size

71
Q

what is step 3 for GP lens fit

A

choose a design : sphere or toric: consider a spherical design when K cyl is less than 2.00 D ( if refrc. cy with 0.75D of K cyl use sph GP, if not use soft toric); if K cyl is 2.00-3.00 use sph BC first and if not a goot fit then use toric bc. if more than 3.00D use toric bc and if ref cyl = 1.5 K cyl then use back surface toric and if not use bitoric

72
Q

T or F: 1.00 WTR is the best fit for a spherical GP

A

T

73
Q

what is step 4 in GP lens fit

A

choose a material : based on D of lens ; if pt needs EW we need high Dk and if rough on lenses we need lower Dk

74
Q

what are some low Dk lenses

A

paragon thin, boston ES, optimum classic ; Dk of 30 ; good for thin designs - lower Dk = lens more stable

75
Q

what are some moderate Dk lenses

A

Paragon HDS, boston EO, optimum comfort; Dk of 60; daily wear myopes

76
Q

what are some high Dk lenses

A

paragon HDS 100, Boston XO, Optimum Extra, Dk of 100; Extended wear, daily wear hyperopes

77
Q

what is step 5 of fitting gps

A

choose a curvature

78
Q

when K cyl is 0-0.50 what do you do with BC:

A

fit 0.50 D flatter than K

79
Q

when k cyl is 0.75-1.25 what do you with bc

A

0..25 flatter than K

80
Q

when k cyl is 1.50, what do you do with bc

A

fit on K

81
Q

when K cyl is 1.75-2.00 , what do you do with BC

A

0.25 steeper than K

82
Q

when K cyl is 2.25-2.75 , what do you do with BC

A

fit 0.50 D steeper than K

83
Q

for every 0.4 mm change diameter what do youhave to do to the BCR

A

change by 0.25 flatter or steepr

84
Q

whats step 6 to fit a GP lens

A

choose a lens power

85
Q

what is choosing the gp lens power based on

A

pts rx and calculated tear film power

86
Q

what is step 7 for fitting the lens

A

evaluates the lens

87
Q

how do we observe and grade the fluorescein pattern

A

center/midperiphery is graded on brightness : 0 = no green and 3= bright green and the periphery is graded on width where 0 = thin and 3 = wide

88
Q

what is the last step in GP fits

A

modify as needed, GPs are made to order

89
Q

what happens with a flat fit on capillary attraction

A

the lens decenter and moves excessively

90
Q

what happens with a steep fit on capillary attraction

A

this is a tight fit ; forces centration of the lens away and inhibits movement

91
Q

what is the pearl theory for BC changes

A

change BC by at least 0.50D for 0.1 mm change

92
Q

whats the relationship between optic zone size and sag depth

A

wider chord increases the sag depth; bigger lens with same curvature has a deeper sag ( fits tight ) ; smaller lens with same curvature has a shallow sag

93
Q

describe sag depth in relationship to tear film etc

A

sag deepens-> tear film thickens-> chord increases ->diameter increases -> steeper fit

94
Q

in what two ways does gravity affect the lens characteristics

A

center of gravity and specific gravity

95
Q

what alters the center of gravity of the lens

A

lens power, base curve, diameter, and thickness

96
Q

T or F: plus lenses will drop more than minus lenses

A

T

97
Q

T or F: thick lenses will drop less than thin

A

F : thick lenses will drop more than thin lenses

98
Q

T or F: small lenses will drop more than big lenses

A

T

99
Q

T or F: flat BC will drop more than steep

A

T

100
Q

T or F: a Center of gravity means more attraction to the cornea and better positioning

A

T

101
Q

this refers to the weight of the CL material itself

A

Specific gravity ; high SG = heavy ( boston is a heavier material and paragon is lighter)

102
Q

this is a characteristic of the lens itself ( distance btw the lens posterior and continuation of spherical back surface of central optic zone of Cls )

A

edge lift

103
Q

this depends on the cornea and how much gap is between the cornea and lens

A

edge clearance

104
Q

T or F: the amt of edge lift will influence the movement and positioning of the lens

A

T ( increase edge lift to increase lid attachment and decrease edge lift to decrease lid attachment )

105
Q

what is the standard amt of edge lift

A

0.13 mm of edge lift ; clinically sig change is 0.03 mm

106
Q

T or F: to change the SCR and TCR by 0.5 mm each you have to change the edge lift by .03 mm

A

T ( steepen the curves to decrease edge lift and flatten the curves to increase edge lfit )

107
Q

what are some probs with a bad edge lift clearance

A

3 & 9 staining : peripheral dessication and /or corneal chaffing from incorrect edge lift ; increase or decrease edge lift as needed

108
Q

T o F: anything more plus than -1.00 will be plus shaped due to peripheral curves

A

T- but this can be a prob bc a thin edge is squeezed out from the lid easily and lens drops too easily ; a lenticulation can be added to change the edge contour to a shape that the lid can hold

109
Q

T or F: Lenticulars on plus can either have a “regular “ carrier ( parallel periphery ) or a minus carrier ( thicker at edge than lenticuklar junction area )

A

T

110
Q

what is a plus lenticular

A

we add a plus lenticular to a minus lens to thin the edge ( esp on lens powers over -5.00); we add minus lenticulars to plus lens to thicken the edge

111
Q

is a high Dk assoc with a thicker or thiner lens

A

thicker

112
Q

how do you get flare in the lens

A

caused by reflections from PC and from tear meniscus

113
Q

T or F: silicone is good for oxygen transmission but not for wettability

A

T

114
Q

T or F: low wetting angle = better wetting

A

T ( highly beaded up = bad so high angles means more beaded up water on the lens)

115
Q

how has wetting improved

A

now they use pitch ( wax coating applied to protect and they offer wet shippinh) , and plasma treatment

116
Q

what are some acquired reasons for poor wetting

A

protein film on lenses and cosmetics

Contact Lens Part One (1 decks)

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