Exam one Material Flashcards
1
Q
what was phase one of contact lenses
A
understanding corneal neutralization
2
Q
what was phase two of contact lens
A
linking neutralization with on eye device
3
Q
what was phase three of contact lens
A
clinical experiments
4
Q
who were the three men credited for invention of Cls
A
Muller, Kalt, and Fick
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
6
Q
this man developed scleral lenses for keratoconus ; realized keratoconus had ectasia and could flatten the cornea
A
Eugene Kalt
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
8
Q
this guy recognized the adaptational process “FIcks Phenomenon” -
A
Adolf Fick
9
Q
What is Ficks Phenomenon
A
less edema when air trapped behind lens on insertion
10
Q
what was phase 4 of CLs
A
getting the lenses to fit, getting pts to adapt and working on materials and designs
11
Q
phase 5 of Cls development
A
plastic Cls
12
Q
phase 6 of Cls development
A
hydrogels
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
14
Q
Do we usually fit GP lenses off from K
A
yes: we usually fit the lens flatter/steeper than K
15
Q
what is the index of the cornea
A
1.3375
16
Q
what happens to the tear film when the Cls is the same curvature of the cornea
A
tear film will be plano
17
Q
is a longer radius of curvature flatter or steeper power
A
flatter
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 )
19
Q
What is the formula to find the BC
A
F= 337.5/ radius in mm
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
21
Q
TL = ?
A
front of tears + back of tears
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
23
Q
If BC is flatter than K what happens to tear film
A
it becomes negative
24
Q
If bc is steeper than K what happens to the tear film
A
it becomes positive
25
If BC is on k what happens to the tear film
it becomes plano
26
will the tear lens have the same cyl as the cornea
Y ( CL can be spherical and still correct astigmatism ; HUGE advantage for GPs)
27
will the TL correct all of the patients astigmatism
Maybe: TL will match and correct for the corneal Astigmatism but it cant correct for the crystalline lens cyl
28
T or F: for a rigid lens, the RA is simply the amt of crystalline lens cyl
T
29
what amt of uncorrected RA do we have to worry about
> 0.75 D
30
what if the axes don't match when trying to find RA on GP lenses
rule of thumb: 20 degrees or less we can consider them the same axis ; more than that and we cant work the problem
31
where does the cornea mostly get its oxygen from
the atmosphere ( endothelium oxygen comes from aqueous too )
32
oxygen Is what % of atmosphere
21% independent of elevation
33
what is total atm pressure at sea level
760 mm Hg ( so 21% x 760 = 159.6 mmHG actual value 155)
34
what are the routes of oxygen to the cornea while wearing a Cls
through the active tear pump or through the lens material
35
what is the tear pump
open eye, movement, waste, debris
36
is the tear pump more active in the GP lens
Y: they move more; they are non draping - 10-20% of tears are exchanged per blink a SCL has 1% tear exchange
37
what are the diff sources of oxygen to the cornea
tears, and aqueous from anterior chamber( major source for endothelium)
38
where does the OPEN eye get its oxygen from
atmosphere ( 21%), aqueous ( 7.4%) and 1 mm below the superior limbus ( 10.4%)
39
where does the CLOSED eye get its oxygen frmo
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)
40
how much oxygen is needed
12% needed or you get a reduction in mitosis and 8% needed or you get a decrease in corneal sensitivity
41
this is the rate of flow for a given material - rep by Dk numbers
permeability
42
what is the relationship between water content and permeability for standard hydrogels
more water content= more oxygen
43
What does D in Dk stand for
diffusion coefficient - the flow rate
44
What does k in Dk stand for
solubility coefficient of oxygen in material ; expressed as some number x 10^11
45
what affects permeability
initial gas pressure, ambient temp ( warmer = more oxygen transmitted), and surrounding pressure
46
what is permeability
how fast oxygen moves in a given material
47
what permeability number is a good range
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
what is the Dk for the Bostons
Boston ES 18-25
Boston EO 60
Boston XD 100
49
Whats the Dk for the Paragons
Paragon HDS 60
| Paragon HDS100 -100
50
Whats the Dk for the Menicon Z
170
51
what is transmissibility
this takes into account the distance traveled by oxygen ; rep as Dk/t; units are 10^-9
52
What is the Equivalent Oxygen %
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
what is the relationship of EOP to Dk/t
non linear; no matter how good the Dk/t value , the EOP eventually tapers off
54
why do we suggest daily wear
to avoid swelling ; EOP of 10 % or DK/t of 24- these values are holden mertz criteria
55
WHy do we suggest EW
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
what is the emerging transmissibility number for overnight wear
125 Dk/t units
57
T or F: Dk/t will be less in thicker areas
T
58
what is the diff between an empirical fit and a diagnostic fit
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
what is an empirical fitting and why is it common
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
what are some disadvantages of an empirical fit
you lose valuable information on lids/lens interaction, movement ( should move 2-3 mm per blink ) , and topography , you lose the warranty lens
61
with GP lenses will you have looser or tighter fit with a flatter cornea
flatter /looser and steeper/ tighter
62
which lenses should you never try empirically
MF and irregular corneal fits
63
what are the advantages of a diagnostic fitting
evaluate on eye performance; first custom lens will be more accurate; can tweak parametes before buying the lens
64
what are some disadvantages of diagnostic GPs fit
more chair time, first time pts tries its blurry and not really comfortable
65
what is the first step in fitting steps for GPS
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
T or F: normal lid tension facilitates lid attachment
T
67
T or F: the lens will move in the direction of least resistance along the steep meridian
T; the lens will slide more on the steep meridian ( think about a slope, you move more on a steep slope)
68
how will GP lenses move on specific corneal shapes of astigmatism
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
which lenses do we fit on the different astigmats
WTR : tend to do Lid attachment
ATR: tend to do intrapalpebral
oblique: coujld do either
70
what is step 2 for fitting GP lenses
choose a diameter; based on lid position/ fitting philosophy, corneal diameter, and pupil size
71
what is step 3 for GP lens fit
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
T or F: 1.00 WTR is the best fit for a spherical GP
T
73
what is step 4 in GP lens fit
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
what are some low Dk lenses
paragon thin, boston ES, optimum classic ; Dk of 30 ; good for thin designs - lower Dk = lens more stable
75
what are some moderate Dk lenses
Paragon HDS, boston EO, optimum comfort; Dk of 60; daily wear myopes
76
what are some high Dk lenses
paragon HDS 100, Boston XO, Optimum Extra, Dk of 100; Extended wear, daily wear hyperopes
77
what is step 5 of fitting gps
choose a curvature
78
when K cyl is 0-0.50 what do you do with BC:
fit 0.50 D flatter than K
79
when k cyl is 0.75-1.25 what do you with bc
0..25 flatter than K
80
when k cyl is 1.50, what do you do with bc
fit on K
81
when K cyl is 1.75-2.00 , what do you do with BC
0.25 steeper than K
82
when K cyl is 2.25-2.75 , what do you do with BC
fit 0.50 D steeper than K
83
for every 0.4 mm change diameter what do youhave to do to the BCR
change by 0.25 flatter or steepr
84
whats step 6 to fit a GP lens
choose a lens power
85
what is choosing the gp lens power based on
pts rx and calculated tear film power
86
what is step 7 for fitting the lens
evaluates the lens
87
how do we observe and grade the fluorescein pattern
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
what is the last step in GP fits
modify as needed, GPs are made to order
89
what happens with a flat fit on capillary attraction
the lens decenter and moves excessively
90
what happens with a steep fit on capillary attraction
this is a tight fit ; forces centration of the lens away and inhibits movement
91
what is the pearl theory for BC changes
change BC by at least 0.50D for 0.1 mm change
92
whats the relationship between optic zone size and sag depth
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
describe sag depth in relationship to tear film etc
sag deepens-> tear film thickens-> chord increases ->diameter increases -> steeper fit
94
in what two ways does gravity affect the lens characteristics
center of gravity and specific gravity
95
what alters the center of gravity of the lens
lens power, base curve, diameter, and thickness
96
T or F: plus lenses will drop more than minus lenses
T
97
T or F: thick lenses will drop less than thin
F : thick lenses will drop more than thin lenses
98
T or F: small lenses will drop more than big lenses
T
99
T or F: flat BC will drop more than steep
T
100
T or F: a Center of gravity means more attraction to the cornea and better positioning
T
101
this refers to the weight of the CL material itself
Specific gravity ; high SG = heavy ( boston is a heavier material and paragon is lighter)
102
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 )
edge lift
103
this depends on the cornea and how much gap is between the cornea and lens
edge clearance
104
T or F: the amt of edge lift will influence the movement and positioning of the lens
T ( increase edge lift to increase lid attachment and decrease edge lift to decrease lid attachment )
105
what is the standard amt of edge lift
0.13 mm of edge lift ; clinically sig change is 0.03 mm
106
T or F: to change the SCR and TCR by 0.5 mm each you have to change the edge lift by .03 mm
T ( steepen the curves to decrease edge lift and flatten the curves to increase edge lfit )
107
what are some probs with a bad edge lift clearance
3 & 9 staining : peripheral dessication and /or corneal chaffing from incorrect edge lift ; increase or decrease edge lift as needed
108
T o F: anything more plus than -1.00 will be plus shaped due to peripheral curves
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
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 )
T
110
what is a plus lenticular
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
is a high Dk assoc with a thicker or thiner lens
thicker
112
how do you get flare in the lens
caused by reflections from PC and from tear meniscus
113
T or F: silicone is good for oxygen transmission but not for wettability
T
114
T or F: low wetting angle = better wetting
T ( highly beaded up = bad so high angles means more beaded up water on the lens)
115
how has wetting improved
now they use pitch ( wax coating applied to protect and they offer wet shippinh) , and plasma treatment
116
what are some acquired reasons for poor wetting
protein film on lenses and cosmetics
