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ortho k Flashcards

1
Q

why did the first ortho k lens result in increased astigmatism

A

due to lens decentration

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2
Q

what was the average reduction in early lenses

A

1 to 1.5 diopters

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3
Q

for the first ortho k lenses, they were usually only worn at what time of day?

A

during the day

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4
Q

when did first clinical trials start for ortho k?

A

the 70s

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5
Q

why did rgl lenses become more available in the 90s

A

better technology to monitor changes and developed higher DK materials for overnight wear

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6
Q

when did ortho k first get fda approval

A

2002

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7
Q

what is the main theory behind how ortho k works?

A

central epithelial thinning, and mid peripheral thickening
(although there are different theories about how this happens:
1. central cell compression
2. epithelial cell redistribution
3. bending of cornea
4. cell migration)

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8
Q

for cell migration swarbick found that corneal flattening happened within how many minutes of lens wear

A

within 10 minutes (unlikely that migration can occur this quickly though)

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9
Q

true/false it is thought that for central epithelial thinning in ortho k lenses the cells are flat and there is no migration

A

true.

*negligible change to central stromal thickness

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10
Q

stromal thickening in mid peripheral epithelial cells is disputed to be caused by what?

A

DK/T of material

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11
Q

why are there epithelial changes in the mid peripheral cells?

A

epithelial cells are more oval shaped and larger; this is thought to be because of delayed surface expholeiation; not sloughing off as quickly

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12
Q

t/f there are no short term or long term effects on endothelium up to three years

A

true

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13
Q

ortho k lenses can correct myopeia up to what?

A

CRT up to -6, VST up to -5

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14
Q

t/f success rates increase with higher myopeia

A

false

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15
Q

ortho k can correct astigmatism up to

A

CRT up to -1.75 VST up to -1.50

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16
Q

ortho k lenses are fda approved to treat hyperopeia up to what?

A

+3(better outcome with +1-+1.50)

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17
Q

ortho k is better for what kind of astigmatism

A

WTR, corrects about half of corneal astigmatism (correcting half of -1.50 is good)
*ATR and oblique astigmatism harder to treat, usually done with -.75 or less

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18
Q

t/f amblyopic patients are good candidates for ortho k

A

false

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19
Q

for ortho k lenses you want a patient with what kind of E value

A

you want a patient with higher E value because the cornea is more curver and able to be flattened, whereas smaller E equals smaller cornea, harder to flatten.

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20
Q

what is the follow up schedule for ortho k

A

1 day later in the morning. then 1 week. then 2 weeks. then 1 month. 3 months. 6 months, every 6 months.

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21
Q

what is the topography pattern with ortho k wear?

A

a central flat zone larger than the pupil with a ring of elevation in the periphery.

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22
Q

how long does it take for the full effect of the lenses

A

10-14 days

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23
Q

how does corneal historisis affect ortho k treatment

A

with a less ridged cornea there will be a quicker change but harder to maintain, but with a stiffer cornea, it will take longer to treat but will be more permanent.
*older patients have more ridged corneas.

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24
Q

after one night, the patient must wear the correction for how long

A

all day

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25
Q

after one week the patient must wear correction for how long

A

later in the day

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26
Q

after how much time will the patient not have to wear correction all day long

A

2 weeks to 1 month

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27
Q

why shouldnt you wear the corneal reshaping lenses during the day

A

because the lenses will lid attach and treat multiple areas

28
Q

after one month, you can go how many nights without wearing the lenses

A

1 night

29
Q

after six months of wear, cornea and refractive error will go back to normal within how long of no wear

A

within one week

30
Q

what kind of corneal topography map should you use with ortho k follow ups

A

tangential map

31
Q

t/f you will see 4 diopters of corneal topography change with 4 diopters of refractive change

A

false, keratomotry values are 75% of refractive changes

32
Q

what kind of cleaning system should you use with ortho k

A

gp cleaning systems

33
Q

if there is central staining, what change should you make with the lens

A

increase sadgital depth of the lens because the lens is rubbing on the apex

34
Q

what does it indicate if you have staining at 3 and 9 oclock

A

indicative of daytime wear and lenses rocking back and forth as they blink

35
Q

why would you get a corneal iron ring with ortho k lenses

A

tears pulling in this location; appears 6-12 months after lenses wear and will go away

36
Q

why might you get an abrasion with ortho k lenses

A

the lens are too flat or from adherence

37
Q

t/f MK in OK wearers than in daily GP wearers

A

true, but it is similar to other overnight soft contact wearers

38
Q

t/f the more myopeia you have the more SA induced with correction

A

true.

39
Q

why might you get monocular diplopia with ortho k

A

could be SA or lenses decentration

40
Q

how does ortho k affect binocular vision

A

no change in ACC/convergence, may even be slight improvement

41
Q

what are some other changes to the cornea from long term ortho k wear

A

corneal dimpling
fibulary lines in the anterior stroma
reduced iop measurements
maybe decreased corneal sensitivity

42
Q

most people have their max effect from ortho k in what time frame

A

1 week to 1 month

43
Q

what kind of patients are more likely to see a plateau in correction

A

people with low ecentricity

44
Q

t/f in creasing the optic zone will increase the effect of the lense

A

false

45
Q

t/f higher refractive errors will have a smaller treatment zone

A

true

46
Q

axial elongation is associated with what 3 other sight threatening conditions

A

maculopathy
retinal detachment
glaucoma

47
Q

what was the outcome of the loric study

A

study 35 children, progression in OK group was ~-.2 and -1.2 in the control group

48
Q

what was the outcome of the crayon study

A

it compared OK lenses to soft contract lenses in 40 kids and eye growth was slowed by 55% with OK.

49
Q

what was the outcome of the romio study

A

100 kids with myopeia between .5-4 and the control group was glasses wearing and there was a 43% less axial elongation in the control group

50
Q

what was the outcome of the 2C study

A

there was a 52% reduction in myopeia progression at 24 months.

51
Q

for what RX is ortho k good at slowing myopeia progression

A

over 3 diopters

52
Q

what do you need to know in order to order OK lenses

A

you just need the spherical component of their RX and flat K

53
Q

the patient is over corrected by what with ortho k lenses

A

over corrected by -.5

you calculate the base curve by taking flat K - sphere - .5

54
Q

what is the standard lenses diameter for OK lenses

A

10.5

55
Q

what lens factor controls the sagital depth of the lens

A

the return zone depth

56
Q

what happens if you have too much rzd

A

it de-centers inferiorly (if it is too shallow it de-centers superiorly)

57
Q

if the lenses is positioning superiorly, what change should you make to the lens

A

increase rzd (change in 25 micron steps)

58
Q

an excessie edge lift corresponds to what kind of a landing zone angle.

A

low landing zone angle.

59
Q

for a landing zone angle, an increase in the number e.g. 33-34 will push the lens superiorly by how many microns

A

15 microns.

60
Q

what should the O refraction be with OK lenses

A

it should be plaino

61
Q

if the O refraction is greater than +-.25 you want to change the base curve in ____ steps

A

.1 steps

62
Q

if the OR is minus, then base curve is too __ flat or steep

A

too steep

63
Q

t/f the CRT dual axis design is for patients with higher amoutns of astigmatism and corrects that astigmatism

A

false it doesnt actually correct the astigmatism, it jus has two peripheral curves to stabilize the lens better

64
Q

what changes would you make if there is lateral de-centration

A

increase diameter

65
Q

what changes should you make for an inferior lens position

A

decrease the landing zone or return zone

CL (6 decks)

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