ortho k Flashcards
why did the first ortho k lens result in increased astigmatism
due to lens decentration
what was the average reduction in early lenses
1 to 1.5 diopters
for the first ortho k lenses, they were usually only worn at what time of day?
during the day
when did first clinical trials start for ortho k?
the 70s
why did rgl lenses become more available in the 90s
better technology to monitor changes and developed higher DK materials for overnight wear
when did ortho k first get fda approval
2002
what is the main theory behind how ortho k works?
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)
for cell migration swarbick found that corneal flattening happened within how many minutes of lens wear
within 10 minutes (unlikely that migration can occur this quickly though)
true/false it is thought that for central epithelial thinning in ortho k lenses the cells are flat and there is no migration
true.
*negligible change to central stromal thickness
stromal thickening in mid peripheral epithelial cells is disputed to be caused by what?
DK/T of material
why are there epithelial changes in the mid peripheral cells?
epithelial cells are more oval shaped and larger; this is thought to be because of delayed surface expholeiation; not sloughing off as quickly
t/f there are no short term or long term effects on endothelium up to three years
true
ortho k lenses can correct myopeia up to what?
CRT up to -6, VST up to -5
t/f success rates increase with higher myopeia
false
ortho k can correct astigmatism up to
CRT up to -1.75 VST up to -1.50
ortho k lenses are fda approved to treat hyperopeia up to what?
+3(better outcome with +1-+1.50)
ortho k is better for what kind of astigmatism
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
t/f amblyopic patients are good candidates for ortho k
false
for ortho k lenses you want a patient with what kind of E value
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.
what is the follow up schedule for ortho k
1 day later in the morning. then 1 week. then 2 weeks. then 1 month. 3 months. 6 months, every 6 months.
what is the topography pattern with ortho k wear?
a central flat zone larger than the pupil with a ring of elevation in the periphery.
how long does it take for the full effect of the lenses
10-14 days
how does corneal historisis affect ortho k treatment
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.
after one night, the patient must wear the correction for how long
all day
after one week the patient must wear correction for how long
later in the day
after how much time will the patient not have to wear correction all day long
2 weeks to 1 month
why shouldnt you wear the corneal reshaping lenses during the day
because the lenses will lid attach and treat multiple areas
after one month, you can go how many nights without wearing the lenses
1 night
after six months of wear, cornea and refractive error will go back to normal within how long of no wear
within one week
what kind of corneal topography map should you use with ortho k follow ups
tangential map
t/f you will see 4 diopters of corneal topography change with 4 diopters of refractive change
false, keratomotry values are 75% of refractive changes
what kind of cleaning system should you use with ortho k
gp cleaning systems
if there is central staining, what change should you make with the lens
increase sadgital depth of the lens because the lens is rubbing on the apex
what does it indicate if you have staining at 3 and 9 oclock
indicative of daytime wear and lenses rocking back and forth as they blink
why would you get a corneal iron ring with ortho k lenses
tears pulling in this location; appears 6-12 months after lenses wear and will go away
why might you get an abrasion with ortho k lenses
the lens are too flat or from adherence
t/f MK in OK wearers than in daily GP wearers
true, but it is similar to other overnight soft contact wearers
t/f the more myopeia you have the more SA induced with correction
true.
why might you get monocular diplopia with ortho k
could be SA or lenses decentration
how does ortho k affect binocular vision
no change in ACC/convergence, may even be slight improvement
what are some other changes to the cornea from long term ortho k wear
corneal dimpling
fibulary lines in the anterior stroma
reduced iop measurements
maybe decreased corneal sensitivity
most people have their max effect from ortho k in what time frame
1 week to 1 month
what kind of patients are more likely to see a plateau in correction
people with low ecentricity
t/f in creasing the optic zone will increase the effect of the lense
false
t/f higher refractive errors will have a smaller treatment zone
true
axial elongation is associated with what 3 other sight threatening conditions
maculopathy
retinal detachment
glaucoma
what was the outcome of the loric study
study 35 children, progression in OK group was ~-.2 and -1.2 in the control group
what was the outcome of the crayon study
it compared OK lenses to soft contract lenses in 40 kids and eye growth was slowed by 55% with OK.
what was the outcome of the romio study
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
what was the outcome of the 2C study
there was a 52% reduction in myopeia progression at 24 months.
for what RX is ortho k good at slowing myopeia progression
over 3 diopters
what do you need to know in order to order OK lenses
you just need the spherical component of their RX and flat K
the patient is over corrected by what with ortho k lenses
over corrected by -.5
you calculate the base curve by taking flat K - sphere - .5
what is the standard lenses diameter for OK lenses
10.5
what lens factor controls the sagital depth of the lens
the return zone depth
what happens if you have too much rzd
it de-centers inferiorly (if it is too shallow it de-centers superiorly)
if the lenses is positioning superiorly, what change should you make to the lens
increase rzd (change in 25 micron steps)
an excessie edge lift corresponds to what kind of a landing zone angle.
low landing zone angle.
for a landing zone angle, an increase in the number e.g. 33-34 will push the lens superiorly by how many microns
15 microns.
what should the O refraction be with OK lenses
it should be plaino
if the O refraction is greater than +-.25 you want to change the base curve in ____ steps
.1 steps
if the OR is minus, then base curve is too __ flat or steep
too steep
t/f the CRT dual axis design is for patients with higher amoutns of astigmatism and corrects that astigmatism
false it doesnt actually correct the astigmatism, it jus has two peripheral curves to stabilize the lens better
what changes would you make if there is lateral de-centration
increase diameter
what changes should you make for an inferior lens position
decrease the landing zone or return zone
