orthokeratology Flashcards
what is orthokeratology?
a technique for correcting refractive errors in vision by changing the shape of the cornea with the temporary use of progressively flatter hard contact lenses
is there any touch with ortho k lenses?
NEVER
how do ortho k lenses work?
+ compression in the centre of the lens and -ve tension in the periphery
in terms of the layers of the cornea, what does an ortho k lens cause?
central epethelial thinning
mid peripheral thickening of the stroma and epithelium
considerations for px selection
1.max correction -4.50 / -5.00
FULL correction may not be possible - therefore manage expectations
2.age
3.history
4.occupation - e.g. shift workers
5.compliance
6.hygiene
7.motivation- need to be highly motivated
what equipment do you need to fit an ortho k lens?
normal equipment (SL, keratometer etc)
CORNEAL TOPOGRAPHER !!!!
features of topographer
- high degree of accuracy and repeatability
- statistical analysis of repeated readings of apical radius and eccentricity or elevation
- axial, tangential and refractive power and curvature maps
- a “difference” or subtractive map function
- pupil recognition
- a large area of corneal coverage with minimal interpolation
what is the minimum area of the cornea you need to measure?
10mm
which topography map is the best indicator of corneal shape and centration after orthok?
tangential
which topography map is good for monitoring change and showing central island post orthok?
axial/refractive
which topography map represents localised changes and peripheral data BEST?
tangential
what is an axial subtractive map?
shows change in axial corneal surface. power
what is a tangential subtractive map?
shows centration
what is a reffractive subtractive map?
identifies the size of treatment zone and change in refractive power
how to take a good topography map
eyes eide open
tilt head if needed
normal blink rate required
good tear quality (use artificial tears if needed)
take a minimum of four images to compare
delete poor images
how many good images should you use as basleine?
3 or 4
assess this ortho k fit?
OPTIMAL ! :)
clear central portion with barely any nafl (3-5mm)
mid peripheral ring of nafl
peripheral bearing
good clearence around the edge
assess this ortho k fit?
STEEP :/
small central clearence
massive amount of mid peripheral nafl
narrow peripheral clearence
assess this ortho k fit?
FLAT
sit laterally or inferiorly
excessive movement
large area of bearing
wide annulus of mid peripheral nafl
wide peripheral clearance
why do topography before treatment?
helps you determine initial lens
can exclude abnormal corneas
allows you to fit with caution (tilted cornea, abnormal lids, limbus to limbus astigmatism)
why do topography after treatment?
determine centration, treatment zone size, refractive change
what are the 7 topographical patterns?
1 - bulls eye
2 - smiley face
3 - frowny face
4- true central island
5 - smiley face with false central island
6 - lateral displacement
7 - central divot
what is the ideal topography pattern with someone being treated with ortho k?
bulls eye
even if you get an ideal topography map, why would you consider changing the lens?
you get an overrefraction
blurred vision
unresponsive cornea
what happens when you have a small treatment zone?
size small
flare
poor vision
high target reduction
small BOZD
what do you do if you have a small treatment zone?
consider partial reduction
what do you do if you have an under response?
increase target reduction or chnage BOZR
what does a smiley face or frowny face topography map indicate?
FLAT FIT
what kind of astigmatism do you get when you have a smiley or frowny face topography map?
WTR
features of a flat fit
ghosting
glare
flare
why would you have a flat fitting lens?
underestimated cornel sag or over estimated eccentricity
what do you do to fix a FLAT lens?
increase lens sag
steepen AC
steepen RC/BOZR
increase RZD, LZA (landing zone) or BOZR
decrease cone angle
what is the difference between smiley face and frowny face
smiley face - red ring is decentred up
frowny face = red ring is decentred down
where is the red ring in true central island?
centre
what is true central island indicative of?
steep fitting lens
what kind of over refraction do you get with a true central island?
no clear end point
poor bcva
why does true central island occur
over estimated lens sag or under estimated eccentricity
how do you manage true central island?
if it is small (<1D) - self resolve in a week
if island doesnt resolve - reduce sag
2 main benefits of ortho k are,…
vision correction and lifestyle
how is ortho k a benefit in terms of vision correction?
successful overnight wear = good vision maintained throughout the day post lens removal
completely reversible
what is the optimum rx for max rate of success?
-4
how is ortho k a benefit in terms of lifestyle
convenient for those who do sports
complications with dryness, dust and allergies are avoided
what are the disadvantages of ortho k
need more time to fit and topographer is essential
aftercare is more frequent to ensure efficacy and safety
poor compliance due to lens care or handling
effects vary on px
top up CLs may be needed
is ortho k safe?
very
what are the main causes of infectious keratitis in ortho k wear?
lack of practitioner training
improper fitting procedures
poor compliance
loss to follow up
what are the ain causes of corneal staining in ortho k wear?
sub optimal lens fit
solution sensitivity
what are the causes of lens binding in ortho k wear?
deposits on lens
fit issues
why would you see central staining with ortho k lens?
flat fit - increase sag
why would you see conjunctival staining
inferior = steep fit
superior = flat fit
why would you see dimple veil staining?
steep fit = too much clearance
optimal fit = lens insertion
why would you see lens binding staining?
poor fit
increased tear viscosity
heavily deposited
when you’re myopic, how much does the risk of glaucoma increasy by?
2 or 3 times
what is the trigger for axial length elongation?
hyperopix defocus in periphery of retina
what are the 4 main myopia management techniques?
myopia control SCLs and soft multifocus lense s
ortho k
atropine
myopia control specs
lenses available for ortho k myopia control?
menicon bloom night
which menicon range is available for myopia management?
menicon BLOOM
what does a red ring show??
thickening of corneal cells at that point
