Ortho-K Flashcards
reverse geometry lenses: designed in the 80s-90s; which curve is the steepest??
-advantages?
SECONDARY curve is steeper than BC
-improves centration (less disruption to cornea), lenses were more effective/predictable
what year did ortho-K gain FDA approval? About how many pts currently do it?
2002; >80,000
conclusive theory that is known to be true: central epithelial (thinning/thickening) and mid-peripheral (thinning/thickening)
epi thinning, mid-peri thickening
-possible that cell compression/migration/distribution also have a role
Swarbrick, Wong, and O’Leary concluded that that there indeed is a ______ of epithelial cells w/ ortho-K lenses
redistribution: shift to mid-periphery
- MIGRATION (in such a small amt of time) is unlikely
T/F: stromal bending is a likely way in which the cornea changes shape
FALSE. and it would never be able to maintain that structure
It’s been confirmed that the central corneal epithelium (thins/thickens), but in the mid-periphery - which layers thin/thicken?
epi thins centrally (central stromal change is negligible)
epi AND STROMA thicken mid-peripherally
ortho-K can correct ~_-_D of myopia, and realistically only ___ of corneal CYL (but up to 1.5D)
-max hyperopia correctable?
myopia: 5-6D
astigmatism: 1.5, but only HALF correctable
hyperopia: approved for 3D, but you’ll only get 1-2D
do NOT try ortho K in pts w/ this much astigmatism:
- corneal astig >___D
- lenticular astig >___D
- ATR astig > ___D
corneal >1.75D
lenticular >0.75
ATR >0.75
T/F: the more corneal eccentricity, the harder it is to correct myopia
FALSE: more eccentricity = steeper cornea = easier to compress
What’s the F/U schedule s/p Ortho-K?
1 day (AM) - 7 days - 14 days 1 month - 3 months - 6 months - q6 months thereafter
normally takes about how long to work? max effect when?
works in 10-14 days; max effect 1 wk-1 month (depending on resistance of cornea).
-At ~1 month, effect should last entire day - should wear 7-8 hrs (SLEEPING HOURS)
Which type of topography map should be used to evaluate ortho-K pattern?
- SMILEY-face: _____ decentration
- Central island: b____
- FROWNEY-face: ____ decentration
TANGENTIAL
- SSSmiley = SSSuperior decentration
- central island = bridging
- frowney = inferior decentration
what becomes extremely important to educate patient about regarding their lenses toward the end of the night/day?
CLEANING/DISINFECTION schedule - NO TAP WATER - lenses are in at night and can more easily cause infection
give 4 mild changes-
give 4 moderate changes-
give the most SEVERE complication?
mild: redness, discomfort, staining, iron ring
med: transient blurry VA, variable VA, glare, abrasion
SEVERE: MICROBIAL KERATITIS/CORNEAL ULCER
following Ortho-K, there’s a significant increase in ____ aberrations: what’s the most COMMON symptom of these aberrations?
SPHERICAL aberration ==> GLARE.
T/F: ortho-K lenses can change IOP - if so, how?
T/F: they may also decrease corneal sensitivity
TRUE. Lower it by ~1mmHg
TRUE.
CRAYON study showed that eye growth slowed by about what percentage? minusha.
55% slowing in myopia progression/eye growth w/ corneal reshaping
ROMIO study showed that there was 43% less ____ elongation in the ortho-K group.
axial
Myopia control - mechanism
-myopic eyes have PERIPHERAL (myopia/hyperopia) retinal defocus
peripheral HYPEROPIA - it gets reduced significantly in ~90% of cases
T/F: you must be certified even to get a fit set for ortho-K in your practice
true
in the paragon CRT system, you use the (spherical or cyl) component and the correct FLAT K to determine which lens you need
spherical ONLY - no cyl.
-and yes, FLAT K
goal of CRT: what’s the equation to calculate the needed base curve?
Flat K - Spherical - 0.50D
PURPOSELY over-correct for lasting vision. Negate signs on sph
T/F: you can change the BC to correct the fitting on an ortho-K lens
FALSE. The only thing you’ll correct by changing the BC is the POWER
return zone depth: the PARA-CENTRAL area where you’ll see _____
-landing zone angle: ideally, you want it to lay HOW on the sclera?
pooling of fluorescein
-tangentially - nice and flat
FFA pattern:
- central TOUCH should be ~__mm
- pooling (return zone) ~__mm (on EACH side)
- mid-peripheral zone ~__mm (on EACH side)
TOUCH - 4mm
pooling - 1mm (x2)
mid-peri - 2mm (x2)
if the OR is MINUS, the BC is too (flat/steep)
STEEP - and if OR is PLUS, BC is too FLAT
landing zone affects which three aspects of the fit?
[CEO]
-LESS (smaller) angle - results in (more/less) edge lift and (more/less) sagittal depth
- centration
- edge lift
- overall sagittal depth
SMALLER angle = MORE edge lift (pushing off!) = LESS sagittal depth (over cornea)
-opp is true for large angle
Lens diameter should be ___% of the HVID
90%
-increasing LD will improve centration and lateral decentration
how do you fix the following patterns:
- smiley face (superior decentration):
- frowney face (inferior):
- central island (bridging):
- lateral decentration:
SSSmiley - SSSTEEPEN (increase return zone depth)
frowney - FLATTEN/decrease RZD
island - same as frowney
-lateral decentration - increase LD
