Ortho-K

Question 1

reverse geometry lenses: designed in the 80s-90s; which curve is the steepest??

-advantages?

Answer 1

SECONDARY curve is steeper than BC

-improves centration (less disruption to cornea), lenses were more effective/predictable

Question 2

what year did ortho-K gain FDA approval? About how many pts currently do it?

Answer 2

2002; >80,000

Question 3

conclusive theory that is known to be true: central epithelial (thinning/thickening) and mid-peripheral (thinning/thickening)

Answer 3

epi thinning, mid-peri thickening

-possible that cell compression/migration/distribution also have a role

Question 4

Swarbrick, Wong, and O’Leary concluded that that there indeed is a ______ of epithelial cells w/ ortho-K lenses

Answer 4

redistribution: shift to mid-periphery

- MIGRATION (in such a small amt of time) is unlikely

Question 5

T/F: stromal bending is a likely way in which the cornea changes shape

Answer 5

FALSE. and it would never be able to maintain that structure

Question 6

It’s been confirmed that the central corneal epithelium (thins/thickens), but in the mid-periphery - which layers thin/thicken?

Answer 6

epi thins centrally (central stromal change is negligible)

epi AND STROMA thicken mid-peripherally

Question 7

ortho-K can correct ~_-_D of myopia, and realistically only ___ of corneal CYL (but up to 1.5D)
-max hyperopia correctable?

Answer 7

myopia: 5-6D
astigmatism: 1.5, but only HALF correctable
hyperopia: approved for 3D, but you’ll only get 1-2D

Question 8

do NOT try ortho K in pts w/ this much astigmatism:

• corneal astig >___D
• lenticular astig >___D
• ATR astig > ___D

Answer 8

corneal >1.75D
lenticular >0.75
ATR >0.75

Question 9

T/F: the more corneal eccentricity, the harder it is to correct myopia

Answer 9

FALSE: more eccentricity = steeper cornea = easier to compress

Question 10

What’s the F/U schedule s/p Ortho-K?

Answer 10

1 day (AM) - 7 days - 14 days
1 month - 3 months - 6 months - q6 months thereafter

Question 11

normally takes about how long to work? max effect when?

Answer 11

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)

Question 12

Which type of topography map should be used to evaluate ortho-K pattern?

• SMILEY-face: _____ decentration
• Central island: b____
• FROWNEY-face: ____ decentration

Answer 12

TANGENTIAL

• SSSmiley = SSSuperior decentration
• central island = bridging
• frowney = inferior decentration

Question 13

what becomes extremely important to educate patient about regarding their lenses toward the end of the night/day?

Answer 13

CLEANING/DISINFECTION schedule - NO TAP WATER - lenses are in at night and can more easily cause infection

Question 14

give 4 mild changes-
give 4 moderate changes-
give the most SEVERE complication?

Answer 14

mild: redness, discomfort, staining, iron ring
med: transient blurry VA, variable VA, glare, abrasion
SEVERE: MICROBIAL KERATITIS/CORNEAL ULCER

Question 15

following Ortho-K, there’s a significant increase in ____ aberrations: what’s the most COMMON symptom of these aberrations?

Answer 15

SPHERICAL aberration ==> GLARE.

Question 16

T/F: ortho-K lenses can change IOP - if so, how?

T/F: they may also decrease corneal sensitivity

Answer 16

TRUE. Lower it by ~1mmHg

TRUE.

Question 17

CRAYON study showed that eye growth slowed by about what percentage? minusha.

Answer 17

55% slowing in myopia progression/eye growth w/ corneal reshaping

Question 18

ROMIO study showed that there was 43% less ____ elongation in the ortho-K group.

Answer 18

axial

Question 19

Myopia control - mechanism

-myopic eyes have PERIPHERAL (myopia/hyperopia) retinal defocus

Answer 19

peripheral HYPEROPIA - it gets reduced significantly in ~90% of cases

Question 20

T/F: you must be certified even to get a fit set for ortho-K in your practice

Answer 20

true

Question 21

in the paragon CRT system, you use the (spherical or cyl) component and the correct FLAT K to determine which lens you need

Answer 21

spherical ONLY - no cyl.

-and yes, FLAT K

Question 22

goal of CRT: what’s the equation to calculate the needed base curve?

Answer 22

Flat K - Spherical - 0.50D

PURPOSELY over-correct for lasting vision. Negate signs on sph

Question 23

T/F: you can change the BC to correct the fitting on an ortho-K lens

Answer 23

FALSE. The only thing you’ll correct by changing the BC is the POWER

Question 24

return zone depth: the PARA-CENTRAL area where you’ll see _____

-landing zone angle: ideally, you want it to lay HOW on the sclera?

Answer 24

pooling of fluorescein

-tangentially - nice and flat

Question 25

FFA pattern:

• central TOUCH should be ~__mm
• pooling (return zone) ~__mm (on EACH side)
• mid-peripheral zone ~__mm (on EACH side)

Answer 25

TOUCH - 4mm
pooling - 1mm (x2)
mid-peri - 2mm (x2)

Question 26

if the OR is MINUS, the BC is too (flat/steep)

Answer 26

STEEP - and if OR is PLUS, BC is too FLAT

Question 27

landing zone affects which three aspects of the fit?
[CEO]

-LESS (smaller) angle - results in (more/less) edge lift and (more/less) sagittal depth

Answer 27

• centration
• edge lift
• overall sagittal depth

SMALLER angle = MORE edge lift (pushing off!) = LESS sagittal depth (over cornea)
-opp is true for large angle

Question 28

Lens diameter should be ___% of the HVID

Answer 28

90%

-increasing LD will improve centration and lateral decentration

Question 29

how do you fix the following patterns:

• smiley face (superior decentration):
• frowney face (inferior):
• central island (bridging):
• lateral decentration:

Answer 29

SSSmiley - SSSTEEPEN (increase return zone depth)
frowney - FLATTEN/decrease RZD
island - same as frowney
-lateral decentration - increase LD