Orhto K

Question 1

How old is ortho k

Answer 1

1960’s

Question 2

What is the limitations of an ortho K lens

Answer 2

Comfort?
Stability on cornea
up to 2D
convinience?
cost
ethical?

Question 3

what’s topography

Answer 3

measurement of corneal shape/ contour

keratomotry only does central 3mm

Question 4

analysis of keratoscopy reflections

Answer 4

if mires are thin and close together- STEP CORNEA

if mires are flat and far apart- FLAT CORNEA

Question 5

what do generated colour maps show:

Answer 5

WARM- red colours show STEEPENING
COOLER- blue colours show FLATTENING

u should expect centre to be red and periphery to be blue.

Question 6

what is ortho k

Answer 6

overnight lens wear- reverse geometry- stable fit

Question 7

WHY would u want ortho k

Answer 7

reversibility- overnight- recovery after not wearing it. Thickness recovered after a day, curvature recovered after a week, rx recovered after a week
freedom- no lost lenses- can do sports/swimmin, improved vdu use, easy to handle
comfort- CL use dry eyes not an issue, i.e environment, vdi use. Leaves tear film un disrupted throughout day
control- how much rx u want to correct?

Question 8

how does ortho k lenses work

Answer 8

flatten central cornea
refocuses light on correct part of retina
central thinning+ mid peripheral thickening- we re-distribute the cells/tissue.
Owen found flattening of anterior and posterior corneal surfaces

Question 9

more on how ortho k works

Answer 9

calculations of posterior curvature and shape based on anterior topography and corneal thickness.
posterior cornea doesn’t flatten- instead oblates- peripheral corneal thickness changes

Question 10

How many curves on an ortho k lens

what are they yo

Answer 10

4 curves
clearance curve- periphery curve
perifere curve- alignment curve
reverse curve- fitting curve
base curve radius

Question 11

whats the central base zone

Answer 11

treatment zone
flattens
0.2 flattening-1D
over flatten by 0.5D to last for daytime
approx 6mm
use Munnerlyns formula- Ablation depth=(Rx D²)/8(n-1)
refractive index of corns is 1.377

Question 12

whats the reverse zone/fitting curve

Answer 12

closest to base zone
v steep- to bring lens in LANDING ZONE- cl is parallel to eye
we adjust here for cent ration
0.6mmm
space for the replaced epithelial tissue which is re-distributed

Question 13

what’s the alignment zone

Answer 13

parallel to cornea
responsible for cent ration
increases effect of OrhtoK lens
channel for tear film

Question 14

peripheral zone-

Answer 14

edge
for tear pump- tear exchange
0.4mm width and 11mm radius

Question 15

overall diameter

Answer 15

LARGE DIAMETER-
10.50-11.00mm
aids centration and also makes lens comfortable

Question 16

who can u do ortho k on

Answer 16

low myopes-
-1 to -4.50ds
with the rule can be corrected unto -1.50
and against the rule can be correct dot -1.00

Question 17

how do u asses ortho k fittings

Answer 17

with fl

Question 18

if a px comes into ur practice how do u fit ortho k lenses

Answer 18

FITTING SET- Initial trial
can dispense from stock
can of fl assessment
expensive/time consuming
infection?
don't need topog

EMPIRICAL- custom made-lower chair time
can lose control of parameters
simple and cost effective
toruble shooting including
need good topog and accurate rx

Question 19

which corneal torridity are ok to use ortho k on

Answer 19

central astigmatism
if limbus to limbus then WTR is ok
however AVOID ATR

however now there is newer designs

back surface torics
improved fit
correction for larger amounts of cyls

Question 20

wot about hyperopia and ortho k

Answer 20

more difficult
only to +2
differnet design

Question 21

what about presbyopia and ortho k

Answer 21

multifocal cornea?- effect of pupil size, quality of vision problems

try mono vision

Question 22

how does orhto k control myopia progression

Answer 22

peripheral retina responsible for emmetropisation
rays hitting peripheral retina control axial growth
need to be optimal rx correction tho as image shell needs to be at the back of the eye

Question 23

what are some ortho k studies that show myopia progression being limited

Answer 23

COOKI
LORIC
CRAYON
CANDY
SMART