Lec 18 Ortho K

Question 1

In ortho K what’s a reverse curve

Answer 1

Reverse curve is a peripheral curve that’s steeper than the central curve

Question 2

3 popular ortho K designs in NZ

Answer 2

Brighten optic OK

Forge

Paragon CRT

Question 3

How to select a base curve for ortho K

Answer 3

BC = flat K - (target myopia + over correction)

Question 4

What’s a good ortho K fit

Answer 4

Centre on eye with applanation centre over pupil

Donut of NaFl

Some movement 0.75-1mm

Some edge lift

Lens diameter covers 90% cornea

Question 5

Ideal topography for ortho K

Answer 5

Bulls eye

- red symmetrical circle centred over pupil surrounded by consistent blue (flatter)

Question 6

Good ortho K candidates

Answer 6

Myope under 4D

Strong motivation like water sports, myopia control

Normal sleep pattern + normal pupils (not too large) + normal tears/surface

Cornea not flat under 41D, less than 1.5 cyl, good eccentricity ~0.8

Question 7

What are advanced design options for ortho K

Answer 7

Hyperopia of +2

High astig using toric periphery ortho K or Bitoric ortho K design

Myopes over 4 using smaller treatment zone options to compress everything in mid and then flatten

Question 8

Ideal corneas to fit ortho K on

Answer 8

If astig then central, WTR

High eccentricity

Steep corneas e.g higher than 42

Placido mires even space and no distortion

Larger HVID and smaller pupil size

Question 9

Bad candidates for ortho K

Answer 9

Low eccentricity

Corneal cyl doesn’t match spec cyl

Large pupils

Ocular surface problems

<6hrs sleep