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CL 3 Final > Orthokeratology > Flashcards

Orthokeratology Flashcards

1
Q

What layer does OrthoK work on?

A

Epithelium (~50 microns thick)

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2
Q

How does OrthoK work?

A

causes fluid to move from the center to the periphery; central epithelial cells are flattened and midperipheral cells are elongated

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3
Q

What does reverse geometry mean?

A

first peripheral curve is steeper than the base curve

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4
Q

What is the benefit of reverse geometry in OrthoK lenses?

A

Helps with centration, comfort and creating a predictable/ stable change in the cornea

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5
Q

How long does it take for full treatment to happen?

A

1-2 weeks depending on Rx

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6
Q

About how much of the prescription is corrected each night?

A

50%

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7
Q

Why do we overcorrect in OrthoK?

A

Long term expected daily regression is 0.25-0.75D; we want the patient to be close to emmetropic by the end of the day

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8
Q

How long does it take for reversal of OrthoK?

A

up to 1 month for full reversal; repeat topography to confirm back to baseline

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9
Q

How long to sleep in OrthoK lenses?

A

6-8 hours; higher myopia has more sleep required while low myopes may be able to wear lenses every other night

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10
Q

What is the Munnerlyn Formula

A

Depth = (optic zone diameter 2x refractive error)/3

use SE for astigmatism

may need to choose smaller OZD to get a smaller treatment zone

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11
Q

Do higher or lower prescriptions require a smaller treatment zone?

A

higher prescription

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12
Q

Why might a patient using OrthoK experience nighttime glare?

A

pupil size larger than treatment zone (beneficial for myopia control)

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13
Q

When might someone using OrthoK experience a slight decrease in visual acuity?

A

low contrast, low illumination (pupil size increased)

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14
Q

What Dk is used in OrthoK?

A

High Dk

Higher Dk= less wettable

No abrasive cleaners d/t plasma or other surface treatments

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15
Q

Which lens is the first therapeutic lens approved by FDA for overnight OrthoK for temporary reduction of myopia?

A

Paragon CRT

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16
Q

What are the refractive error limits of Paragon CRT?

A

up to -6.00 D of myopia, with or without -1.75 D of astigmatism

flat K between 40- 46 D

17
Q

What are the 3 adjustable curves/ zones of a paragon CRT lens?

A

Return Zone depth, Landing Zone Angle, Base Curve

18
Q

Which area of a Paragon lens is the key factor in centration and central applanation?

A

RZD

fit issue: change RZD

Desired applanation: 3-4 mm

19
Q

What does the LZA do?

A

Provide appropriate edge lift

adjusted in 1 degree steps

larger (-) #: closer to cornea, less edge lift

20
Q

Is the BC steeper or flatter than the corneal apex for OrthoK?

A

flatter

21
Q

What should OrthoK over-refraction be to ensure proper over-correction?

A

plano to +0.50D

Paragon CRT lenses have a power of +0.50 D to neutralize overcorrection

22
Q

What materials are Paragon lenses availabe in?

A

HDS100 (Dk=100); Menicon Z (Dk= 163)

tints: green, blut, red, yellow

23
Q

What is the lens modification if there are large bubbles in the RZD of an OrthoK lens?

A

decrease RZD (25 micron steps)

bubbles form d/t excessive central clearance or no central applanation

24
Q

How do you fix inferior positioning for an OrthoK lens?

A

Decrease sag depth by decreasing LZA by 1 degree

If doesn’t work, go back to original lens, decrease RZD by 1 step

25
Q

What parameter is changed to correct Rx?

A

BC

RZD changes the fit

26
Q

If over-refraction of an OrthoK lens yields minus power, the BC is too flat/steep

A

steep

flatten in 0.1mm steps for every 0.50 D until desired ROL

27
Q

If ROL for OrthoK is plus power, the BC is too flat/ steep

A

flat

steepen in 0.10mm for every 0.50D until desired ROL

28
Q

When treating a higher myope (>5.00), is it best to prioritize centration or treatment?

A

Centration

Munnerlyn’s formula

High myopes: smaller tx zone

29
Q

What is the follow up schedule for OrthoK?

A
  • first-morning
  • one-week
  • two-week
  • one-month

don’t change parameters until 2-week mark

30
Q

If patient is bothered by glare/ haloes at night, what can be prescribed?

A

Alphagan (brimonidine 0.2%)

miotic drop used off-label

CL 3 Final (8 decks)

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