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III. Advanced Contact Lenses > Corneal Reshaping (M2) > Flashcards

Corneal Reshaping (M2) Flashcards

1
Q

What types of refractive errors are corrected with corneal refractive therapy (CRT) (with FDA approved values)?

A
  1. myopia (-6.00 or less)

2. astigmatism (less than 1.75)

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2
Q

What are the benefits of the Paragon CRT lens?

A
  1. first to get FDA approval
  2. dispensing fitting set
  3. change parameters on own
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3
Q

What are the disadvantages of the Paragon CRT lens?

A
  1. new terminology

2. change parameters on own

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4
Q

What material properties should a CRT lens contain?

A
  1. high Dk/t
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5
Q

What are the conditions in which CRT lenses are not the best choice?

A
  1. over 0.75 D ATR toricity
  2. final tx takes BC below 38.00D
  3. cylinder greater than sphere
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6
Q

What are the terms for the areas of the orthokeratology contact lens?

A
  1. base curve (treatment zone)
  2. return zone depth (reverse curve)
  3. landing zone angle (alignment curve)
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7
Q

How much is the eye “overcorrected” for when using CRT? 1. Why? 2

A
  1. +0.50

2. rebound throughout the day

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8
Q

How wide is a typical base curve on a CRT lens?

A

6mm diameter

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9
Q

How wide is a typical return zone depth on a CRT lens? 1. What are the step sizes for adjustment purposes? 2

A
  1. 1mm wide

2. 25 micron steps

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10
Q

What is the return zone depth on a CRT lens responsible for?

A
  1. centration

2. treatment applanation

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11
Q

What is the landing zone on a CRT lens responsible for?

A
  1. contour peripheral cornea

2. stability and centration

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12
Q

What are the step sizes for adjustment purposes are available for the landing zone of CRT lenses?

A

1deg steps (less angle means flatter in peripheral)

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13
Q

What is the typical diameter of a CRT lens and what are the step sizes?

A

10.5mm and 0.5mm

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14
Q

What is laser marked on a CRT lens (in order)?

A
  1. BC
  2. RZD (without last number and rounded)
  3. LZA
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15
Q

What are examples of great candidates for CRT?

A
  1. don’t want to wear correction during day
  2. swim regularly
  3. work around toxic substances
  4. has CL related dry eye
  5. wants LASIK but too big of pupils
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16
Q

What is the preliminary testing that needs to be done before fitting CRT lenses?

A
  1. manifest refraction
  2. keratometry or topography
  3. slit lamp exam
17
Q

What is the equation to find the proper base curve of a CRT lens?

A

BC = (flat K) - (spherical myopia correction) - (0.50 to 0.75)

18
Q

What should the size of the treatment zone of CRT lenses be?

A

3 to 4 mm

19
Q

What should be done with a CRT lens if the lens decenters lateral or superior?

A

increase sagittal depth by increasing RZD (0.25)

20
Q

What should be done with a CRT lens if the lens decenters inferior?

A

decrease sagittal depth by:

  1. decrease landing zone
  2. return to original LZA, then decrease return zone
21
Q

What should be done with a CRT lens if the lens has insufficient central applanation?

A

decrease return zone/ flatten reverse curve

22
Q

What are the key fitting aspects to look for with CRT lenses (and which is the most important)?

A
  1. centration (most important)
  2. good edge lift
  3. 3 to 4mm tx zone
  4. moderate tear film touch in mid periphery
23
Q

Which type of astigmatism causes problems with CRT lenses? 1. What is a solution to this problem? 2

A
  1. limbal to limbal astig

2. dual axis CRT

24
Q

What are good cleaners for CRT lenses?

A
  1. Progent
  2. Boston Simplus
  3. Unique pH
  4. Clerz plus
  5. Clear Care
25
Q

What should be done for every +0.50 D found on over refraction after CRT?

A

steepen BC (subtract) by 0.10mm

26
Q

What should be done for every -0.50 D found on over refraction after CRT?

A

flatten BC (add) by 0.10mm

27
Q

What is the follow up schedule for CRT patients?

A
  1. 10 days
  2. 1 month
  3. 6 months
28
Q

How is the risk of overnight wear affected by CRT lenses?

A

same risk of MK as other overnight modalities

29
Q

What can be done if the patient is experiencing poor vision during the adaptation period for CRTs?

A
  1. wear lenses during day
  2. soft CLs
  3. kids can wear old glasses

III. Advanced Contact Lenses (16 decks)

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