Corneal Reshaping (M2)

Question 1

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

Answer 1

1. myopia (-6.00 or less)

2. astigmatism (less than 1.75)

Question 2

What are the benefits of the Paragon CRT lens?

Answer 2

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

Question 3

What are the disadvantages of the Paragon CRT lens?

Answer 3

1. new terminology

2. change parameters on own

Question 4

What material properties should a CRT lens contain?

Answer 4

1. high Dk/t

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

1. +0.50

2. rebound throughout the day

Question 8

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

Answer 8

6mm diameter

Question 9

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

Answer 9

1. 1mm wide

2. 25 micron steps

Question 10

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

Answer 10

1. centration

2. treatment applanation

Question 11

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

Answer 11

1. contour peripheral cornea

2. stability and centration

Question 12

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

Answer 12

1deg steps (less angle means flatter in peripheral)

Question 13

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

Answer 13

10.5mm and 0.5mm

Question 14

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

Answer 14

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

Question 15

What are examples of great candidates for CRT?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

3 to 4 mm

Question 19

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

Answer 19

increase sagittal depth by increasing RZD (0.25)

Question 20

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

Answer 20

decrease sagittal depth by:

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

Question 21

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

Answer 21

decrease return zone/ flatten reverse curve

Question 22

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

Answer 22

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

Question 23

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

Answer 23

1. limbal to limbal astig

2. dual axis CRT

Question 24

What are good cleaners for CRT lenses?

Answer 24

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

Question 25

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

Answer 25

steepen BC (subtract) by 0.10mm

Question 26

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

Answer 26

flatten BC (add) by 0.10mm

Question 27

What is the follow up schedule for CRT patients?

Answer 27

1. 10 days 2. 1 month 3. 6 months

Question 28

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

Answer 28

same risk of MK as other overnight modalities

Question 29

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

Answer 29

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