CLM - Keratoconus II - Week 2

Question 1

Describe the format for specifying RGP parameters.

Answer 1

BOZR (BOZD), periphery: BPR (BPCD), BPR (BPCD), BPR (BPCD)

Question 2

What happens to peripheral flattening as BOZR decreases?

Answer 2

It increases

Question 3

Would apical clearance of RGPs on fluorescein staining be considered too steep or flat?

Answer 3

Too steep

Question 4

What is the purpose of apical clearing for keratoconus? What does it minimise the likelihood of? How does it affect VA and why? What may it induce?

Answer 4

Central curve vaults the steepest part of the cone
Minimises the likelihood of scarring and central staining
May have reduced acuity due to lens flexure after blinking
Steep central curve mau induce corneal steepening of the thin cornea

Question 5

How may steeper lenses reduce tear exchange and what is a consequence of this?

Answer 5

It may seal off the periphery and reduce tear exchange with reduced wearing times and comfort

Question 6

What can occur with a large tear film thickness and in what kind of lens steepness can it generally be seen?

Answer 6

Tear film thickness >90um may develop dimple veiling in steep lenses

Question 7

Is apical clearance too steep?

Answer 7

Yes

Question 8

What is meant by feather clearance and waht else is it known as? What should the central clearance look line?

Answer 8

Three point touch
Point of contact to the cornea by the RGP on the superior and inferior margins (not right at the edge but close) and one more point of contact on the apex of the corneal cone
Central clearance should be slight

Question 9

What is the goal with feather clearance? What does this minimise (2)?

Answer 9

Attempt for minimal clearance above the steepest part of the cone
Minimises mechanical stress to the epithelium
Minimises possibility of dimple veiling

Question 10

What does a flatter base curve in feather clearance minimise?

Answer 10

Corneal moulding

Question 11

What does reduced central clearance in feather clearance minimise?

Answer 11

Minimises lens flexure, giving more stable visiond

Question 12

What is the steepness of apical bearing?

Answer 12

Too flat

Question 13

How does apical bearing appear in contrast to feather clearance (3)?

Answer 13

Excessive edge clearance
Marked bearing and staining on the cone
Edge lift

Question 14

Is the likelihood of eputhelial staining on the cone small or large with apical bearing? What does this increase the risk of?

Answer 14

Large - increasing the risk of corneal scarring

Question 15

What is the concept of therapeutic treatment of keratoconus with apical bearing and does it hold weight?

Answer 15

Misconceived concept of retarding progression of keratoconus by holding it in place with pressure

Question 16

Can apical bearing give good VA? Explain why this is so.

Answer 16

Occasionally better visual acuity due to hard bearing and corneal compression.

Question 17

Describe the CCE acronym for RGP fitting.

Answer 17

Centre - feather clearance centrally
Centration - central fitting with lid attachment if possible
Edge - adequate edge clearance

Question 18

What constitutes adequate edge clearance for a RGP lens?

Answer 18

0.6-0.8mm

Question 19

For what types of keratoconus and eyes are small diameter RGPs typically selected (3)? Specify the diameter.

Answer 19

Advanced nipple
Smaller cones
Narrower palpebral apertures
<9.0mm

Question 20

For what types of keratoconus and eyes are larger diameter RGPs typically selected (4)?

Answer 20

Early keratoconus
Oval and globus
Wider palpebral apertures

Question 21

With what BOZR (BC) should you begin with and what diameter? What about if there is obvious central clearance (2)?

Answer 21

Start with 0.2mm steeper than the average K readings
Start with 9.0mm overall diameter
If central clearance, then go flatter in larger steps of 0.3-0.4mm until there is slight central touch, then 0.1mm steeper

Question 22

Does better RGP centration equal better vision?

Answer 22

Yes

Question 23

What does better centration do to flaring, especially at night and in people with what size pupils?

Answer 23

Less flaring at night, especially with larger pupils

Question 24

What should you do if the lens keeps dropping?

Answer 24

Try a larger diameter

Question 25

Why is adequate edge clearance important (2)?

Answer 25

Allows sufficient tear exchange Creates better centration

Question 26

What constitutes adequate movement of the RGP lens?

Answer 26

1.0 - 2.0mm

Question 27

Does a tight edge often have better or reduced comfort?

Answer 27

Reducted comfort

Question 28

List two problems with a loose edge.

Answer 28

May dislodge on excursions or unusual movements Susceptible to foreign bodies

Question 29

Describe what is meant by inferior tuck. Is it standard design?

Answer 29

Reduce excessive inferior edge clearance with a steeper inferior peripheral radii Is standard design

Question 30

Do nipple cones and advanced keratoconus need larger or smaller diameters to more accurately fit over the cone?

Answer 30

Smaller

Question 31

What are larger diameter RGP lenses more likely to achieve?

Answer 31

Lid attachment

Question 32

Why do larger diameter RGP lenses cause less flaring at night?

Answer 32

Often the BOZR is larger than the dilated pupil

Question 33

When increasing the overall diameter, what needs to change in order to maintain the same sag? Does vice-versa apply? Give numbers (2).

Answer 33

To maintain the same sag, the base curve needs to be increased Increase overall diameter by 1.0mm, increase BOZR by 0.1mm Vice versa applies - decrease overall diameter by 1.0mm, decrease BOZR by 0.1mm

Question 34

Approximate a 0.1mm base curve change to the equivalent change in power. Is it accurate? Provide the full formula for power change.

Answer 34

0.1mm base curve change - 0.50D power change Inaccurate for moderately steep or flat base curves Formula: 336/BOZR1 - 336/BOZR2 = power change

Question 35

What is the centration and comfort of corneoscleral lenses like?

Answer 35

Excellent centration and comfort

Question 36

Do corneoscleral lenses have consistent or varying edge clearance?

Answer 36

Can vary edge clearance by changing rate of peripheral flattening

Question 37

Where do corneoscleral lense sprimarily rest and is there generally any movement?

Answer 37

On the cornea just inside the limbus Minimal movement

Question 38

What are minisclerals designed to do (2)?

Answer 38

Vault the cornea and land on the sclera

Question 39

Are minisclerals comfortable? Does it have any lid interactions?

Answer 39

As comfortable as soft lens, no lid interactions

Question 40

Do minisclerals dislodge or have a foreign body sensation?

Answer 40

Neither

Question 41

Do minisclerals generally give good or poor centration?

Answer 41

Excellent centration

Question 42

Do minisclerals generally move?

Answer 42

Minimal movement

Question 43

What technique is best to assess lens clearance and edge profile for minisclerals?

Answer 43

Anterior OCT

Question 44

What is an important consideration for minisclerals regarding surrounding blood vessels?

Answer 44

Important to avoid compression of conjunctival blood vessels at the scleral landing zone

Question 45

Does central clearance usually increase or decrease as the scleral landing area settles on the conjunctiva? What percentage of this change occurs within the first 30 minutes of wear? Does the use of saline vs gel (celluvisc) have any effect on this?

Answer 45

It decreases by 50-100um 50% of this decrease occurs in the first 30 minutes of wear No difference between saline and celluvisc

Question 46

What happens to corneal thickness with wearing minisclerals? Compare it to overnight eyelid closure.

Answer 46

2% induced central corneal oedema, not clinically significant Overnight eyelid closure induces 4% corneal oedema

Question 47

Is there any association between the post lens tear vault and corneal oedema/?

Answer 47

No

Question 48

What is the optimal central clearance for minisclerals?

Answer 48

100-300um

Question 49

What can insufficient miniscleral lens clearance lead to? What about excessive clearance (2)?

Answer 49

Insufficient - may lead to bearing on the corneal apex Excessive - may cause excessive suction and tightness causing discomfort and difficulty removing the lens

Question 50

How often are minisclerals replaced generally?

Answer 50

6 monthly

Question 51

How are minisclerals or hybrids inserted? What should be done if bubbles are present?

Answer 51

Insert vertically face down, and full of solution Insert using fingers or large DMV scleral inserter If bubbles are present, needs to be removed and reinserted

Question 52

How are minisclerals or hybrids removed?

Answer 52

Need to break the seal by pushing under the lower lid to create a bubble to break the suction suction cup can also be used