Lec 7 Keratoconus

Question 1

Associations with keratoconus

Answer 1

Eye rubbing/atopy

Sleep apnoea

CT disorders like Marfans/Ehlers Danlos

Maori/Pacifica/NZ

Trisomy 21

Question 2

Properties of keratoconic corneas

Answer 2

Thinner fragile and less sensitive

Prone to corneal moulding and NaFl staining from RGP

Prone to apical scarring - Vortex scarring

Question 3

What’s special about keratoconus and CL tolerance

Answer 3

They have reduced corneal sensitivity from scarring and increased nerve fibre tortuousity

BUT if RGP intolerant use sclerals/mini scleral

Question 4

Topographer vs keratometer

Answer 4

Topographer maps out cornea and gives K readings but keratometer just gives K readings

Question 5

Categorisation of nipple oval and global cone

Answer 5

Nipple is <3mm

Oval is 3-5.5mm

Global is >5.5mm

Question 6

What does forme fruste mean

Answer 6

Topographer is Good at early cone detection?

So means watch out if you pick up keratoconus one eye as it means the other eye prob has some too

no such thing as monocular keratoconus

Question 7

What topography indices are good for keratoconus

Answer 7

True elevation maps better than axial or tangential

Tangential maps are good for cone location and normalise scale

Question 8

Topographer have an inbuilt CL fitting programme and what is this good and bad for

Answer 8

Good at predicting final CL fitting success and is good starting point and cuts chair time instead of using set of trial lens

Manual better for more severe Kc

Question 9

Advantages of topography

Answer 9

Confirms diagnosis

Finds location/size of cone ape

Monitors progression

Differentiates pellucid/terriens

Demonstrates to patient the problem

Question 10

Signs of keratoconus on non slit lamp

Answer 10

Pachymetry <480um

Topography indices I-S To show if inferior is diff to superior K reading

Scissoring/swirling ret reflex

Irregular astig/monocular diplopia/poor spec VA

Question 11

Signs of keratoconus on slit lamp

Answer 11

Vogt striae- vertical lines in epi due to buckling of posterior cornea

Corneal nerve visibility

Fleishers ring

Apical scarring

Hydrops

Question 12

What are hydrops

Answer 12

Sudden corneal oedema as AQ humour invades posterior cornea through split Decemets membrane

Painful but self resolving though scarring can reduce vision

Question 13

What’s good about hydrops

Answer 13

Fibrosis occurs and this causes the corneal curvature to flatten over time so makes CL fitting easier ;)

Question 14

What’s the Fitting options for a keratoconic amount

Mild <45, moderate (45-52), severe >52, post graft

Answer 14

Mild - spec ok, soft toric lenses ok BUT if VA 6/12 or better than no subsidy

Moderate - RGP or hybrids

Severe - RGP/Hybrid/Semi scleral/soft piggyback/grafting

Post graft - may get better spec VA/may use CL still

Question 15

Difference between a standard RGP and a keratoconic design

Answer 15

Keratoconus cornea steeped in a specific area but then flattens at high rate so:

1) increase edge lift
2) small OZ to vault cone area

Question 16

Main rule for fitting an RGP on keratoconic

Answer 16

First definite apical clearance fit

As if you get touch/bearing then get apical scarring AND if u get too much vaulting then visions bad

Question 17

How can a toric periphery help a keratoconic cornea

Answer 17

KC corneas usually WTR so toric peripheries can avoid tightness at 3&9 o’clock as well as reducing inferior standoff

Question 18

Biochemistry of a normal cornea

Answer 18

Normal stress turns into ROS/RNS but antioxidant enzymes and lipid peroxidation enzymes eliminates them

So minimal mtDNA damage = good cell function

Question 19

Biochemistry of keratoconic cornea

Answer 19

Abnormal antioxidant enzymes which means ROS/RNS accumulate activating/up regulating ECM degradation enzymes thinning cornea

ROS/RNS also cause MtDNA damage increasing ROS production and decreasing Oxidative phosphorylation = bad cell function

Question 20

Therapies for Keratoconus

Answer 20

Corneal cross linking

INTACS

Question 21

Describe corneal cross linking

Answer 21

Riboflavin drops with UVA stiffens cornea by anterior corneal collagen cross linking resulting in increased stiffness and improves resistance to swelling and enzyme degradation

Good for progressing teens

Question 22

Describe INTACS

Answer 22

Corneal rings that flatten shape for mild Kc improving VA

20% ineffective and not suitable for thinned or scarred corneas so can range from 0-7lines improvement

Question 23

Does keratoconus slow down with age

Answer 23

KC onset is teens and progresses till 30-40 cuz natural cross linking of collagen fibres

Question 24

What’s pellucid marginal degeneration and what’s good about it

Answer 24

Steep at bottom of cornea “crab claws” or “kissing swans”

Hard to fit with CL as flat superior and stele inferior

GOOD as has regular astig usually so specs OK

Question 25

What happens after a graft for keratoconus (keratoplasty)

Answer 25

More regular cornea so better in glasses than CL but still often need fit in CL or semi sclerals
- semi scleral better than RGP when elevation diff across cornea is >350

Question 26

What’s the key eligibility for grafts in keratoconus

Answer 26

CONTACT LENS INTOLERANCE

Question 27

What’s important in grafts for keratoconus

Answer 27

Grafts have endothelial cell density ECD reduced and hypoxia can reduce ECD even more which can lead to graft rejection so must avoid limbal pressure