Week 10 - Keratoconus

Question 1

Describe Keratoconus

Answer 1

• Definition: Non-inflammatory, progressive ectasia (distortion) of the cornea causing an irregular, thinned corneal shape and therefore blurred vision.

• Incidence: 1 in 3000 to 1 in 10,000 depending on ethnicity

• Age of onset: typically late teens or early twenties

• Usually bilateral but often asymmetric

Question 2

Risk factors/associations with Keratoconus

Answer 2

• Asian ethnicity
• Family History
• Collagen/connective tissue disorders
• Atopy
• Eye rubbing

Question 3

Sub clinical keratoconus:

Answer 3

• No signs on slit lamp examination
• Unaided vision 6/6 or better
• Patient asymptomatic
• Retinoscopy reflex may be a little irregular
• Mild thinning & irregularity on topography
• May go undetected/undiagnosed
  GCU

Question 4

Early Keratoconus:

Answer 4

• No signs on slit lamp examination or subtle Vogts’s striae; (fine stress mark-like folds in the Posterior stroma)
• Subtle thinning of corneal section
• Fleischer’s ring; (iron deposits at base of cone)
• Mild scissor ret reflex
• Low myopic/astigmatic Rx
- VA refracts well
- Pachymetry under 550 microns

Question 5

Moderate Keratoconus:

Answer 5

• Very split/scissors ret reflex
• Oil droplet reflex
• Moderate - high myopia and astigmatism.
• Difficult end point on refraction
• VA poor
• Pachymetry under 450 microns - thinning seen on corneal section

Question 6

Advanced Keratoconus

Answer 6

• No useful ret reflex as cornea so distorted
• Poor VA
• Munsen’s sign
• Hydrops - breaks in Descemets membrane causing oedema, which resolves with scarring
• CCT under 440microns

Question 7

Differential diagnosis for keratoconus:

Answer 7

• Pellucid marginal degeneration
• Keratoglobus
• Post Lasik/Lasek ectasia

Question 8

Presentation of keratoconus:

Answer 8

• Blurred or poor quality vision
• Frequent changes in prescription recently, particularly with increasing myopia/astigmatism
• Dissatisfaction with glasses or with previous optometrist
• Monocular diplopia or ghosting
• Glare

Question 9

Investigations of keratoconus:

Answer 9

• Refraction with retinoscopy
• Slit lamp examinatiom
• Pachymetry (average normal cornea 550microns)
• Keratometry (normal range 7.10- 8.60)
Are the mires distorted?

Question 10

What options can be considered with karatoconus?

Answer 10

• Prescribe glasses but warn x may change
Consider partial x or balance lens if high cyls and/or significant anisometropia
• Refer routinely to local cornea service
• Consider contact lenses

Question 11

What are the steps from a hospital eye dept?

Answer 11

• Patient assessed with refraction, topography and dilated ocular examination - diagnosis made
(Mild-Mod CCT>400)
• Repeat assessment
3-4 months later to see if KC has progressed
- Progressive: List for collagen cross linking
- Stable: Continue to monitor every 6-12 months for 5 years
(Advanced, CCT<400, scarring)
• Fit contact lenses if indicated
• If CLs unsuccessful consider graft

Question 12

Corneal collagen cross linking (CXL) aim:

Answer 12

• AIM: To stop progression of keratoconus (and other ectasias). Success rate >90% DOES NOT CURE KERATOCONUS OR IMPROVE THE IRREGULARITY - IT JUST STOPS IT GETTING WORSE

Question 13

Corneal collagen cross linking (CXL) procedure:

Answer 13

PROCEDURE: Epithelium removed with alcohol, riboflavin 0.1% (vitamin B2) drops applied to stroma for 10 mins, exposed stroma irradiated with pulsed UV light (every 1.5secs for 8 mins)
- this strengthens bonds between collagen fibres of cornea. Bandage contact lens applied, post op drops prescribed. Usually done as day surgery under local anaesthetic.

Question 14

Before vs after CXL?

Answer 14

• Before: Weaker bonds in collagen
• After: Stronger bonds in collagen

Question 15

Why not cross link everyone with KC?

Answer 15

1. No progression = no point in crosslinking!
2. Risks!
   - Infection
   - Scarring/haze
   - Poor healing of epithelium

Question 16

Exclusion criteria for CXL:

Answer 16

-No progression
-CCT under 400 microns
-Corneal scarring
- Caution taken if facial/periorbital eczema - higher complication risk
- Re-treatment possible on same eye in CCT still > 400

Question 17

Corneal graft/transplant:

Answer 17

• Corneal Graft / Transplant: Penetrating
- Life long risk of grafted tissue rejecting
- Long recovery (12-18 months) before tissue stable
- Long term topical steroid use
- Often results in regular or irregular astigmatism of the graft surface, meaning the need for glasses x with high cyls/anisometropia or the need for post graft contact lenses.

Question 18

Penetrating keratoplasty steps:

Answer 18

1. Diseases or injured cornea
2. Corneal button removed
3. Clear donor button
4. Donor cornea sutured in place

Question 19

Deep anterior lamellar keratoplasty “DALK”

Answer 19

• Lower risk of graft failure as patient keeps their own endothelium
• Similar refractive outcome to PK

Question 20

Other surgical options:

Answer 20

• INTACS or Kerarings
Intra-stromal ring implants
• No longer offered on NHS due to inconsistent results.
• CXL Plus
- Crosslinking with laser correction of
irregularity
- Not offered on NHS

Question 21

Contact lenses for KC

Answer 21

• RGP
• SOFT
• HYBRID (soft exterior, rigid RGP centre)
• Semi-scleral
• Scleral

Question 22

How does RGP help keratoconus?

Answer 22

• The images entering through the KC corneal surface create distortion and blurring.
• With RGP: The smooth surface of the RGP contact lens and the tear film layer between the lens and the irregular KC cornea allow a clear image to enter the eye.

Question 23

RGP: Pros

Answer 23

• Good acuity, particularly in moderate or advanced eyes
• Long lasting (1 year at least) and can be more cost effective in long term than soft lenses
• Lower risk of infections than soft
• Lower risk of hypoxic complications as good tear exchange and high DK

Question 24

RGP: Cons

Answer 24

• Can be difficult to adapt to - initially uncomfortable
• Small and easily lost
• Can displace off cornea in advanced cones
• Apical touch can cause epithelial erosions
• Flare/haloes from lens edge if small diameter
• Fluctuating vision immediately after removal

Question 25

Parameters for RGP:

Answer 25

• BOZR 5.60 - 8.20 mm
• BOZD 8.60 - 9.60 mm
• BVP usually myopic
• Peripheral curves often need to be modified to fit contour of cone (either reduced or increased edge lift around whole lens, or by segment)
• Material: -focon
• Handling tint: blue, green or violet
• Unplanned replacement schedule… Should last a year minimum

Question 26

Three point touch fitting technique:

Answer 26

Four zones created:
• Slight apical touch
• Paracentral clearance
• Mid-peripheral bearing
• Peripheral clearance

Question 27

What is Piggybacking RGP lens?

Answer 27

• Piggyback - RGP over plano soft monthly or daily disposable.
• Can improve comfort and centration
• More hassle for I&R and cleaning, higher risk of complications as px has 2 lenses on eye

Question 28

Soft lenses for keratoconus: Pros

Answer 28

• Good initial tolerance, wear time can be built quickly
• Large diameter, flare not problematic
• Vision good in mild - moderate KC
• Stable fit - don’t tend to fall out or displace

Question 29

Soft lenses for keratoconus: Cons

Answer 29

• Don’t mask irregularity as well as hard lenses - VA not as good in moderate to advanced KC
• Can have thick edges (but silicone hydrogel materials tend to avoid hypoxic problems)
• Higher infection risk than with RGPs It can be difficult to ensure stable vision in high cyls

Question 30

Typical Parameters for soft lenses for keratoconus:

Answer 30

• BOZR 7.40mm - 9.40mm
• BOZD 14.00mm - 15.50mm
• BVP usually myopic with astigmatism - can go up to +/- 30.00DS or -15.00D
• Peripheral curves often need to be modified to fit contour of cone (either reduced or increased edge lift around whole lens, or by segment)
• Material: -filcon. Tend to be higher modulus than other soft lenses to mask irregularity
• Handling tint: none or pale blue
• 3-12 months replacement schedule depending on material

Question 31

• Tight/steep soft lenses and
• Flat soft lens

Answer 31

• Tight/steep soft lenses
- Limbal compression
- Hyperaemia often seen after removal
• Flat soft lens
- Excessive lag on eye movements and blink
- Rotation of marking seen
- Variable vision
- Increase lens awareness

Question 32

Pros and Cons of hybrid lenses:

Answer 32

• PROS
- Acuity of RGP but with better comfort Don’t displace or fall out like RGPs can
• CONS
- Can be difficult to insert & remove
- Bubbles can form at junction
- Solution must be suitable for both materials
- Time consuming to fit

Question 33

Describe semi-scleral lens:

Answer 33

• Large diameter RGP material (14-16mm)
• Fitted to vault whole cornea with lens resting on sclera
• Liquid reservoir between cornea and lens

Question 34

Semi-scleral lens: Pros

Answer 34

• GOOD ACUITY
• LESS LID INTERACTION SO CAN BE MORE
COMFORTABLE THAN RGPS
• TUCKED UNDER LIDS SO NO ISSUES WITH LENSES DISPLACING OR FALLING OUT
- GOOD FOR ADVANCED CONES
• HELPFUL IF IRREGULAR AREA OF CORNEA
VERY PERIPHERAL

Question 35

Semi-scleral lens: Cons

Answer 35

• DIFFICULT TO INSERT AND REMOVE - HAVE TO GO IN FULL OF SALINE, REMOVED LIKE A BIG RGP OR WITH SUCKER
• DIFFICULT TO JUDGE FIT - PX HAS TO INSERT WITH SALINE WITH ADDED FLUOROSCEIN AS THERE IS NO TEAR
EXCHANGE
• HAVE TO ENSURE LIMBAL HEALTH ISN’T
COMPROMISED
• NOT IDEAL IF INFLAMMATION OF OCULAR SURFACE AS NO TEAR EXCHANGE

Question 36

Considerations when fitting:

Answer 36

• Atopic/allergic keratoconjunctivitis. A lot of patients with keratoconus have seasonal or year-round dust, animal hair or pollen allergies

• Always take a medical and ocular history at the start of the fit appointment.
• Examine the tarsal plate by everting the lids
• Consider starting patient on topical antihistamines or mast cell stabilisers before proceeding with fitting to get any ocular allergy under control
• Explain any potential problems to the patient

Question 37

Considerations in fitting lenses for amount worn:

Answer 37

• Patients could be wearing lenses for the next 50 years!
• CLAPC, hypoxia or dry eye could be an issue
• Patients who are attending for topography every 6 -12 months to check for progression have to leave their lenses out for 2 weeks prior to topography to ensure scans are accurate.