Week 10 - Keratoconus Flashcards
Describe Keratoconus
• 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
Risk factors/associations with Keratoconus
• Asian ethnicity
• Family History
• Collagen/connective tissue disorders
• Atopy
• Eye rubbing
Sub clinical keratoconus:
- 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
Early Keratoconus:
• 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
Moderate Keratoconus:
• 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
Advanced Keratoconus
• 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
Differential diagnosis for keratoconus:
• Pellucid marginal degeneration
• Keratoglobus
• Post Lasik/Lasek ectasia
Presentation of keratoconus:
• 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
Investigations of keratoconus:
• Refraction with retinoscopy
• Slit lamp examinatiom
• Pachymetry (average normal cornea 550microns)
• Keratometry (normal range 7.10- 8.60)
Are the mires distorted?
What options can be considered with karatoconus?
• 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
What are the steps from a hospital eye dept?
• 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
Corneal collagen cross linking (CXL) aim:
• 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
Corneal collagen cross linking (CXL) procedure:
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.
Before vs after CXL?
• Before: Weaker bonds in collagen
• After: Stronger bonds in collagen
Why not cross link everyone with KC?
- No progression = no point in crosslinking!
- Risks!
- Infection
- Scarring/haze
- Poor healing of epithelium
Exclusion criteria for CXL:
-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
Corneal graft/transplant:
• 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.
Penetrating keratoplasty steps:
- Diseases or injured cornea
- Corneal button removed
- Clear donor button
- Donor cornea sutured in place
Deep anterior lamellar keratoplasty “DALK”
• Lower risk of graft failure as patient keeps their own endothelium
• Similar refractive outcome to PK
Other surgical options:
• 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
Contact lenses for KC
• RGP
• SOFT
• HYBRID (soft exterior, rigid RGP centre)
• Semi-scleral
• Scleral
How does RGP help keratoconus?
• 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.
RGP: Pros
• 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
RGP: Cons
• 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
Parameters for RGP:
• 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
Three point touch fitting technique:
Four zones created:
• Slight apical touch
• Paracentral clearance
• Mid-peripheral bearing
• Peripheral clearance
What is Piggybacking RGP lens?
• 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
Soft lenses for keratoconus: Pros
• 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
Soft lenses for keratoconus: Cons
• 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
Typical Parameters for soft lenses for keratoconus:
• 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
• Tight/steep soft lenses and
• Flat soft lens
• 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
Pros and Cons of hybrid lenses:
• 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
Describe semi-scleral lens:
• Large diameter RGP material (14-16mm)
• Fitted to vault whole cornea with lens resting on sclera
• Liquid reservoir between cornea and lens
Semi-scleral lens: Pros
• 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
Semi-scleral lens: Cons
• 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
Considerations when fitting:
• 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
Considerations in fitting lenses for amount worn:
• 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.
