Lecture 18 Keratoconus

Question 1

What is keratoconus?
When is the onset?
What is the prevalence?
More common in males or females?

Answer 1

-corneal thinning that leads to protrusion in the form of a cone

-teenage years to mid 30’s

1 in 500 to 1 in 2000.
higher rates in southern Asia and middle east

males

Question 2

Is there a genetic link for keratoconus?

Answer 2

*Does show autosomal dominant inheritance in some families
-not sex linked
-if one parent has the disease, each child has 50% chance of inheriting it
*KC is most commonly sporadic

Question 3

What are the signs of KC on the slit lamp?

Answer 3

Vogt’s striae: thin white lines visible in cornea
-Fleischer’s ring: faint brownish ring
-apical scarring
-Munson’s ring: deviation of the eye, advanced case

Question 4

Does a normal slit lamp examination exclude KC diagnosis?

Answer 4

no- early KC doesn’t show slit lamp signs

Question 5

How can we use keratometry to look for KC?

Answer 5

-distorted k mires, described as egg shaped

Question 6

How can retinoscopy indicate KC?
How can topography indicate KC?

Answer 6

-irregular reflex, scissoring of reflex
-not possible to fully neutralise

-inferior steepening but not always
-centra, oval or inferior cone
-always has flattening in opposite meridian to cone
-quality of vision depends on how close the cone is to the visual axis

Question 7

What is the management of KC?

Answer 7

*Have a discussion with px
*Have a leaflet or link to give px
*Find out if local hospital trust has information sheet for px
*Moorfields has an online leaflet
*Consider how a newly diagnosed patient is feeling

referral to HES

Question 8

What happens post referral?

Answer 8

*Px will see ophthalmologist
*Will conduct corneal exam
*Diagnosed confirmed by topography
*May carry out OCT, pachymetry
*May recommend px for collagen cross-linking if px is progressing

Question 9

What is the aim of collagen cross-linking?

What is the best time to do it?

How is the procedure done?

When can they resume CL wear?

Answer 9

to stabilise KC

*Best done in early disease before cornea becomes too thin (below 360 microns)

*CXL is done under topical anaesthetic
*Epithelium is abraded with a blunt spatula
*Riboflavin eye drops are applied to the eye
*The cornea is exposed to UVA radiation
*Collagen cross linking stabilises and increases the bond between collagen fibres

*Can resume CL wear 6 weeks post treatment
*Px will need a refitting as CXL causes cornea to flatten.

Question 10

What are the contact lens options for KC?

Answer 10

1. Soft KCL lenses
2. Corneal GP’s
3. Scleral lenses
4. Hybrid lenses

Question 11

What properties should soft lenses have to be used in a KC px?

What are the advantages?

What are the disadvantages?

Answer 11

*To be able to correct aberrations caused by KC, they need to be deliberately thicker
*When there thicker, this enables a tear layer to be created underneath the lens to correct corneal irregularity
*They must be made from a high oxygen material (e.g, silicone hydrogel) due to increased thickness

*Great initial comfort
*Familiarity to lots of px
-usually straightforward to fit
*Good in dust environments

*Thick lenses so even high Dk/t isn’t great
*Best for early-moderate KC
*May not improve VA enough in advanced disease

Question 12

What is a standard design RGP not suitable for a KC px?

Answer 12

the periphery doesn’t flatten enough to consider the difference between cone and flatter parts of cornea
*This can cause mid peripheral compression and lack of edge clearance

Question 13

What RGP design is good for KC corneas?

Answer 13

3 POINT TOUCH
light feather touch at the apex-still clearing cornea
mid-peripheral bearing- takes the weight of the lens on the healthy part of the cornea
paracentral annulus of clearance is where the cone is the steepest
more edge clearance than standard design

example lens: rose K2

Question 14

What are the pros and cons of traditional RGP’s?

Answer 14

pros:
-Great vision
*Don’t control the disease, fitted according to progression
*Cheap

cons:
*Poor initial comfort
*Adaptation can take a while
*not good in dusty environments, become more uncomfortable

Question 15

When is the piggy-back system used?

What is it?

What are the considerations?

Answer 15

*used in cases of:
- poor centration
-poor comfort
-recurrent corneal abrasions
-chronic 3 and 9 o clock staining

hard RGP lens is placed on top of a soft lens

-oxygen transmission
-care system may be different for each eye
-cost of daily disposables
-daily disposables may be too flat to fit

Question 16

What are hybrids?

What are the advantages?

Answer 16

*RGP centre bonded with a soft skirt.

*You get optics of RGP which give good vision
*Lid interaction is with soft lens rather than GP edge so gives better comfort
*Soft part of lens seals on conjunctiva so no foreign bodies
*high Dk material allows for healthy wear

Question 17

How do you fit hybrid lenses on a normal eye?

What type of Nafl should you use?

Answer 17

*GP centre is ordered to be closest to flattest K
*Skirt is then fitted as a soft lens
*Look for small amount of movement for tear exchange and easier removal.

high molecular NaFl so it doesn’t stain soft skirt

Question 18

What are the 2 types of hybrid fitting stratergies for irregular corneas?

Answer 18

1.Fit as regular GP for irregular corneas and add skirt
2.Fit empirically for regular corneas

Question 19

What are the benefits of hybrid lenses?

What are the cons?

Answer 19

*Improved comfort
*No dust under the lens
*good vision
*Some familiarity due to soft skirt

*Handling can be tricky, especially removal

Question 20

How do you insert a hybrid lens?

When may you have to remove and re insert the lens?

Answer 20

*Put some saline and large molecular weight fluorescein into the bowl of the lens before insertion
*Get px to bend down and look at the floor
*Gently place lens on the cornea with a DMV inserter

air bubbles

Question 21

What is the aim of scleral lens fittings?

Answer 21

*Aim to completely clear the cornea (no touch with cornea so no need to fit the corneal irregularity)
*Aim to land the lens on the sclera (much less sensitivity)
*Fitted by fitting set (no topographer needed)

Question 22

What is the definition of a scleral lens?

Answer 22

*A lens which rets at least partially on the sclera
*Scleral lenses vary in size from 13-24 mm +

Question 23

What criteria is used to fit scleral lenses?

What are the types of scleral lenses and their size?

Answer 23

sag

corneo-scleral 12.9-14.9mm
mini scleral 15-18mm
full scleral 18-24mm

Question 24

How do you insert a scleral lens?

Answer 24

*Fill the lens with unpreserved saline and Nafl
*Px should look down to the floor
*Get them to control the lower eyelid whilst we control the upper eyelid
*Place lens onto the eye

Question 25

What are the fitting principles of scleral lenses?

Answer 25

1. lens should clear entire cornea
   2.lens should clear the limbus
   3.lens should land on the sclera

Question 26

What are the benefits of a scleral lens?

How do you remove a scleral lens?

Answer 26

*Easier to fit now
*More applications: post graft, dry eye px
*Comfortable due to fluid layer

*Place small Stucker on the edge of the lens and lifting it up to remove the lens
*Can use lids to get under the lens and remove it

Question 27

What must you check using a slit lamp in a scleral lens fitting?

Answer 27

amount of apical clearance- after 45-60 mins of lens settling, look at high mag optic section
-need at least 2oo-300 um of clearance of the back surface of lens and apex of cornea

-use white light to see where lens lands

-check how well lens edge is aligning with sclera
-inappropriate scleral landing: cutting oc conjunctival vessels, blanching and impingement

Question 28

What are the 2 types of corneal grafts?

Answer 28

1. Full thickness penetrating keratoplasty
2. DALK (deep anterior lamellar keratoplasty)

Question 29

How does full thickness penetrating keratoplasty work?

Answer 29

*The entire thickness of the cornea is removed and replaced with donor corneal section
*The px will be on anti-rejection steroids for many years
*May develop steroid induced ocular hypertension
*Cornea may take up to a year to settle and the sutures may not be removed until then
*The graft may need replacing after 10-15 years

Question 30

what are the benefits of deep anterior lamellar keratoplasty work?

Answer 30

*Less invasive than a full PK
*Lower risk of rejection
*Beter visual result
*faster healing process
*will be able to taper off steroids early

Question 31

What are INTACS?

Answer 31

Small semi-circular plastic rings that are inserted in stromal area of cornea. Helps to stabilise and regress the progression of KC. Not common in the UK, only available in private healthcare system.