Lecture 18 Keratoconus Flashcards
What is keratoconus?
When is the onset?
What is the prevalence?
More common in males or females?
-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
Is there a genetic link for keratoconus?
*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
What are the signs of KC on the slit lamp?
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
Does a normal slit lamp examination exclude KC diagnosis?
no- early KC doesn’t show slit lamp signs
How can we use keratometry to look for KC?
-distorted k mires, described as egg shaped
How can retinoscopy indicate KC?
How can topography indicate KC?
-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
What is the management of KC?
*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
What happens post referral?
*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
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?
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.
What are the contact lens options for KC?
- Soft KCL lenses
- Corneal GP’s
- Scleral lenses
- Hybrid lenses
What properties should soft lenses have to be used in a KC px?
What are the advantages?
What are the disadvantages?
*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
What is a standard design RGP not suitable for a KC px?
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
What RGP design is good for KC corneas?
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
What are the pros and cons of traditional RGP’s?
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
When is the piggy-back system used?
What is it?
What are the considerations?
*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