2-21 Keratoconus Flashcards
Keratoconus
- What is it?
Characteristics?
1) When it occurs?
2) One or both eyes?
Non-inflammatory, progressive thinning of central/paracentral corneal stroma. Progressive protrusion + steepening.
1) Late puberty. Can still progress variably.
2) Bilateral mostly (asymmetry possible)
Keratoconus associations?
- Associated w/ systemic disorders such as Marfans, Down’s, Ehler-Danlos (Connective Tissue disorders) or some autoimmune diseases
- Genetic factors (some have family history but most are sporadic).
- More likely in Maori and pacific.
- Atopy (asthma, hay fever, eczema) more common in KC. Theoretically, either eye rubbing causes KC or KC causes eye rubbing.
Ppl w/ KC more allergy, itch, and eye rubbing.
Keratoconus symptoms?
- Progressive vision loss
- Poor vision (distance and near)
- Glare sensitivity
- Monocular double vision (or even polyopia from irregular astig)
- Itchy eyes
- Sudden reduced vision + pain = Corneal hydrops
List the signs of keratoconus
- Corneal thinning + central/paracentral actasia
- Steep keratometry readings
- Changing refraction w/ more myopia + astig
- Abnormal reflex on ret or ophthalmoscopy (scissoring/swirling)
- Prominent corneal nerves
- Vogt’s striae (Fine, usually vertical, white lines deep in corneal stroma or descemet’s membrane due to mechanical stress)
- Fleischer’s ring (Iron pigment deposited as ring at base of cone in deep layers of epithelium. Easier to see w/ cobalt blue filter.)
If advanced,
- Munson’s sign (look down)
- Corneal hydrops
– Descemets membrane ruptures
– Aqeuous flows into cornea to swell stroma + epithelium
– Sudden painful vision loss
– Leads to opacification, + vascularisation
– When resolved, cornea may be flat
– Corneal scar afterwards (graft needed to improve vision)
3 types of keratoconus cones?
- Nipple cone (small area of lots of steepening)
- Oval cone (Large oval cone)
- Keratoglobus (Large part of cornea is thin)
What happens to nerve plexus in keratoconus?
The sub-basal nerve plexus (layer below + parallel to epithelium) is less dense, disorganised, and tortuous.
- Severity of keratoconus is based on…
- How to describe fellow eye in KC?
No standard definition. Can be:
- best spec-corrected VA
- Keratometry readings
- Inferior vs superior differences in thickness
- Clinical signs.
“Forme Fruste” KC = Non-inflammatory thinning of cornea w/o clinical signs. Often used to refer to fellow eye of affected KC eye.
Describe stromal and endothelial changes in keratoconus
- Compaction + loss in ant. stroma
- Thinning + ectasia w/ re-orientation of collagen
- Reduced keratocyte (collagen laying cells) count, especially anteriorly
- Due to chronic epithelial injury releasing enzymes, increasing apoptosis
Abnormal endothelium (but just may be due to RGP wear which does that).
- Pleomorphism + polymegathism.
List the management of keratconus
- Spectacles
- Soft CLs
- Rigid CLs
- Intacs corneal implants
- Corneal collagen cross-linking
- Corneal transplant
Describe refractive Tx of keratoconus
Specs used early but don’t correct irregular
Soft CLs also used but don’t correct irregular either
RGPs are mainstay treatment options as they mask underlying irregular cornea.
If RGPs not stay on eye,
- Give RGP on top of soft CLs (Piggyback)
- Semi-scleral/scleral rigid lenses (larger diameter)
- Hybrid lens (rigid centre w/ soft surround)
Describe corneal intacts for KC Tx
Intacs corneal implants = Thin, semi-circular plastic ring segments inserted into stroma.
- Ring location depends on cone
- Flattens cornea, reduces distortion, improves vision.
- Best for mild/moderate, still prob need refraction afterwards.
Describe corneal cross linking (CXL) for KC Tx
- Slows progression of KC
Steps: - Remove epithelium
- Give vitamin B2 (0.1% riboflavin drops). These help UV absorption.
- UVA (370nm) light. Causes collagen cross-linking which slows progression.
Note: Endothelium could be damaged so require 400nm thickness.
Either: - Conventional (use B2)
- Iontophoretic (riboflavin concentrated deeper into stroma at 200 instead of 80 micrometers due to electrical current).
Describe corneal grafts for KC Tx
When cornea dangerously thin and/or no other treatment possible.
Either:
- Full thickness transplant
- When stroma very damaged or endothelial status unknown
- Higher chance of graft rejection
- Partial thickness (descemet’s + endothelium untouched)
- When stroma inolved but endothelium healthy.
- Lower chance of graft rejection.
