Ophthalmology 6: Problem Solving - Corneal Ulcers Flashcards
- Difference between cornea and sclera?
- Where do the cornea and sclera meet?
- What structures live here? – what do these structures do?
- Cornea is made up of organised collagen, sclera made up of disorganised collagen.
- At the limbus.
- stem cells of the cornea – create new epithelium and stroma all the time.
- How is the cornea transparent?
- Corneal structure.
- Collagen very highly arranged in rows and layers. Also relatively dehydrated to keep it from becoming oedematous and cloudy.
No vessels, no pigments, non-keratinised. - Superficial to deep.
Epithelium mechanical barrier.
- lipophilic layer 6-8 cells thick.
- constantly regrown from basal cells.
- basal cells replaced by centripetal migration from limbal system cells.
Endothelium.
- 1 cell thick, nutrition from aqueous.
- on Descemet’s basement membrane.
- contain Na+/K+ATPase physiological pumps to constantly remove water.
- gets all nutrition from aqueous humour.
Descemet’s basement membrane = thick specialised basement membrane, which keeps the pressure in the eye.
Total thickness of canine cornea = 0.55mm.
Remember the functional lacrimal unit and how thing are interconnected!
Exam techniques and diagnostic tests for cornea.
Spot opacities w/ distant direct.
- localise using parallax (gauge depth of opacity).
Examine colour change w/ close direct.
Examine structural change w/ slit beam.
Sampling for cytology/culture?
Fluorescein testing for ulcers.
Using a slit beam.
Narrow beam of light.
Highlights contours and deviations in depth.
Also used for spotting particulates in aqueous as ‘flare’ - turbid/muddy.
Check colour and determine if active infection.
Sampling.
Sterile cotton bud/Cytobrush over conjunctiva or cornea.
For cytology / C&S / PCR.
Can apply LA first e.g. Proxymetacaine.
NOT after diagnostic drops - affects culture and other dyes.
Fluorescein staining.
Available as minims or strips.
Best flushed out w/ saline.
Highlights defects in corneal surface.
Helps check nasal flow of tear drainage w/ ‘Jones’ test.
Fluoresces green when w/ water but orange otherwise.
Mildly irritant - LA first.
Does not adhere to normal corneal epithelium.
Binds to exposed corneal epithelium.
Will penetrate epithelia over time if concentrated so use small amount and flush out w/ saline.
Corneal healing process - epithelial repair.
- detachment – basal epithelial cells release attachments to the basement membrane.
- movement – cells slide to fill defect across B.M. (roughly migrate 1mm per day), holding on w/ desmosomes.
- proliferation –epithelial cell mitosis within 24-36hrs. Increase thickness epithelium.
- reattachment – to basement membrane and adhesion complexes.
- normal epithelium in ~2w.
- bacteria in the ulcer will slow the process.
Corneal healing process - Stromal repair.
- complex.
- much slower.
- fibroblastic proliferation, new collagen components form.
- new extracellular matrix produced.
- disorganised arrangement of fibres = corneal scarring.
- remodelling occurs over months to years.
Corneal healing process - Endothelium repair.
- cells at margin of wound elongate.
- cells get spread thinner and migrate.
- no mitosis possible.
- not as effective.
Ocular clinical signs of corneal ulcer.
Epiphora, blepharospasm, conjunctival hyperaemia.
Colour change in cornea.
Pain - behaviour changes, pain face, head shy, pain aggression on approach to examine.
+/- anisocoria:
- asymmetry to pupil size.
- relative miosis on affected side.
- sign of ‘reflex uveitis’.
- Layer of a superficial ulcer.
- Layer of a deep ulcer.
- Descemetocoele?
- Perforation?
- epithelial ulcer (entire epithelial loss).
- stromal ulcer (difficult to assess how much stroma lost).
- complete stromal loss (layer of Descemet’s membrane starts to bulge through ulcer) - potential for rupture.
- rupture of entire cornea, including Descemet’s membrane.
Approach to a suspected corneal ulcer.
Thorough ophthalmic exam.
Assess depth of ulcer.
Check fluorescein uptake.
Aim to identify and treat inciting cause e.g.:
- abnormal lids.
- exposure e.g. ineffective blink.
- aberrant hairs.
- foreign body.
- KCS.
- any other change to Surface Lacrimal Unit.
Removal of foreign body from the eye.
E.g. grass seeds or plant matter.
Wedged into 3EL or conjunctiva, deep in fornix.
Sedate for thorough exam.
Grasp and remove FB, flush eye w/ saline jet through needle.
Approach once FB removed.
Should heal rapidly w/ supportive care (w/in 1w):
- analgesia (systemic NSAIDs).
- ABX prophylactically.
- lubrication.
- +/- buster collar.
Minimal scar formation.
E.g. incidental scratch / FB removed.
Reflex uveitis.
2’ to anterior ocular pain e.g. ulcer.
Occasional finding.
Reflex causes spasm of ciliary body.
Miosis.
Painful spasm like ‘cramp’.
Other signs of uveitis may develop.
Treat w/ mydriatics e.g. atropine.
Can give NSAIDs systemically.
Blue - oedema.
May see blue tinge in area of anterior eye before applying fluorescein.
Epithelial defect leads to focal oedema:
- diffuse.
- focal.
- hazy.
White colour change in healed ulcers.
Corneal fibrosis - scarring.
Inflammatory cell infiltrates initially.
Remodel stroma and return to near normal structure.
Scars contract but remain visible.
Scars do not uptake fluorescein.
Once healed, can stop ABX and stop analgesia once comfortable.
Inherited corneal dystrophy.
Non-pathological white changes.
Bilateral.
Recognised in young dogs e.g. CKCS, husky, Dachshund.
Lipid/mineral dystrophy.
Little progression or impact on vision.
Rarely ulcerate.
No treatment in most cases.
Lipid deposits / mineral deposits.
Both are uncommon.
Seen in older dogs, likely to be systemically ill.
Can sometimes ulcerate quite dramatically.
Lipid deposits may form an arc and are associated w/ hyperlipidaemia or endocrinopathies so recommend bloods.
Mineral deposits are associated w/ endocrine disease and occur in geriatric patients.
White corneal colour changes w/ no ulceration might need some further investigation.
SCCED.
Spontaneous chronic corneal epithelial defect.
Superficial ulcer not heal in 1-2w.
Middle aged dog (average 7-9yrs).
ANY BREED - commonly SBT/boxer.
Can persist for weeks, months, even years if not treated effectively.
No apparent inciting cause.
NOT ‘wrong’ ABX.
Also called ‘Boxer ulcers’, ‘indolent (lazy) ulcers’.
SCCED pathogenesis.
Not fully understood.
Poor epithelial adhesion to stroma.
Abnormal basement membrane.
Abnormal superficial stroma - has a superficially hyalinised acellular zone.
Typically a glancing abrasion knocks off poorly adhered epithelium.
Often created a ‘flap’ of loose epithelium.
SCCED clinical signs.
Superficial ulcer (epithelium loss only).
Loose epithelial edges.
Halo of fluorescein.
‘Under-run’ edges.
Minimal corneal oedema (easy to miss).
Potential neovascularisation in time.
Variable pain.
Can recur in novel corneal sites.
SCCED supportive medical treatment.
Prophylactic topical ABX.
- e.g. fucidic acid BID (L), or chloramphenicol TID-QID (off-L).
Lubrication.
Systemic NSAID analgesia (meloxiam, paracetamol).
+/- topical atropine if reflex uveitis/miosis.
+/- oral doxycycline 5mg/kg SID may promote epithelialisation.
Buster collar.
BUT unlikely to heal w/ meds alone as defective epithelium persists.
SCCED surgical treatment.
Epithelial debridement.
Remove loose, detached epithelium.
Use dry, sterile cotton buds.
Disrupts anterior stroma / removes hyalinised zone.
Alone overall 50% healing rate.
Can be repeated after 7-14 days.
Under LA (Proxymetacaine).
SCCEDs are the only ulcer you should debride!
