Corneal ulcers Flashcards
What are corneal ulcers?
break in continuity of corneal epithelium with exposure of underlying stroma
How does the cornea stay transparent?
- smooth optical surface
- relatively dehydrated state
◦ Epithelium above has tight junctions to prevent water from tear film entering
◦ Endothelium below has Na/K ATPase pump: pumps ions from stroma into aqueous humour - very regular arrangement of collagen fibrils
- low cell density
- no keratin, blood vessels or melanin
Describe the healing of a superficial ulcer on the epithelium?
- epithelial loss -> cells slide rapidly across to cover defect (hours-days)
◦ cell proliferation, migration and adhesion
Describe stromal wound healing?
Starts once re-epithelialisation is complete
Fibroblasts migrate in & lay down new collagen
Requires vascularisation
Results in scar tissue: remodelling over time
What are causes of corneal ulcers?
- Trauma
- Common
- Foreign bodies, abrasions, laceration, chemical injury (serious but uncommon)
- Tear film problem – KCS
- Quantitative lack of tears – KCS (dry eye) – very common in dogs
- Qualitative tear film problem – less common
- NB Ulcers secondary to dry eye often have a circular ‘punched out’ appearance and deteriorate rapidly
- Adnexal conditions i.e. involving eyelids, eyelashes and conformation
- entropion
- eyelid mass
- ectopic cilia
- brachycephalic conformation (macropalpebral fissure, trichiasis and medial entropion)
- Primary corneal disease – SCCEDs
- Spontaneous Chronic Corneal Epithelial Defect
- Infection
- Bacterial keratitis (and occasionally fungal) in dogs and cats - Usually secondary to trauma to allow colonisation
- Feline herpesvirus-1
- Virus replicates within corneal epithelial cells
- URT disease, conjunctivitis, ulcerative and non-ulcerative keratitis
This cat has a superficial ulcer in the ventrolateral cornea. From the image below, what are the 2 most likely underlying causes?
- Brachycephalic conformation
- Entropion
- Distichiasis
- KCS (dry eye)
- FHV-1 infection
- entropion
- FHV-1 infection
Describe diagnostic approach to corneal ulcers
- Hands-off examination: Signs of pain? Nature of any discharge? Eyelid conformation?
- Palpebral +/- corneal reflex
- STT (unless risk of rupture) – remember ulcers will increase tears
- Examine anterior segment with focal light source +/- magnification
- Look at ulcer itself and health of surrounding cornea
- Careful examination of eyelids
- Distant direct – check for reflex uveitis
- Fluorescein staining
- Orange dye that stains corneal stroma green
- No uptake by intact corneal epithelium or by Descemet’s membrane
- Fluorescein strips preferable
- Touch onto bulbar conjunctiva
- Always flush – water, saline or false tears
- Use blue light to highlight dye uptake
- Corneal cytology and culture/sensitivity – if suspect infected
What clinical signs are associated to corneal ulcers?
- Pain - classic TRIAD of ocular pain
◦ Increased lacrimation (high STT)
◦ Blepharospasm - closing eye
◦ Photophobia - avoiding bright light - Conjunctival hyperaemia - a “red eye”
- Ocular discharge
- Corneal oedema
- Reflex uveitis
What are the types of corneal ulcers?
- superficial
- stromal
- descemetocoele
- melting ulcers
What are the characteristics of superficial corneal ulcers?
- Epithelial loss only
- Acute onset
- Painful (higher density of nerve endings in superficial layers of cornea)
- Sharp distinct borders
- Minimal corneal inflammatory response
- +/- Reflex uveitis
What are the characteristics of stromal ulcers?
- Loss of epithelium and stroma
- Acute or chronic
- Fluorescein stains walls and floor of ulcer
- Superficial stromal or deep stromal
- Anterior uveitis common
- Loss of stroma will distort contours of cornea – visible crater
What are the characteristics of descemetocoeles?
- Acute or chronic
- Complete stromal loss - defect down to Descemet’s membrane
- Walls of ulcer/crater usually obvious
- Descemet’s membrane is 10-15μm – similar to cling film
- staining pattern
◦ Walls stain positive (exposed stroma)
◦ Descemet’s membrane does not stain with fluorescein
◦ Floor/base of ulcer looks black or clear - Beware false negative
What are melting ulcers? Describe pathogenesis
- Beware the animal with an acute closed painful eye with copious discharge – probably “melting”
- Acute, painful
- Lots of gelatinous “gloopy” discharge
- Ill-defined, rounded, soft edges – like melting butter/candle wax…
- Variable appearance – varying amounts of stromal involvement
- Ill-defined, rounded, soft edges
- Marked corneal oedema
- Marked anterior uveitis (pain, miosis, hypopyon, low IOP)
- Can progress rapidly and perforate within hours: ophthalmic emergency
Pathogenesis
* Enzymes (proteinases and collagenases) break down or ‘digest’ corneal stroma
* Two origins
◦ Cornea itself: epithelial cells, stromal fibroblasts, WBCs
◦ Bacterial infection, e.g. Pseudomonas sp, β-hemolytic Streptococcus sp
* Topical corticosteroids cause local immune suppression and potentiate collagenase activity
How would you treat an ulcer?
Treatment of superficial stromal ulcers
* Similar principles to superficial epithelial ulcers
* Monitor closely - any stromal ulcer can become complex
* Take care especially in brachycephalics
Treatment of complex corneal ulcers
* What is a “complex” ulcer?
◦ Deep stromal ulcer
◦ Descemetocoele
◦ Perforated ulcer
◦ Melting ulcer
* All require intensive treatment +/- surgery
* All make good referrals if an option
What diagnostics would you run if you suspected a melting or infected ulcer?
- Corneal cytology
◦ Gently scrape margin of ulcer (not base) - Corneal swab
◦ Bacterial culture and sensitivity
◦ Swab margin of ulcer (not base) - Care with very deep lesions – procedure can cause corneal perforation!
How would you treat a melting ulcer?
What is SCCED? How is it diagnosed? How is it treated?
spontaneous chronic corneal epithelial defect
* Aka non-healing ulcer, indolent ulcer, ‘Boxer ulcer’
* Superficial ulcer that affects middle-aged dogs (>7 years old)
* Can affect any breed (esp Boxers and corgis)
* Usually unilateral (but can be bilateral, recurrent)
* Epithelium loss only
* NO stromal involvement
* Characterised by lip of loose epithelium – epithelium grows across but cannot adhere to underlying stroma
Fluorescein staining pattern
* Indistinct, irregular border which under-runs with fluorescein
* Variable inflammatory response – from no neovascularisation to granulation tissue ++
Diagnosis based on
* Signalment: older dogs
* Clinical appearance: superficial, non-adherent epithelium
* Ruling out other underlying causes e.g. ectopic cilium, foreign body, eyelid mass, KCS…
Treatment
- debridement
- +/- keratotomy or keractectomy
- all in conjunction with medical treatment
