Corneal ulcers

• What are corneal ulcers?

  Break in continuity of corneal epithelium with exposure of underlying stroma.
• What is the structure of cornea?

  Stratified epithelium and its basement membrane.

  Collagenous stroma - 90% of the corneal thickness.

  Descemet’s membrane - basement membrane of the endothelium.

  Endothelium.

  There are nerve endings in the epithelium and stroma:

  • Superficial lesions can be more painful than deep lesions.
• What is the corneal physiology?

  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.
• What is the corneal pathology with oedema?

  Breach of or dysfunctional barrier layers (epithelium and endothelium)

  • Increased water content.
  • Distorts collagen fibrils, creating opacity.

  
• What is the corneal pathology for vascularisation?

  Superficial or deep in-growth of blood vessels.

  Promotes healing (but can increase scarring).
• Corneal wound healing - epithelium

  Corneal epithelium is self-renewing: continual cell turnover.

  • Proliferation of basal cells at limbus (mitosis).
  • Movements of peripheral cells towards centre of cornea.
  • Epithelial cells lost from corneal surface into tear film.
• Healing - superficial ulcer (epithelial defect only)

  Epithelial loos -> cells slide rapidly across to cover defect (hours - days): cell proliferation, migration and adhesion.

  If you have a healthy cornea then can heal real quickly.

  
• Corneal healing - stroma

  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.

  Descemet’s membrane:

  • Elastic, limited ability to repair.

  Endothelium:

  • Very poor ability to repair.
• What are the causes of corneal ulcers in dogs?

  Trauma

  Tear film problems - KCS

  Adnexal conditions i.e. involving eyelids, eyelashes and conformation.

  Primary corneal disease - SCCEDs

  Infection

  Neurological disease.
• Trauma causing corneal ulcers

  Common.

  Foreign bodies, abrasions, laceration, chemical injury (serious but uncommon).

  
• Tear film problems causing corneal ulcers

  Quantitative lack of tears - KCS (dry eye) - very common in dogs.

  Qualitative teary film problem - less common.

  NB Ulcers secondary to dry eye often have a circular ‘punched out’ appearance and deteriorate rapidly.

  
• Brachycephalic conformation causing corneal ulcers

  Pugs with macro palpebral fissure resulting in lagophthalmos (eyelids don’t function properly) and exposed cornea.

  Pug with medial entropion causing chronic corneal trauma and ulceration.

  Shih tzu with trichiasis resulting from pronounced nasal fold.

  
• This cat has a superficial ulcer in the ventrolateral cornea. From the image below, what is the most likely underlying cause?

  1 Brachycephalic conformation

  2 Entropion

  3 Distichiasis

  4 KCS (dry eye)

  5 FHV-1 infection.

  2

  
• What are the clinical signs of corneal ulceration?

  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 is superficial corneal ulcer?

  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 is a stromal ulcer?

  Loss of epithelium and stroma.

  Acute or chronic.

  Fluorescein stains walls and the floor of the ulcer.

  Superficial stromal or deep stromal.

  Anterior uveitis common.
• What is a Descemetocoele?

  Complete stromal loss - defect down to Descemet’s membrane.

  Acute or chronic.

  Walls of ulcer/crater usually obvious.

  Descemet’s membrane is 10-15um - similar to cling film.
• What is the fluorescein staining in Descemetocoele?

  Wall stain positive (exposed stroma).

  Descemet’s membrane does not stain with fluorescein.

  Floor/base of ulcer looks black or clear.
• What are melting corneal ulcers?

  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 - likel melting butter/candle wax.
• What do melting corneal ulcers look like?

  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.

  
• What is the pathogenesis of melting ulcers?

  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.

  Topical corticosteroids cause local immune suppression and potentiate collagenase activity, which is why we never use topical steroids on a corneal ulcers.
• How do you treat superficial ulcers?

  Identify and treat underlying cause.

  Prevent/ treat secondary infection - chloramphenicol

  Analgesia - e.g. systemic NSAID.

  Treat any reflex uveitis - single drop atropine usually enough.

  Arrange re-check and safety net - re-check in 3-5 days, sooner if any concerns.
• What counts as a complex ulcer?

  Deep stromal ulcer.

  Descemetocoele

  Perforate ulcer

  Melting ulcer.

  All require intensive treatment +/- surgery.

  All make good referrals if an option.
• How do you diagnose if you suspect an infected/melting ulcers?

  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.

  If see neutrophils then this shows infection.
• What is the treatment for melting ulcers?

  Treat as it is infected.

  Treat the secondary infection - ideally based on cytology/C+S, Topical FQ, Anticollagenase, consider systemic antibiotics.

  Analgesia - systemic NSAID +/- opioid.

  Treat any reflex uveitis - atropine to effect.

  Monitor closely and hospitalise if necessary.
• What is the treatment for deep ulcers?

  Intensive medical therapy following general principles.

  Prompt grafting surgery to prevent corneal perforation:

  • Provide immediate tectonic support.
  • Provide blood supply.
  • May need referral - best performed with magnification and microinstrumentation.

  If perforated or referral not an option, enucleation may be required.
• What is a SCCED?

  Spontaneous, chronic corneal epithelial defect.

  • Do not effect the deeper layers.

  AKA non-healing ulcer, indolent ulcer.

  Superficial ulcer that affects middle-aged dogs (>7 years old).

  Can affect any breed.

  Usually unilateral (but can be bilateral and recurrent).
• What is the fluorescein staining pattern for SCCEDs?

  Indistinct, irregular border which under-runs with fluorescein.

  Variable inflammatory response - from no neovascularisation to granulation tissue ++.

  
• What is the treatment for SCCEDs?

  Need to disrupt the epithelial basement membrane/anterior stroma to allow epithelium-to-stroma attachment - medical treatment alone not enough.

  • Debridement alone:
  • Removes loose epithelium.
  • Debridement + keratotomy or keratectomy:
  • Procedures involving corneal stroma.
  • All in conjunction with medical treatment:
  • Same principles as for superficial ulcers.

  
• Treatment of SCCEDs - keratotomy

  Keratotomy - to incise cornea.

  Grid keratotomy:

  • Sedation often required.
  • Debride first.
  • 25-27 gauge needle, bevel up.
  • Needle parallel to corneal surface, drag (don’t push).
  • Cross-hatch of superficial lines 1mm apart from clear cornea to clear cornea (i.e. debrided area plus 1-2mm into surrounding normal cornea).

  Success rate up to 85%
• You examine a dog which is already receiving medical treatment for a corneal ulcer. In addition to providing analgesia, how would you treat this eye?

  1 Continue chloramphenicol and add in exocin and serum every 2 hours.

  2 Continue chloramphenicol drops 4 times daily.

  3 Debride with cotton bud, perform grid keratotomy and place contact lens.

  4 Enucleation (or referral) - might have some iris that has ruptured.

  4

  
• What are the common causes of ulcers in cats?

  Infection - feline herpesvirus infection (FHV-1)

  Trauma - cat fight injuries, FB.

  Corneal sequestrum
• What is the treatment for non-healing ulcers in cats?

  Gentle debridement with cotton bud and contact lens fine.

  Keratotomy techniques for SCCEDs predispose to sequestrum formation so do not do it!!!!!