corneal ulcers

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

  entropion

  
• name the ulcer

  A) melting

  B) superficial

  C) stromal

  D) descemetocele

  
• The cornea consists of…

  • Stratified epithelium and its basement membrane
  • Collagenous stroma
  • Descemet’s membrane (basement membrane of the endothelium)
  • Endothelium

  There are nerve endings in the epithelium and stroma and hence superficial lesions can be more painful than deep lesions.
• The epithelium above has tight junctions to prevent water from tear film entering the cornea
• The endothelium below the cornea has a Na/K ATPase pump which pumps ions from the stroma into aqueous humour.
• Corneal epithelium is self-renewing with continual cell turnover. When epithelial loss occurs, cells slide rapidly across to cover the defect (hours – days). There is then cell proliferation, migration and adhesion.

  • The superficial ulcer is an epithelial defect only. Hence epithelial/superficial ulcers heal very quickly
• Stromal wound healing starts once re-epithelialisation is complete…

  • Fibroblasts migrate in and lay down new collagen
  • This process requires vascularisation and results in scar tissue and remodelling over time

  Clarity may come back with collagen remodelling
• Descemet’s membrane = Elastic, limited ability to repair
• There are many possible causes…

  • Trauma
  • This is common and can be caused by foreign bodies, abrasions, laceration, chemical injury (serious but uncommon)
  • Tear film problem e.g., KCS
  • Ulcers secondary to dry eye often have a circular ‘punched out’ appearance, sudden onset and deteriorate rapidly
  • Adnexal conditions i.e. involving eyelids, eyelashes and conformation 
  • Primary corneal disease e.g., SCCED's
  • Infection
  • Neurological disease e.g., facial or trigeminal nerve paralysis
• SCCED's = Spontaneous Chronic Corneal Epithelial Defect
• A corneal facet is a stromal deficit that has epithelized and will be negative on fluorescein testing.
• There are different types of ulcer depending on how deep they are…

  • Superficial ulcers are where there is epithelial loss only
  • Stromal ulcers are deeper, there is a loss of the epithelium and stroma
  • There are two types superficial stromal or deep stromal
  • Descemetoceles is where there is complete epithelial and stromal loss which reaches Descemet's membrane
• Descemetoceles is where there is complete epithelial and stromal loss which reaches Descemet's membrane. These ulcers can be acute or chronic and the walls of ulcer/crater are usually obvious

  • Descemet’s membrane is 10-15μm, similar to cling film
  • The walls stain positive, due to exposed stroma but Descemet’s membrane does not stain with fluorescein and hence the floor/base of ulcer looks black or clear
• Stromal ulcers can be acute or chronic and fluorescein will stain the walls and floor of the ulcer. The loss of the stroma will distort contours of cornea causing a visible crater. There are two types superficial stromal or deep stromal

  • Anterior uveitis common
• “Melting” corneal ulcers (keratomalacia, an infected ulcer) are acute, painful and present with lots of gelatinous “gloopy” discharge. These ulcers are ill-defined and rounded with soft edges, like melting butter/candle wax. They have a variable appearance with varying amounts of stromal involvement. There is often marked corneal oedema and marked anterior uveitis (pain, miosis, hypopyon, low IOP). they can progress rapidly and even perforate
• Melting ulcers occur due to the enzymes (proteinases and collagenases) breaking down or ‘digesting’ the

  corneal stroma. There are two origins…

  • The cornea itself: epithelial cells, stromal fibroblasts, WBCs
  • A bacterial infection, e.g. Pseudomonas spp, β-hemolytic Streptococcus spp
• To diagnose an infected or melting ulcer perform the following but be careful as corneal perforation can occur…

  • Corneal cytology
  • Gently scrape margin of ulcer (not base)
  • Corneal swab
  • Bacterial culture and sensitivity
  • Swab margin of ulcer (not base)
• Cytology for melting ulcers…

  • Rods are most likely
  • Pseudomonas is most likely to respond to fluroquinolones
  • Cocci are most likely B-haemolytic Strep
  • Most respond to chloramphenicol but there are exceptions to these rules! 
  • If cocci is present then it is probably sensible to also use a fluroquinolone while waiting on culture results
• how would you treat a superficial ulcer or a superficial stromal ulcer?

  systemic NSAIDs and topical chloramphenicol drops
• SCCEDs are also known as the non-healing ulcer, indolent ulcer or the boxer ulcer
• SCCED ulcers have no stromal involvement, there is only epithelium loss. They are characterised by a lip of loose epithelium as the epithelium grows across but cannot adhere to underlying stroma.
• SCCED ulcers have a different fluorescein staining pattern than simple ulcers. They have indistinct, irregular borders which under-runs with fluorescein. There is a variable inflammatory response, from no neovascularisation to granulation tissue.
• Debridement/keratotomy procedures are only for SCCEDs and can be repeated after 10-14 days
• Debridement alone removes loose epithelium in SCCED ulcers

  • Apply topical anaesthetic eye drops prior to the procedure. Use a sterile cotton bud with gentle but firm action to remove all loose epithelium. This allows the true extent of ulcer to become apparent.
  • Less than 50% heal with debridement and medical treatment
• with SCCEDs the best management is NSAIDs, topical chloramphenicol, debridement and then either keratotomy or keratectomy
• With non-healing ulcers in cats, gentle debridement with cotton bud and contact lens is fine but keratotomy techniques for SCCEDs predispose to sequestrum formation