Cornea: ulcerative keratitis

• Important ocular disease characterized by loss of corneal epithelium plus variable amounts of stroma.
• Cause: complex; trauma, collagenase activity and bacterial/viral infections should be considered.
• Mycotic infection is more common in dogs than cats in the USA.
• Signs: ocular discharge, red eye, corneal ulceration, painful eye.
• Diagnosis: relatively straightforward; use of fluorescein dye and ultraviolet/cobalt blue light is strongly advised.
• Treatment: remove causative agent(s) and create an environment suitable for healing.
• Prognosis: corneal rupture is a possibility in cases of deep ulceration. Recurrence is likely if the underlying cause is not identified and treated.

• Same as keratitis Keratitis.
• Ocular pain manifested as excessive lacrimation and blepharospasm.
• History of trauma in some cases.

• Laboratory investigation of infectious etiology and subsequent treatment can be expensive.
• Deep ulcers that require microsurgical intervention can be expensive.
• Small corneal erosions (superficial ulcers), can heal quickly with few expenses needed, although recurrence is possible if feline herpesvirus (FHV-1) is the cause Feline herpes virus: feline rhinotracheitis virus Cornea: herpesvirus keratitis.

• Trauma: blunt, penetrating or perforating.
• Collagenases.
• Bacteria.
• Viruses - FHV-1 ulceration common.
• Adnexal abnormalities, eg exposure keratitis, entropion, eyelid mass rubbing, eyelid agenesis Eyelid: abnormality.
• Corneal necrosis (corneal sequestrum) Cornea: sequestration.

General

• Brachycephalic breeds. Lagophthalmos, poor distribution of the tear film, entropion at the medial aspect of the lower eyelids, and globe exposure making trauma more likely are all factors involved.

Specific

• Feline herpes virus Feline herpes virus: feline rhinotracheitis virus.
• Trauma.
• Keratoconjunctivitis (KCS) Eye: keratoconjunctivitis sicca. This is not common in cats.

• Rapid progression of superficial ulcers to corneal rupture, may occur as a result of collagenase activity. Liquefactive corneal necrosis, or corneal 'melting' is a very serious potential complication of all forms of corneal ulceration.
• Indolent ulcers are non-healing epithelial erosions which do not penetrate the corneal stroma. FHV-1 may be the cause.

• Same as keratitis Keratitis.
• Initial corneal injury  →  allows bacteria to adhere to ocular surface.
• Melting ulcers occur following liberation of collagenase enzymes from invading microorganisms, white blood cells or keratocytes, which cause rapidly collagenolysis and loss of corneal structure.
• If stroma overlying Descemet's membrane is absent  →  descemetocele (the exposed membrane then may bulge forwards as a result of intra-ocular pressure).
  Descemetoceles do not stain with fluorescein dye at the base, but the edges of the ulcer are fluorescein positive.
• FHV-1 keratitis is epithelial unless topical steroid causes immunosuppression leading to stromal keratitis.
• Corneal sequestrum occurs as a result of stromal collagen necrosis.

• Melting ulcers can progress over a matter of hours.
• Superficial ulcers can be chronic and present for several weeks.
• Ulcers that become corneal sequestra can be present for many months to years.

• Ocular pain (blepharospasm and excessive lacrimation).
• Red eye.
• Ocular discharge Eye: ocular discharge - overview.
• Cloudy eye.

• Ocular discharge.
• Cloudy eye.
• Nictitans protusion.
• Trauma.

• Same as keratitis Keratitis.
• Indolent ulcers have an epithelial lip - non-adherent epithelium surrounding the ulcer.
• Deep ulcers appear as a crater-like defect.
• Conjunctivitis.
• Direct visualization of ulceration.

Bacteriology

• Always take swabs for culture before applying topical anesthesia/vital stains.
• Linear, dendritic ulcers are pathognomonic for Feline herpesvirus (FHV-1).

Cytopathology

• Corneoconjunctival scrapings may be useful to identify cell type involved and infectious agents such as bacteria or fungi.

Virology

• Viral isolation or PCR (polymerase chain reaction) for FHV-1 DNA.

Other

• Fluorescein staining - stain binds to denuded corneal stroma Fluorescein test, and is therefore diagnostic of corneal ulceration. A descemetocele is negative for stain uptake at the deepest part, the base, but positive at the edges or walls of the defect.
  Assess tear production (Schirmer tear test Schirmer tear test) before adding fluid to eye.
• Corneal opacity Eye: corneal opacity makes intraocular examination difficult to impossible. Ultrasound may give valuable information Ultrasonography: eye.

• Epithelial cells undergo mitosis and migration to heal a superficial ulcer.
• Stromal ulcers heal by fibrovascular infiltration.
• Deep ulcers tend to scar, although cats scar less than dogs.

• Keratoconjunctivitis.
• Same as keratitis Keratitis.

• Remove causative agent.
• Topical antibiotics are used to treat all corneal ulcers.
  Do not use topical corticosteroids.

• Topical atropine Atropine and systemic non-steroidal anti-inflammatories to prevent concurrent reflex uveitis. Some cats don't tolerate topical atropine well, and tropicamide Tropicamide can be used as an alternative, although it is much shorter-acting and it is not a cycloplegic.
• Agents to prevent corneal melting, eg autogenous serum or plasma (most effective) or acetylcysteine Acetylcysteine or EDTA Ethylenediamine.
• Prevent self-trauma by physical restraints, eg Elizabethan collar    .

• Topical nonsteroidal drugs (eye therapeutics Therapeutics: eye) may reduce pain, but should be used with caution when the cornea is ulcerated as they can cause melting.

• FHV-1 infection manifests with dendritic ulceration or geographic superficial ulceration. It may be confirmed by viral isolation or PCR.
• Topical and/or systemic anti-virals are used to treat cats with herpes keratitis.
• Treat infection in cases of bacterial involvement based on results of bacteriology Therapeutics: eye.
• Improve blood supply to affected region and support cornea using a conjunctival pedicle for deeper ulcers. Tectonic support and good clarity can be provided with a corneo-conjunctival transposition surgery.
• Direct corneal suturing Cornea: suturing in cases of corneal laceration.
• Replacement of prolapsed iris tissue and corneal suturing if feasible - otherwise application of a pedicle flap if corneal rupture has occurred (as for corneal and scleral lacerations/perforations).
• Anticollagenases such as autogenous serum/plasma, acetylcysteine, EDTA to prevent corneal 'melting'.
• Third eyelid flaps have a limited role in the treatment of deep ulcers.
  Third eyelid flaps are not advised in the treatment of rapidly progressing ulcers, infected ulcers or those that are greater in depth than one-half of the corneal thickness.

• Topical atropine can reduce tear production, although this is less of a problem in cats than it is in dogs.
• Increase in uveitis signs is associated with poor corneal healing.

Treatment

• Refractory ulcers may require surgical removal of non-adherent epithelium by epithelial debridement using a sterile dry cotton-tipped applicator or a diamond burr. Performing a grid or punctate keratotomy Cornea: debridement is contraindicated as it is thought to increase the risk of corneal sequestrum formation. Application of a membrane flap Eyelid: third eyelid flap or a contact lens   may be used in conjunction with this treatment regime.
• Superficial keratectomy Cornea: superficial keratectomy to improve corneal transparency can be carried out 8-9 months after corneal repair to remove areas where there is considerable scarring. This is not commonly necessary in cats however, as corneal scarring tends to be a lot less dense than in dogs.
  Topical corticosteroids should only be used once epithelialization has occurred - check using fluorescein. However, as topical steroids can reactivate latent virus, their use should not be routine.

• Same as keratitis Keratitis.
• May leave a corneal defect (facet).

• Same as keratitis Keratitis.
• Rapid healing of superficial ulcers.
• Corneal clarity and vision.
• Absence of pain.

Refereed papers

• Recent references from PubMed and VetMedResource.
• La Croix N C, van der Woerdt A & Olivero D K (2001) Nonhealing corneal ulcers in cats - 29 cases (1991-1999)​. JAVMA 218 (5), 733-735 PubMed.
• Featherstone H & Sansom J (2000) Intestinal submucosa repair in two cases of feline ulcerative keratitis. Vet Rec 146 (5), 136-138 PubMed.
• Kern T J (1990) Ulcerative keratitis. Vet Clin North Am Small Anim Pract 20 (3), 643-666 PubMed.

Other sources of information

• Petersen-Jones S & Crispin S (2002) BSAVA Manual of Small Animal Ophthalmology. 2nd edn. British Small Animal Veterinary Association. ISBN 0 905214 54 4