How to Reach the Medical Standards of Care for Ulcerative and Non-Ulcerative Equine Keratopathies

1. Introduction

Keratopathies may be ulcerative or nonuclerative in the horse. Ulcerative keratopathies may be infectious or sterile but are always associated with increased tear film protease activity. Ulcerative infectious keratopathies in horses may be caused by bacteria, fungi, and possibly viruses. Sterile ulcers may be caused by foreign bodies, tear film problems, corneal denervation, or basement membrane corneal dystrophies. 

Nonulcerative keratopathies may also be infectious or sterile and range from cellular invasions of the stroma by inflammatory or neoplastic cells to persistent corneal edema. Infectious stromal abscesses, glaucoma-induced stria, uveitis-associated endothelial edema, eosinophilic keratitis, calcific band keratopathy, neoplasia, and immune mediated keratitis (IMMK) are major concerns.^1,2 

2. Medical Standards of Care

Ulcers

The current medical standard of care of treatment of ulcerative keratitis (Fig. 1) in the horse is a topical broad spectrum, nonirritating antibiotic, careful utilization of a mydriatic/cycloplegic, and an antiprotease compound such as serum. A systemically administered nonsteroidal drug is also critical to quick healing.
 

Ulcer Expectations

If the ulcer does not diminish in size at a rate of ~1 mm/day, the cornea does not vascularize at a rate of 1 mm/day, and/or the signs of uveitis do not improve when therapy is initiated, then consider culture and/or cytology to document a change in the infection to decide if different antimicrobials are indicated. Additional antiproteases may also be beneficial. A suspicion of fungal involvement should always exist in ulcers that do not vascularize or heal. If the ulcer deepens, then amnion, conjunctival, or corneal grafting surgery is recommended. Contact lenses, chemical cautery with phenol or trichloroacetic acid, debridement of loose epithelium, gridding, and/or burring can be used for superficial noninfected ulcers.

Stromal Abscesses (SA)

The current medical standard of care of treatment of superficial and deep stromal abscesses (Fig. 2) is topical antimicrobials (including antifungals), atropine, and systemic antimicrobials and NSAIDs.
 

SA Expectation

Stromal abscesses must vascularize to heal. Therapy may take weeks. Vascularization and a reduction in the associated uveitis are signs of improvement. As the SA resolves, the blood supply leaves and the lesion will appear pale and then white. Superficial SAs tend to respond better to medical therapy than deep SAs. Intrastromal voriconazole may have some use in specific cases of SA. Surgery may be necessary to remove the abscess if medical therapy fails to resolve the inflammation in 2 to 4 weeks.

Linear Keratopathy or Stria

Broad white linear opacities can follow blunt globe trauma or immune mediated endotheliitis in the horse. These are single and nonprogressive (Fig. 3). Stria are breaks in Descemet’s membrane following elevated IOP in glaucoma. Stria in glaucoma are multiple and branching in nature (Fig. 4).
 

Linear Keratopathy and Stria Expectations

Intraocular pressure measurement is important. Careful monitoring over months to years is recommended. Therapy is generally not available or helpful, but if edema is present topical steroids are indicated.

Corneal Neoplasia

The current medical standard of care of treatment of epithelial dysplasia (Fig. 5) is topical 1% 5FU or 0.04 mitomycin C.
 

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