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Basics ⬇

Outline

BASICS

Overview!!navigator!!

A corneal abscess may develop after epithelial cells adjacent to a small defect migrate over the wound to seal infectious agents or foreign bodies in the stroma. This re-epithelialization forms a barrier that protects the bacteria or fungi from topical antimicrobial medications.

Signalment!!navigator!!

All ages and breeds of horses are at risk.

Signs!!navigator!!

  • The eye may be cloudy and red. Blepharospasm and epiphora are usually present. Slight downward deviation of the upper eyelashes may be a subtle sign of ocular pain
  • The diagnosis of stromal abscess is based on the presence of a focal, yellow-white infiltrate within the cornea. A mild to fulminating iridocyclitis occurs secondary to what appears initially to be a relatively benign corneal disease, causing severe pain and potentially blinding sequelae. Corneal vascularization is variable at presentation
  • Initial clinical signs suggestive of minor corneal trauma. Fluorescein dye retention may be present initially and treatment for corneal ulceration results in re-epithelialization. Days to weeks later, the iridocyclitis worsens and a corneal abscess is visible

Causes and Risk Factors!!navigator!!

Corneal stromal abscesses can be sterile or caused by bacteria or fungi.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Ocular pain may be caused by corneal ulcers, anterior uveitis, or equine recurrent uveitis
  • A history of trauma or corneal ulceration and a yellow-white cellular stromal infiltrate will facilitate diagnosis of stromal abscess

Diagnostic Procedures!!navigator!!

  • Cytologic, microbiologic, and histologic specimens may fail to yield an etiology. It may be that toxins released by dying bacteria and fungi and degenerating leukocytes continue the stimulus for keratitis and anterior uveitis
  • Keratectomy specimens may be the only way to obtain an etiologic diagnosis

Treatment ⬆ ⬇

TREATMENT

  • Many stromal abscesses initially respond positively with improving uveitis to topical mydriatics/cycloplegics and topical antimicrobials and systemic NSAIDs
  • Scraping over the stromal abscess may aid drug penetration in the early stages but it may damage the superficial cornea, which may limit surgical options
  • The use of systemic NSAIDs should be carefully adjusted to allow the control of anterior uveitis without significantly inhibiting necessary corneal vascularization
  • Deep corneal abscesses respond poorly to medical therapy. Most stromal abscesses involving Descemet's membrane are fungal infections. Deep lamellar and penetrating keratoplasties are utilized in eyes with deep abscesses, and eyes with rupture of the abscess into the anterior chamber. This aggressive surgical therapy can be very successful and is done to eliminate antigenic stimulation from the sequestered organisms and to remove the necrotic debris, metabolites, and toxins
  • Horses that undergo surgery early in the course of this disease tend to have a more rapid recovery than those in which surgery is delayed. If a positive response to medical therapy is not seen quickly, especially when the stromal abscesses are deep or severe uveitis is present, surgery should be considered
  • The decision to perform surgery is based on continued progression of anterior uveitis despite medical therapy or relapses of uveitis when treatment is tapered, or imminent or preexistent rupture of the abscess into the anterior chamber
  • Corneal transplantation is an effective treatment

Medications ⬆ ⬇

MEDICATIONS

Drug(s) of Choice

Topically applied antibiotics and antifungals (natamycin, miconazole, voriconazole every 4–6 h), atropine (1%; QID) are recommended. Systemic NSAIDs (flunixin meglumine 1 mg/kg BID PO, IM, IV) are also indicated. In some cases where surgical removal of the abscess is not possible, an intracorneal injection of voriconazole may improve healing.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Ocular pain should diminish with resolution of the abscess. Self-trauma can be minimized with hard- or soft-cup face-masks or hoods
  • Topical atropine may alter gastrointestinal motility and horses should be monitored for colic
  • Horses should be stall rested until the condition is healed
  • Diet should be consistent with the activity and training level of the horse

Possible Complications!!navigator!!

Endophthalmitis, persistent uveitis, synechiae, and cataract are complications of stromal abscesses.

Expected Course and Prognosis!!navigator!!

  • Most stromal abscesses do not completely heal until they become vascularized
  • Enucleation of painful blind eyes is necessary in some cases

Miscellaneous ⬆ ⬇

MISCELLANEOUS

Abbreviations

NSAID = nonsteroidal anti-inflammatory drug

Suggested Reading ⬆ ⬇

Brooks DE. Ophthalmology for the Equine Practitioner, 2e. Jackson , WY: Teton NewMedia, 2008.

Brooks DE, Matthews AG. Equine ophthalmology. In: Gelatt KN, ed. Veterinary Ophthalmology, 4e. Ames, IA: Blackwell, 2007:1165–1274.

Gilger BC, ed. Equine Ophthalmology, 3e. Philadelphia, PA: WB Saunders, 2017.

Author(s) ⬆

Author: Caryn E. Plummer

Consulting Editor: Caryn E. Plummer

Acknowledgment: The author/editor acknowledges the prior contribution of Dennis E. Brooks.