Fungal keratitis and secondary endophthalmitis in a horse

By Emma Scurrell

Enucleation of the right eye was performed in a 10-year-old male thoroughbred with persistent corneal ulceration, keratitis and uveitis. The following are H&E sections from the formalin-fixed globe.

Fig 1. . The cornea contains a deep stromal abscess that is demarcated in this section by the blue arrows. The green arrows highlight Descemet’s membrane.

Fig 2. Fragments of fungal hyphae (blue arrow) are identified within the degenerate neutrophilic infiltrate in the deep corneal stroma. Low numbers of fungal hyphae also infiltrate Descemet’s membrane (green arrow). Descemet’s membrane is pathologically ruptured in multiple places (not shown in this image).

Fig 3. Fungal hyphae (black arrows) are associated with neutrophilic exudate in the anterior chamber of the eye.

Final Diagnosis

Fungal keratitis and endophthalmitis

Discussion

Fungi are opportunistic pathogens of the equine cornea and usually involve saprophytic fungi that are part of the resident fungal population found around the eye/adnexae. Species most commonly involved include Aspergillus spp, Alternaria spp. Penicillium spp. and Fusarium spp. Corneal injury is a common predisposing cause and apparent increased risk of fungal keratitis is also associated with increasing age, topical corticosteroid treatment and prolonged antibiotic therapy. Corneal abscesses secondary to fungal infection are often deep and therefore superficial corneal scrapes may yield false negative results. Perforation of Descemet’s membrane and secondary mycotic endophthalmitis such as what has occurred in this particular case, is a possible complication.