Fungal keratitis: Mechanisms of infection and management strategies

Abstract

Fungal corneal ulcers are an uncommon, yet challenging, cause of vision loss. In the United States, geographic location appears to dictate not only the incidence of fungal ulcers, but also the fungal genera most encountered. These patterns of infection can be linked to environmental factors and individual characteristics of fungal organisms. Successful management of fungal ulcers is dependent on an early diagnosis. New diagnostic modalities like confocal microscopy and polymerase chain reaction are being increasingly used to detect and identify infectious organisms. Several novel therapies, including crosslinking and light therapy, are currently being tested as alternatives to conventional antifungal medications. We explore the biology of Candida, Fusarium, and Aspergillus, the three most common genera of fungi causing corneal ulcers in the United States and discuss current treatment regimens for the management of fungal keratitis.

Keywords: Confocal microscopy; Fungal; Keratitis; Keratolysis; Yeast.

Figure 1:

Clinical appearance of typical fungal ulcer at slit lamp exam paired with confocal images in the same patient. The organism from (A) could not be cultured but was confirmed to be fungal on KOH preparation. Causative organisms were determined to be (B, C) Fusarium and (D) Exserohilum.

Figure 2:

Pathology slides obtained from an excised cornea infected with Fusarium spp. (A) PAS and (B) GMS stains show the presence of acute branching hyphae and conidia consistent with Fusarium. (C) CD15 stain showing dense neutrophils infiltration, an immune typical of fungal infections, into the infected tissue. Bar 50μm.

Figure 3:

Candida infections in corneal transplants. (A) External photograph of an early infection in the graft-host interface of a PKP graft secondary to Candida albicans. (B) External photograph of a severe corneal ulcer secondary to Candida involving the graft tissue as well as the host limbus and sclera.

Figure 4:

Appearance of Candida infection following endothelial keratoplasty. (A) External photograph of a post-operative endophthalmitis secondary to Candida albicans following DSAEK. (B) PAS stain shows candida invading the corneal stroma, and (C) KOH preparation with calcofluor white stain showing yeast cells, pseudohyhae and hyphae, present on the surface of removed IOL. Bar 75μm.