Fungal keratitis results from invasion of the cornea by a fungal organism. While fungi are ubiquitous, they are responsible for a relatively small percentage of overall corneal infections worldwide. Unfortunately, however, because of the difficulty in diagnosing and treating these infections, they often result in devastating ocular consequences. The incidence of fungal keratitis has risen substantially in the last 20 to 30 years, probably due to the increased use of topical corticosteroids and broad spectrum antibiotics and due to better diagnostic techniques.

Fungal organisms include single cell yeasts, such as Candida, and multicellular filamentous fungi, such as the Fusarium species. Fungi do not invade the cornea easily and seem to require epithelial trauma, contact lens wear, ocular surface disease, corneal surgery, chronic keratitis, or immunosuppression for infection. The most common organism responsible for fungal keratitis on a worldwide basis is Aspergillus; however, keratomycosis is climate specific. In the southern United States, Fusarium is the most common cause of keratomycosis, whereas Candida and Aspergillus are isolated most frequently in the northern states. Up to 70 different fungi have been implicated as etiologic agents of fungal keratitis (Figs. 8-1 and 8-2).

The clinical presentation of keratomycosis may vary—the findings in a filamentous fungal keratitis may be somewhat different than those seen in a yeast infection. The patient’s immune status, duration of involvement, and prior treatment may also modify the findings.