Mycotic keratitis--an underestimated mycosis

Abstract

Mycotic keratitis, an important ophthalmologic problem, especially in outdoor workers in the tropics, is frequently caused by filamentous fungi such as species of Fusarium, Aspergillus and Curvularia, and by yeast-like fungi such as Candida. A rapid, presumptive diagnosis can be made by recognition of certain typical clinical features and by direct microscopic detection of fungi in corneal scrapings stained by various methods. The diagnosis is confirmed by culture. In difficult cases, microbiological studies on corneal biopsies or histopathological studies on tissue sections may need to be performed. The use of fluorescein-conjugated lectins and similar diagnostic tools is aimed at providing rapid, species-specific detection of fungi in corneal tissue. Antifungal therapy must be instituted as soon as the diagnosis is made. While keratitis due to Aspergillus, Candida and dematiaceous fungi can be successfully treated by many of the currently available polyenes and azoles, the treatment of Fusarium keratitis still frequently requires the use of pimaricin or econazole. Treatment by the oral and parenteral routes may prove useful in severe mycotic keratitis. Surgery may need to be performed on cases unresponsive to medical therapy or where serious complications are likely to occur. The pathogenesis of mycotic keratitis appears to involve agent factors, such as invasiveness and toxigenicity, and host factors, such as trauma and intrinsic defects in resistance. Areas for future research include the development of rapid, species-specific diagnostic aids, of broad-spectrum antifungal compounds active by various routes, and of therapeutic modalities which act on the fungus and on molecules involved in the pathogenesis of the condition.