Current Perspectives on Ophthalmic Mycoses

Abstract

Fungi may infect the cornea, orbit and other ocular structures. Species of Fusarium, Aspergillus, Candida, dematiaceous fungi, and Scedosporium predominate. Diagnosis is aided by recognition of typical clinical features and by direct microscopic detection of fungi in scrapes, biopsy specimens, and other samples. Culture confirms the diagnosis. Histopathological, immunohistochemical, or DNA-based tests may also be needed. Pathogenesis involves agent (invasiveness, toxigenicity) and host factors. Specific antifungal therapy is instituted as soon as the diagnosis is made. Amphotericin B by various routes is the mainstay of treatment for life-threatening and severe ophthalmic mycoses. Topical natamycin is usually the first choice for filamentous fungal keratitis, and topical amphotericin B is the first choice for yeast keratitis. Increasingly, the triazoles itraconazole and fluconazole are being evaluated as therapeutic options in ophthalmic mycoses. Medical therapy alone does not usually suffice for invasive fungal orbital infections, scleritis, and keratitis due to Fusarium spp., Lasiodiplodia theobromae, and Pythium insidiosum. Surgical debridement is essential in orbital infections, while various surgical procedures may be required for other infections not responding to medical therapy. Corticosteroids are contraindicated in most ophthalmic mycoses; therefore, other methods are being sought to control inflammatory tissue damage. Fungal infections following ophthalmic surgical procedures, in patients with AIDS, and due to use of various ocular biomaterials are unique subsets of ophthalmic mycoses. Future research needs to focus on the development of rapid, species-specific diagnostic aids, broad-spectrum fungicidal compounds that are active by various routes, and therapeutic modalities which curtail the harmful effects of fungus- and host tissue-derived factors

Pathogenesis of microbial keratitis

“…The use of corticosteroids, ocular surgery, ocular surface disease and contact lens wear has now also been increasingly identified as a significant risk factor. Conversely, C. albicans and related fungi are only linked to keratitis when there is a pre-existing ocular condition like insufficient tear secretion, defective eye closure, or some systemic illness such as diabetes mellitus or immunosuppression [195]. This form of keratomycosis may also supervene on a pre-existing epithelial defect caused by herpes keratitis or abrasion due to contaminated contact lenses.…”

“…Fungal pathogens display a variety of adhesins that are capable of adhering to various cell types and interact with a variety of host proteins and glycoproteins present in host cells [68]. The outer fibrillar layer of yeast and filamentous fungal cell wall is composed of mannan or mannoprotein [75,195]. The adhesive mannoproteins play an essential role in fungal binding to corneal tissues.…”

“…which also play a role in keratitis [195]. [199] demonstrated the importance of an outer fibrillar layer of the germ tube in the process of adhesion to plastics.…”

“…Polyenes, including natamycin, nystatin and amphotericin B, disrupt fungal cell by binding to the cell wall ergosterol of both filamentous as well as yeast-like fungi. However their tissue penetrating ability is poor and therefore is mostly recommended in cases of superficial corneal infections [7,195]. Administration is every 30 min during the first 24 h and then every hour for the next 24 h and then gradually tapered off according to the response.…”

Afilamento escleral em paciente com rinosporidiose conjuntival

“…As infecções oculares fúngicas vêm sendo cada vez mais reconhecidas como uma importante causa de morbidade e cegueira (6) . Os fungos são agentes oportunistas no olho, uma vez que raramente infectam olhos sadios ou que apresentem sua estrutura íntegra.…”