Septate filamentous fungi
The vast majority of external ocular mold infections are caused by septate fungi. Fusarium species (eg, Fusarium solani and Fusarium oxysporum) are common pathogens encountered in warm, humid environments as a cause of fulminant keratitis. Among the genera that have been isolated from the external eye are Aspergillus, Alternaria, Curvularia, Paecilomyces, Scedosporium, and Phialophora. Most cases of oculomycosis occur following trauma with soil or vegetable matter and, less frequently, with contact lens usage.
Nonseptate filamentous fungi
Nonseptate filamentous fungi include the Mucor, Rhizopus, and Absidia species in class Zygomycetes, order Mucorales, family Mucoraceae. These ubiquitous fungi are an uncommon cause of external ocular infections. They can also cause life-threatening infections of the paranasal sinuses, brain, and orbit in immunocompromised patients, particularly those with diabetes mellitus.
Thomas PA, Geraldine P. Oculomycosis. In: Merz WG, Hay RJ, eds. Medical Mycology. 10th ed. London: Hodder Arnold; 2005:273–344. Topley & Wilson’s Microbiology and Microbial Infections; vol 5.
Pythium insidiosum is an oomycete (water mold) unrelated to the fungal pathogens described previously. It is increasingly recognized as a corneal pathogen, primarily in South-east Asia, but has also been reported worldwide. P insidiosum is more closely related to kelp or brown algae and is therefore resistant to currently available antifungals. Identification of P insidiosum is very difficult because of clinicians’ unfamiliarity with this pathogen and because identification is based solely on morphology and evolving PCR techniques. Cure of associated keratitis is achieved mainly through early suspicion, recognition, and keratoplasty, with most keratitis cases progressing to either enucleation or evisceration, although reports of successful medical therapy have emerged.
Sharma S, Balne PK, Motukupally SR, et al. Pythium insidiosum keratitis: clinical profile and role of DNA sequencing and zoospore formation in diagnosis. Cornea. 2015;34(4): 438–442.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.