Commentary on: A case report of fungal keratitis due to Fusarium oxysporum after an injury by fingernail

Fungal keratitis (FK) has an estimated incidence of over 1 million cases per year, with predominance in the tropical areas accounting for over 80% of microbial keratitis (MK) in parts of south and south-east Asia as opposed to less than 1% of cases in some occidental countries.[1] Fusarium solani is the most commonly implicated organism in keratomycoses (invasive fungal corneal infections); however, cases due to Fusarium oxysporum, a cross-kingdom fungal pathogen, have been reported to be on the rise since its first isolation in 2001.[1] Lineage-specific (LS) chromosomes homolog of ceruloplasmin and the genes that contribute to the expansion of the alkaline pH-responsive transcription factor PacC/Rim1p, determining the host-specific pathogenicity, explains Fusarium keratitis outbreak to some extent in these predominantly plant pathogens. Improper lens cleaning regimens and fungal biofilms have been incriminated as additional predisposing factors for F. oxysporum keratitis.[2] F. oxysporum keratomycoses have devastating visual outcomes. Misdiagnosis as bacterial keratitis is a common pitfall in instituting appropriate therapy and thus is the missed diagnosis due to indolent progression of the disease, accounting for delayed restitution of antifungal therapy. Early and accurate diagnosis with appropriate antifungal therapy is quintessential for the resolution of the lesion and restoration of vision. Preponderance of fungal keratitis in tropical and subtropical regions where the main risk factors are defects in the corneal epithelium caused by vegetative matter, makes it an important entity to be diagnosed.[3] The article in the current issue of the Indian Journal of Ophthalmology titled, “A Case Report of fungal keratitis due to Fusarium Oxysporum after an injury by fingernail” (IJO_771_22), highlights a rare case of F. oxysporum keratomycoses, which was diagnosed promptly and treated methodically, with good visual outcomes.[4] The aforesaid case report has some very important revelations. The inciting predisposing factor was fingernail trauma as opposed to vegetative matter trauma, contact lens usage, and inadvertent use of topical corticosteroids cited in most cases.[4,5] The affected patient was a homemaker as opposed to other cases where male patients and those engaged in outdoor activities such as farming were mostly affected.[4,5] This history makes F. oxysporum an important diagnostic consideration to heed in all cases of keratomycoses, especially because the entity remains a rarity because of underdiagnosis. F. oxysporum has difficult recovery on culture, making the diagnosis delayed and often missed. Direct microscopic examination of KOH wet preparation is a must for early diagnosis as it clearly reveals the presence of septate, branched, hyaline hyphae, indicative of filamentous fungi. White, cottony colonies on SDA and lactophenol cotton blue mount with sickle-shaped macroconidia in clusters confirm the species diagnosis, prompting adjuvant antifungal therapy, but the KOH mount is sufficient to commence with the first-line anti-fungal therapy as was done in the reported case, thus averting blinding consequences.[4,6] Raised intraocular pressure requires attention as cited in this case report. This emphasizes the importance of simple bedside digital tonometry, which should not be ignored in the presence of obvious corneal pathology. Treatment options for Fusarium keratitis include systemic, topical, and intraocular administration of antifungals such as natamycin, amphotericin B, fluconazole, and voriconazole and though natamycin 5% has been hailed to be the first line therapy against Fusarioses, no single treatment has been found to be solely effective on its own. Lack of routine natamycin susceptibility testing also acts as a hindrance. Povidone iodine eye drops, tobramycin chlorhexidine, posaconazole, and oral fluconazole have also been reported to be effective. Therapeutic penetrating keratoplasty and finally enucleation for end-stage endophthalmitis can be considered in fulminant disease. Natamycin with adjuvant voriconazole and systemic fluconazole led to substantial symptomatic improvement in the patient over a 3-week course, proving to be an effective regime, which can be adhered to, ensuring vision salvage in these infections.[4,7] Promising development has been made in the recent past in the early detection and management of keratomycoses. Menassa et al.[8] advocated rapid detection of fungal keratitis with DNA-stabilizing Flinders Technology Associates (FTA) filter paper-based DNA extraction with polymerase chain reaction (PCR). Corneal collagen CXL has emerged as adjunctive therapy to medical and surgical options as reported by Chan et al.[8] Cyclodextrin ternary complex enhances the solubility and permeability of voriconazole, thus augmenting its antifungal activity and making voriconazole-cyclodextrin supramolecular ternary complex-loaded ocular films a potential agent in the management of fungal keratitis. Luliconazole, which has the strongest in vitro antifungal activity among all drugs used against broad-range filamentous fungi has been hailed as a new medical treatment option for fungal keratitis.[8] Though the diagnostic and treatment horizon for F. oxysporum keratomycoses has been expanding, early detection using KOH mounts, confirmatory culture, and prompt institution of first-line anti-fungal therapy in the form of natamycin and adjuvant voriconazole therapy remain the gold standard of managing these vision threatening infections, as documented in this case report.