Fungal keratitis (FK) is a severe ocular infection involving the cornea, caused by filamentous or yeast-forming fungi.^1,2 Whilst filamentous fungi – most commonly Fusarium and Aspergillus species – account for the majority of causes, uncommon pathogens such as Colletotrichum coccodes can also cause FK, particularly amongst elderly individuals and those with agricultural exposure.^3,4

Colletotrichum coccodes is an exceptionally rare cause of FK, with only a limited number of cases reported in the literature.^5,6 Delayed pathogen identification and the use of inappropriate antifungal therapy may lead to rapid and severe disease progression, frequently culminating in corneal thinning or perforation.⁷

This report presents a case of chronic FK caused by C. coccodes in an elderly woman, emphasising the diagnostic challenges, the influence of diabetes mellitus on disease severity and the clinical utility of molecular diagnostic techniques.

Figure 1 illustrates the clinical examination findings during examination and were as follows:

The right eye examination was normal.

Initial corneal scrapings for bacterial and fungal cultures were negative. Owing to the chronic course and ongoing clinical suspicion for FK, empirical therapy with fortified topical antibiotics was continued, and topical voriconazole was added whilst oral fluconazole was maintained pending culture results.

After 4 weeks without clinical improvement, progressive stromal thinning necessitated emergency placement of a glycerol-preserved corneal patch graft for tectonic support. The excised corneal button obtained during the procedure was submitted for fungal culture and pan-fungal polymerase chain reaction (PCR) analysis.

During this admission, routine laboratory testing revealed previously undiagnosed type 2 diabetes mellitus, evidenced by an elevated Hemoglobin A1c (HbA1c). Metformin therapy was subsequently initiated.

Phenotypic identification of cultured fungus: Colletotrichum coccodes.

Macroscopic characteristics:

Microscopic characteristics:

These morphological features are consistent with Colletotrichum spp.; however, species-level identification based solely on morphology may be unreliable.⁸

Pan-fungal PCR assay on culture:

Molecular identification is considered the gold standard for rare filamentous fungi, particularly when culture is slow-growing or inconclusive.⁹ The final report was issued 43 days after specimen collection.

The treatment regimen was continued based on culture susceptibility:

Antifungal susceptibility testing was not performed using formal quantitative methods such as broth microdilution. The organism was identified through culture at the National Health Laboratory Service, with species confirmation by pan-fungal PCR at the National Institute for Communicable Diseases.

Based on known susceptibility patterns of Colletotrichum species, the isolate was reported to be susceptible to amphotericin B and voriconazole, and resistant to fluconazole. These findings are consistent with published literature and informed the clinical decision to discontinue fluconazole and continue targeted antifungal therapy.

Fluconazole was discontinued owing to limited efficacy against filamentous fungi.¹⁰ Treatment continued for 6 weeks, with gradual tapering as symptoms improved. The patient was closely monitored for hepatotoxicity, in anticipation of potential escalation to systemic antifungal therapy should clinical progression occur, and clinical deterioration.

The glycerol-preserved patch graft provided immediate tectonic support in the presence of stromal melt and served as a scaffold for ongoing intensive antifungal therapy. Patch grafts provide effective support in severe FK to preserve globe integrity when penetrating keratoplasty carries a high risk, especially in elderly patients.¹¹

Clinical progress during follow-up was as follows:

Antifungal therapy was continued with close clinical monitoring, and gradual stabilisation was achieved thereafter. The graft ultimately remained structurally stable but developed scarring, resulting in a persistently opaque graft.

The patient was newly diagnosed with type 2 diabetes mellitus during her hospital admission, with HbA1c indicating chronic hyperglycaemia. Metformin therapy was initiated. Diabetes is a well-recognised risk factor for infectious keratitis, particularly of fungal origin, owing to impaired corneal wound healing, altered local immunity and increased epithelial fragility. Immunomodulatory defects associated with diabetes create a milieu favourable to invasive fungal pathogens, including rare species. Delayed corneal healing and suboptimal response to conventional antifungal therapy in this case are partly attributable to this systemic comorbidity. Chronic hyperglycaemia is known to exacerbate corneal infections and increase the risk of perforation.¹⁴

The patient was initially treated with oral fluconazole, an antifungal agent primarily effective against yeasts rather than filamentous fungi, such as Colletotrichum.¹⁰ This contributed to a prolonged clinical course without improvement, underscoring the importance of early culture and molecular diagnostics. The initial 4-week fluconazole course potentially exacerbated disease progression via:

Voriconazole and amphotericin B, administered in combination in this case, provide broad-spectrum coverage against most filamentous fungi, including Colletotrichum species.¹⁵ Combination therapy with amphotericin B and voriconazole has been reported to improve outcomes in filamentous FK, particularly in rare dematiaceous organisms. Published case reports of Colletotrichum keratitis similarly describe prolonged treatment courses and the frequent need for surgical intervention to achieve infection control. The clinical response observed in our patient is consistent with these findings.

In South Africa, the epidemiology of FK differs from that reported in temperate regions, with filamentous fungi accounting for the majority of cases. These organisms, including Fusarium, Aspergillus and rare dematiaceous species such as Colletotrichum, demonstrate a propensity for early stromal and anterior chamber invasion.

Whilst initial empiric therapy in this case included oral fluconazole, this agent is largely ineffective against filamentous fungi. In high-risk presentations – particularly in elderly patients, those with environmental exposure, or in regions with a known predominance of filamentous pathogens – early consideration of systemic antifungal therapy such as oral voriconazole may be justified.

Systemic voriconazole has demonstrated the ability to achieve therapeutic concentrations in the aqueous humour, potentially addressing deeper fungal penetration that topical agents alone may not adequately reach.

Earlier initiation of systemic therapy may therefore reduce disease progression and the need for surgical intervention in selected cases.

Initial cultures and scrapings were non-diagnostic, a common occurrence in FK.¹⁶ This may reflect low fungal load, prior antimicrobial therapy or sampling error. Repeat sampling, particularly deep corneal biopsies, enhances diagnostic yield.¹⁷ Definitive diagnosis was achieved through PCR analysis, confirming C. coccodes. This reinforces the value of molecular diagnosis in culture-negative, treatment-refractory keratitis, particularly in elderly patients or those with immunocompromised status.⁹

Progressive corneal thinning with impending perforation necessitated application of a glycerol-preserved corneal patch graft to reinforce globe integrity. Glycerol-preserved tissue offers several advantages in infectious keratitis, including immediate availability, reduced antigenicity and resistance to secondary infection.¹¹ The graft, as shown in Figure 2, provide tectonic support during antifungal therapy, permitting infection resolution and subsequent epithelialisation. Whilst therapeutic penetrating keratoplasty remains the gold standard in some cases of severe FK, patch grafting is a valuable interim strategy in elderly patients or those unsuitable for major surgery.

In this case, the glycerol-preserved patch graft served a dual role: providing tectonic support in the setting of stromal melt and facilitating therapeutic debulking of infected tissue. Additionally, submission of the excised corneal button enabled definitive microbiological diagnosis.

Whilst traditionally considered a plant pathogen, Colletotrichum is increasingly detected in ocular infections, particularly in tropical and subtropical regions.³ The mechanisms underlying ocular pathogenicity remain unclear but likely involve trauma-related inoculation (including microtrauma), immune compromise and environmental exposure. Fewer than 20 cases of Colletotrichum keratitis have been reported globally, with Colletotrichum dematium and Colletotrichum gloeosporioides being the most frequently identified species.^3,5 This report represents one of the very few documented cases of keratitis caused by C. coccodes in an elderly patient.

This case underscores several important considerations: