Jawad Ahmad

Learning Points

• Fungal keratitis is a sight-threatening corneal infection caused by filamentous fungi or yeasts.
• It typically follows trauma with plant material or contact-lens contamination.
• Diagnosis rests on corneal scraping, microscopy, and culture confirmation.
• Delay in diagnosis is the strongest predictor of poor visual outcome.
• Early natamycin therapy and timely surgical intervention prevent irreversible vision loss.

Summary

Fungal keratitis (FK) is an infection of the cornea caused mainly by Fusarium, Aspergillus, or Candida species. It remains a leading cause of corneal blindness in tropical regions and is increasingly reported in temperate countries due to contact-lens wear and corticosteroid misuse. This review summarises the epidemiology, clinical presentation, diagnostic work-up, and evidence-based management of FK, highlighting current best practice derived from recent clinical trials and reviews. Early recognition, prompt microbiological testing, and initiation of topical antifungal therapy are vital to preserve vision (1-4).

Introduction

Fungal keratitis is a severe corneal infection that can cause rapid stromal destruction and scarring. Although long considered a tropical disease, recent data indicate global incidence approaching one million cases annually (2). The pathogenesis involves corneal epithelial breach permitting fungal inoculation. The organisms proliferate within the stroma, eliciting an intense neutrophilic reaction that may end in perforation (1, 3).

Epidemiology

In tropical climates FK may account for up to half of microbial keratitis cases, while in the United Kingdom it represents fewer than 5 percent (3, 5). Agricultural trauma is the dominant risk in developing countries, whereas contact-lens wear, chronic ocular-surface disease, and topical corticosteroid use predominate in temperate zones (5, 6). Men aged 30–60 years are most frequently affected because of outdoor occupations (4).

Pathophysiology

Fusarium and Aspergillus species are the main filamentous pathogens; Candida albicans predominates in eyes with pre-existing surface disease (1, 7). These fungi secrete proteases that degrade collagen and invade the corneal stroma. Yeasts typically infect already compromised corneas after surgery or chronic epithelial defects (7, 8).

Clinical Presentation

Symptoms develop gradually and include ocular pain, redness, watering, photophobia, and blurred vision. Examination shows a gray-white stromal infiltrate with feathery borders, satellite lesions, an immobile hypopyon, and often dry-looking ulceration (1, 7). Pigmented fungi (e.g., Curvularia) may produce a brown lesion. Failure to respond to broad-spectrum antibiotics should always raise suspicion of FK.

Differential Diagnosis

Important alternatives include bacterial keratitis (Pseudomonas = rapid, purulent, wet lesion), Acanthamoeba keratitis (pain ≫ signs, ring infiltrate, contact-lens exposure), and viral keratitis (dendritic pattern, reduced corneal sensation) (7).

Investigations

• Corneal scraping and microscopy remain the diagnostic cornerstone. KOH wet-mount or calcofluor-white staining demonstrates branching hyphae with high sensitivity (9, 10).
• Culture on Sabouraud dextrose agar confirms the organism and guides treatment (3).
• Molecular methods such as PCR improve sensitivity and specificity for early detection (11).
• In-vivo confocal microscopy (IVCM) reveals filamentous structures within the stroma and is invaluable when culture is delayed or unavailable (12, 13).

Management

General Principles

Successful management combines prompt topical antifungal therapy, careful monitoring, and surgery when required (1, 14).

Medical Therapy

Topical natamycin 5 % remains the first-line treatment for filamentous FK and outperforms voriconazole in the Mycotic Ulcer Treatment Trial I (MUTT I) (14).
Amphotericin B 0.15 % is preferred for Candida infections, and voriconazole 1 % can be added for deep stromal involvement. Drops are applied hourly, then tapered gradually. Systemic azoles (fluconazole, itraconazole) are reserved for deep or scleral extension (1, 15). Topical corticosteroids are contraindicated in the active phase.

Surgical Management

Therapeutic penetrating keratoplasty (TPK) is indicated for perforation or non-response to maximal medical therapy (16, 17). Lamellar grafting may suffice for superficial disease, and amniotic membrane transplantation can aid epithelial healing. Post-TPK antifungal cover must continue until all signs of infection have resolved (1).

Complications

Delayed or inadequate treatment may lead to corneal perforation, endophthalmitis, secondary glaucoma, or eventual loss of the eye (1, 15). Even after cure, scarring often causes irregular astigmatism and visual impairment.

Prognosis

Prognosis depends on organism, depth of invasion, and timing of therapy. Predictors of poor outcome include deep stromal infiltration, large ulcer size, prior steroid use, and delayed presentation (15). Early diagnosis and natamycin therapy markedly improve the chance of visual recovery (14, 18).

Recent Advances

Newer diagnostic tools such as high-resolution confocal microscopy and PCR enable rapid detection (11–13). Research into nanoparticle drug delivery and antifungal photodynamic therapy shows promise for future treatment (7). Surveillance studies highlight emerging azole resistance, reinforcing natamycin as the preferred first-line drug (18).

Prevention

Patient education on safe contact-lens hygiene, eye protection during agricultural work, and avoidance of unsupervised steroid use can greatly reduce disease burden (2). Public-health initiatives ensuring ready access to natamycin in endemic areas have demonstrably lowered FK-related blindness (2).

Conclusion

Fungal keratitis remains a major global cause of monocular blindness. Its subtle early presentation often delays therapy, yet timely microbiological confirmation and appropriate antifungal treatment can preserve vision. Clinicians must maintain suspicion in any corneal ulcer associated with vegetative trauma or poor antibiotic response, and ensure urgent ophthalmic evaluation.

References

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