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Fungal Keratitis

URGENT — Cornea

Symptoms

pain, photophobia, and redness

tearing and mucopurulent discharge

indolent clinical course compared to bacterial keratitis

history of minor trauma with vegetable matter (e.g., branch, plant material)

contact lens wear or chronic ocular surface disease

poor response to conventional antibacterial therapy

Clinical Findings

Corneal signs

  • stromal infiltrate with characteristic feathery edges
  • satellite lesions surrounding the primary infiltrate
  • infiltrate may extend beyond the borders of the epithelial defect

Other signs

  • conjunctival injection and chemosis
  • mucopurulent discharge
  • anterior chamber reaction or hypopyon

Etiology

Filamentous fungi

  • fusarium species: most common (especially post-vegetative trauma or contact lens wear)
  • aspergillus species

Yeasts

  • candida species: common in chronic surface disease or topical steroid use

Risk factors

  • warm, humid climates
  • poor contact lens hygiene
  • immunocompromise or chronic steroid use

Red Flags

history of vegetative trauma (plant, branch, or soil)

feathery infiltrate margins and satellite lesions

clinical worsening while on broad-spectrum antibacterials

deep stromal involvement or endothelial plaques

Investigations

Corneal scraping

  • scrape deep into the edge of the ulcer
  • gram and giemsa stains
  • koh prep or calcofluor white for fungal elements
  • specialized histology: pas, gomori methenamine silver (gms), and h&e

Cultures

  • sabouraud agar (incubated at 25°c and 37°c)
  • concurrent bacterial cultures
  • culture of contact lens case and solution

Adjunctive

  • confocal microscopy: may visualize hyphae in vivo
  • corneal biopsy if cultures are persistently negative

Treatment

Topical therapy

  • natamycin 5% suspension q1h: first-line for filamentous fungi (fusarium)
  • voriconazole 1% or amphotericin b 0.15% q1h: for yeasts or aspergillus
  • epithelial debridement to improve drug penetration

Systemic & adjunctive

  • oral voriconazole: 200 mg b.i.d. (load 400 mg b.i.d.) for deep disease
  • intracameral or intrastromal voriconazole (50 mcg/0.1 ml) for refractory cases
  • cyclopentolate 1% or atropine 1% for pain and synechiae prevention

Surgical

  • therapeutic penetrating keratoplasty (pk) for perforation or medical failure

Clinical Pearl

High clinical suspicion is critical — delayed diagnosis is common. Key distinguishing features: feathery margins + satellite lesions + hypopyon + scanty secretions + history of plant/vegetative trauma or contact lens use in warm climates. Prognosis is poor: 26-63% experience severe visual loss; 15-20% require evisceration. Epithelialization may inhibit drug penetration — debridement helps.

Differential Diagnosis

  • bacterial keratitis
  • herpes simplex stromal keratitis
  • acanthamoeba keratitis
  • sterile corneal infiltrate

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