Heterotrophic eukaryotes: depend on exogenous food sources (either saprophytes or parasites)
Yeasts: unicellular
Moulds: branching filaments called mycelium, bear spores and grow as hyphae
Long-lasting infections that can be difficult to treat
Fungal infections are more common than bacterial
Moulds are the most common fungal infection worldwide

Filamentous fungi are typically implicated in corneal infections associated with trauma

## Candida albicans

Candidal infection of the oesophagus, trachea or lung is an AIDS-defining illness

## Cryptococcus neoformans

## Aspergillus (and Fusarium) keratitis

Septate fungi
Saprophytic mould (ie. filamentous)
Spores (“conidia”) are dispersed in association with plant material or insects
Opportunistic pathogen
Mycelia spark an IgE mediated allergic response in the bronchi (type I hypersensitivity) or complement activation and polymorph infiltration (type II hypersensitivity)
Aspergilloma: compact mass of mycelia
If the corneal stroma is exposed (eg. following corneal injury) conidia germinate and hyphae penetrate the stroma

Hyphae contain proteases eg collagenases that facilitate penetration through the stroma and into the AC (hypopyon)

C-type lectins bind to cell wall components (beta-glucan and alpha-mannose) leading to chemotactic/inflammatory cytokine release

Contact lens wear is the main risk factor
Fungal biofilms are complexes of hyphae and extracellular carbohydrates with resistance to antimicrobials
The deep penetration of hyphae makes antimycotics less effective.
Treatment options

Natamycin
Voriconazole
Full thickness keratoplasty
Enucleation
Steroid use is risky as will cause hyphal growth if given before the infection is controlled

## Histoplasma capsulatum

Presumed ocular histoplasmosis syndrome (POHS) is not truly an infectious process
Hence anti-fungal therapy is not beneficial

## Mucoraceae

Histopathology: non-septate fungi with wide angle branching (cp to Fusaria and Aspergillus which are septate fungi)

Ubiquitous saphrophytic fungi in soil, air, ventilation systems, bodily orifices
Usually phagocytosed by macrophages
In acidic conditions of diabetes, metabolic acidosis or uraemia: spores can germinate and hyphae establish infection
Causes orbital fungal infection: mucormycosis