Fusarium is a filamentous mold commonly found on plants and in soil. It is the most common fungal intraocular infection resulting from keratitis with contiguous spread from the ocular surface [7]. During an outbreak of Fusarium keratitis occurring due to one brand of contact lenses from 2004 to 2006, 6 % of the keratitis patients progressed to endophthalmitis [13]. It has also been reported as a rare cause of fungal endophthalmitis following cataract surgery [14].

Endogenous spread of Fusarium is infrequent, and those cases that have been reported are limited to immunocompromised patients with disseminated fungal infection. In immunocompromised patients, Fusarium may cause sinusitis, pneumonia, and cellulitis at sites of skin breakdown or onychomycosis. Ocular disease typically manifests as a more localized inflammation or fungal mass confined to the anterior chamber or anterior vitreous, but disease can extend to the posterior vitreous in severe cases. While rare, these cases are often severe, presenting with a robust inflammatory reaction in the anterior chamber, vitritis, and varying degrees of retinal ischemia and necrosis [15] (Fig. 20.2).

Histoplasma capsulatum is a thermally dimorphic fungus which grows as a mold in soil and as a yeast in human or animal hosts. When involved in eye infections, it typically affects a relatively young population, usually in the third or fourth decade of life. The fungus is endemic to the Central United States including the Ohio River Valley and Mississippi River Valley. Like many of the other fungal pathogens, its route of inoculation is most commonly through the respiratory tract. Humans usually acquire the infection via inhalation of spores (conidia) from soil that is contaminated with bat or bird droppings. While healthy patients may be asymptomatic, immunocompromised patients present with fever, pancytopenia, hepatosplenomegaly, and oropharyngeal or gastrointestinal lesions. Adrenal, brain, and skin lesions may additionally be seen in these patients [16]. Ocular clinical manifestations include punched-out choroidal scars, peripapillary pigmented degeneration, and macular choroidal neovascularization (CNV) or disciform scarring. The ocular disease is marked by little or no vitreous inflammation. As most cases of ocular histoplasmosis occur in healthy patients who are largely asymptomatic, regular follow-up for the possible occurrence of CNV is required [17, 18].

Histoplasma capsulatum is a very rare cause of endogenous endophthalmitis and when present occurs mostly in immunocompromised patients, such as those with AIDS, causing severe visual loss. Endogenous Histoplasma endophthalmitis is usually characterized by a granulomatous chorioretinitis and rarely by subretinal [22] and intraretinal exudates and retinal detachment [19].

Coccidioides immitis is a dimorphic fungus found in dust in the endemic areas of the San Joaquin Valley of California, Arizona, and some parts of Central and South America. Agricultural and construction workers are among those at greatest risk for infection. Infection occurs through the inhalation of spores and in most patients leads to a self-limited disease. However, those patients who are re-exposed to the fungus may develop a chronic respiratory disease [20].

Coccidioides is a rare cause of endophthalmitis, and when it does cause intraocular infection, spread is hematogenous to the choroid. Cases of acute infection manifest with a multifocal choroiditis with scattered small lesions, vascular sheathing, exudative retinal detachment, and vitritis [21]. Other patients may remain asymptomatic and present only with chorioretinal scars [22].

Cryptococcus neoformans is an encapsulated yeast causing opportunistic infection in AIDS patients or other severely immunocompromised patients. Pigeons play an important role in its pathogenesis as the Cryptococcus spores survive up to 2 years in pigeon droppings. Human infection is acquired via the respiratory tract through the inhalation of spores. The fungus is then disseminated hematogenously and has a predilection for the central nervous system, most commonly resulting in fungal meningitis [23]. The organism reaches the eye either by direct extension from the optic nerve sheath or via hematogenous spread to the choroid. Ocular cryptococcosis is very rare, manifesting as a multifocal choroiditis with discrete, yellowish white lesions of differing size. Other manifestations include optic nerve edema, vascular sheathing, and exudative retinal detachment [24].