Histoplasmosis is a fungal infection (causative agent Histoplasma capsulatum). Infection with this organism occurs throughout the world but is more common in the Mississippi Valley and does not occur in the UK. A severe pneumonitis can occur but most cases are asymptomatic.
Presumed ocular histoplasmosis is not seen in patients with active histoplasmosis. The evidence for infection in the originally described cases was necessarily circumstantial - hence the expression "presumed ocular histoplasmosis". The syndrome consists of a certain type of haemorrhagic macular lesion (choroidal neo-vascularisation) combined with discrete foci of peripheral choroiditis and peripapillary scars.
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