Histoplasmosis is a fungal infection that initially affects the lungs. Many people are unaware that they have contracted histoplasmosis because it typically produces only mild symptoms that are similar to having a cold. But the infection often travels from the lungs to the eyes and settles in the choroid. The choroid is part of the middle layer of the eye, containing numerous veins and arteries that provide blood to the retina. This can lead to the development of ocular histoplasmosis syndrome, which is a serious condition and among the leading causes of vision loss in people between the ages of 20 and 40.
Histoplasmosis causes abnormal blood vessels to form near the retina. Lesions develop called choroidal neovascularization, producing scar tissue that can result in a loss of vision. In addition, the abnormal blood vessels sometimes leak beneath the retina into the macula. If left untreated, this leakage can damage the fovea, causing problems with central vision that may be permanent.
The main risk factor for histoplasmosis is living in an area in which this infection is common. In the United States, that includes many states stretching from the mid-Atlantic to the South and Midwest. While the condition may never develop in many people exposed to this fungus, it is still essential to undergo regular eye exams if you have ever lived in the region where it is prevalent to catch any evidence of changes at an early stage.
Histoplasmosis is often asymptomatic, but a doctor can determine the presence of the infection by miniscule scars known as histo spots that appear and remain within the eye. In many cases, the histo spots are harmless and complications never arise. However, sometimes many years later, the retina becomes inflamed due to abnormal vessel growth. If visual disturbances such as a blind spot or unclear vision occur, it is a signal that the infection has reactivated and medical attention is required immediately.
Treatment for histoplasmosis is most effectively achieved by laser photocoagulation. This minimally invasive procedure is used to seal or destroy the abnormal blood vessels before they can do permanent damage.