For young adults, age 20 to 40, a leading cause of vision loss is ocular histoplasmosis syndrome. If you have ever lived in the “Histo Belt”, there's a high probability that you have been infected with the histoplasma fungus at some time, and are at risk for the eye condition. The Histo Belt includes all of Arkansas, Kentucky, Missouri, Tennessee, and West Virginia, as well as large parts of Alabama, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Mississippi, Nebraska, Ohio, Oklahoma, Texas, and Virginia.
Histoplasmosis is often so mild that it has no obvious symptoms, or resembles a cold. It is caused by inhaling spores from the Histoplasma capsulatum fungus, which is found in the soil. This fungus is found worldwide, but is so common in the Histo Belt that up to 90 percent of the adult population has been infected. Most people recover fully within a few days. But in a few cases, spores may spread from the lungs to the eyes. According to reference one, the fungus has not actually been detected in the affected eyes, but it is believed to be the cause of the vision loss. Several articles in the medical literature refer to “presumed ocular histoplasmosis syndrome.”
The mechanism for vision loss is the growth of abnormal blood vessels under the retina. These can form a lesion known as choroidal neovascularization. The first sign of eye infection is tiny scars called “histo spots,” which an eye doctor can see in a standard eye exam. Swelling of the retina may also be apparent. A fluorescein angiography can give the doctor a better view of the lesions: in this procedure, a dye is injected into a vein in the patient's arm.
Reference one, published in 2008, reports that the only proven treatment is laser surgery. Since that time, the medical literature has reported positive results for a different surgical technique and for a drug (bevacizumab) that inhibits the growth of abnormal blood vessels.
In the early stages, ocular histoplasmosis has no symptoms. Regular eye exams are the only way to find it before significant damage is done.
1. Amy L. Sutton, ed, “Eye Care Sourcebook”, Omnigraphics, 2008.