Histoplasmosis is an infection caused by the spores of a fungi (Histoplasma Capsulatum). This fungi is endemic to the Ohio and Mississippi River valley. People become infected by inhaling the spores from multiple sources: bird or bat droppings, plowing or tilling fields, or construction projects. People working in construction, landscaping, and farming may be at higher risk of exposure.

The spores initially enter the lungs and in the majority of people do not cause any symptoms. Most individuals never know they were exposed or infected. Some individuals develop symptoms a few weeks after exposure, including fever, chills, cough, body aches or pains. The fungus can travel through the blood stream and infect the eye. This is called “presumed ocular histoplasmosis.” Most people are unaware that histoplasma has spread to their eyes, and only on routine dilated eye exams can eye care professionals see evidence of retinal scars or “histo spots” on the retina.

It’s estimated that up to 60% of people living in endemic areas test positive for exposure to this fungus, but only about 1.5% show retinal lesions. And among those who show evidence of spread to the eye, under 4% develop bleeding under their retina leading to vision changes or loss.

It’s unclear if the fungus itself causes atrophy of the retina (destruction and scarring) or if it is the body’s immune response that causes it. When this “atrophy” occurs outside of the central visual field people are unaware. But if the lesions develop in the macula (the area responsible for our fine central vision) they may note symptoms. In its most severe form the fungus causes choroidal neovascular membranes or bleeding under the retina. The symptoms are very similar to that of patients with “wet” macular degeneration.

Individuals without “histo spots” in the macula are at a lower risk of developing a bleed in the retina and only observation is needed. If a patient develops a bleed that is not located in the center of their vision they may be observed or their doctor may recommend treatment with anti-vascular endothelial growth factor or laser treatment with or without Verteporfin.

• Anti-Vascular Endothelial Growth Factor (Anti-VEGF) medications: these drugs are administered into the eye by an injection. The medication works by reducing the new blood vessels growing under the retina causing bleeding.
• Laser Therapy: if bleeding occurs under the retina and it is not near the central visual field, laser therapy may be applied to destroy the new blood vessels growing under the retina. In cases where the bleeding is under the central visual field a medication called Verteporin may be given through an IV that travels through the circulation into the eye. Once the medication has travelled into the eye laser therapy can be applied to close off the bleeding vessels.

In individuals who become symptomatic, require treatment and get that treatment in timely fashion can have good visual outcomes. If you are experiencing the symptoms listed above please seek a consultation with an eye care provider with experience in treating this condition.