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What is Ocular Histoplasmosis Syndrome? | Symptoms | Causes | Treatment | Consequences

What is Ocular Histoplasmosis Syndrome?

Ocular Histoplasmosis Syndrome (OHS) is the leading cause of blindness in ages twenty to forty. It is a complication of histoplasmosis caused by airborne spores of the fungus Histoplasma capsulatum that are inhaled into the lungs. These fungal spores are found everywhere in the world -- in the soil or in bird or bat droppings. If plowing fields, sweeping chicken coops, or digging holes disturbs the spores, they are released into the air and can be inhaled.

Histoplasmosis itself is mild and may not produce any symptoms. In fact, if you had symptoms, you probably would think it was a cold. The immune system usually gets rid of histoplasmosis within a few days without treatment. The highest incidence of the disease is in the "histo belt," the Ohio-Mississippi River Basin. Ninety percent of the infected adults are in Alabama, Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Missouri, Nebraska, Ohio, Oklahoma, Tennessee, Texas, Virginia, and West Virginia.

In Ocular Histoplasmosis Syndrome, spores spread from the lung to the eye where they lodge in the choroid, the layer of blood vessels that provides blood and nutrients to the retina. Fragile, abnormal blood vessels grow underneath the retina and form lesions known as choroidal neovascularization (CNV). They can turn into scar tissue and replace normal tissue in the macula. This results in blindness.

Symptoms

In the early stages of Ocular Histoplasmosis Syndrome there are no symptoms. The initial infection usually goes away without treatment leaving tiny scars called "histo spots." These spots don't generally affect vision, but may cause problems years later by causing the growth of the abnormal blood vessels. One of the early signs is that straight lines appear wavy, and the person develops a blind spot. To make a definitive diagnosis the ophthalmologist will dilate the eyes. The presence of histo spots indicates previous exposure to histo fungus spores. The swelling of the retina indicates new abnormal blood vessels. The ophthalmologist may do fluorescein angiography where they inject dye into the patient's arm. When the dye goes to blood vessels in the retina, the doctor can see CNV lesions and tell how much the bleeding has spread.

 If you are experiencing some of the symptoms described here, it does not necessarily mean you have Ocular Histoplasmosis Syndrome. However, if you experience one or more of these symptoms, you should contact your eye doctor for a complete exam. Click here for information on emergency or immediate care.

Causes

In Ocular Histoplasmosis Syndrome, histoplasmosis spores spread from the lung to the eye where they lodge in the choroid layer. Fragile, abnormal blood vessels grow underneath the retina forming lesions known as choroidal neovascularization (CNV). These can turn into scar tissue and replace normal tissue in the macula, causing the loss of center vision.

Treatment

The treatment is laser surgery or photocoagulation where fragile, abnormal blood vessels are destroyed. The surgery also destroys overlying retinal tissue. Although this will destroy some vision, the goal is to save the macula. Laser surgery will not restore vision that has already been lost, but will help prevent further loss. Patients with histoplasmosis should check their eyes daily with the Amsler Grid to make sure straight lines aren't beginning to appear wavy.

Corticosteroids can be given to reduce inflammation. Subretinal surgery is sometimes done to remove abnormal blood vessels.

Consequences

Patients suffering from Ocular Histoplasmosis Syndrome will lose their central vision. The condition cannot be cured, and abnormal blood vessels may form repeatedly. People who have had histoplasmosis should be checked regularly by an ophthalmologist to see if they are experiencing any changes in their vision.