What is Histoplasmosis?
Histoplasmosis is a disease caused by a fungal organism, which is commonly found in the soil mostly in the Midwestern United States. There are two basic types of histoplasmosis, systemic and ocular. Systemic histoplasmosis produces an influenza-like illness with fever and weakness that usually lasts about two weeks. After recovery, the infection can leave small, usually harmless, scars throughout the body. The eye can be involved and the scars can be detected during an examination of the retina. Visual problems never develop during the initial, acute infection.

What Is Ocular Histoplasmosis?
Most people with healed “histo” scars in the eye do not develop further problems. However, abnormal blood vessels may begin to grow through the healed histoplasmosis scars many years later. These abnormal blood vessels may cause bleeding and further scarring which can damage the retina. If the abnormal blood vessels are near the central part of the retina (the macula), reading vision may be damaged. Early diagnosis and treatment of these abnormal blood vessels is very important. Visual problems from ocular histo can occur long after the systemic phase.

How Will I Know if I Am Developing Ocular Histoplasmosis?
Most people with active ocular histoplasmosis have blurred or distorted vision in one or both eyes. Distorted vision is a very important symptom and should be reported promptly to your doctor. This may appear as straight lines looking wavy (doorways, telephone poles, flagpoles, etc.). Many people with decreased vision in one eye may not realize they have a problem because the remaining good eye compensates so well. It is very important to check each eye separately. Ocular histoplasmosis may affect both eyes, although the second eye may not become involved for many years.

Ocular histoplasmosis is diagnosed with an eye examination involving dilation of the pupils. A special photograph test, which is often helpful, is fluorescein angiography. In this test, dye is injected through an arm vein and pictures are taken of the eye as the dye circulates through the retina. These pictures are helpful in diagnosis and also serve as a road map for possible laser treatment.

What Treatment Is Available for Ocular Histoplasmosis?
There are no eye drops or antibiotics known to be effective in ocular histoplasmosis. When abnormal vessels grow outside of the centermost part of the macula, laser surgery has the best chance of stopping the progression of abnormal blood vessels. If the vessels are growing in the very center, newer laser techniques may help. Sometimes it is possible to do a delicate operation to reach under the retina and physically remove them.

What Is Laser Treatment Like?
Laser is a precisely focused beam of light, which can seal (cauterize) tissue in the retina. The laser beam seals abnormal vessels but does not help already damaged retinal tissue to function better. If some of the visual decrease is due to swelling from leaky blood vessels rather than scar tissue per se, then laser may actually help vision by allowing the swelling to subside. Laser surgery is done in the office and is not painful. After the treatment, you will be free to return home. Unfortunately, laser surgery does not always eliminate abnormal blood vessels. In some cases, additional treatment may be needed. Even if vision is not improved, laser therapy may help to limit visual loss and minimize damage that would have occurred without treatment.

Can I Prevent Ocular Histoplasmosis?
The factors that cause active histo are poorly understood at this time. The body's immune system may play a role. No special diet or medical treatment has been shown to prevent the formation of abnormal blood vessels. If you have macular histo scars, you should monitor your vision at home with an “Amsler Grid”, or a piece of graph paper and report any sign of distortion or decreased vision to your doctor promptly. Remember, the earlier the diagnosis is made, the better the chance of saving the reading vision. Laser treatment for histo scars that are not active has not been shown to be effective.

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