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Ocular histoplasmosis is a possible complication of a type of fungal lung infection. Airborne spores of the fungus Histoplasma capsulatum can attach to the inner lining of lungs and may or may not cause immediate symptoms. If fungal spores manage to reach the bloodstream, they can travel to the eyes and embed in the choroid layer above the retina. People with ocular histoplasmosis can experience mild to severe central vision loss due to blood vessel inflammation and scarring in the eyes. Treatment in the form of laser surgery can usually prevent further damage to the eyes, but most people who develop ocular histoplasmosis do not regain vision they have already lost.
The exact mechanisms by which fungal spores migrate from the lungs to the eyes are not known. In fact, there is usually no direct evidence that fungi exist in the eyes at all in people who are diagnosed with ocular histoplasmosis. Almost every person who has the disorder, however, has a previous history of the fungal lung infection. It may take several months or even years for ocular problems to develop after coming into contact with Histoplasma capsulatum.
The choroid layer of the eye contains tiny blood vessels that feed the retina. Ocular histoplasmosis causes inflammation in existing vessels and the growth of new, very delicate vessels that are prone to leaking blood. Scarring and lesions can arise in the central portion of the retina as a result. An affected eye has trouble with sharp focus, which is needed to read text, make eye contact, or operate a vehicle safely. Peripheral vision is usually left intact.
A person who believes he or she may have symptoms of ocular histoplasmosis should visit an eye doctor as soon as possible. The doctor may be able to see tiny specks in the eye called histo spots, which are small scars above the choroid layer that are common with ocular histoplasmosis. A detailed exam also might reveal retinal swelling and excessive blood vessel growth.
Antifungal medications and anti-inflammatory drugs have not proven useful in treating ocular histoplasmosis. The most effective treatment is a surgical procedure called laser photocoagulation. During the surgery, a high-intensity laser beam is used to burn away abnormal blood vessels. Photocoagulation is very effective in most cases at stopping future sight degeneration. It cannot, however, restore lost vision. Specialized contact lenses and sessions with trained vision specialists may be able to help some patients see better and learn to overcome their handicaps.