What is the ocular histoplasmosis syndrome (OHS)?
OHS is a condition where abnormal blood vessels may grow under the retina causing blurred, distorted vision. The retina is a thin layer of delicate nerve tissue that lines the inside wall of the eye like the film in a camera. In the eye, light is focused onto the retina, which “takes the picture” of objects you look at and sends the image to the brain.
What causes the ocular histoplasmosis syndrome?
Most cases of OHS occur as a result of an infection by the fungus Histoplasma capsulatum. This organism is found in bird and bat dropping and is most common in the Ohio and Mississippi river valley areas. High-risk activities include farmers, pest control workers, poultry keepers, construction workers, roofers, landscapers, and cave explorers. When soil is disturbed by wind or human activity, the fungal spores become airborne. After the spores are inhaled, they may cause a brief “flu-like” infection or may cause no symptoms at all in a healthy individual. In infants, the elderly, and those with compromised immune systems severe complications may include acute respiratory distress syndrome (ARDS), pericarditis, adrenal insufficiency, and meningitis.
Usually there are no visual symptoms at the time of active infection. However, after the infection is gone, scars are left in the body. These scars may be seen on x-rays of the lung, liver, and other parts of the body. Many years after the initial active infection, scars under the retina may cause loss of vision from the growth of abnormal blood vessels. At this stage, there is no active infection and a person with OHS cannot transmit an infection to someone else. The risk of loss of vision from OHS appears greater in those who smoke tobacco.
What are the symptoms of the ocular histoplasmosis syndrome?
Decreased central vision is common. It may be most notable at near and is usually associated with distortion, which means straight lines appear wavy or crooked. These symptoms come from active leakage of fluid and blood under the retina from abnormal blood vessels associated with OHS scars. Without treatment more scare tissue forms under the retina and a permanent blind spot develops in the center of vision.
What treatment is available?
There are a number of treatments for OHS and it is important to start treatment as soon as possible after the start of symptoms. The main treatment for the abnormal leaking blood vessels involves medication injection in the office. Medicine injections may be given painlessly in the office with anesthetics. Repeat injections may be required if leakage from the abnormal blood vessels returns. Most people respond well with an improvement in vision. The eye should be monitored because new areas of leakage may occur at a future date. An Amsler grid chart should be used at home on a regular basis to detect recurrent activity at a future date.
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