What Is It?
Histoplasmosis is a fungal infection caused by the organism histoplama capsulatum. The disease is acquired by inhaling the organism. From the lungs the fungus travels to the spleen, liver and sometimes the eyes.
This disease is most common in the Mississippi and Ohio river valleys. It is also quite common in the Tennessee river valley, including Huntsville.
Both chickens and pigeons have been identified as carriers of the fungus and can play a part in its transmission.
In the vast majority of individuals the disease does not cause any symptoms or problems. A few people will have a flu-like illness with the initial infection.
There are two common eye findings in patients that have had previous infections with histoplasmosis. Neither of these involve actual fungus particles, but are scars in the retina where the fungus presumably traveled during the original infection.
- The first eye finding is scarring around the optic nerve in the back of the eye. This gives the nerve a “bumpy” irregular border.
- The second finding is in the peripheral retina where small round white scars develop. These are called “punched out” lesions.
Less commonly scars can be found near the center of the retina. It is these scars that are the most serious. Usually the Histo scars of the eye are incidental findings at routine eye exams.
However, there are instances when the scars lead to problems and patients should be aware of these symptoms.
Beneath the retina is a dense mass of blood vessels that nourish the eye known as the choroid. The retina is separated from these blood vessels by a strong barrier termed Bruch’s membrane.
The scars from Histoplasmosis can cause breaks in Bruch’s membrane, much like cracks in a sidewalk. A blood vessel acting like a weed will rarely grow through this crack and grow under the retina. This leads to distortion of the retina, and therefore the vision. Untreated, this can expand to destroy the central reading vision.
Signs, Symptoms and Treatment
When a blood vessel grows beneath the retina it causes the vision to be distorted.Things that should be straight become crooked or wavy.
Patients at risk are given a grid with horizontal and vertical lines. This should be checked weekly with each eye for new distortions. People often overlook these distortions unless the other eye is covered.
When a blood vessel is discovered growing beneath the retina, it must be treated urgently. This is usually done by a retina specialist.
First, a dye test is performed. Dye is injected into the arm and pictures are taken of the retina. This shows the exact location and extent of the problem. Then a laser is used to seal and destroy the blood vessel. This will leave a small blind spot but can save the central reading vision in many cases.
A new surgery is now being performed to remove large undermining vessels that are too big for laser and have already taken away central vision.