Vision Information - Ocular Histoplasmosis Syndrome
When the airborne spores of the fungus Histoplasma capsulatum are inhaled into the lungs, the disease histoplasmosis results. The fungus is found throughout the world in river valleys and soil that is laden with bird or bat droppings. When the soil is plowed, holes dug, or chicken coops swept, the fungus is released into the air.
Histoplasmosis usually is very mild with little or no symptoms, and if symptoms are present they resemble those of colds or flu. As with a cold or flu, the body's immune system deals with it in a few days without treatment. But histoplasmosis, even in mild cases, can later cause ocular histoplasmosis syndrome (OHS), a serious eye disease that is a leading cause of vision loss in Americans between the ages of 20 and 40.
How are Histoplasmosis and Ocular Histoplasmosis Syndrome related?
Although scientists have not been to detect the histoplasmosis fungus in the eyes of patients with ocular histoplasmosis syndrome, they believe the spores are spread from the lungs to the eye and lodge in the choroid, a layer of blood vessels providing blood and nutrients to the retina. This is good reason to suspect the histoplasmosis organism as the cause of OHS.
What are the Symptoms of Ocular Histoplasmosis Syndrome?
Initially there are seldom any symptoms and the condition is cured by the body's immune system after a few days.
But if the disease has remained latent, OHS symptoms may appear later. Some of these include straight lines appearing crooked or wavy, or a blind spot appearing in the field of vision. This will suggest that OHS has progressed enough to affect vision, and anyone who has been exposed to histoplasmosis, and is aware of even the slightest change in vision, should consult an ophthalmologist immediately.
Who is at Risk for OHS?
It is important to bear in mind that only a very small percentage of people infected with the histoplasmosis fungus develop OHS. But anyone aware of having been exposed should be alert for the changes in vision described above. Clinical studies have revealed that OHS patients usually test positive for previous exposure to histoplasmosis.
The highest incidence in the United States occurs in a region popularly referred to as the "Histo Belt", where up to 90 percent of the adult population has been infected with histoplasmosis. This region includes Arkansas, Kentucky, Missouri, Tennessee, West Virginia and large portions of Alabama, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Mississippi, Nebraska, Ohio, Oklahoma, Texas and Virginia.
Since most cases of histoplasmosis go undiagnosed, anyone living in â€" or who has lived in â€" a high risk area should have their eyes examined for histo spots, which are scar evidence of the inflammation caused by histoplasmosis.
How is Ocular Histoplasmosis Syndrome diagnosed?
OHS is the diagnosed condition if a comprehensive eye examination reveals:
The diagnosis is confirmed by carrying out a dilated eye examination that involves enlarging the pupils temporarily with special drops so the ophthalmologist can examine the retina more closely.
Should the ophthalmologist deem it necessary, further tests will be carried out to confirm whether or not the disease is present.
How is OHS treated?
OHS has been treated successfully with a form of laser surgery called photocoagulation. The laser destroys the abnormal blood vessels and a small portion of the overlying retinal tissue. This procedure can cause some loss of vision but it is performed in the hope of protecting the fovea (a depression in the retina that provides acute eyesight) and preserving the sharp vision it provides.
Is laser surgery effective?
Clinical trials have shown that photocoagulation can reduce vision loss from OHS by more than 50 percent.
The treatment is more effective when the abnormal blood vessels have not grown into the center of the fovea, where vision can be affected, or when the ophthalmologist is able to identify and destroy the entire area of abnormal blood vessel growth.
Will laser surgery restore lost vision?
Usually, laser photocoagulation does not restore lost vision. But it does reduce the chances of further abnormal blood vessel growth and consequent vision loss.
It is important to bear in mind that laser surgery cannot cure OHS. Once contracted, the disease remains a threat to an individual's vision for life. OHS patients who experience one bout of abnormal blood vessel growth can suffer a recurrence. That is why early detection and treatment is so vital.
Is there help for patients with significant vision loss from OHS?
There are many useful devices available for people suffering severe visual impairment. These are generally referred to as low vision aids and incorporate the use of special lenses or electronics to create enlarged visual images.
Your ophthalmologist can suggest sources that provide information on counseling, training and special services for people with low vision.