Histoplasmosis is an infection caused by fungus histoplasma capsulatum. The spores of fungus are responsible for the disease. Histoplasmosis is distributed worldwide, particularly in temperate climate along the river valleys. The fungus grows best in places contaminated by blackbird, chicken and bat dropping. When the soil becomes dry and is dug for planting crops or the chicken coop is swept, the infectious spores of the fungus become airborne and can get inhaled and lodged into the lungs.
What is OHS and How It Is Caused
Ocular histoplasmosis syndrome (OHS) is rare but serious disease affecting eyes. It can cause loss of vision. It occurs in people who have suffered from histoplasmosis infection. In a small percentage of patients, the spores may travel from its primary site-the lungs into the choroid. Choroid is a layer made up of blood vessels in the retinal area of the eye. This vascular structure provides blood and nutrition to the retina.
Symptoms of OHS:
Ocular histoplasmosis syndrome in majority of cases remains asymptomatic. This means the patient may not experience any symptoms and the spots or scars may be detected accidentally by the ophthalmologist during routine eye test. Symptoms only develop when there is neovascularization. Formation of new fragile vessel can occur beneath the retina any time once the scar is formed. Sometimes it may take years after the initial infection. These abnormal blood vessels of retina can leak and bleed as they are fragile. The spots from where neovascularization develops are called histo spots. If the bleeding is left untreated and the scar is near macula, this may cause changes in vision. The best example is a straight line may appear as crooked and distorted. Patient may experience a blind spot in his central vision. Gradually there is permanent vision loss.
Diagnosis and Treatment
Ocular histoplasmosis syndrome is diagnosed during eye examination. It can be confirmed with special tests called OCT (optical coherence tomography). In this test the damage to retina can be detected. Another test called fluorescein angiogram can help in locating the bleeding vessel.
Once the diagnosis is confirmed, patient may or may not need treatment. This may depend if he has symptoms or remains asymptomatic. Oral antifungal medication has no role to play. Actually there is no fungus present in the eye. The spore has formed a scar. Hence the focus of treatment if any is to stop damage to retina from the neovascularization. The only proven treatment is laser photocoagulation. In this technique a powerful laser beam is focused on the leaking blood vessel and the fragile blood vessel is coagulated. Laser treatment is best suitable when the leaking blood vessel is located outside the central vision. If the bleeding is near the central vision medications are used. The medicine is introduced through intraocular injection in the eye. This may need frequent repetition sometime.
Usually the prognosis is good with modern day techniques and medicine. Actually the damage that is already done cannot be restored back. But further deterioration and formation of CNV can be stopped. Patient thus living in histo belt must consult eye specialist, if he has slightest visual changes. This will help early detection and treatment, reducing risk of vision loss.