Histoplasmosis is an infectious condition caused by the fungus Histoplasma capsulatum. It is caused when the spores of the fungus are inhaled into the lungs. Histoplasma capsulatum lives in river valleys and soil with accumulation of bird or bat droppings.
Those living in the region now known as the 'Histo belt', which includes Arkansas, Kentucky, Missouri, Tennessee and West Virginia are at the highest risk of getting histoplasmosis.
Rarely lung infection with histoplasmosis may affect the eyes as well leading to ocular histoplasmosis. 1-5
Symptoms of ocular histoplasmosis
Ocular histoplasmosis usually has no symptoms in its early stages.
The initial infection in most individuals subsides without treatment. Most histoplasmosis infections (of the lungs) do not need treatment and manifest as a bout of cold or flu. The symptoms resolve without treatment and often patients are unaware of a histoplasma infection.
Histo spots within the eyes
If the eyes are affected there is formation of histo spots within the eyes. These are areas where there is formation of abnormal fragile blood vessels underneath the retina. This leads to an abnormal growth under the retina called the choroidal neovascularization (CNV).
This CNV lesion, as it heals, turns into a scar that damages a significant area of the retina causing loss of vision at that area in later years. Sometimes the abnormal blood vessels may bleed or leak leading to loss of vision.
Histo spots do not generally affect vision in the early stages. However, years after the initial infection is healed, these spots and scars may damage eye sight. This may occur decades of the initial infection.
The disease that emerges months or years later is known as presumed ocular histoplasmosis syndrome and is caused by growth of new and fragile blood vessels, which may leak and scar the tissues of the retina. It is thought to be caused due to sensitivity to the original fungi Histoplasma capsulatoum rather than the primary infection itself.
In later years patients often complain of black spot(s) in the center of their visual field. This happens because the CNV and the histo spots affect the central most sensitive part of the retina called the macula. This region normally helps us focus to read, write or drive. There may be appearance of a single blind spot in the center of the visual field.
Patients may complain of straight lines appearing crooked or wavy and difficulty in focussing while reading. These may include straight objects like telephone or light posts, doorways and windows etc.
There may be blurred or distorted vision in some patients. This may affect one or both eyes.
If one eye is affected, most people fail to notice the problem early as the good eye compensates for the defect.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)