Summary about Disease
Ocular Histoplasmosis Syndrome (OHS) is an eye condition believed to be caused by a previous infection with the fungus Histoplasma capsulatum. The fungus is common in soil, particularly soil enriched with bird or bat droppings. While most people infected with *Histoplasma* have no symptoms or mild respiratory illness, in some individuals, it can lead to OHS years later. OHS doesn't involve active fungal infection in the eye; instead, it's thought to be an immune response to the prior infection that damages the retina. This damage can result in vision loss.
Symptoms
Most people with OHS are unaware they even have the condition until vision problems develop. Common symptoms include:
Blurred vision
Distorted vision (metamorphopsia)
Blind spots (scotomas) in the central or near-central vision
Difficulty seeing at night
Causes
OHS is presumed to be caused by a previous infection with the fungus Histoplasma capsulatum. The exact mechanism is not fully understood, but it is believed that the body's immune system reacts to the presence of the fungus or its remnants in the eye, leading to inflammation and damage to the retina and choroid (the layer of blood vessels behind the retina). Histoplasmosis is contracted by inhaling fungal spores from the air, typically in areas where the fungus is present in soil. It is important to note that most people who are infected with Histoplasmosis do not develop OHS.
Medicine Used
Treatment for OHS focuses on managing the inflammation and preventing further damage to the retina, particularly from choroidal neovascularization (CNV), the growth of new, abnormal blood vessels under the retina. Common treatments include:
Anti-VEGF (Vascular Endothelial Growth Factor) injections: These medications (e.g., ranibizumab, bevacizumab, aflibercept) are injected directly into the eye to inhibit the growth of new blood vessels. This is the primary treatment for active CNV.
Corticosteroids: These can be given as eye drops, injections, or oral medications to reduce inflammation. Steroids are used with caution, as they can have side effects.
Laser photocoagulation: In certain cases, laser treatment may be used to seal off abnormal blood vessels, although this can sometimes create blind spots.
Photodynamic therapy (PDT): This involves injecting a light-sensitive drug into the bloodstream, which is then activated by a laser to destroy abnormal blood vessels.
Is Communicable
No, Ocular Histoplasmosis Syndrome is not communicable. It is not spread from person to person. It is a result of an individual's immune response to a previous histoplasmosis infection.
Precautions
Since OHS is a result of a previous Histoplasma infection, primary prevention focuses on minimizing exposure to the fungus. This can be difficult, as the fungus is widespread. General precautions include:
Avoiding activities that disturb soil in areas known to have Histoplasma, such as cleaning chicken coops or exploring caves.
Wearing a mask when disturbing soil in potentially contaminated areas.
No specific precautions are effective in preventing the development of OHS in someone who has already been infected with Histoplasma. Regular eye exams are crucial for early detection and treatment if OHS develops.
How long does an outbreak last?
OHS isn't an "outbreak" in the traditional sense of a contagious disease spreading rapidly. Histoplasmosis infection (the initial infection that can lead to OHS) can occur at any time when someone is exposed to the fungal spores. However, the *ocular* manifestations of OHS can be chronic and recurrent. CNV can develop, regress with treatment, and then reactivate later. The duration of active CNV and inflammation varies from person to person and depends on the severity of the condition and the effectiveness of treatment.
How is it diagnosed?
Diagnosis of OHS involves a comprehensive eye exam by an ophthalmologist. Key diagnostic procedures include:
Dilated fundus examination: To visualize the retina and choroid for characteristic signs of OHS, such as histospots (small, atrophic scars), peripapillary atrophy (thinning of the tissue around the optic nerve), and CNV.
Optical coherence tomography (OCT): This imaging technique provides detailed cross-sectional images of the retina and choroid, helping to identify and monitor CNV, fluid accumulation, and other structural changes.
Fluorescein angiography (FA): A dye is injected into the bloodstream, and images of the retinal blood vessels are taken to detect leakage and abnormal blood vessel growth.
Indocyanine green angiography (ICGA): Similar to FA, but uses a different dye that penetrates deeper into the choroid, allowing for better visualization of choroidal blood vessels.
Visual field testing: To assess for blind spots or other visual field defects.
Patient History: Includes questioning about residence and activities in areas where Histoplasma capsulatum is endemic.
Timeline of Symptoms
The timeline of OHS symptoms is variable:
Initial Histoplasmosis Infection: Most people have no symptoms or mild, flu-like symptoms.
Latency Period: Years or even decades can pass between the initial histoplasmosis infection and the development of OHS.
Early OHS: The first sign may be the incidental finding of histospots during a routine eye exam. These spots are usually asymptomatic.
Active OHS (CNV Development): Symptoms like blurred vision, distorted vision, and blind spots usually appear when CNV develops. The onset of these symptoms can be gradual or sudden.
Recurrence: CNV can recur even after successful treatment, leading to fluctuating vision.
Important Considerations
Regular Eye Exams: People living in or who have lived in areas where histoplasmosis is endemic (e.g., the Ohio and Mississippi River valleys) should have regular dilated eye exams, especially if they experience any vision changes.
Prompt Treatment: Early diagnosis and treatment of CNV are crucial to minimize vision loss.
Long-Term Monitoring: OHS is a chronic condition that requires ongoing monitoring for recurrence.
No Cure: While treatments can effectively manage CNV and inflammation, there is currently no cure for OHS.
Differential Diagnosis: It is essential to rule out other eye conditions that can cause similar symptoms, such as age-related macular degeneration (AMD).
Geographic Prevalence: Being aware of the prevalence of histoplasmosis in certain geographic areas is important for risk assessment.