Histoplasmosis is a fungal infection caused by Histoplasma capsulatum. This fungus is often found in soil that contains bird or bat droppings.
One possible complication of histoplasmosis is ocular histoplasmosis syndrome (OHS) or presumed ocular histoplasmosis syndrome (POHS). This occurs when histoplasmosis affects your eyes, resulting in chorioretinal scars and possible choroidal neovascularization (CNV).
The key to preserving vision is early detection and treatment if you have histoplasmosis in your eye.
Histoplasmosis and its systemic manifestations
Histoplasmosis starts as a systemic infection, meaning it can affect the entire body.
The systemic infection
You get histoplasmosis by breathing in fungal spores. It mainly affects the lungs, and in many people, it either has no symptoms or the symptoms are very mild.
Histoplasmosis is endemic to certain parts of the world, especially the Ohio and Mississippi River valleys, also known as the “Histo Belt.” In these areas, a large percentage of people have positive skin tests for histoplasmosis, indicating that they’ve been exposed to the fungus at some point.
How it spreads to the eye
In rare cases, the Histoplasma capsulatum fungus can travel through the bloodstream to other parts of the body.
Ocular histoplasmosis syndrome (OHS) or presumed ocular histoplasmosis syndrome (POHS) happens when the fungus makes its way to the eyes, causing scarring in the choroid and retina. It’s worth noting that most people with POHS don’t even realize they ever had a systemic histoplasmosis infection.
Ocular Histoplasmosis Syndrome (OHS/POHS): Pathology and Pathophysiology
Ocular histoplasmosis syndrome, or presumed ocular histoplasmosis syndrome (OHS/POHS), has some characteristic features that can help doctors make a diagnosis.
Characteristic Features of OHS/POHS
- Histo spots: These small, atrophic chorioretinal scars are a telltale sign. Often, they don’t cause any symptoms early on.
- Peripapillary atrophy (PPA): This refers to atrophy, or wasting, around the optic nerve.
Choroidal Neovascularization (CNV)
One of the most serious complications of ocular histoplasmosis is the development of choroidal neovascularization, or CNV.
- Development of CNV: This involves the growth of abnormal blood vessels that originate in the choroid. CNV is the main reason people with OHS/POHS experience vision loss.
- Pathophysiology of CNV: The CNV vessels can leak fluid and blood into the macula, which distorts the structure of the retina and causes vision to deteriorate.
Role of Inflammation and Immune Response
- Inflammation in the choroid: OHS/POHS causes inflammation in the choroid, the layer of blood vessels between the retina and sclera.
- Potential autoimmune component: Certain HLA haplotypes, such as DRw2 and B7, may be associated with POHS, which suggests there may be an autoimmune component at work.
Who’s at risk for ocular histoplasmosis?
The biggest risk factor for ocular histoplasmosis syndrome (OHS) is where you live. People living in areas where Histoplasma is common are more likely to develop the condition.
For example, up to 90% of adults who live in the “Histo Belt” (the Ohio and Mississippi River valleys) have been infected with Histoplasma at some point.
OHS is also more common in:
- People between 20 and 50 years old
- Men
- Caucasians
Finally, smoking and low education levels may increase your risk of developing choroidal neovascularization (CNV) if you have presumed ocular histoplasmosis (POHS).
Clinical presentation and diagnosis of OHS/POHS
So, how does someone find out they have ocular histoplasmosis syndrome?
Symptoms
In the early stages, OHS/POHS is often asymptomatic, meaning the person doesn’t notice any symptoms. In fact, the condition may not be detected until choroidal neovascularization (CNV) occurs.
If CNV develops, symptoms may include:
- Blurred vision
- Metamorphopsia (wavy or distorted vision)
- Blind spots (scotomas)
Diagnostic procedures
Several diagnostic procedures are used to detect and monitor OHS/POHS:
- Fundoscopic examination. In this dilated eye exam, the ophthalmologist will look for histo spots, peripapillary atrophy (PPA), and CNV.
- Fluorescein angiography (FA). FA is used to detect and characterize CNV.
- Optical coherence tomography (OCT). OCT provides cross-sectional images of the retina and choroid to assess CNV and macular edema.
- Amsler grid. This simple tool allows patients to monitor their vision for distortion at home.
Management and Treatment Strategies for OHS/POHS-Related CNV
If you’ve been diagnosed with CNV related to presumed ocular histoplasmosis syndrome (POHS), there are several ways your ophthalmologist may choose to manage and treat the condition. Here are a few of the most common approaches.
Medical Therapies
Anti-VEGF Therapy
Anti-VEGF (vascular endothelial growth factor) therapy is usually the first treatment doctors turn to when treating CNV. These medications include bevacizumab (Avastin), ranibizumab (Lucentis), and aflibercept (Eylea). They work by blocking neovascularization and decreasing leakage in the eye.
Studies have shown that anti-VEGF therapy improves visual acuity in people with POHS-related CNV.
Laser Photocoagulation
Before anti-VEGF medications were available, laser photocoagulation was the go-to treatment for CNV. During this procedure, the doctor uses a laser to destroy the CNV.
Photodynamic Therapy (PDT)
Another option for CNV is photodynamic therapy (PDT). This treatment combines a photosensitizing drug with a nonthermal laser to reduce further vision loss from OHS.
Corticosteroids
Corticosteroids may be used along with other treatments to tamp down inflammation in the eye.
Surgical Interventions
In some situations, surgery may be warranted.
Submacular Surgery and Macular Translocation
Submacular surgery and macular translocation are rarely used to treat CNV.
Monitoring and Follow-Up
Even after treatment, careful monitoring of your eyes is key to preserving your vision.
Regular Eye Exams
If you have histoplasmosis scars in your macula, it’s important to get regular eye exams so your doctor can check your central vision.
Amsler Grid Monitoring
Your doctor may ask you to use an Amsler grid at home to monitor for any changes in your vision between appointments.
What is the outlook for ocular histoplasmosis?
If you catch and treat choroidal neovascularization (CNV) early, the outlook for your vision is generally good. With proper treatment and monitoring, the long-term prognosis is excellent for most people.
However, CNV can come back, so you’ll need to stay in touch with your eye doctor for consistent monitoring and treatment.
Also, treatments such as laser photocoagulation or anti-VEGF injections can lead to complications.
For people who experience significant vision loss, several low-vision aids and support systems are available. Resources and rehab programs can help you adapt to vision changes and continue to live an independent life.
Summary
Ocular histoplasmosis syndrome (OHS), also known as presumed ocular histoplasmosis syndrome (POHS), is a vision-threatening condition that can occur after someone has been infected with the histoplasmosis fungus. The hallmark features of OHS/POHS are histospots, peripapillary atrophy (PPA), and choroidal neovascularization (CNV).
If you have OHS/POHS, getting diagnosed and treated early for CNV is essential to preserving your sight.
If you live in an area where histoplasmosis is common or you know you’ve been infected with the fungus, you should have routine eye exams to look for signs of OHS/POHS.
With the latest diagnostic tools and treatment options, most people with OHS/POHS can maintain good vision and a high quality of life.