Presumed Ocular Histoplasmosis Syndrome (POHS)
Presumed ocular histoplasmosis syndrome (POHS) is a retinal condition associated with a previous exposure to Histoplasma capsulatum, a fungus commonly found in certain parts of the United States, especially the Ohio and Mississippi River valleys.
POHS can cause small scars in the retina and may lead to abnormal blood vessel growth beneath the macula, the central part of the retina responsible for sharp vision. These abnormal blood vessels can leak fluid or bleed, causing vision loss.
Many people exposed to histoplasmosis never develop eye problems, and most patients with POHS have no symptoms unless complications occur.
What Causes POHS?
POHS is believed to result from a prior exposure to the Histoplasma fungus. The fungus is commonly found in:
- Soil contaminated by bird or bat droppings
- Farms and rural areas
- Chicken coops
- Caves
The infection usually begins in the lungs and often causes few or no symptoms.
Years later, some individuals may develop characteristic scars in the retina associated with POHS.
Importantly, POHS itself is not an active eye infection. The retinal changes are thought to represent an old inflammatory response to prior exposure.
Who Is at Risk?
POHS is more common in people living in areas where histoplasmosis exposure is common, including:
- The Midwest
- The Mississippi River Valley
- The Ohio River Valley
Risk factors for vision-threatening complications include:
- Smoking
- Presence of retinal scars near the macula
- Development of abnormal blood vessels (choroidal neovascularization)
Symptoms of POHS
Most patients have no symptoms unless abnormal blood vessels develop beneath the retina.
Symptoms may include:
- Blurred central vision
- Distorted or wavy vision
- Dark spots in central vision
- Difficulty reading
- Sudden vision loss
Peripheral vision is usually normal.
Patients may first notice distortion when looking at straight lines or reading text.
How Is POHS Diagnosed?
A retinal specialist diagnoses POHS through a dilated eye examination and retinal imaging.
Classic findings of POHS include:
- Small punched-out retinal scars called “histo spots”
- Changes around the optic nerve
- Absence of significant inflammation inside the eye
Optical Coherence Tomography (OCT)
OCT creates detailed cross-sectional images of the retina and helps detect:
- Fluid beneath the retina
- Macular swelling
- Abnormal blood vessels
Fluorescein Angiography
This test uses fluorescent dye injected into a vein in the arm to identify leaking abnormal blood vessels.
Fundus Photography
Retinal photographs help document retinal scars and monitor progression over time.
Choroidal Neovascularization (CNV)
The main vision-threatening complication of POHS is choroidal neovascularization (CNV).
CNV occurs when abnormal blood vessels grow beneath the retina and leak fluid or blood.
Without treatment, CNV can cause:
- Scar tissue formation
- Permanent central vision loss
Fortunately, modern treatment has significantly improved outcomes for many patients.
Treatment for POHS
Treatment is usually only needed if CNV develops.
Anti-VEGF Injections
Anti-VEGF medications are the primary treatment for CNV caused by POHS.
These medications help:
- Reduce leakage
- Decrease retinal swelling
- Stabilize or improve vision
Common anti-VEGF medications include:
- Bevacizumab
- Aflibercept
- Ranibizumab
- Faricimab
Treatment often requires repeated injections over time.
Laser Treatment
Older forms of laser treatment were once commonly used but are less frequently needed today because anti-VEGF therapy is highly effective.
Photodynamic Therapy (PDT)
PDT laser may occasionally be used in selected cases.
What Is the Prognosis?
The outlook for POHS varies depending on whether CNV develops and how quickly treatment begins.
Many patients:
- Maintain good vision for years
- Never develop complications
- Respond well to anti-VEGF therapy
Untreated CNV can lead to permanent central vision loss.
Regular retinal monitoring and prompt evaluation of new symptoms are very important.
Living With POHS
Patients with POHS should:
- Monitor vision changes carefully
- Use an Amsler grid if recommended
- Keep regular retina appointments
- Avoid smoking
- Seek prompt care for new distortion or blurry vision
Early detection of CNV offers the best chance of preserving vision.
Frequently Asked Questions
Is POHS an active fungal infection?
No. POHS is not considered an active eye infection. It is believed to represent scarring related to prior exposure to histoplasmosis.
Can POHS cause blindness?
POHS mainly affects central vision if abnormal blood vessels develop beneath the retina. Early treatment greatly improves the chance of preserving vision.
Is POHS contagious?
No. POHS is not contagious and cannot spread from person to person.
More Information
For additional patient information, visit the American Society of Retina Specialists POHS Page
References