Presumed Ocular Histoplasmosis Syndrome (POHS)
Presumed ocular histoplasmosis syndrome (POHS) is a condition that can cause vision loss. Many scientists believe POHS could be a long-term complication of histoplasmosis. However, no one has completely proven that Histoplasma (the fungus that causes histoplasmosis) causes POHS.1 People can get histoplasmosis after breathing in the microscopic fungal spores from the air, but most people who breathe in the spores don’t get sick. Scientists are still not sure exactly how Histoplasma spreads from a person’s lungs to affect their eyes in POHS. Some people with signs of POHS in their eyes never have any symptoms, but other people can lose their vision because of it.
What are the symptoms of POHS?
People with POHS can have:
- Small white spots that can appear deep inside the eye. Only an eye care professional can identify these spots.
- Choroidal neovascularization, a condition in which new blood vessels form inside the eye. This condition can cause vision loss.
Where is POHS most common?
In the United States, most patients with POHS live where histoplasmosis is common, in areas around the Ohio and Mississippi River Valleys.
How common is POHS?
Based on the large population living in areas where histoplasmosis is most common, POHS could potentially impact hundreds of thousands of people in the United States.1 However, scientists don’t know the exact number of people who have POHS or how many people lose their vision from it. One study found that the rate of POHS among people with private health insurance was 13 cases per 100,000 people in 2014 (map).1 This study also showed that 1 in 4 people with POHS had choroidal neovascularization (new blood vessels inside the eye that can cause vision loss).
What is the treatment for POHS?
Some people with POHS do not need any treatment. An eye care professional might want to monitor the small white spots in the eye to make sure they do not get worse over time. For people who have vision loss from POHS, injections into the eye with a treatment called anti-vascular endothelial growth factor can help. Another treatment option called photodynamic therapy uses a laser.
For Healthcare Professionals
The clinical manifestations of POHS include:
- “Punched out” round chorioretinal scars
- Peripapillary atrophy
- The absence of vitritis (i.e., inflammation of the vitreous cavity of the eye)
- Choroidal neovascularization (CNV)
For some patients, chorioretinal scarring does not impair vision and only requires routine monitoring. Patients with both POHS and CNV often experience vision loss; treatment options include intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections or photodynamic therapy (PDT).
Although scientists are still not sure exactly how Histoplasma spreads from a person’s lungs to affect their eyes in POHS, scientists do not believe that people with POHS have active fungi in their eyes. As a result, unlike other fungal infections, antifungal medications are not typically recommended as treatment for POHS. However, disseminated histoplasmosis infections involving the eye do require antifungal treatment. These infections are distinct from POHS and have rarely been reported.
Increased awareness surrounding POHS and histoplasmosis is one of the most important ways to improve early recognition and prevention and to reduce delays in diagnosis and treatment.
Overall, more research is needed about:
- Histoplasma as a potential cause of POHS
- The prevalence of and risk factors for POHS
- The personal and public health impact of POHS-associated vision loss
- Benedict K, Shantha JG, Yeh S, Beer KD, Jackson BR. Presumed ocular histoplasmosis syndrome in a commercially insured population, United Statesexternal icon. PLoS One. 2020 Mar 13