Presumed ocular histoplasmosis syndrome (POHS) is an eye disorder that doctors believe is a complication of a fungal infection with the Histoplasma species. Although this has yet to be proven, this is why the diagnosis is “presumed.”

An infection with Histoplasma (histoplasmosis) typically affects the lungs. However, it can cause long-term complications or spread to other organs in some people. Very rarely, it can lead to problems within the eye.

Early treatment for POHS is very important since it can prevent eye scarring and vision loss.

Read on to learn more about presumed ocular histoplasmosis.

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Histoplasmosis occurs due to an infection with a fungus called Histoplasma capsulatum. The infection can move away from the lungs and to the eyes. The fungus travels in the bloodstream to reach the choroidal vessel, causing eye problems, such as POHS.

Many people may be unaware that they have histoplasmosis and most experience no symptoms.

POHS can cause scarring at the back of the eye, around the retina, and the optic nerve. This, in turn, can cause new blood vessels to accumulate and cause vision changes or loss.

However, the link between Histoplasma and POHS is still controversial. More research into how this fungus might cause POHS, and its impact on vision loss, is necessary.

Learn more about histoplasmosis.

According to the Centers for Disease Control and Prevention (CDC), scientists do not have reliable statistics on this disease. POHS likely affects hundreds of thousands of people each year.

A study looking at people with private health insurance in 2014 found that 13 per 100,000 people had POHS. Of people diagnosed with POHS, 1 in 4 had new blood vessels in the eye that could lead to vision loss. This study likely underestimates the real prevalence since it only looked at a small, and comparatively, privileged group.

Some people with POHS have no symptoms, especially in the early stages. While a person would not notice if they have choroidal neovascularization, a condition that leads to new blood vessels forming in the eye, they would notice its effects, such as:

  • changes in their vision, such as blind spots
  • distortions in the shape of objects, such as straight lines that look crooked
  • blurred vision

An eye specialist can detect choroidal neovascularization though. They may also notice that small white spots occur in the eye.

POHS does not usually cause pain.

A person may suspect they have this condition if they have a history of histoplasmosis and develop vision problems. However, not all people with a history of histoplasmosis will have had symptoms or a diagnosis. As such, a person cannot rule out POHS solely because they think they have never had histoplasmosis.

Therefore, people with any concerns or changes in their eye health should visit a specialist.

The leading theory for explaining POHS is that it begins when people inhale spores from the fungus Histoplasma capsulatum.

This fungus is endemic in the soil in certain regions of the United States, especially in the Ohio and Mississippi River valleys. As many as 60% of adults in these regions test positive on a skin test.

Certain activities that involve handling soil with bird or bat droppings may expose a person to the fungus and increase their likelihood of inhaling spores. For example, cleaning chicken coops or gardening.

POHS is more common in areas where histoplasmosis is common. Antifungal treatments may not be necessary, as scientists believe the fungus is not present in the eyes.

Risk factors

Not everyone who inhales the spores will develop histoplasmosis or POHS, but anyone can. Certain factors may increase a person’s risk of developing these conditions, such as those who:

  • have a weakened immune system, for example, someone living with HIV or AIDS
  • are 55 or older
  • are a smoker
  • have a preexisting lung condition

To diagnose POHS, a doctor will ask a person about their recent symptoms and examine their eyes.

In most cases, they dilate the pupils to look at the back of the eyes. A doctor may also use specific imaging tests, such as ocular coherence tomography (OCT) and fluorescein angiography (FA), to see the vessels at the back of the eye.

If there is scarring or atypical blood vessel growth, a doctor will usually diagnose POHS.

A doctor may also recommend a skin test for histoplasmosis, which can show whether a person has a history of exposure to the fungus.

Not everyone with POHS requires treatment. However, those who experience changes to their vision, or those who are vulnerable, may benefit from certain interventions.

Rather than focussing on the fungal infection, POHS treatment reduces the inflammation and damage to the eyes.

Injectable drugs can stop the overgrowth of the blood vessels. A doctor applies numbing drops to the eye before the injection, so a person should not feel anything. Examples of anti-vascular endothelial growth factor (anti-VEGF) drugs include:

A doctor may sometimes use photodynamic therapy, which uses light energy and light-sensitive drugs, alongside anti-VEGF medications.

A doctor can also perform laser surgery to stop extra blood vessels from growing.

The outlook for POHS is generally good if a person receives early treatment for the blood vessels before they cause harmful scars.

In some cases, even if scarring is already present, it may be possible to reverse some vision loss. Eye specialists may also continue monitoring symptoms, for example, whether the white spots in the eye are worsening.

Experts continue to poorly understand presumed ocular histoplasmosis syndrome. While doctors think histoplasmosis causes it, there is no direct proof of this claim. No one knows why some people with histoplasmosis exposure develop POHS and others do not.

People who have eye health issues should seek care as early as possible. The outlook for many issues, including POHS, is best with early intervention. The right treatment can prevent harmful scarring and save a person’s vision.