What is Presumed Ocular Histoplasmosis Syndrome (POHS)?
Presumed ocular histoplasmosis syndrome (POHS) is a disease of the eye that is believed to be due to infection with Histoplasma species.
Histoplasma is known to affect the lungs and can also lead to long-term complications in other organs and can also very rarely affect the eye. The fungus travels through the blood vessels and causes eye problems.
Many people do not know they have histoplasmosis as they may not experience any symptoms.
Presumed ocular histoplasmosis syndrome (POHS) can lead to scarring in the back of the eye, around the retina, and the optic nerve. This can cause the new blood vessels to accumulate and cause changes in vision or vision loss.(1)
The link between Histoplasma and Presumed ocular histoplasmosis syndrome (POHS) is still controversial and how the fungus may be causing POHS is not clear and needs more research.(2)
A study done in 2014 on 100000 found that 13 people had Presumed ocular histoplasmosis syndrome (POHS) and among them, 1 in 4 had new blood vessels that could lead to vision loss.(3)
Causes of Presumed Ocular Histoplasmosis Syndrome (POHS)
According to a leading theory, Presumed ocular histoplasmosis syndrome (POHS) begins when a person inhales the spores of the fungus Histoplasma capsulatum.(4) This fungus is endemic in the soil in certain regions of the United States, including the Mississippi and Ohio River valley. 60% of adults in these regions test positive on skin tests.(1)
Also, there are certain activities involving handling soil with bird and bat dropping, which may increase the likelihood of inhaling fungus.(5)
Presumed ocular histoplasmosis syndrome (POHS) is found to be common in areas where histoplasmosis is common. Antifungal treatment may not be needed as it was believed that fungus is not present in the eyes.
Not everyone who inhales spores develops histoplasmosis or Presumed ocular histoplasmosis syndrome (POHS). There are certain factors that may increase a person’s risk of developing these conditions, which include:
- A weakened immune system
- Being 55 years or older
- Having a pre-existing lung condition
Symptoms of Presumed Ocular Histoplasmosis Syndrome
Some people have no symptoms of Presumed ocular histoplasmosis syndrome (POHS) in the early stages. A person may not know if he has choroidal neovascularization but would notice the following symptoms:
- Blurred vision
- Changes in vision or blind spots
- Distortion in the shape of objects, such as straight lines appearing crooked.
An eye specialist may notice choroidal neovascularization on the eye as they may notice small white spots in the eye.(3)
A person may be suspected to have Presumed ocular histoplasmosis syndrome (POHS) if they have a history of histoplasmosis and develop vision problems. But this does not apply that every person with a diagnosis of Presumed ocular histoplasmosis syndrome (POHS) has a history of histoplasmosis. Therefore, if symptoms are seen the diagnosis of POHS cannot be ignored.
Diagnosis of Presumed Ocular Histoplasmosis Syndrome
For diagnosis, a person is enquired about the symptom by the doctor.(6) The pupils are dilated to look at the back of the eyes. Specific imaging tests such as ocular coherence tomography (OCT) and fluorescein angiography (FA) are performed to look at the vessels at the back of the eye.
If scarring or atypical blood vessels are detected the doctor may diagnose Presumed ocular histoplasmosis syndrome (POHS).
A skin test may also be recommended for histoplasmosis.
Treatment of Presumed Ocular Histoplasmosis Syndrome
Not everyone with Presumed ocular histoplasmosis syndrome (POHS) may need treatment. Some may experience vision changes and may benefit from certain interventions. Presumed ocular histoplasmosis syndrome (POHS) treatment does not focus on the treatment of fungal infection but on the inflammation that causes eye damage.
Injectable drugs can be helpful in stopping the overgrowth of the blood vessels. This is done by numbing the eyes before injection so people do not feel anything.
Sometimes photodynamic therapy may be used in which light energy and light-sensitive drugs are used along with anti-VEGF medications.
Laser surgery can be performed to stop extra blood vessels from growing.(6)
Outlook of Presumed Ocular Histoplasmosis Syndrome
The outlook for Presumed ocular histoplasmosis syndrome (POHS) is mostly good if a person receives early treatment for blood vessels before they get scarred.
In some cases, even with scarring, reversing the vision loss is possible. Regular eye monitoring is important, to keep the spots in the eye from worsening.