Presumed Ocular Histoplasmosis Syndrome: A Patient Guide
Understanding Presumed Ocular Histoplasmosis Syndrome
POHS is an eye condition associated with a fungus called Histoplasma capsulatum. This fungus is found in soil, especially in areas with bird or bat droppings. When a person breathes in the fungal spores, typically during childhood, the infection spreads through the bloodstream. The fungus can reach the choroid, a layer of blood vessels beneath the retina at the back of the eye.
The body fights off the infection, but small scars called 'histo spots' remain in the choroid long after the original illness resolves. These scars may stay quiet for years. The condition is called 'presumed' because researchers have not directly proven that H. capsulatum causes the eye findings, even though the link is strongly suspected.
When the fungus reaches the choroid, it causes a localized inflammatory reaction. This inflammation damages a thin barrier called Bruch's membrane, which sits between the choroid and the retinal pigment epithelium (a support layer for the retina). Small breaks develop in Bruch's membrane at the sites of the histo spots.
In some patients, abnormal blood vessels grow through these breaks. This growth is called choroidal neovascularization (CNV). These new blood vessels are fragile and prone to leaking fluid or blood beneath the retina. When CNV develops in or near the macula, the central part of the retina responsible for sharp vision, it can cause serious vision loss.
Retina specialists identify POHS by a characteristic combination of findings during an eye exam. The three hallmark features are:
- Atrophic chorioretinal scars (histo spots) scattered in the retina
- Peripapillary atrophy, which is tissue damage around the optic nerve head
- The absence of vitritis, meaning there is no active inflammation in the gel-like interior of the eye
The lack of active inflammation inside the eye is an important distinction. It helps retina specialists separate POHS from other conditions that cause similar-looking scars but also produce visible inflammation.
Who Is Affected and Risk Factors
POHS is most common in the United States in states along the Ohio and Mississippi River valleys. The fungus thrives in the moist soil of these regions. People who have lived in or traveled through these areas are more likely to have been exposed to Histoplasma capsulatum.
The overall age- and sex-adjusted incidence of POHS in a predominantly White U.S. county population was approximately 1.35 per 100,000 per year, or roughly 1 in 74,000 patients (PMC, 2022). Vision-threatening complications from POHS most frequently appear between the second and fifth decades of life, typically in people between their 20s and 50s.
Not everyone with histo spots will develop the abnormal blood vessels that threaten vision. Choroidal neovascularization occurred in 17.4% of affected eyes in one study population (PMC, 2022). Several factors increase the risk of developing CNV.
- Smoking is the most significant risk factor. The odds of a smoker developing CNV secondary to POHS are nearly 3 times those of a nonsmoker (PubMed, 2011).
- Increasing age raises the likelihood of CNV forming at the sites of existing histo spots.
- Lower levels of formal education have been statistically associated with higher rates of CNV.
- Rural residence is independently correlated with POHS development.
- Diabetes may also be correlated with POHS without CNV.
Smoking deserves special emphasis because it is the strongest modifiable risk factor for CNV in POHS. Quitting smoking is one of the most important steps a person with histo spots can take to reduce the chance of vision-threatening complications. If you have been diagnosed with POHS or live in an endemic area, talk with your primary care provider about smoking cessation resources.
Signs and Symptoms
Many people with histo spots have no symptoms at all. The small scars sit quietly in the choroid without affecting vision. These individuals may not know they have POHS unless a retina specialist or eye care provider notices the spots during a routine dilated eye exam. Asymptomatic POHS does not require treatment, but it does require monitoring.
When abnormal blood vessels begin to grow beneath the macula, symptoms can develop quickly. Recognizing these changes early is critical because prompt treatment offers the best chance of preserving vision. Key warning signs include:
- Metamorphopsia, which means straight lines appear wavy or distorted
- Blurred central vision that does not improve with glasses
- A central or paracentral scotoma, which is a blind spot in or near the center of your visual field
- Painless loss of vision in one eye
During a retina exam, a macular lesion that changes in color from yellow to gray-green may signal the development of CNV. Any new visual distortion or blurriness in a person known to have POHS should be evaluated by a retina specialist promptly.
Retina specialists often recommend that patients with known histo spots use an Amsler grid to monitor their vision daily. An Amsler grid is a simple chart with a grid of straight lines and a central dot. You cover one eye, look at the dot, and check whether any lines appear wavy, broken, or missing. If you notice any changes, contact a retina specialist as soon as possible.
Diagnosis and Testing
The first step in diagnosing POHS is a thorough dilated eye exam. A retina specialist examines the inside of the eye using specialized lenses and lights. During this exam, the specialist looks for the classic triad of histo spots, peripapillary atrophy, and the absence of inflammation inside the eye. If all three features are present, a clinical diagnosis of POHS is made.
When CNV is suspected, additional imaging helps confirm the diagnosis and guide treatment decisions. The most common tests include:
- Optical coherence tomography (OCT), which uses light waves to create detailed cross-sectional images of the retina, revealing fluid or thickening caused by leaking blood vessels
- Fluorescein angiography (FA), in which a fluorescent dye is injected into a vein in the arm and photographs are taken as the dye passes through the blood vessels in the retina, highlighting areas of leakage
- OCT angiography (OCTA), a newer non-invasive imaging method that can detect abnormal blood vessel networks without the need for dye injection
Several other eye conditions can look similar to POHS. These include age-related macular degeneration, multifocal choroiditis, and other inflammatory conditions of the choroid. A retina specialist considers the patient's history, geographic background, and exam findings to distinguish POHS from these other diagnoses. The absence of vitreous inflammation is a particularly helpful clue.
Treatment Options
Anti-VEGF (vascular endothelial growth factor) therapy has become the primary treatment for CNV caused by POHS. These medications block the signals that drive abnormal blood vessel growth and leakage. They are delivered as intravitreal injections, meaning the medication is injected directly into the gel-like interior of the eye.
Common anti-VEGF medications used for POHS-related CNV include Eylea (aflibercept), Lucentis (ranibizumab), and Avastin (bevacizumab). Avastin is FDA-approved for cancer treatment and is used off-label for eye conditions, including POHS. It is important to note that no anti-VEGF agent is currently FDA-approved specifically for POHS. However, these medications are widely used and supported by clinical evidence.
The HANDLE study examined different dosing schedules of intravitreal aflibercept for POHS-related CNV. At 12 months, researchers found no statistically significant difference in visual or anatomic outcomes between patients who received a sustained-dosing regimen (an average of 7.5 injections) and those treated on an as-needed basis (an average of 4.6 injections). These results suggest that individualized, as-needed treatment may be a reasonable approach for some patients, potentially reducing the total number of injections while maintaining good outcomes.
Photodynamic therapy (PDT) is a light-activated drug treatment that has been FDA-approved for CNV in POHS. During PDT, a light-sensitive medication called verteporfin is injected into a vein. A low-energy laser is then directed at the abnormal blood vessels in the eye, activating the drug and sealing the vessels. PDT was a standard treatment before anti-VEGF therapy became widely available. It may still be used in certain cases, sometimes in combination with anti-VEGF injections.
If a retina specialist finds histo spots or peripapillary atrophy but no CNV, treatment is typically not needed. Instead, the specialist will recommend regular dilated eye exams and daily self-monitoring with an Amsler grid. The goal is to detect any new blood vessel growth as early as possible so treatment can begin before significant vision loss occurs.
What to Expect
If CNV develops and anti-VEGF treatment is recommended, the injection is performed in the retina specialist's office. The eye is numbed with anesthetic drops, and the surface is cleaned with an antiseptic solution. A very fine needle is used to inject the medication into the vitreous cavity. Most patients report feeling pressure or mild discomfort during the procedure. The injection itself takes only a few seconds.
After the injection, some patients experience temporary floaters, mild redness, or a gritty sensation. Serious complications such as infection are rare. Your retina specialist will provide specific instructions on what to watch for after the procedure.
Anti-VEGF treatment for POHS-related CNV often begins with a series of injections given every four to six weeks. After the initial loading phase, your retina specialist may extend the interval between injections or switch to an as-needed schedule based on how your eye responds. Regular follow-up visits that include OCT imaging help the specialist monitor for fluid, blood vessel activity, and changes in vision.
Some patients achieve stable results and can stop injections for a period, while others may need ongoing treatment. CNV can recur months or even years after initial treatment, so continued monitoring remains important.
Early detection and treatment of CNV offer the best chance of preserving central vision. Many patients who receive timely anti-VEGF therapy maintain or improve their vision. However, outcomes depend on factors such as the size and location of the CNV, how quickly treatment begins, and individual response to the medication. Some degree of permanent vision change may occur if the macula has already been damaged before treatment starts.
Living With POHS
Living with POHS means staying alert to changes in your vision. Using an Amsler grid every day is one of the simplest and most effective ways to catch problems early. Check each eye separately and look for new waviness, blurring, or missing areas in the grid. Keep the grid in a place where you will remember to use it, such as on the refrigerator or next to your bathroom mirror.
Because smoking nearly triples the risk of developing CNV in POHS, quitting smoking is the single most impactful lifestyle change you can make. Maintaining overall cardiovascular health through regular exercise, a balanced diet, and management of conditions like diabetes and high blood pressure may also support eye health. Wearing UV-protective sunglasses outdoors is a reasonable general practice for eye protection.
A diagnosis of POHS can cause anxiety, especially if you have already experienced some vision changes. It can be helpful to learn as much as you can about the condition and to maintain open communication with your retina specialist. Low vision resources and rehabilitation services are available if vision loss does occur. These services can help you adapt daily activities and maintain independence.
When to See a Retina Specialist
If you have been told you have histo spots or peripapillary atrophy, keep all scheduled follow-up appointments with your retina specialist. Even without symptoms, regular dilated exams allow for early detection of CNV before it causes noticeable vision loss. Your specialist will determine how often you need to be seen based on your individual risk factors and exam findings.
Contact a retina specialist or go to the emergency room immediately if you experience any of the following:
- Sudden new distortion of straight lines in one eye
- A new blind spot or dark area in your central vision
- Sudden blurring of central vision that does not clear
- Any rapid change in the vision of an eye known to have POHS
These symptoms may indicate that CNV has developed or worsened. Prompt evaluation and treatment provide the best opportunity to limit vision loss.
Questions and Answers
There is no proven way to prevent POHS if you live in or have traveled through the Ohio or Mississippi River valleys. Histoplasma capsulatum is widespread in the soil of these regions, and most exposures occur during childhood without causing noticeable illness. The most effective strategy is awareness. If you know you have been exposed or live in an endemic area, regular dilated eye exams can detect histo spots early. Avoiding smoking significantly reduces the risk of the most serious complication, choroidal neovascularization.
Not necessarily. Treatment duration for POHS-related CNV varies from person to person. Some patients respond well to a course of anti-VEGF injections and can eventually stop treatment, with continued monitoring. Others may need periodic injections over a longer time frame if CNV recurs. The HANDLE study showed that as-needed dosing can produce outcomes comparable to more frequent dosing schedules, which may reduce the overall number of injections required. Your retina specialist will tailor your treatment plan based on how your eye responds.
No. Although both conditions can involve choroidal neovascularization and threaten central vision, they have different causes and typically affect different age groups. POHS is associated with a prior fungal infection and tends to appear in younger adults, often between the ages of 20 and 50. Age-related macular degeneration is a degenerative condition primarily affecting people over 50. The treatment for CNV in both conditions is similar, relying on anti-VEGF injections, but the underlying disease processes are distinct.
Yes. Histo spots can be present in both eyes because the fungus spreads through the bloodstream during the initial infection. However, vision-threatening CNV does not necessarily develop in both eyes, and it may appear in one eye years before the other. If you have POHS in one eye, your retina specialist will monitor both eyes carefully during follow-up visits.
POHS-related CNV primarily affects central vision, which is used for reading, recognizing faces, and other detail-oriented tasks. Peripheral (side) vision is typically preserved. With early detection and treatment, many patients maintain functional central vision. Complete blindness from POHS is uncommon, especially with modern anti-VEGF therapy. However, delayed treatment can result in significant and lasting central vision loss, which is why prompt evaluation of any new symptoms is so important.