Ocular Histoplasmosis Syndrome (OHS) is a condition that affects the eyes and is associated with an earlier infection by the fungus Histoplasma capsulatum. Histoplasma capsulatum is a fungus found in soil, often in areas with bird or bat droppings. The infection typically occurs when individuals inhale airborne spores of the fungus. While most people who are exposed to Histoplasma do not develop symptoms, some may experience a respiratory illness known as histoplasmosis.
In a small percentage of individuals with a history of histoplasmosis, the infection can lead to Ocular Histoplasmosis Syndrome. OHS is characterized by the formation of small scars or lesions beneath the retina in the back of the eye. These scars can result in vision problems, including blind spots or distortion in the central vision.
The exact mechanism by which the fungus causes ocular complications is not fully understood. However, it is believed that the immune response triggered by the initial histoplasmosis infection can lead to inflammation and scarring in the eye.
Not everyone with a history of histoplasmosis will develop Ocular Histoplasmosis Syndrome, and the condition is more likely to occur in individuals who had a significant exposure to the fungus in the past. OHS is more common in certain geographic regions, including areas around the Mississippi and Ohio river valleys in the United States.
Regular eye examinations are crucial for individuals with a history of histoplasmosis, as Ocular Histoplasmosis Syndrome can lead to vision problems. Management and treatment may involve monitoring the condition, addressing symptoms, and, in some cases, using laser therapy to seal leaking blood vessels associated with the lesions. It’s essential for individuals at risk to work closely with eye care professionals to address any potential vision issues associated with OHS.
The fungus causes small areas of inflammation and scarring of the retina. These are called “histo spots” and may be found in both eyes. The affect on vision depends on the location of the scars. Scarring in the peripheral area of the retina may have little or no impact on vision, while a central scar affecting the macula may cause a prominent blind spot. The accompanying image shows a macular scar from histoplasmosis and also from an untreated choroidal neovascular membrane. This person has no central vision in the affected eye.
For reasons that remain unknown, a network of blood vessels may occasionally develop originating from the periphery of a pre-existing histoplasmosis scar. When this network encroaches upon the central field of vision, it can manifest symptoms of distortion and visual impairment. If the network extends directly beneath the central vision, it may lead to central vision loss. The accompanying image, captured through an indocyanine green angiogram, vividly illustrates the intricate network of abnormal blood vessels stemming from the old scar. In this case, the patient has experienced vision loss for approximately two weeks, likely triggered by a recent bleeding event that abruptly manifested symptoms.
Left untreated, the progression of blood vessel growth typically culminates in the formation of a scar, damaging the overlying retina and resulting in permanent vision loss. However, if intervention occurs early in the process, the growth of these blood vessels can be halted, preventing their transformation into a scar and averting further vision impairment.
Macular neovascularization (MNV) associated with Presumed Ocular Histoplasmosis Syndrome (POHS) can be managed with various treatment options. The goal of treatment is typically to prevent or reduce abnormal blood vessel growth and leakage in the macula, thereby preserving vision. Common treatment approaches include:
- Anti-VEGF Therapy: Anti-vascular endothelial growth factor (anti-VEGF) drugs, such as ranibizumab (Lucentis), aflibercept (Eylea), and bevacizumab (Avastin), are commonly used to treat macular neovascularization. These drugs work by inhibiting the activity of vascular endothelial growth factor, a protein that promotes the growth of new blood vessels. Anti-VEGF injections are typically administered directly into the eye.
- Laser Photocoagulation: Laser therapy, specifically focal laser photocoagulation, may be used to treat abnormal blood vessels in the macula. The laser is used to create small burns that seal off leaking blood vessels and reduce the risk of further damage. However, laser treatment is often less commonly used than anti-VEGF therapy.
- Photodynamic Therapy (PDT): PDT involves the use of a light-activated drug (verteporfin) and laser light to selectively damage abnormal blood vessels. This treatment may be considered in certain cases of macular neovascularization.
- Corticosteroids: In some instances, corticosteroids, either in the form of injections or implants, may be used to reduce inflammation and address macular neovascularization.
The choice of treatment depends on factors such as the size and location of the neovascularization, the extent of leakage, and the overall health of the eye. Additionally, individual patient factors and preferences may influence the decision-making process.
Early detection and prompt treatment are critical in managing macular neovascularization with POHS to maximize the chances of preserving vision and preventing further complications. The specific treatment plan is determined on a case-by-case basis after a comprehensive evaluation by an eye care professional. Patients should discuss their options and potential outcomes with their healthcare provider to make informed decisions about their eye care.