Ocular Histoplasmosis

A disease that results from infection by airborne spores of a fungus.

Williamson Eye Insititute Histoplasmosis is a disease caused when airborne spores of the fungus Histoplasma capsulatum are inhaled into the lungs, the primary infection site. This microscopic fungus, which is found throughout the world in river valleys and soil where bird or bat droppings accumulate, is released into the air when soil is disturbed by plowing fields, sweeping chicken coops, or digging holes. In the United States, it is most commonly found in the Mississippi-Ohio River Valley region. Any symptoms that might occur are often similar to those from a common cold. In fact, if you had histoplasmosis symptoms, you might dismiss them as those from a cold or flu, since the body’s immune system normally overcomes the infection in a few days without treatment.

However, histoplasmosis, even mild cases, can later cause a serious eye disease called presumed ocular histoplasmosis syndrome (POHS), a leading cause of vision loss in Americans ages 20 to 40. The fungus causes small areas of inflammation and scarring of the retina which are called histo spots.

Despite significant advances in treatments, POHS still cannot be cured. Once contracted, POHS remains a threat to a person’s sight for their lifetime. People with POHS who experience one bout of abnormal blood vessel growth may have recurrent episodes. Each recurrence can damage vision and may require additional therapy. It is crucial to detect and treat POHS as early as possible before it causes significant visual impairment.

Symptoms may include:

Many patients with histo spots in their eyes have no symptoms. Others may experience the following:

  • Distorted vision
  • Blind spots
  • Scars in the retina, ranging in severity

Treatment options include:

  • Observation and management
  • Thermal Laser Therapy
  • Photodynamic Therapy
  • Intraocular Injections
  • Submacular Surgery
  • Low Vision Aids

Ocular histoplasmosis requires no treatment except when abnormal blood vessels develop in the central retina. Regular eye exams and routine use of an Amsler Grid to monitor central vision is recommended for anyone with histo spots.

By looking at an Amsler grid, if the macula has been damaged, the vertical and horizontal lines of the grid may appear curved, or a blank spot may seem to appear. If there are changes in the grid from baseline, call within 24 hours to set up an appointment.

Photocoagulation therapy uses a small, powerful beam of light to destroy the abnormal blood vessels as well as the overlying retinal tissue. Although the destruction of retinal tissue during the procedure itself causes some loss of vision, this is done to try to protect the fovea. Photocoagulation can reduce future vision loss from POHS by more than half. The treatment is most effective when:

  • The CNV has not grown into the center of the fovea, where it can affect vision.
  • The eye care professional is able to identify and destroy the entire area of CNV.

Laser photocoagulation usually does not restore lost vision. However, it does reduce the chance of further CNV growth and any resulting vision loss.

Photodynamic therapy (PDT or OPT) was initially developed for CNV due to macular degeneration. This treatment uses a light-sensitizing dye injected into a vein to more selectively destroy the vessels and spare the overlying retinal tissue. This is generally used for vessels that involve the direct center of the retina or fovea.

 

The dye, called verteporfin (Visudyne), is infused into the patient’s arm over a ten minute period. Five minutes later a laser is used to treat the vessels for an 83 seconds. Because this photosensitizing dye is injected into a patient’s vein, the dye travels throughout their body and there are strict restrictions to avoid direct sunlight for five days. This treatment does not eliminate the original cause of the vessel growth, and patients generally need more than one treatment.

Intravitreal Kenalog

Triamcinolone acetate (Kenalog) is a long-acting anti-inflammatory steroid which is used in ocular histoplasmosis for its action against blood vessel growth and retinal swelling. It may be difficult to differentiate between inflammatory and early neovascular lesions, but kenalog has activity against both. Four milligrams are injected through the white part of the eye directly into the vitreous cavity. Topical and subconjunctival anesthesia make this a quick and painless procedure. The drug lasts in the eye for three months on average. Patients are followed monthly to monitor intraocular pressure which may rise after this injection.

 

Intravitreal Bevacizumab (Avastin)

Bevacizumab is an anti-VEGF antibody that was originally approved by the FDA for treatment of colorectal cancer. Through pioneering work at the Bascom Palmer Eye institute in Miami, Dr. Phil Rosenfeld and colleagues have shown this to be a very effective treatment for exudative macular degeneration. Based on a similar mechanism of choroidal neovascularization, patients with POHS have also been successfully treated with this medication. Because this is considered by most insurance carriers to be experimental, this involves out-of-pocket expenses for patients in Indiana.

Virata’s mentors, Dr. Matthew Thomas and Dr. Henry Kaplan, are credited with developing the technique at the Barnes Retina Institute and Washington University in St. Louis.

The technique involves removing the vitreous gel, creating a small retinal detachment, gently pulling the abnormal vessels from under the retina, and reattaching the retina. Unfortunately, this also does not address the underlying trigger of the CNV and recurrences can be quite common.

Scientists and engineers have developed many useful devices to help people with severe visual impairment in both eyes. These devices, called low vision aids, use special lenses or electronics to create enlarged visual images. An eye care professional can suggest sources that provide information on counseling, training, and special services for people with low vision. Many organizations for people who are blind also serve those with low vision.

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