What You Should Know About Ocular Histoplasmosis

What is the Ocular Histoplasmosis Syndrome?
The fungus is inhaled early in life and causes a usually asymptomatic and self-limited infection throughout the body, including the lungs and choroid (the vascular layer lining the retina). For unknown reasons, several decades after the initial infection, the choroidal scars may develop abnormal blood vessels (choroidal neovascularization) which leak fluid and blood. This leakage can only be seen on a careful, dilated eye examination since the eye looks normal from the outside. Distorted central vision and loss of reading vision occurs when the leakage involves the macula.

Normal Macula.		Histoplasmosis with scarring around the nerve and in the macular center.

The goals of treatment are to prevent choroidal neovasculatization (CNVM) from spreading into the macular center (laser photocoagulation), or limit the size of and leakage from the CNVM once it reaches the macular center (photodynamic therapy, vascular endothelial growth factor inhibitors).

Who gets the Ocular Histoplasmosis Syndrome?
People who live in endemic areas, such as the Ohio-Mississippi river basin, who are exposed to the histoplasmosis fungus early in life are at greatest risk for developing eye problems later in life. A person with ocular histoplasmosis cannot infect other people since the organisms die soon after the initial infection. Adults who move to endemic areas, although they may get infected with the histoplasmosis fungus, do not usually develop eye disease.

What are the symptoms of the Ocular Histoplasmosis Syndrome?
People usually have no eye symptoms during the initial infection. The choroidal scars that later form also do not usually cause any symptoms. If leakage and bleeding involves the reading area of vision (the macula), symptoms such as distortion and loss of reading vision occur. Patients never go completely blind, since the part of the eye responsible for peripheral vision is not affected by this disease.

Normal Vision.		Ocular Histoplasmosis.

Patients are often asked to check their central vision every day with an Amsler grid. This grid is a pattern that resembles a checkerboard. You will be asked to cover one eye and stare at a black dot in the center of the grid.  While staring at the dot, you may notice that the straight lines in the pattern appear wavy to you. You may notice that some of the lines are missing. These may be signs of choroidal neovascularization. Click here to view a full-sized Amsler grid yourself.

Blurry areas and black spots.		Wavy or crooked lines.

How do we diagnose the Ocular Histoplasmosis Syndrome?
The most important step in accurately diagnosing the ocular histoplasmosis syndrome consists of a careful eye examination by an eye doctor familiar with all aspects of this disease. During the examination, your doctor will dilate your pupils and look for histoplasmosis scarring, leakage, and bleeding. Your doctor may need to perform fluorescein angiography to better evaluate the histoplasmosis scars. Fluorescein angiography is a photographic test, not involving x-rays, in which a colored vegetable dye is injected into an arm vein which then travels through the blood vessels in the eye. A series of photographs are taken of the retina as the dye passes through the back of the eye. This allows your doctor to better diagnose the presence and extent of choroidal neovascularization to decide whether treatment can be offered.

What treatments are available for ocular histoplasmosis?

1) Observation.
Patients with inactive histoplasmosis scarring and those who have been successfully treated with laser are usually asked to look at a special grid, the Amsler Grid, daily for any central visual changes. If a change in the central vision or Amsler grid develops, the patient should seek prompt attention. A careful examination and fluorescein angiogram may be needed to look for choroidal neovascularization that can possibly be treated.

2) Corticosteroids.
Steroids are potent medicines that can reduce inflammation. Some doctors will occasionally recommend steroid pills or shots for the rare patient experiencing visual symptoms from acute histoplasmosis inflammation.

3) Laser photocoagulation.

Fluorescein angiogram showing choroidal neovascularization (arrow).		Dry laser scar following successful laser photocoagulation surgery.

Laser surgery is often effective in preventing severe visual loss in patients with choroidal neovascularization not involving the part of the eye responsible for the very central reading vision. The Macular Photocoagulation Study, a scientific study sponsored by the National Institute of Health, showed that laser was successful in decreasing the risk of severe visual loss by at least 50%.
   
The laser works by sealing shut the abnormal areas of leakage.  Following an anesthetic drop, and possibly an anesthetic injection around the eye, you will be seated at the laser machine. A contact lens will be placed on the eye and you will be asked to look in certain directions of gaze so that your doctor will be able to direct the laser to the abnormal areas of leakage.  You will be able to go home following the laser, although your vision may be blurred from the treatment for several days. It is not uncommon for patients to notice blurring of vision or a blind spot off to the side of the central vision after laser treatment. This is an unavoidable potential side effect of successful laser treatment, and is necessary in order to prevent total loss of the central reading vision. Rarely, laser treatment itself may cause a permanent reduction in central vision.

Patients with choroidal neovascularization involving the central reading area of the eye are not treated with laser, since this treatment would destroy whatever central vision was left. Photodynamic therapy, vascular endothelial growth factor inhibitors, or subretinal surgery are sometimes able to preserve central vision in selected cases.

Unfortunately, approximately 1 out of every 3 patients treated with laser will have the choroidal neovascularization recur, usually within the first month or two of treatment. Recurrences need to be promptly diagnosed and treated in order to maintain reading vision. For this reason, your doctor will ask you to return for examinations every few weeks until the outcome is known. Fluorescein angiography will usually be performed at each of the return visits since this is the only way that residual or recurrent blood vessels can be detected. Your doctor will then decide whether or not additional treatments are necessary.

4) Photodynamic therapy.
Laser photocoagulation surgery is currently the standard treatment for patients with ocular histoplasmosis and choroidal neovascularization outside the macular center. When choroidal neovascularization is beneath the center of the macula (subfoveal), laser not only destroys these abnormal vessels but also permanently damages the overlying retina.  Patients are thus left with a dry scar but no central vision.

Photodynamic therapy makes it possible to selectively destroy choroidal neovascularization without damaging the overlying retinal tissue. The outpatient procedure is painless and performed in our office.  A special photodynamic dye is injected into an arm vein. Fifteen minutes later, a "cold" laser light is aimed at the choroidal neovascularization which selectively absorbs the dye. The laser light activates the dye, causing the production of a very active form of oxygen (singlet oxygen) that destroys the vessels. Patients can go home immediately following photodynamic therapy but must avoid direct sunlight for 2 days following treatment to avoid skin burns from the dye.

Recent data regarding photodynamic therapy offer new hope for patients with histoplasmosis-related subfoveal choroidal neovascularization. In an open label safety study involving 26 patients with ocular histoplasmosis, visual acuity improved by an average of more than 1 line on a standard eye chart at 12 months with 28% of patients experiencing a visual acuity improvement of 3 lines or more. Visual acuity decreased by less than 3 lines of vision in 88% of patients during the same time period.

Macular hemorrhage before photodynamic therapy.		All leakage resolved following photodynamic treatment.  A dry central macular scar remains.

OCT scans before (top) and following (bottom) photodynamic therapy. The swollen, cystic appearing macula returns to its normal configuration following treatment.

5) Vascular Endothelial Growth Factor (VEGF) Inhibitors.
VEGF inhibitors (Macugen, Avastin, and Lucentis) are a new class of potent medications that prevent choroidal neovascularization from growing and leaking. They have been extensively studied in patients with age-related macular degeneration, and also appear to be effective in ocular histoplasmosis. Click here to learn more.

6) Subretinal surgery.
Using advanced surgical techniques, abnormal blood vessels growing beneath the part of the eye responsible for central vision can be removed. This surgery is sometimes successful in restoring reading vision, and appears mostly effective for eyes with vision worse than 20/100. Your doctor will discuss this option with you if he feels you could benefit from this procedure.

What happens if I lose my reading vision?
Except for airplane pilots, military personnel, surgeons, etc., most patients who lose reading vision in one eye usually continue their normal lifestyle and job without change. The major problem is adjusting to the initial lack of depth perception required for near vision. Eventually, patients learn to compensate for this and obtain new clues from the environment to judge close distances. Patients are usually able to thus gain back much of their lost depth perception. Patients should be able to drive a car as long as their vision in the good eye is at least 20/60.

Low Vision examination.
We may recommend that you see a specialist for a low vision examination. Magnifying lenses or other devices can be prescribed to help with reading and other central vision tasks.

The low vision experts at Lighthouse International have created Living Better: A Guide for People with Vision Loss. This is a national campaign to promote safety, independence, and accessibility in the home. Please click here to learn more about available online content and a free printed kit filled with useful information and products.


What are my chances of abnormal blood vessels affecting my good eye?
Patients who have no signs of abnormal blood vessels in either eye have a minimal chance of losing central vision. This risk is increased, however, if abnormal blood vessels have already affected one eye. The yearly risk for the second eye becoming involved then increases to approximately 1 in 50.

What can I do to prevent visual loss from histoplasmosis?
There is nothing that a person with histoplasmosis can do to prevent abnormal vessels from developing. The most important thing is to carefully monitor the central vision with daily vision checks (i.e. the Amsler grid) and frequent, regular eye examinations. Any sudden change in the central vision necessitates an immediate examination by your eye doctor.

Summary.
Ocular histoplasmosis is a fairly common cause of central vision loss in the Ohio-Mississippi river basin. Patients are asymptomatic unless abnormal blood vessels cause leakage and bleeding into the reading area of vision. Timely diagnosis and treatment are often successful in preventing loss of reading vision.