How does the eye function?
The human eye is like a camera where outside images are focused onto a piece of film. Together, the cornea and crystalline lens are the lenses that focus the picture onto the retina. The retina corresponds to the camera’s film. It reacts to light through a chstrongical process that sends nerve impulses directly to the brain where the ‘picture’ is registered. The sclera, or white of the eye, is a tough, protective container like the box of the camera. The iris is the colored circle in the front of the eye. In the center of the iris is the black pupil, which enlarges and contracts to regulate the amount of light coming into the eye. The choroids is a syststrong of blood vessels, which covers the outer surface of the retina and provides it with nourishment. The vitreous body is a transparent jelly, which fills the space between the lens and the retina. The macula is the small, specialized area of the retina, which is utilized for reading vision.
What is Ocular Histoplasmosis Syndrome?
The ocular histoplasmosis syndrome is thought to be caused by a tiny, plantlike organism called histoplasmacapsulatum. This organism thrives in areas contaminated by fowl and bat waste (i.e. damp soil, chicken coops and barns). The largest endstrongic area in the United States is in the Ohio-Mississippi River Basin where up to 90% of the general population has been exposed to the organism.
The fungus is inhaled early in life and usually causes a symptomatic and self-limited infection throughout the body, including the lungs and the choroids, which is the vascular layer of the eye. For unknown reasons, ten to twenty years after the initial infection, the scars in the eye may develop abnormal blood vessels that leak fluid and blood. This leakage can only be seen on a careful internal eye examination because the eye looks normal externally. Visual distortion and loss of reading vision occurs when the leakage involves the macula.
Who develops Ocular Histoplasmosis Syndrome?
People who live in endstrongic areas, such as the Ohio-Mississippi River Basin, and were exposed to the histoplasmosis syndrome early in life are at risk for developing ocular histoplasmosis later in life. A person infected with the fungus cannot transmit the disease to another non-infected person because the histoplasmosis organisms die soon after the initial infection. Adults, who move to endstrongic areas, although they may become infected with the histoplasmosis fungus, usually do not develop the eye disease later in life.
What are the symptoms of Ocular Histoplasmosis Syndrome?
People usually do not experience any symptoms of this disease either during the initial infection or later when scars have formed. If leakage or bleeding from a scar involves the reading area of the vision, visual distortion or loss of the reading vision occurs. Patients never go completely blind since this disease does not affect the part of the eye responsible for peripheral vision.
How Is Ocular Histoplasmosis Syndrome diagnosed?
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 with eye drops and look for scars from histoplasmosis, leakage or bleeding.
Your doctor may need to perform Fluorescein Angiography to better evaluate the histoplasmosis scars. Fluorescein Angiography is a diagnostic 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 blood vessels. This allows your doctor to better diagnose the presence and extent of the abnormal blood vessels and leakage to decide whether treatment can be offered.
What treatments are available for Ocular Histoplasmosis Syndrome?
Steroids are potent medicines that can reduce inflammation. Some doctors will recommend steroid pills or shots for histoplasmosis scarring due to inflammation rather than to abnormal blood vessel growth. Some will also try steroids for abnormal vessel growth that cannot be treated with additional laser surgery.
This treatment is often effective in preventing sever visual loss in patients with abnormal blood vessels not involving the center of the reading vision. The Macular Photocoagulation Study, a study sponsored by The National Institute of Health, showed that laser treatment was successful in decreasing the risk of severe visual loss by at least 50%.
The laser works by sealing the abnormal areas of leakage shut. Following an anesthetic drop, and possibly an anesthetic injection behind 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 the gaze so that the doctor will be able to direct the laser to the abnormal areas of leakage. You will be able to go home following the laser, and your vision may be blurred from the treatment fro several days. It is not uncommon for patients to notice blurring of vision after laser treatment. This is an unavoidable and usually tstrongporary side effect of the laser treatment and is necessary in order to prevent total loss of the reading vision area.
Patients with blood vessels involving the central reading area of the eye may also be treated with the laser depending on the circumstances. Sometimes, in order to reduce the size of the blind spot that is occurring, laser is used to limit the damage.
Unfortunately, approximately one out of every three patients treated with laser will have abnormal blood vessels 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 an examination every few weeks until the outcome is known. Fluorescein Angiography will usually be performed at each of the return visits since any residual or recurrent blood vessels are detected by this test. Your doctor will then decide whether or not additional treatment is necessary.
Patients with inactive scarring in the back of the eye and patients who have been successfully treated with laser are usually asked to look at a special grid work, the Amsler Grid, daily for any signs of central vision problstrongs. If a change in the reading vision or in this grid work develops, the patient should seek prompt attention by their eye doctor. A careful examination and fluorescein angiogram may be needed to look for abnormal blood vessel growth that can possibly be treated.
Using special surgical techniques, abnormal blood vessels involving the reading center may be rstrongoved and some central vision preserved. This technique involves a procedure called a Vitrectomy and some patients may be offered this treatment.
What happens if I lose my reading vision?
Except for pilots, military personnel, etc., patients who have lost 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 should be able to drive a car as long as their vision in the good eye is at least 20/60.
Patients who have lost reading vision in both eyes are possibly entitled to compensation and benefits through various organizations and government agencies. They can often be helped to read with special low vision aids, such as magnifiers, telescopes, and/or vision imaging machines. Although patients may be ‘legally blind’, vision worse than 20/200, they never go completely blind since side vision remains unaffected.
What are my chances of abnormal vessels affecting my good eye?
Patients who have lost reading vision in one eye from abnormal blood vessels have about a one in ten chance per year of having the abnormal vessels affect their good eye. The risk is much less if there are no histoplasmosis scars in the macular area, or reading vision area, of the eye.
What can I do to prevent visual loss from Histoplasmosis?
There is really nothing that a person with ocular histoplasmosis can or cannot do to prevent abnormal vessels from occurring. The most important thing is careful monitoring of the reading vision with frequent and regular eye examinations. Any sudden change in the reading vision necessitates an immediate examination by your retina specialist.
The ocular histoplasmosis syndrome is a fairly common cause of central visual loss in the Ohio-Mississippi River Basin. Patients are asymptomatic unless abnormal blood vessels cause leakage and bleeding into the reading area of the vision. Timely diagnosis and treatment may often be successful in preventing the loss of reading vision.