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Dr. Les Harrell Optometric Physician

Ocular Toxoplasmosis - Eye Infection 

Introduction
Ocular toxoplasmosis is a type of inner eye infection.  It is a leading cause of retinochoroiditis in the United States.  Retinochoroiditis affects the retina, located at the back of the eye, and the choroid, its blood supply. 
 
Ocular toxoplasmosis is a condition that develops in some people after toxoplasmosis parasite infection.  The infection may be transmitted because of contamination, or it may be transmitted from an infected mother to a baby during pregnancy.  People with suppressed immune systems are the most vulnerable to the effects of toxoplasmosis. 
 
Toxoplasmosis can cause blurred vision, mild eye pain, and lead to vision loss.  It can cause blindness and severe medical problems in newborns.  Ocular toxoplasmosis is treated with medications.  Surgery may be necessary in severe cases.

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Anatomy
The sclera is the white part of your eye.  The sclera is a tough protective coat that covers most of your eye.  It is composed of several layers and contains many blood vessels.  Light rays enter the front of your eye and are interpreted by your brain as images.  Light rays first enter your eye through the cornea, the “window” of your eye.  The cornea is a clear dome that helps your eyes focus.
 
The anterior chamber is located behind the cornea and in front of the iris.  The anterior chamber is filled with a fluid that maintains eye pressure, nourishes the eye, and keeps it healthy.  The iris is the colored part of your eye.  The iris contains two sets of muscles.  The muscles work to make the pupil of your eye larger or smaller.  The pupil is the black circle in the center of your iris.  It changes size to allow more or less light to enter your eye.
 
After light comes through the pupil, it enters the lens.  The lens is a clear curved disc.  Muscles adjust the curve in the lens to focus clear images on the retina.  The retina is located at the back of your eye.
 
The retina is a thin tissue layer that contains millions of nerve cells.  The nerve cells are sensitive to light.  A main purpose of your eye is to focus light on the retina.  The choroid is the lining underneath the retina.  The choroid contains blood vessels that supply your retina with blood and oxygen to keep it healthy.
 
Cones and rods are specialized receptor cells in the retina.  Cones are specialized for color vision and detailed vision, such as for reading or identifying distant objects.  Cones work best with bright light.  The greatest concentration of cones is found in the macula and fovea at the center of the retina.  The macula is the center of visual attention.  The fovea is the site of visual acuity or best visual sharpness.  Rods  are located throughout the rest of the retina.
 
Your eyes contain more rods than cones.  Rods work best in low light.  Rods perceive blacks, whites, and grays, but not colors.  They detect general shapes.  Rods are used for night vision and peripheral vision.  High concentrations of rods at the outer portions of your retina act as motion detectors in your peripheral or side vision. 
 
The receptor cells in the retina send nerve messages about what you see to the optic nerve.  The optic nerve extends from the back of each eye and joins together in the brain at the optic chiasm.  From the optic chiasm, the nerve signals travel along two optic tracts in the brain and eventually to the occipital cortex  where you process and perceive vision.

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Causes
Ocular toxoplasmosis can result from an infection with the Toxoplasma gondii parasite.  People can get the infection from ingesting contaminated soil, cat litter, contaminated vegetables, or raw or undercooked meat or dairy products.  Transmission can occur from a mother to her baby during pregnancy.  It is possible to contract the infection through a blood transfusion or organ transplant.  Not all people with the parasite experience symptoms or difficulties.  The parasite most frequently causes problems in people that have suppressed immune systems.  Cancer treatments, HIV, AIDS, or  medications given after organ transplantation can cause suppressed immune systems. 
 
Ocular toxoplasmosis can cause inflammation  that can lead to scarring and lesions.  This may destroy the affected retina and result in vision loss.  In some cases, treatments can help to reduce vision loss.  Ocular toxoplasmosis can be a recurrent condition.

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Symptoms
Ocular toxoplasmosis can cause eye pain.  Bright light may increase the pain. Your vision may look blurred or hazy.  You may see floating spots in your vision.  In some cases there is eye redness and tearing.
 
In addition to affecting the eyes, toxoplasmosis may affect the brain, lung, heart, or liver.  People with suppressed immune systems may experience fever, headache, confusion, seizures, and neurological problems.  Newborns that contract toxoplasmosis from their mothers during pregnancy may experience significant medical problems.  Not only is toxoplasmosis associated with blindness, but it may also cause brain disorders, enlargement of the liver and spleen, and mental retardation.

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Diagnosis
Your doctor can diagnose ocular toxoplasmosis by conducting a thorough eye exam and diagnostic tests.  Blood tests can detect the presence of the infection.  

Diagnostic tests may include slit lamp evaluation, fluorescein angiography (FA), and Indocyanine green (ICG) angiography.  A slit lamp evaluation uses a microscope and beam of light that allows your doctor to see the structures inside of your eye.   Fluorescein angiography is used to show the retinal blood supply.  Photos of your retina are taken after a dye is injected into your bloodstream.  Indocyanine green angiography also uses injected dye and a camera system.  It can produce pictures of the blood vessels beneath the retina.  ICG can detect subtle changes in the blood vessels.

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Treatment
Ocular toxoplasmosis may be treated with oral medications sometimes taken for a month or more.  In some cases, surgery may be recommended.  Procedures may include laser  therapy, cryotherapy, or vitrectomy.  Laser therapy  involves using a short burst of high-energy light to destroy abnormal cells on the retina.  Cryotherapy is another method used for treating the retina.  After numbing the eye, cold temperature is transmitted through the eye to treat the blood vessels in the retina.  A vitrectomy is an outpatient hospital procedure.  It is a microscopic operation that involves removing the gel-like liquid from the eye.  This procedure can promote healing by removing debris and reducing swelling.

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Prevention
Cooking foods thoroughly especially wild game is important.  Cleaning cat litter boxes should be done carefully to avoid inhalation of dust from the box and hands should be thoroughly washed afterwards.  Pregnant women should be checked for toxoplasmosis as treatment can prevent complications to the fetus.

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Complications
Toxoplasmosis can cause a range of complications from mild disturbances in vision to severe vision loss.  If treated early severe complications can usually be avoided.  However treatment does not cure the condition but forces it back into a non active state. 

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This information is intended for educational and informational purposes only. It should not be used in place of an individual consultation or examination or replace the advice of your health care professional and should not be relied upon to determine diagnosis or course of treatment.

The iHealthSpot patient education library was written collaboratively by the iHealthSpot editorial team which includes Senior Medical Authors Dr. Mary Car-Blanchard, OTD/OTR/L and Valerie K. Clark, and the following editorial advisors: Steve Meadows, MD, Ernie F. Soto, DDS, Ronald J. Glatzer, MD, Jonathan Rosenberg, MD, Christopher M. Nolte, MD, David Applebaum, MD, Jonathan M. Tarrash, MD, and Paula Soto, RN/BSN. This content complies with the HONcode standard for trustworthy health information. The library commenced development on September 1, 2005 with the latest update/addition on April 13th, 2016. For information on iHealthSpot’s other services including medical website design, visit www.iHealthSpot.com.