What are the other Names for this Condition? (Also known as/Synonyms)

• Ocular Toxoplasma
• Ocular Toxoplasmic Infection
• Toxoplasmosis of the Eye

What is Ocular Toxoplasmosis? (Definition/Background Information)

• Infection by Toxoplasma gondii, a very common protozoan microorganism, causes toxoplasmosis. The infection normally does not affect individuals (such as an adult or child) with healthy immune systems; else, the condition may only cause mild flu-like symptoms in them
• The infection may be congenital in nature, meaning it may be transmitted from the mother to the child during pregnancy or immediately after delivery; or acquired during childhood or adulthood stage, typically through consumption of contaminated food and water
• After entering the body, when the T. gondii parasite reaches the retina of the eye and spreads in the host cells causing lesions in the eye structures, it results in a condition known as Ocular Toxoplasmosis. A majority of retinal infections are caused by this particular parasite; and, in immunocompromised individuals, it can result in severe symptoms including loss of vision
• Traditionally, it was thought that most active Ocular Toxoplasmosis represented reactivation of congenital toxoplasmosis acquired transplacentally from the mother. Recently, however, it has been shown that acquired infections occur more frequently than previously suspected
• Acquired toxoplasmosis is generally caused by consuming meat, milk, or vegetables that are contaminated by the parasitic microorganism. The contamination can occur even during the cooking or preparation stage
• Cats are host to the microorganism; and, cat feces are a possible source of the protozoa from accidental exposure and ingestion. Pregnant women and those with various immunodeficiencies, such as patients with AIDS or on chemotherapy, may be severely affected
• Ocular Toxoplasmosis may present blurred or decreased vision, eye redness and eye pain. Most children with congenital transmission present bilateral infection, where both eyes are affected. Delayed diagnosis and treatment may result in severe complications, such as cataract formation, macular edema, and optic nerve atrophy, including irreversible eye injury
• In a majority, the condition is self-resolving and may not require any treatment. In those with severe symptoms (mostly immunocompromised patients) presenting large lesions and in pregnant women, the treatment measures for Ocular Toxoplasmosis may include prescription medications, antibiotics, and steroid therapy. In some, regular medical checkup and prophylactic treatment may be recommended to prevent recurrences
• The prognosis of Ocular Toxoplasmosis is dependent upon various factors, but is good in many cases with appropriate treatment. However, in congenital cases involving young children and those with poor immune system, the prognosis may be unpredictable. Also, the condition can be progressive and recurrent leading to reduced visual function

Who gets Ocular Toxoplasmosis? (Age and Sex Distribution)

• Any individual, young or old, may contract Ocular Toxoplasmosis; there is no age or gender preference noted
• It is the most common cause of infection in the retina and individuals with weak immune systems are prone to developing severe symptoms
• A baby in the womb or a newborn child can be infected by the mother, who is recently infected. The infection may be transmitted transplacentally from the mother to the developing fetus; or during childbirth, as the baby passes through the womb
• In general, toxoplasmosis is very common in parts of Europe, South America, Asia, and Africa; especially, in regions with hot-humid climate. A majority of the human population carry this parasite in a latent state within their bodies

What are the Risk Factors for Ocular Toxoplasmosis? (Predisposing Factors)

The risk factors of Ocular Toxoplasmosis may include:

• Consuming meat (beef, lamb, pork, and venison) that is partially-cooked, or cooked improperly (without maintaining proper hygiene standards, using contaminated hands, vessels, knives, etc.)
• Inadvertently touching one’s face, mouth, while or after handling contaminated raw meat; not following safe meat preparation procedures
• Eating raw vegetables and fruits, without washing or cleaning them
• Drinking untreated water from a stream or a well, or from any such source that is contaminated
• Exposure to cat feces or to soil contaminated by the feces
• Living in crowded neighborhoods and/or travelling to areas with poor sanitation facilities
• Eating food that is mass-prepared using contaminated meat and without proper hygiene and quality control
• Infected blood transfusion or organ transplant recipients
• Individuals with weak immunity constitution due to several factors/conditions, such as AIDS/HIV infection, cancer, organ transplant, long-standing diabetes, on long-term corticosteroids for various conditions, etc. are easily infected
• A newborn baby is at risk if the mother is ‘recently’ infected by the parasitic microorganism (just prior to or during pregnancy). When a pregnant woman is infected within 6 months of conception, intrauterine transmission is reportedly observed in about 35% of the cases
• Individuals working in high-risk occupations, such as meat processing/packing plants, pet stores, zoos, and veterinary hospitals, are prone to toxoplasmosis infection to a higher degree

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Ocular Toxoplasmosis? (Etiology)

Toxoplasmosis is caused through a parasitic infection by Toxoplasma gondii (a unicellular organism). These parasites are protozoans that are found in nearly a third to half of all human population and other warm-blooded animals. After an initially mild infection that may present flu-like symptoms, the parasite remains inactive in the body, since healthy humans have a strong and robust immune system.

• When the parasite travels to the eye and causes eye infection, it results in Ocular Toxoplasmosis
• The involvement of the eye takes place more frequently than other body regions
• According to researchers, the retina seems to be a preferred site for parasitic infection. This results in retinitis (retinal necrosis) and injury to the choroid and surrounding tissue regions

In immunocompetent individuals, the condition is self-limited, and therefore, minimal to no (treatment) intervention is needed; although, the parasite remains inactive (latent) in the body/eye. In individuals with a highly vulnerable or compromised immune system, T. gondii is activated or gets reactivated and causes severe eye symptoms.

Ocular Toxoplasmic Infection may be acquired or congenital. In acquired infections, the parasite is mostly transmitted via the gastrointestinal tract; while congenital infections occur via the placental bloodstream.

• Acquired Ocular Toxoplasmosis (postnatal infection):
  • Consuming undercooked or improperly cooked meat
  • Handling raw meat
  • Using kitchen items contaminated by raw meat that are unclean
  • Drinking untreated or unclean water
  • Domestic cats are hosts for this pathogen and cat feces commonly serve as a transmission route to humans. Handling cat feces and/or feces-infected soil, cleaning the resting area/shelter box of cats, etc.
  • Infected (with cat feces) garden soils, where plants/vegetables/fruits are grown, may also serve as transmission agents for the pathogen
  • Eating raw fruits and vegetables without cleaning or washing them
  • Rarely, the parasitic infection is passed on via a blood transfusion or from an infected organ donor (during organ transplant)
  • When food prepared for a large community is contaminated, such as at restaurants or school dormitories, or when prepared for social or festival occasions; toxoplasmosis may simultaneously affect large masses, resulting in local endemic infections
• Congenital Ocular Toxoplasmosis (prenatal infection):
  • According to some studies, between 20-80% of children with congenital transmission develop the disease and present ocular lesions from the infection within 24 months
  • Congenital transmission of the infection can take place from a mother to the infant child in the womb (vertical transplacental transmission of infection)
  • It can take place at any time during pregnancy or immediately on or after delivery, if the mother is infected

What are the Signs and Symptoms of Ocular Toxoplasmosis?

The onset of signs and symptoms of Ocular Toxoplasmosis depend on the health status of the individual and the severity of the infection. Normally healthy individuals (including most newborn babies) usually do not exhibit any signs of the infection, but act as carriers of the protozoa. Individuals with weak immune systems may be severely affected. In such cases, either the parasite (which the individual carried from a congenital infection) gets reactivated due to favorable conditions, or a recent infection might have occurred. At this stage, the eye symptoms may be severe and vision threatening.

In many cases of Ocular Toxoplasmosis, individuals with latent form of the condition that is transmitted congenitally are known to exhibit symptoms during the ages 10 to 30 years, due to reactivation of the disease pathogen. In congenital transmission with immediate disease manifestation, the ocular lesions in babies may be severe and present complications.

The signs and symptoms of Ocular Toxoplasmosis may occur suddenly or slowly over a period of time. It may include:

• Reduced vision or blurred vision
• Redness of the eyes
• Increased or excessive tearing (flow of tears)
• Eye floaters: The individuals experience illusions that some small objects such as spots, hairs, or strings are moving in the eye
• Presence of blind spots, or scotoma, causing partial vision loss
• Light-sensitivity (photophobia)
• Impaired color vision
• Eye pain, in some cases
• Posterior uveitis: In several geographical regions, infection by T. gondii is the main cause of posterior uveitis
• Retinochoroiditis: Inflammation of both the retina and choroid; the retina is involved first (with retinal hemorrhages) and subsequently the choroid. It is observed that retinochoroiditis occurs in nearly 80% of the congenital cases
• The condition may affect only one eye (unilateral) or both the eyes (bilateral); bilateral Ocular Toxoplasmosis is noted in 85% of children with congenital manifestation

The signs and symptoms of toxoplasmosis involving various other body regions and systems may also be noted.

How is Ocular Toxoplasmosis Diagnosed?

Some of the exams and tests that could be ordered for Ocular Toxoplasmosis include:

• Physical examination and analysis of previous medical history
• Eye examination by an eye specialist (ophthalmologist or retinal expert)
• Blood samples are examined to detect the presence of the microorganism causing the infection. Some of these tests for toxoplasmosis include:
  • Polymerase chain reaction test (PCR test)
  • ELISA test
  • Sabin-Feldman dye test
• Other blood tests may include:
  • To check for the presence of antibodies in blood
  • Blood culture for infections
  • Complete blood count (CBC) with differential
  • Erythrocyte sedimentation rate (ESR)
• Antibody titer in aqueous humor and vitreous humor fluid samples
• Fundoscopic (ophthalmoscopic) examination by an eye specialist, who examines the back part of the eye (or the fundus)
• Visual acuity test using a special and standardized test chart (Snellen chart)
• Slit-lamp examination: Examination of the eye structure using a special instrument called a slit-lamp. In this procedure, the pupils are dilated and the internal eye structure is examined
• Tonometry: Measurement of intraocular pressure or eye fluid pressure, especially to detect conditions such as glaucoma
• Fundus fluorescein angiography (FFA): In this technique, the eye blood vessels are examined using a fluorescein dye
• Fundus autofluorescence (FAF): It is a non-invasive diagnostic technique to examine the fundus of the eye without using a fluorescent dye by a specialized fundus camera
• Indocyanine green (ICG) angiography: It is used to examine the blood vessels of the choroid using a dye, called indocyanine green, particularly to study the choroid
• B-scan ultrasonography: Special ultrasound scan of the eye through a non-invasive diagnostic tool, to assess health of eye structures
• Electroretinogram (ERG): It is a technique to measure electrical activities in the retinal cells
• Optical coherence tomography (OCT) of eye: It is an ocular imaging technique to visualize the eye structure

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Ocular Toxoplasmosis?

A few complications of Ocular Toxoplasmosis include:

• Secondary glaucoma: A condition that can cause blindness due to higher intraocular pressure
• Cataract formation: When the lens of the eye becomes clouded and cause vision loss; this is especially noted in children
• Amblyopia: Cataracts may cause “lazy eye” in children, necessitating surgical interventions
• Vitritis or vitreous inflammation, which may result in the development of epiretinal membranes
• Anterior uveitis; a condition causing inflammation of the iris
• Cystoids (macular edema)
• Optic nerve atrophy: A permanent visual impairment that occurs when the optic nerve is damaged
• Choroidal neovascularization: It occurs during the later stages of Ocular Toxoplasmosis and can result in loss of vision
• Retinal detachment: An eye condition wherein the retina gets separated from the eye structures that holds the retinal layers together
• Over time and due to a lack of proper treatment, the condition can affect other (surrounding) eye structures such as the lens, optic nerve, and vitreous fluid
• Permanent damage to eye structures and vision loss: The condition can lead to permanent blindness, if it is left untreated
• Individuals with weak immune systems can be ‘severely-to-fatally’ affected, with the infection spreading all over the body
• In severe cases of congenital Ocular Toxoplasmosis, when the involvement of other parts of the body is noted, the child may develop growth abnormalities and mental disorders
• In immunocompromised individuals, it can result in encephalitis
• The toxoplasma is retained in the body even after recovery. This may get reactivated when conditions are favorable and the infection can recur; sometimes, multiple recurrences have been noted
• Side effects of treatment medication including toxicity and/or allergic reactions to the drugs

How is Ocular Toxoplasmosis Treated?

Many cases of Ocular Toxoplasmosis are self-limiting, meaning that a healthy individual (adult or child) usually recovers from the condition within a few weeks. In such cases, no treatment is usually required; or, the infection may be treated symptomatically by the physician as required.

Treatment may be considered for individuals with poor immunity, large lesions, lesions involving the macula or optic nerve, visual impairment, and in pregnant women. The goal of the treatment is to stop further growth/spread of the parasite and minimize damage to the retinal structures.

The following measures may be considered for Ocular Toxoplasmosis for cases that require treatment.

• Anti-parasitic medication such as pyrimethamine
• Use of antibiotics (such as sulfadiazine) and corticosteroids for inflammation
• Intravitreal drug therapy, where medication is delivered directly to the eye
• In case of severe complications, surgery may be attempted after medication therapy. Surgery is also considered for retinal detachment
• In pregnant women, the healthcare provider may undertake a ‘wait and watch’ approach, especially for recurrent conditions
• Pregnant women and infants may require medication and sometimes extensive treatment, if the infection is systemic
• Prolonged treatment of toxoplasmosis, with antibiotics and even antimalarial drugs, may be required for immunocompromised individuals
• Long-term follow-up and prophylactic treatment may be necessary to prevent recurrent infections, in some cases

Pregnancy: It is very important to note that the condition should be carefully evaluated by a qualified healthcare provider, before starting and/or performing any treatment. This is because the treatment has the potential to affect the developing fetus and the guidance of a healthcare expert is crucial.

How can Ocular Toxoplasmosis be Prevented?

To reduce the incidence of Ocular Toxoplasmosis, proper precautions have to be taken to prevent transmission of the harmful protozoa via food and water. This has to be considered even while traveling to other geographical regions and countries. According to current studies, postnatal infections are more common than prenatal infections. Pregnant women have a high risk for infection transmission to their babies; hence, they must be particularly careful and kept well-informed by their healthcare providers.

Some preventative measures for toxoplasmosis include:

• Avoid undercooked food (mainly meat) and contaminated water; always drink water that is clean and from a reliable source
• Avoid spoilt or contaminated milk
• Follow basic rules while cooking and consuming food, such as:
  • Carefully washing food items (such as meat and vegetables)
  • Washing food vessels, cutting boards, etc. before use
  • Cooking meat to the required temperatures, to kill any microorganism
  • Keeping food items covered, stored properly
  • Washing hands before eating, or immediately after handling raw meat
• Sample tasting of meat, while it is being cooked (or while still undercooked) is to be avoided
• Fruits and vegetables have to be washed and cleaned well, particularly if they are to be consumed raw
• Avoid eating raw or undercooked seafood, such as clams and oysters, which may be contaminated with seawater
• Be extremely careful while handling cat feces, or while cleaning cat litter boxes (use hand gloves). Also, ensure that the litter boxes are cleaned regularly
• Avoid touching or playing with stray cats, especially if you are pregnant
• Train children to understand the importance of washing their hands, especially after playing in the mud, or after playing outdoors
• Garden soil may be contaminated with Toxoplasma found in cat feces - wash hands thoroughly with soap and water after being in contact with the soil (after activities such as gardening or backyard cleaning)
• Public health screening for pregnant women to reduce risk of fetal infections
• Individuals that belong to certain high-risk groups, such as working at a vet clinic, a pet store, or having a weak immune system, are required to ensure that adequate safety precautions are taken while handling cats (or other pets)

The treatment and prevention of toxoplasmosis can be accomplished to a good extent through mass-education. This should include providing information on proper hygiene, maintaining good food preparation practices, and following the outlined (above-mentioned) preventive measures.

What is the Prognosis of Ocular Toxoplasmosis? (Outcomes/Resolutions)

• In healthy individuals, the prognosis of Ocular Toxoplasmosis is generally good and no treatment may be necessary. The condition is frequently self-resolving and recovery takes place within about 4-8 weeks
• However, the prognosis is also dependent on several factors, such as what region of the eye is affected, the severity of the infection, and the presence of any complications. Any damage to the macula or retinal region at the optic nerve is a potential threat to loss of visual acuity and/or complete vision loss
• Prompt treatment of the infection is necessary, if the patients are newborn babies, young infants, or pregnant women. If treatment is delayed, it may result in complications including total loss of vision and the prognosis may be guarded
• According to a long-term study, a recurrence rate of nearly 80% was noted over a 5-year period; also, some individuals (both with good and weak immune systems) were known to have multiple recurrences. Hence regular checkups, medical screening, and prophylactic treatment may be required for prolonged periods, in some cases

Additional and Relevant Useful Information for Ocular Toxoplasmosis:

• Animals belonging to the cat family (or Felidae that include domesticated and wild cats, lions, tigers, leopards, etc.) are stated to be the definitive hosts for T. gondii parasite; the parasites are known to undergo sexual reproduction within these hosts
• It is best not to get pregnant, if you have had a recent infection of Toxoplasmosis. It is advisable to consult your gynecologist to plan your child, in such cases