What is Ocular Toxocariasis?

Helminths, also known as parasitic worms, have been causing illnesses in humans for a long time. There are two main types of these worms, called Nemathelminthes and Platyhelminthes. Nematodes, which are a type of Nemathelminthes, include human worms such as Ascaris lumbricoides and Trichuris trichiura, as well as animal worms like Toxocara canis and Toxocara catis. Platyhelminths include trematodes, such as Schistosoma mansoni, and cestodes, such as Taenia solium. Around one billion people worldwide are infected with these types of worms.

These worms can cause disease in humans. They live in the intestine and cause damage to body tissue by invading it directly. The infection of the eye known as ocular toxocariasis is one such disease, caused by the worm species Toxocara canis and Toxocara cati.

Studies conducted from the 1950s found nematode larvae, the immature stage of the worm, in the liver biopsies of children and in removed eye specimens. These findings established Toxocara as a common cause of diseases affecting various body systems, including the eyes.

Ocular toxocariasis can show up in different ways, including peripheral granuloma, posterior granuloma, or endophthalmitis, all of which describe different inflammations of the eye. This document reviews the causes, spread, clinical signs, examinations needed, possible diagnoses, treatment, complications, and the importance of teamwork among health professionals in managing patients with ocular toxocariasis.

What Causes Ocular Toxocariasis?

Ocular toxocariasis, an eye infection, is caused by a type of microscopic worm called Toxocara. Among the 21 species of Toxocara, Toxocara canis is the most common one responsible for this infection. This species is usually seen in dogs, especially puppies.

The adult Toxocara canis worms are rather long, with males measuring between 42.5 to 45 mm, and females between 54 to 60 mm. Puppies, in particular, act as hosts to these worms, meaning these parasites live inside them. Pregnant dogs and puppies often have these adult worms in their small intestines.

The puppies can get the parasite in two main ways – either it can be passed onto them from their mother or by eating soil and feces that have been contaminated with the parasite. Once inside the puppies, the larvae, which are like baby worms, travel up to the lungs. Here, they cause the puppy to cough, and when swallowed, end up in the stomach. Here they quickly grow into adult worms. These adult worms lay eggs which are passed out when the puppy poops.

It takes between 2 to 6 weeks for these eggs to develop into an embryo outside in the environment. People can get infected with the parasite if they accidentally eat contaminated soil or food. Once inside the human body, the embryo develops into a larva in the intestines. The larva can then break through the intestine wall and enters the bloodstream. From here, they can get carried to important organs like the heart, liver, lungs, and even the eyes.

Risk Factors and Frequency for Ocular Toxocariasis

Ocular toxocariasis is common worldwide. It’s an issue where a large portion of people in the US have experienced in the past, but recent studies show that this is slowly decreasing. However, it’s more common amongst blacks than whites, and is typically found in warmer areas like the Southern United States. Furthermore, nearly half of all patients with this condition come from this region.

In other parts of the world, the number of individuals with antibodies against the disease can greatly vary. Some regions in Nigeria even report over 80% of children being affected. The condition most often affects the youth, with the average age of infection being 11.5 years. The majority of patients are male and have some connection with dogs or cats. Most patients experience vision loss, and for a large portion of them, this loss is permanent.

Ocular toxocariasis is a common condition globally.
From 1988 to 1994, 13.9% of the US population tested positive for Toxocara. However, from 2011 to 2014, the number decreased to 5.1%.
The infection is more prevalent among blacks than whites.
This condition is more common in warmer areas like the Southern United States—home to 45% of Toxocara patients.
In different parts of the globe, 2.4% to 76.6% of people test positive for Toxocara antibodies. In some regions of Nigeria, more than 80% of children have been affected.
The average age of infection is 11.5 years, but it can affect individuals from 1 to 66 years.
Most patients are males—an alarming 69% of them reported coming into contact with a dog or a cat.
85% of patients reported vision loss, and sadly, 70% of these cases resulted in permanent vision loss.

A posterior pole toxocara granuloma with a fibrous band extending to the optic
disc.

Signs and Symptoms of Ocular Toxocariasis

Ocular toxocariasis usually affects children around eight years old, who have had contact with dogs, cats, or contaminated soil. Often, parents notice changes in their children’s eyes before any complaints arise. These changes can include squinting, a white color in the eye (leukocoria), and redness. Kids may also experience loss of vision, eye pain, and redness.

Diagnostic examinations may reveal different issues in the eye, such as cells in the front chamber of the eye (anterior chamber), widening of the pupil (flare), cataracts, and cells behind the lens of the eye (retrolental cells).

There are three types of retinal findings in ocular toxocariasis. These can vary from person to person.

Peripheral granuloma: This appears as a raised white mass in the peripheral part of the eye with surrounding vitreal membranes, pigmentation, and tractional detachment. Children with this condition may have unilateral leukocoria, vision loss, or squinting.
Posterior granuloma: Presents as a solitary raised yellow-white mass at the back of the eye (at the macula or around the optic disc). Vision loss can occur due to macular or optic disc involvement, epiretinal membranes, retinal folds, or choroidal neovascularization.
Endophthalmitis: This condition typically affects children between 2 to 9 years old and presents with signs of severe inflammation, pain, redness, watering, and sensitivity to light (photophobia). The intraocular pressure may be lower than normal.

The diagnosis of ocular Toxocara is usually based on clinical findings, supported by antibody testing to Toxocara. If left untreated, this condition can lead to complications such as cataracts, glaucoma, tractional retinal detachment, scarring of the macula, and phthisis bulbi (shrunken and non-functional eye).

Testing for Ocular Toxocariasis

If a child comes in with a sudden loss of vision in one eye or has a squint, the doctor might suspect a condition called ocular toxocariasis. This condition is often confirmed by finding signs of Toxocara (a type of parasite) in tissue samples. However, getting these samples from the eye is not feasible, and other direct tests are often not directly performed. So, most of the time, doctors make the diagnosis based on the patient’s symptoms and medical history.

If there is uncertainty about the diagnosis, the doctor might use imaging tests like ultrasonography (a scan that uses sound waves to create a picture of the inside of your body) or computed tomography (a type of X-ray that provides cross-sectional images of your body). Ultrasonography can show if there’s a dense growth in the back or the side of the eye, which is often stuck to the jelly-like substance inside the eye (the vitreous). Sometimes, the scan also shows small calcified areas in this growth. Computed tomography can further help in identifying any changes in the retinal mass after the infection has been treated.

The doctor might also use an immunological test known as the enzyme-linked immunosorbent assay (ELISA) which helps detect antibodies (proteins produced by your immune system in response to Toxocara infection). While this test is usually reliable, it may still provide a negative result in ocular toxocariasis. Besides, the ELISA test might also react to other types of parasites which could lead to false positive results. Therefore, the accuracy of this test might be improved when using samples from the eye. But one thing to note is that even if you were previously infected and have no symptoms now, the test could still turn out positive. If the antibody count in these tests increases over time, it suggests an ongoing infection.

Other tests may include a complete blood count where an increase in a particular type of white blood cells (eosinophils) may be a clue. You might also observe an increase in a certain type of proteins (immunoglobulins) in the blood. However, stool tests looking for parasite eggs are not useful here since this form of infection does not occur in humans. A tissue biopsy – collecting and examining a small piece of tissue – may at times be used but is rarely recommended. Therefore, if the patient has the mentioned symptoms, has close contact with pets, has a habit of eating non-food materials (pica), shows an increase in eosinophils and antibodies against Toxocara, then the doctors would strongly suspect ocular toxocariasis.

It’s worth noting that the level of immunoglobulin-E (another type of protein in your blood) could be particularly high in patients with toxocariasis. However, in ocular toxocariasis, this level could be lower due to less worm burden.

Treatment Options for Ocular Toxocariasis

Ocular toxocariasis is a condition that can have varying degrees of inflammation in the eye. If there’s active inflammation present, it’s typically managed with corticosteroids. These can be applied directly to the eye or taken as a medication to help reduce inflammation and clear up any haze in the eye.

Eye drops that dilate the pupil can also be given to prevent the pupil from sticking to the lens of the eye and to control increased eye pressure. Although there are drugs designed to treat worm infections, like albendazole and thiabendazole, their effectiveness in treating ocular toxocariasis isn’t clear cut. Although these drugs aren’t proven to kill the Toxocara worm in the eye, some reports do show beneficial results when they’re combined with oral corticosteroids.

In one study, this combined treatment was found to improve vision in all patients and no one experienced a return of inflammation, known as uveitis, during the nearly 14-month long study. In cases where the worm can be seen moving in the space beneath the retina of the eye, the worm can sometimes be destroyed using laser treatment.

Other complications, like abnormal blood vessel growth, can be treated with injections into the eye of specific drugs that inhibit this growth. Some people may come to the doctor when the disease is already advanced, by which point inflammation may no longer be active. Signs of this advanced stage can include specific changes in the periphery of the eye, along with a detached retina or a cataract.

In such cases, surgery may be needed. If a cataract is present, it would be removed and replaced with an artificial lens. If the jelly-like substance that fills the eye becomes cloudy or if there are scar-like tissues in the eye, a surgical procedure called pars plana vitrectomy might be required. This procedure also helps in reattaching the retina. Any scar-like tissues seen over the central region of the retina or the nerve supplying the eye may also be removed.

With these surgical interventions, the vision either improves or stays stable in about 85% of patients. If the retina tears because of scar-like tissue in the periphery of the eye, a surgical approach called a scleral buckle may be done to relieve this and improve vision.

However, the crucial step in managing this condition is prevention. It’s important for children to maintain good hygiene. Direct contact with dogs and cats should be avoided, as should playing with contaminated soil or walking barefoot outdoors. It’s also important to cook meat thoroughly before consuming it and to regularly give dogs worm medication. Dog waste should also be properly disposed of. Teaching parents and children about these healthy habits is key to prevention.

When a doctor is trying to identify toxocariasis, a parasitic infection, they have to consider several other health conditions that can show similar signs. These include, but are not limited to:

Retinoblastoma: an eye cancer that primarily affects children
Endophthalmitis: inflammation of the interior of the eye
Retinopathy of Prematurity: an eye disease occurring in prematurely born babies causing abnormal blood vessels to grow in the retina
Toxoplasmosis: a parasitic infection affecting the retina of the eye
Panuveitis: inflammation of all layers of the eye
Coats disease: a rare congenital, non-hereditary eye disorder
Persistent hyperplastic primary vitreous: a rare birth defect that affects the eye
Familial exudative vitreoretinopathy: a genetic eye disorder characterized by abnormal development of blood vessels
Combined hamartoma of the retina, and retinal pigment epithelium and seasonal hyperacute panuveitis: a rare inflammation of the eye

Each of these conditions has unique characteristics that help doctors determine the correct diagnosis. For example, retinoblastoma usually affects children under the age of three and is identified by an eye scan showing an irregular, solid mass in the eye. Coats disease mainly affects boys and is characterized by abnormal blood vessels in the eye. Retinopathy of prematurity usually presents in premature infants within two months of birth.

Each of these conditions is very serious and requires proper diagnosis and treatment. Thus, it’s vital that doctors carefully consider all possibilities when treating a patient with eye symptoms similar to toxocariasis.

What to expect with Ocular Toxocariasis

Patients who seek medical attention early in the disease’s progression usually have a positive outlook. The inflammation can be effectively managed with oral corticosteroids (medicine to reduce inflammation) and topical cycloplegic mydriatic (eye drops to relax the muscles in your eye). These treatments can prevent loss of vision and long-term issues.

However, for patients who seek treatment later, the outlook for their vision is more uncertain. This is due to complications like optic atrophy (loss of nerve fibers in the eye), changes in the macula (part of the retina responsible for clear, detailed vision), and retinal detachment (when the retina pulls away from the back of the eye).

Possible Complications When Diagnosed with Ocular Toxocariasis

Long-term inflammation can lead to the creation of posterior synechia. This is a condition that can cause the iris to bulge forward and block the fluid drainage channel in the eye, leading to a type of glaucoma known as angle-closure glaucoma. Uncontrolled inflammation can also cause the ciliary body, an eye structure that produces eye fluid, to shut down, resulting in hypotony or low eye pressure.

Persistent inflammation in the vitreous, the clear gel that fills the space between the lens and the retina, can lead to various eye conditions. These include cystoid macular edema, which is swelling or thickening of the macula, the eye’s central part that provides sharp, central vision, an epiretinal membrane, a thin layer of fibrous tissue that can develop on the surface of the retina, and macular degeneration, a condition that destroys sharp, central vision.

Vitreal folds, the creases in the gel filling the eye, can lead to tractional retinal detachment, where the retina is pulled from its normal position.

The end stage of the disease is phthisis bulbi, an ocular condition that leads to the shrinking or atrophy of the eye.

Possible Conditions from Prolonged Inflammation:

Posterior synechia
Angle-closure glaucoma (caused by iris bombe)
Hypotony (due to ciliary body shutdown)
Cystoid macular edema (from long-standing vitritis)
Epiretinal membrane (from long-standing vitritis)
Macular degeneration (from long-standing vitritis)
Tractional retinal detachment (due to vitreal folds)
Phthisis bulbi (end stage of the disease)

Preventing Ocular Toxocariasis

Toxocariasis is a condition that affects the eyes and can lead to permanent loss of vision. Hence, it’s critical for the families of these patients to take preventive steps. Family members should be given clear information about what toxocariasis means for the eyes and why it’s important to keep having check-ups over the long term.

Frequently asked questions

The prognosis for ocular toxocariasis depends on the timing of medical attention. Patients who seek treatment early in the disease's progression have a positive outlook and can prevent vision loss and long-term issues. However, for patients who seek treatment later, the prognosis for their vision is more uncertain due to complications such as optic atrophy, changes in the macula, and retinal detachment.

People can get infected with Ocular Toxocariasis if they accidentally eat contaminated soil or food.

Signs and symptoms of Ocular Toxocariasis include: - Squinting - White color in the eye (leukocoria) - Redness in the eye - Loss of vision - Eye pain - Cells in the front chamber of the eye (anterior chamber) - Widening of the pupil (flare) - Cataracts - Cells behind the lens of the eye (retrolental cells) - Peripheral granuloma: raised white mass in the peripheral part of the eye with surrounding vitreal membranes, pigmentation, and tractional detachment - Posterior granuloma: solitary raised yellow-white mass at the back of the eye (at the macula or around the optic disc) - Endophthalmitis: severe inflammation, pain, redness, watering, and sensitivity to light (photophobia) - Complications if left untreated: cataracts, glaucoma, tractional retinal detachment, scarring of the macula, and phthisis bulbi (shrunken and non-functional eye).

The types of tests that may be needed for Ocular Toxocariasis include: 1. Imaging tests: - Ultrasonography: to detect dense growth in the eye and calcified areas. - Computed tomography: to identify changes in the retinal mass after treatment. 2. Immunological test: - Enzyme-linked immunosorbent assay (ELISA): to detect antibodies against Toxocara infection. However, it may provide false negative or false positive results. 3. Complete blood count: to check for an increase in eosinophils (a type of white blood cell) and immunoglobulins (proteins) in the blood. 4. Tissue biopsy: rarely recommended, but may be used to examine a small piece of tissue. It's important to note that the diagnosis is often made based on the patient's symptoms and medical history, as obtaining tissue samples from the eye is not feasible.

Retinoblastoma, Endophthalmitis, Retinopathy of Prematurity, Toxoplasmosis, Panuveitis, Coats disease, Persistent hyperplastic primary vitreous, Familial exudative vitreoretinopathy, Combined hamartoma of the retina, and retinal pigment epithelium, and seasonal hyperacute panuveitis.

When treating Ocular Toxocariasis, there can be several side effects or complications that may arise. These include: - Posterior synechia: This is a condition where the iris bulges forward and blocks the fluid drainage channel in the eye, leading to angle-closure glaucoma. - Angle-closure glaucoma: This type of glaucoma is caused by iris bombe, which is a result of prolonged inflammation. - Hypotony: Prolonged inflammation can cause the ciliary body, which produces eye fluid, to shut down, resulting in low eye pressure. - Cystoid macular edema: This is swelling or thickening of the macula, the central part of the eye that provides sharp, central vision. - Epiretinal membrane: A thin layer of fibrous tissue that can develop on the surface of the retina due to long-standing vitritis. - Macular degeneration: Prolonged inflammation can lead to the destruction of sharp, central vision. - Tractional retinal detachment: Vitreal folds, the creases in the gel filling the eye, can cause the retina to be pulled from its normal position. - Phthisis bulbi: This is the end stage of the disease, characterized by the shrinking or atrophy of the eye.

An ophthalmologist.

Ocular toxocariasis is a common condition globally.

Ocular toxocariasis is typically treated with corticosteroids to manage inflammation in the eye. These can be applied directly to the eye or taken as medication. Eye drops that dilate the pupil may also be given to prevent the pupil from sticking to the lens and control increased eye pressure. Drugs designed to treat worm infections, like albendazole and thiabendazole, may be used in combination with oral corticosteroids, although their effectiveness in treating ocular toxocariasis is not clear cut. Laser treatment can be used to destroy the worm if it is seen moving beneath the retina. Other complications, such as abnormal blood vessel growth, can be treated with injections into the eye. In advanced cases, surgery may be needed to remove cataracts, perform a pars plana vitrectomy, or reattach the retina. Prevention is also crucial, including maintaining good hygiene, avoiding direct contact with dogs and cats, and teaching healthy habits to prevent the disease.

Ocular toxocariasis is an infection of the eye caused by the worm species Toxocara canis and Toxocara cati. It can manifest in different ways, including peripheral granuloma, posterior granuloma, or endophthalmitis, which are different types of inflammations of the eye.