Ocular toxocariasis, also known as ocular larva migrans (OLM), is a rare parasitic infection that affects the eye. This condition arises when the larvae of Toxocara roundworms invade human ocular tissue. If untreated, these parasites can lead to significant and potentially permanent vision problems.
How the Eye Gets Infected
The origin of these parasites primarily comes from Toxocara canis, the roundworm found in dogs, though Toxocara cati from cats is also a less common source. Humans become accidental hosts when they ingest microscopic Toxocara eggs, often from contaminated soil or objects. Once swallowed, these eggs hatch into larvae within the intestines.
The hatched larvae penetrate the intestinal wall and travel through the bloodstream and lymphatic system. They can travel to various organs throughout the body, including the liver, lungs, and brain. Occasionally, these migrating larvae reach the eye, becoming trapped within the ocular tissues. This migration and encapsulation within the eye triggers an inflammatory response, leading to ocular toxocariasis.
Recognizing the Symptoms
Symptoms of ocular toxocariasis often affect only one eye. Reduced vision in the affected eye is a common complaint, ranging from mild blurriness to severe vision loss. Individuals might also experience eye pain or redness, indicating inflammation within the eye.
Strabismus (crossed eyes) can also develop. Leukocoria, a white reflection in the pupil sometimes called a “cat’s eye reflex,” is another sign, particularly in children. Inflammation (such as uveitis) and granulomas—small inflammatory masses on the retina—are also characteristic findings. Symptoms can vary depending on the exact location of the larva within the eye.
Diagnosis and Treatment
Diagnosing ocular toxocariasis involves a thorough eye examination. Ophthalmoscopy, which visualizes the back of the eye, can reveal granulomas or inflammation on the retina. Blood tests, such as ELISA, can detect Toxocara antibodies, indicating exposure. However, a positive blood test alone does not definitively confirm ocular involvement, as many people can be exposed without developing eye symptoms.
Imaging techniques (ultrasound, CT scans, or MRI) may also help confirm a lesion or differentiate it from other conditions. Treatment aims to minimize eye damage and reduce inflammation. Corticosteroids, given topically or systemically, are commonly used to control inflammation. Anti-parasitic medications (albendazole or mebendazole) might be used, but their effectiveness is debated because encapsulated larvae are difficult to reach. In severe cases, surgery (vitrectomy) may be necessary to remove vitreous opacities, address retinal detachment, or remove the larva.
Preventing Infection
Preventing Toxocara infection involves several practical measures, particularly focusing on hygiene and pet care. Regular handwashing with soap and water is important, especially after playing outdoors, gardening, or handling pets. Prompt disposal of pet waste is also a significant preventive step, as Toxocara eggs become infective in the environment within two to four weeks after being shed in feces.
Regular deworming of pets, especially puppies and kittens, is highly recommended by veterinarians, as young animals are a common source of Toxocara eggs. Covering sandboxes when not in use can prevent animals from contaminating them with feces. Teaching children not to eat dirt or soil can also help reduce the risk of accidental ingestion of parasite eggs.