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Ocular larva migrans is an eye disease caused by the larvae of Toxocara parasites, which can invade the eye and cause visual impairment, pain, and squinting. The disease is often irreversible and can be diagnosed through an examination of the optic disc and exposure history. Treatment involves corticosteroid injections or vitrectomy, but systemic anthelmintic therapy is not recommended.
Ocular larva migrans, also called ocular toxocariasis, is an eye disease that occurs when the eye becomes invaded by larvae of the species Toxocara. The typical symptoms of this disease occur due to the inflammatory reaction of the body to the larvae. A granuloma forms in the retina or optic disc, leading to visual impairment, squinting, and pain in one eye. The damage from this disease is often irreversible, and treatment depends on whether the eye is the only organ affected or whether the organism has invaded the entire body.
Toxocara is a roundworm parasite of dogs and cats. The presence of its larvae in the human body induces the disease called larva migrans. When it involves several organs, the disease is more specifically called visceral larva migrans (VLM). If the disease is confined to the eye, it is referred to as ocular larva migrans.
The two most common causes are Toxocara canis, a parasite of dogs, and Toxocara cati, a parasite of cats. Dogs often shed Toxocara eggs in their feces, which are then deposited in soil or other surfaces. Upon accidental ingestion of these eggs, they hatch as larvae in the small intestine, invade the intestinal mucosa and reach the hepatic portal system. From the liver, the larvae can reach the lungs, eyes, brain and heart by entering the bloodstream. The life cycle of the parasite is limited to the larval stage in humans, but this larval stage causes an inflammatory reaction, leading to the formation of granulomas or abscesses.
Ocular larva migrans involves the entrapment of the larvae in the eye. The larval parasite may be confined to the retina or may extend into the vitreous or choroid. If it enters through the central retina, it usually induces peripheral granuloma formation. In the event that it enters through the posterior ciliary arteries, the granuloma typically forms at the macula or disc.
One-sided vision impairment or loss, one-sided eye pain, red eyes, and squinting are all symptoms of ocular larva migrans. On ophthalmoscopic examination, the granuloma on the optic disc or retina is seen as an elevated white lesion about one disc diameter in size. Complications of ocular larva migrans include chronic endophthalmitis, anterior uveitis, chorioretinitis, and papillitis. Additional symptoms include cough, headache, abdominal pain, weakness, and fever, and can occur when organs other than the eye are involved. Ocular involvement, however, rarely occurs alongside systemic involvement.
Diagnosing ocular larva migrans involves examining the optic disc and interviewing about exposure to soil, feces, or dogs. Your doctor may order an antigen test called an enzyme immunosorbent assay (ELISA) to determine Toxocara antigen titers. Treatment of ocular larva migrans is usually done by periocular corticosteroid injection. Among patients who have significant vitreous opacity or with marked retinal traction, a procedure called a vitrectomy may be performed. Systemic anthelmintic therapy such as mebendazole is not good for ocular larva migrans because it can aggravate the inflammatory granulomatous reaction, leading to worse ocular symptoms.
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