Ocular larva migrans, also called ocular toxocariasis, is an eye disease that occurs when the eye is invaded by the larvae of the species Toxocara. The typical symptoms of this disease occur due to the body’s inflammatory reaction to the larvae. A granuloma forms in the retina or optic disk, leading to visual impairment, strabismus, and pain in one eye. The damage due to this disease is often irreversible, and treatment depends on whether the eye is the only organ affected or the organism has invaded the whole body.
Toxocara is an ascarid parasite of cats and dogs. The presence of its larvae in the human body induces the disease called larva migrans. When it involves different organs, the disease is more specifically called visceral larva migrans (VLM). If the disease is limited to the eye, it is called ocular larva migrans.
The two most common causes are Toxocara canis, a parasite of dogs, and Toxocara cati, a parasite of cats. Dogs often release the Toxocara eggs in their stool, which is then deposited into soil or other surfaces. With accidental ingestion of these eggs, they hatch as larvae in the small bowels, invade the intestinal mucosa, and go to the hepatic portal system. From the liver, the larvae can go to the lungs, eyes, brain, and heart by entering the circulation. The parasite’s life cycle is limited to the larval stage in humans, but this larval stage invokes an inflammatory reaction, leading to granuloma or abscess formation.
Ocular larva migrans involves the trapping of the larvae in the eye. The larval parasite may be limited to the retina or may extend into the vitreous or choroid. If it enters through the central retina, it usually induces a peripheral granuloma formation. In case it enters through the posterior ciliary arteries, the granuloma typically forms at the macula or disk.
Unilateral vision impairment or loss, unilateral eye pain, red eye, and strabismus are all symptoms of ocular larva migrans. Upon ophthalmoscopic examination, the granuloma on the optic disk or retina is seen as a white elevated lesion with a size of approximately one disk diameter. Ocular larva migrans complications include chronic endophthalmitis, anterior uveitis, chorioretinitis, and papillitis. Additional symptoms include coughing, headache, abdominal pain, weakness, and fever, and may occur when organs other than the eye are involved. Ocular involvement, however, rarely occurs together with systemic involvement.
Diagnosis of ocular larva migrans involves examination of the optic disk and interview regarding exposure to soil, feces, or dogs. The doctor may request for an antigen test called enzyme-linked immunosorbent assay (ELISA) to determine Toxocara antigen titers. Ocular larva migrans treatment is usually done through the injection of corticosteroids periocularly. Among patients who have significant opacity of the vitreous or with marked retinal traction, a procedure called vitrectomy may be performed. Systemic antihelminthic therapy like mebendazole is not good for ocular larva migrans because it can aggravate the inflammatory granulomatous reaction, leading to worse ocular symptoms.