Toxocariasis

Ocular toxocariasis is caused by the nematode larvae of a common intestinal parasite of dogs (Toxocara canis) or cats (Toxocara cati). This disease, contracted through ingestion of ascarid ova in soil contaminated by dog or cat feces, primarily affects children. Visceral larva migrans (VLM) is an acute systemic infection produced by these organisms; it commonly occurs at approximately age 2 years. If symptomatic, it is associated with fever, cough, rashes, malaise, and anorexia. Laboratory testing reveals eosinophilia. VLM and ocular toxocariasis, for unknown reasons, seldom occur in the same patient.

Ocular toxocariasis is usually unilateral and is not associated with systemic illness or an elevated eosinophil count. The average age at onset is 11.5 years. The 3 major retinal forms of the disease include posterior pole granuloma, peripheral granuloma with macular traction (Fig 24-3), and endophthalmitis. There is often little external evidence of inflammation. Patients may present with leukocoria, strabismus, or decreased vision. These are also common presenting signs and symptoms of retinoblastoma, which must be differentiated from ocular toxocariasis. Because elevated Toxocara titers may be found in a significant percentage of children, a positive result on tests such as the enzyme-linked immunosorbent assay does not rule out other possibilities, including retinoblastoma.

Figure 24-3 Toxocariasis. A, Distortion of posterior pole vessels, right eye. B, Fundus photograph showing macular granuloma. C, Fundus photograph of peripheral granuloma.

Treatment includes observation of peripheral lesions, periocular or systemic steroids for posterior lesions and endophthalmitis, or surgical intervention to address retinal traction, cataract, glaucoma, or cyclitic membranes. Systemic anthelmintics are not useful in treating ocular toxocariasis because the organism may already be dead or its death can produce significant inflammation.

• Woodhall D, Starr MC, Montgomery SP, et al. Ocular toxocariasis: epidemiologic, anatomic, and therapeutic variations based on a survey of ophthalmic subspecialists. Ophthalmology. 2012;119(6):1211–1217.

Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.