BASICS

DESCRIPTION

• Ocular toxocariasis is a helminthic disease that is a common cause of posterior uveitis, particularly in children.

• 3 major presentations:

– Endophthalmitis

– Peripheral granuloma

– Posterior granuloma

EPIDEMIOLOGY

• Varies by region; actual incidence is unknown

• Constitutes 1–2% of pediatric uveitis

• Average age of onset is 7.5 years

• 80% of patients are <16 years of age

RISK FACTORS

• Exposure to soil contaminated with canine feces infected with Toxocara canis eggs

• Exposure to infected pets or animals

GENERAL PREVENTION

• Good hygiene

• Reducing exposure to contaminated environment

• Periodic treatment of pets

PATHOPHYSIOLOGY

Inflammatory response secondary to parasitic infection resulting in eosinophilic abscess and chronic granulomatous inflammation

ETIOLOGY

Toxocara canis, the dog roundworm, is the primary causative organism. Infectious eggs are ingested and the developing larvae move hematogenously to the eye or other organs.

COMMONLY ASSOCIATED CONDITIONS

• Visceral larval migrans

– Systemic infection secondary to Toxocara resulting from migration of larvae throughout the body, particularly liver, brain, lung, and eye

– Typically in children, 6 months to 3 years of age

– History of contact with puppies and/or ingestion of soil

– Often asymptomatic, but may have fever, weight loss, and coughing

– Laboratory results may show leukocytosis with eosinophilia, elevated Toxocara IgG and IgM.

– Prognosis usually excellent

– Rarely associated with ocular toxocariasis

DIAGNOSIS

• Clinical features of ocular toxocariasis include:

– Typically, young children but may occur in adults

– Usually unilateral

HISTORY

• Exposure to puppies

• History of ingestion of soil or other contaminated substances (e.g., grass)

• Possible history of systemic infection

• Presence or absence of pain. Toxocara, even in the endophthalmitis form, is rarely painful and does not cause significant photophobia.

PHYSICAL EXAM

Ophthalmic Exam

• Variable, multiple presentations

– Endophthalmitis

– Vitreitis

– Granulomatous keratic precipitates

– Hypopyon may be present

– Possible yellowish-white chorioretinal mass

– Retinal detachment may be present

– Leukocoria may be present

– Peripheral granuloma

– White elevated mass present in the peripheral retina and/or ciliary body region

– Retinal dragging and formation of a falciform fold may occur

– Macular heterotopia may be present

– Posterior granuloma

– Overlying vitreitis and inflammation may be present in the acute stage

– White elevated mass typically 0.5–4 disc diameters in size

– Often diagnosed at older age

– Optic papillitis

Localized infection of the optic nerve

Disc edema with telangiectatic vessels

Possible subretinal exudate

Variable peripapillary nodule

• Other associated ophthalmic findings

– Strabismus

– Amblyopia

– Leukocoria

DIAGNOSTIC TESTS & INTERPRETATION

Diagnostic Procedures/Other

• Thorough slit-lamp and indirect ophthalmoscopic exam are critical to diagnosis

• Ultrasonography is vital for evaluating leukocoria to help distinguish between other possible diagnoses (e.g., calcifications for retinoblastoma, hyaloid remnants for PHPV).

• CBC for eosinophilia is useful for visceral larval migrans, but is not useful for ocular disease.

• Serum and vitreous testing for Toxocara IgG

• Vitreous sample with cytopathologic examination for eosinophils

Pathological Findings

In ocular toxocariasis, granulomatous inflammation with eosinophilic abscess is often present. Significant quantities of eosinophils may be present in the vitreous and uveal tract.

DIFFERENTIAL DIAGNOSIS

• Retinoblastoma

• Coat’s disease

• Persistent hyperplastic primary vitreous (PHPV)

• Retinopathy of prematurity

• Familial exudative vitreoretinopathy

• Toxoplasmosis

TREATMENT

MEDICATION

• Anti-helminthic medications are rarely used for ocular disease.

• Topical or periocular steroids may be used for control of ocular inflammation.

• Topical cycloplegics may be useful in cases with severe anterior segment inflammation.

• Oral steroids may also be employed in cases of severe inflammation.

• Amblyopia and strabismus should be addressed, as indicated.

SURGERY/OTHER PROCEDURES

• Diagnostic pars plana vitrectomy may be performed in cases with unclear etiology to obtain vitreous fluid for analysis.

• Pars plana vitrectomy may also be utilized to address various complications related to the infection (e.g., retinal detachment, severe vitreoretinal traction).

• Laser photocoagulation of the Toxocara larva has been reported.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

• Determined based on severity of inflammation and disease

• Consultation with vitreoretinal specialist and/or pediatric ophthalmologist may be appropriate depending on severity

• Monocular precautions (e.g., eye protection) for all patients with severe unilateral vision loss

PATIENT EDUCATION

• Centers for Disease Control Parasitic Disease Information: Toxocariasis (http://www.cdc.gov/NCIDOD/DPD/PARASITES/toxocara/factsht_toxocara.htm)

• The National Institute for Health and Clinical Excellence Clinical Knowledge Summaries: Toxocariasis (http://www.cks.nhs.uk/patient_information_leaflet/toxocariasis)

PROGNOSIS

• Depends on severity of inflammation and location of the infection in the eye

• Some patients will maintain excellent visual acuity with minimal sequelae and others may have severe complications requiring enucleation.

COMPLICATIONS

• Visual loss

• Retinal detachment

• Phthisis

ADDITIONAL READING

• Sabrosa NA, Zajdenweber M. Nematode infections of the eye: Toxocariasis, onchocerciasis, diffuse unilateral subacute neuroretinitis, and cysticercosis. Ophthalmol Clin North Am 2002;15:351–356.

• Shields JA. Ocular toxocariasis. A review. Surv Ophthalmol 1984;28:361–381.

CODES

ICD9

• 128.0 Toxocariasis

• 360.19 Other endophthalmitis

• 363.20 Chorioretinitis, unspecified

CLINICAL PEARLS

• Retinoblastoma can closely mimic some presentations of toxocariasis and must be ruled out.

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