What infectious work‑up is recommended for a child or adolescent presenting with unilateral vision loss, vitritis, and a peripheral or macular retinal granuloma suggestive of ocular toxocariasis?

Infectious Work-Up for Ocular Toxocariasis

The diagnosis of ocular toxocariasis is primarily clinical based on characteristic fundoscopic findings (peripheral or macular granuloma with vitritis), supported by serologic testing with enzyme-linked immunosorbent assay (ELISA) for anti-Toxocara IgG antibodies in serum and, when feasible, in aqueous humor to confirm intraocular antibody synthesis. 1

Diagnostic Algorithm

Initial Clinical Assessment

• Perform detailed fundoscopic examination looking specifically for:

  • Peripheral retinal granuloma (occurs in 50% of cases) 2
  • Macular/posterior pole granuloma (occurs in 25% of cases) 2
  • Moderate to severe vitritis mimicking endophthalmitis (occurs in 25% of cases) 2
  • Retinal vasculitis, hemorrhage, or exudative retinal detachment 3

• Document visual acuity and laterality: Ocular toxocariasis is unilateral in 90.9% of cases, with mean patient age of 16.5 years 2

Laboratory Testing

Serologic Testing (Essential):

• Serum anti-Toxocara IgG antibody by ELISA is the primary diagnostic test 1
• Aqueous humor anti-Toxocara IgG antibody by ELISA confirms intraocular synthesis and provides definitive diagnosis when positive 4, 1
  • This is particularly valuable when serum titers are equivocal or when confirming ocular involvement

Peripheral Blood Analysis:

• Complete blood count with differential to assess for eosinophilia 4

  • Important caveat: Eosinophilia is less common in isolated ocular toxocariasis compared to visceral larva migrans 5
  • High peripheral eosinophilia suggests concurrent visceral involvement and warrants systemic evaluation 4

• Total IgE levels may be elevated, particularly in cases with concurrent visceral involvement 4

Imaging Studies

Ocular Imaging (Recommended):

• Optical coherence tomography (OCT) to evaluate:

  • Macular involvement and cystoid macular edema (cause of vision loss in 47.4% of cases) 2
  • Exudative retinal detachment 3, 1
  • Response to treatment 3

• Fluorescein angiography to assess retinal vasculitis and granuloma characteristics 1

• Ocular ultrasound when media opacity prevents adequate fundoscopic visualization 1

Cross-Sectional Imaging (Selective Use):

• CT orbits with contrast or MRI orbits with/without contrast are not routinely indicated for isolated ocular toxocariasis 6
• Consider imaging only if:
  • Diagnosis is uncertain and intraocular mass requires differentiation from retinoblastoma 6
  • Severe orbital inflammation suggests extension beyond the globe 6

Assessment for Systemic Involvement

Screen for visceral larva migrans if:

• High peripheral eosinophilia is present (>1000 cells/μL) 4
• Systemic symptoms exist: fever, cough, wheeze, abdominal pain, hepatosplenomegaly 5
• Patient reports pica behavior or significant environmental exposure 5

Additional testing when systemic involvement suspected:

• Liver function tests 6
• Abdominal ultrasound for hepatosplenomegaly 6

Critical Pitfalls to Avoid

• Do not delay diagnosis waiting for positive serology: The diagnosis is primarily clinical, and treatment decisions should be based on characteristic fundoscopic findings 1

• Do not assume absence of eosinophilia rules out toxocariasis: Isolated ocular disease frequently presents without peripheral eosinophilia 5

• Do not overlook the possibility of concurrent visceral involvement: Co-occurrence of ocular and visceral larva migrans, though uncommon, can occur and requires more intensive treatment 4

• Do not miss causes of vision loss: Systematically evaluate for vitritis (52.6% of vision loss), cystoid macular edema (47.4%), and traction retinal detachment (36.8%) 2

Follow-Up Considerations

• Long-term clinical follow-up is essential even after treatment, as reactivation of migrating larvae can occur 4

• Serial ophthalmologic examinations should monitor for complications including retinal detachment, which can develop even with treatment 3

• Repeat aqueous humor sampling may be considered if diagnosis remains uncertain or disease progresses despite treatment 4