What is Ocular Toxocariasis
Ocular toxocariasis is a rare parasitic eye infection caused by larvae of the roundworms Toxocara canis (from dogs) or Toxocara cati (from cats) that invade ocular tissues, most commonly affecting children and frequently causing permanent vision loss. 1, 2
Pathophysiology and Transmission
Humans become infected by accidentally ingesting embryonated Toxocara eggs from contaminated soil, unwashed fruits/vegetables, or contact with infected dog/cat feces. 3
After ingestion, larvae migrate through tissues and can reach the eye via hematogenous spread, where they typically involve the uvea and retina. 1
This is distinct from visceral larva migrans—ocular toxocariasis represents isolated eye involvement without systemic disease in most cases. 3
Clinical Presentation
The disease manifests in three primary patterns:
Peripheral retinal granuloma (50% of cases): A raised, white subretinal lesion typically in the peripheral retina. 4
Posterior pole/macular granuloma (25% of cases): Similar lesion but located at or near the macula, with worse visual prognosis. 4
Endophthalmitis-like presentation (25% of cases): Moderate to severe vitreous inflammation mimicking bacterial endophthalmitis. 4
Key Diagnostic Features
The most common presenting symptom is vision loss (83% of patients), with 68% suffering permanent visual impairment. 2
Inflammation is typically unilateral (91% of cases). 4
The median age at diagnosis is 8.5 years, though it can occur at any age (range 1-60 years). 2
Critical pitfall: Eosinophilia is often absent in isolated ocular disease, unlike visceral larva migrans. 5, 6
Causes of Vision Loss
The primary mechanisms of visual impairment include:
- Vitritis (52.6% of cases) 4
- Cystoid macular edema (47.4%) 4
- Traction retinal detachment (36.8%) 4
- Direct macular involvement by granuloma 7, 4
- Choroidal neovascular membrane formation (rare complication) 7
Epidemiology
Ocular toxocariasis accounts for approximately 1% of all uveitis cases seen at specialized referral centers. 4
The disease is more prevalent in the southern United States (57% of cases). 2
Children are at highest risk due to closer soil contact, poor hand hygiene, and pica behavior. 3
Distribution is worldwide, though higher incidence is documented in the United States. 7, 8