Laboratory tests of ocular toxocariasis: From pathological diagnosis to immunological diagnosis

Ocular toxocariasis (OT) is an inflammatory eye disorder caused by intraocular migration of Toxocara canis or Toxocara cati larvae, constituting a significant cause of visual impairment among children in developing countries. Early and precise diagnosis is crucial for patients' optimal treatment and favorable prognosis. We elucidate 2 commonly employed laboratory diagnostic methods, including early pathological diagnosis and the currently predominant immunological diagnosis, and discuss the limitations inherent to each approach. Although pathological diagnosis is the gold standard for OT, the technical difficulty and inherent risks of ocular tissue biopsy limit its routine use in clinical practice. The first detection of anti-Toxocara IgG (T-IgG) in the vitreous and aqueous humor (AH) in 1979 established a basis for the immunological diagnosis of OT. ELISA is a commonly applied immunological detection method, with various commercial kits available targeting different antigens. Isolated serum anti-Toxocara IgG (T-IgG) testing cannot support an OT diagnosis, whereas intraocular T-IgG detection now constitutes the preferred laboratory diagnostic method. AH provides a reliable proxy when vitreous sampling is unfeasible. When T-IgG detection alone proves inconclusive, supplementary measurement of total IgE levels and eosinophil counts in intraocular fluids (IF) may enhance diagnostic accuracy. Furthermore, WB analysis and cytokine profiling of IF can serve as auxiliary diagnostic tools. Currently, Goldmann-Witmer coefficient (GWC) calculation is recommended for the definitive diagnosis of OT. Given the technical complexity and economic burden of total IgG assays, the feasibility of omitting GWC correction in patients with positive intraocular T-IgG and compatible ocular manifestations requires validation through large-scale multicenter studies. In aggregate, definitive parasite identification through ocular histopathology or imaging remains limited in OT clinical management, rendering immunological methods essential for diagnosis when direct parasitological evidence is absent.