Ocular Toxocariasis

Ocular Toxocariasis
SYMPTOMS Decreased central vision, Metamorphopsia, Visual field loss, Floaters, Eye pain, Photophobia
SIGNS Typically unilateral (90% of the time)
Leukocoria, Anterior uveitis, Posterior uveitis, Posterior synechiae, Vitritis (most common sign), Posterior pole or peripheral granuloma, Retina tractional bands, Snowbanking, Epiretinal membrane, Cystoid macular edema, Vitreomacular traction, Dragging/distortion of the optic nerve, Tractional retinal detachment
A posterior pole or peripheral granuloma is formed due to an inflammatory response to the larvae which becomes encapsulated (when inflammation is active, the granuloma appears as white lesion with indistinct margins and an overlying vitritis / when inflammation is resolved, the granuloma will look like a distinct, well demarcated, elevated white lesion). A pigmented area can sometimes be seen in the granuloma and this represents a dead larvae.
Ocular toxocariasis can also present as a chronic endophthalmitis
WORK-UP Pupils, Full eye exam with dilated retinal exam, Gonioscopy, OCT analysis of the macula, OCT analysis of the optic nerve, OCT-Angiography, Fluorescein Angiography, Indocyanine Green Angiography, Fundus Autofluorescence, Fundus photos, Infrared photos, B-scan ultrasound (if unable to view the retina), Watzke-Allen test, Macular photostress test, Amsler grid
TREATMENT Give take home Amsler grid in order to monitor for change
If patient presents with ocular toxocariasis that is stable without inflammation, the patient needs to be monitored
If patient presents with an anterior uveitis with or without posterior synechiae, the patient should be started on a topical steroid (Prednisolone acetate or Durezol) and a topical cycloplegic (patient will most likely also have a posterior uveitis as well as other complications and will ultimately need to be treated by a retinal specialist)
If patient presents with ocular toxocariasis with active posterior inflammation, refer to a retinal specialist ASAP for further evaluation and treatment including an umbrella of steroid treatment (about 25% of patients will also require surgery such as a vitrectomy)
If patient presents with complications associated with ocular toxocariasis including cystoid macular edema and tractional retinal detachments, refer to a retinal specialist ASAP
FOLLOW-UP If patient is being monitored because ocular toxocariasis is stable without any active complications or inflammation, the patient should be seen back in 6 months
Once the patient's ocular toxocariasis is treated by the retinal specialist and ocular inflammation is no longer active with a stable retina/macula/optic nerve, the patient should be seen back every 6 months
ETIOLOGY Occurs due to infection by nematodes (toxocara canis and/or toxocara cati) after ingestion of eggs that mature into larvae and reaches the eye through systemic circulation of the gut (ocular larva migrans)
DIFFERENTIAL DX Retinoblastoma, Coats disease, Retinopathy of prematurity, Ocular toxoplasmosis, Presumed ocular histoplasmosis
NOTES The origin of ocular toxocariasis is typically associated with exposure to feces from dogs, especially puppies (the prevalence of toxocara canis in puppies is about 80%)
The visual acuity that presents with the initial onset of ocular toxocariasis is typically similar to the final visual acuity after resolution or treatment of ocular toxocariasis
Most patients that end up needing surgery for ocular toxocariasis will usually end up seeing worse than 20/400
Ocular Toxocariasis: Fundus photo demonstrating tractional bands causing dragging/distortion of the optic nerve https://imagebank.asrs.org/file/1730/ocular-toxocariasis-slide-1