A 10-year-old female presented in the OPD of an eye care center with a complaint of marked diminution of vision in her left eye for 1 year. Her vision progressively worsened. She also had complained of redness and pain in her left eye in the past.
However, there is no history of discharge, any trauma, no previous history of eye disease. Clinically, the patient was alert and conscious. Her vital signs were stable and was afebrile. Another systemic examination was within normal limits.
On examination, her vision was hand movement in her left eye and 6/6 in her right eye. A gross examination of the eye reveals left exotropia. On slit lamp examination anterior segment was found to be quiet with leukocoria reflex seen in her left eye.
However, her right eye findings were unremarkable. In fundus examination, a large peripheral granuloma/mass superotemporal to disc with dense connective tissue bands in the vitreous that extend from the lesion to the disc margin was present.
In B-Scan ultrasonography, a chorioretinal focal lesion measuring 6*.8 mm in diameter with a “V” shaped vitreous membrane is seen. Diagnosis of ocular toxocariasis was confirmed.
Ocular toxocariasis is a rare infection caused by roundworms, Toxocara canis, and Toxocara cati. It was first recognized to be associated with dogs in the 1940s. It typically affects children and can lead to profound monocular loss of vision despite known medical and surgical therapies.
Its prevalence has been estimated in certain populations and found to be rare. Presentations typically include posterior uveitis with symptoms and signs such as reduced vision, photophobia, floaters, and leukocoria.
Management includes quieting inflammation, eliminating the offending organism, and repairing vitreoretinal sequelae. Prognosis is often correlated to presentation and the degree to which sequelae are present. Vision typically ranges from 20/40 to 20/400 depending on these factors.
The prevalence of this disease has been measured in certain subpopulations as well as the general population. In a North Californian uveitic population, 1% of patients were found to have ocular toxocariasis.
According to Morbidity and Mortality Weekly Report released by the CDC, from September 2009 until September 2010 there were 68 new cases of ocular toxocariasis in the country with an emphasis on new cases from the South (57%).
Typically, this disease manifests in children and early adolescents but 23 case studies found afflicted patients ranging from 8 to 45 years of age. In 2010 the CDC reported an average age in the United States of 8.1 years with a range from 1 to 60 years of age.
Infection by roundworms, Toxocara canis, or Toxocara cati. These nematodes live and mature in dog or cat intestines, respectively. As a mature adult, the organism releases eggs which are passed in the stool. Contact with infected materials leads to human infection.
Management of this disease focuses on three main points:
- Minimizing inflammation
- Eliminating the offending organism
- Addressing vitreal and retinal complications secondary to infection
Topical steroids are typically used to limit inflammation in order to prevent the development of tractional membranes and resulting retinal detachments.
Other options include periocular injections and oral corticosteroids at 0.5-1 mg/kg. In the case of anterior segment inflammation, cycloplegics are also used to prevent the formation of synechiae.
The use of these drugs is unproven in the case of ocular toxocariasis. There is some support for the use of albendazole or thiabendazole to eradicate the organism. Albendazole is the preference of some physicians as it has increased blood-brain barrier penetration.
Medical follow up
There is no standard protocol for medical follow-up specific to ocular toxocariasis. Patients are typically followed as those with other forms of uveitic disease.
The CDC reports that 25% of patients presenting with new cases of ocular toxocariasis require surgery. Vitrectomy is the most common surgical therapy for ocular toxocariasis. The most common indications for surgical intervention are persistent vitreous opacification, hemorrhage, tractional retinal detachment, and epiretinal membranes.
Other indications for retinal surgery include rhegmatogenous retinal detachments. Tractional retinal detachments are more common in cases that include granulomas located in the peripheral retina.
During surgery, it is important to just circumcise the membranes instead of delaminating or peeling them as they tend to be quite adherent. Even though excision of the granuloma has been reported, it is not widely recommended due to the possibility of disastrous complications.
With modern vitreoretinal techniques, anatomical success is 83-100%. Preoperative visual acuity and the presence of a retinal fold across the macula can affect postoperative visual outcomes.
Other interventions include laser photocoagulation and cryotherapy to treat the larva and granuloma respectively.
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Fundus photography is superior to fundus analysis as it enables intraocular pathologies to be photo-captured and encrypted information to be shared with colleagues and patients.
- Brown DH. “Ocular toxocara canis.” J Pediatr Ophthalmol. 1970;7:182-91.
- CDC. “Ocular toxocariasis – United States, 2009-2010.” MMWR. 2011;60:734.
- Good B, Holland CV, et al. “Ocular toxocariasis in school children.”Clin Infect Dis. 2004;39:173-8.
- Gillespie SH, Dinning WJ, et al. “The spectrum of ocular toxocariasis.” Eye. 1993;7:415-8.
- Gioliari GP, Ramirez G, et al. “Surgical treatment of ocular toxocariasis: anatomic and functional results in 45 patients.Eur J Ophthalmol. 2011;21:490-4.
- Schneier AJ, Durand ML. “Ocular toxocariasis: advances in diagnosis and treatment.” Int Ophthalmol Clin. 2011;51:135-44.