To the Editor,
Ocular toxocariasis often presents with posterior pole granulomas. Peripheral retina and the macula are frequently involved, but optic nerve granulomas are rare (6–19%).Citation1 A comprehensive literature search found no imaging reports of this presentation in the existing literature. To our knowledge, our study is the first to investigate the morphologic features of the optic nerve lesion in a patient with toxocariasis, with images obtained by enhanced-depth imaging optical coherence tomography (EDI-OCT) and fundus autofluorescence (FAF) using a Heidelberg Spectralis SD-OCT (Heidelberg Engineering, Heidelberg, Germany).
A 6-year-old boy living with pet dogs presented with reduced vision of the right eye for 3 months. Examination revealed visual acuity of 20/200, right exotropia, normal pupillary response, 2+vitreous cell and haze, a yellowish lesion overlying the optic nerve, and a raised fibrotic lesion in the temporal periphery. The left eye was normal. The patient’s serum was positive for Toxocara Ab ELISA but negative for toxoplasma IgG and IgM, ANA, herpes simplex virus I & II IgG, CMV IgG and IgM, Lyme IgG and IgM, HLA-B27, and rheumatoid factor, along with an unremarkable CBC.
The patient was treated with oral and topical corticosteroids and mebendazole. Two weeks later the patient’s vitritis had improved, vision improved modestly to 20/100, and he was referred to a pediatric ophthalmologist for amblyopia treatment. The patient’s vitritis completely resolved and visual acuity improved to 20/70 by 2 months. Over an 8-month interval, the patient reached a visual acuity of 20/30 without recurrence of vitritis and with continued amblyopia treatment.
Eight months after the resolution of vitritis, clinical exam and color fundus photography demonstrates a fibrotic lesion at the optic disc. On FAF the lesion has a heterogeneous punctate hyperfluorescent pattern.This modality served as a supplement to fundus photography in defining the boundaries of the lesion over the optic nerve.
Previous macular OCT studies of Toxocara granulomas have reported these lesions as round, subretinal masses associated with surrounding fluid.Citation2,Citation3 Histological examinations of Toxocara granulomas in monkeys were also found to be nodular with fibrous capsules.Citation4 The mass in this study has a similarly nodular appearance and is associated with a hyperreflective fibrotic cap on OCT, though it was not associated with fluid. The mass fills the optic cup and remains superficial over the optic disc, while involving all the layers of the adjacent retina and sparing vasculature. EDI-OCT allows imaging of the deeper levels of the optic nerve than standard techniques and, despite shadowing in some views that preclude definitive judgment, certain views support sparing of deeper nerve layers in our case.
The optic nerve has been suggested as a route of entry for Toxocara larvae into the eye. The presence of an optic nerve granuloma with adjacent vascular sparing supports perineural invasion of the globe. Good visual recovery and lack of afferent pupillary defect in our patient suggests that a significant portion of optic nerve was spared. In conclusion, EDI-OCT of optic nerve Toxocara granulomas identify possible sparing of the deeper nerve layers despite deep involvement of adjacent retina. These lesions can allow good visual recovery.
FIGURE 1 Color fundus photograph (top left) shows a yellow fibrotic lesion on the inferonasal portion of the optic disc. Autofluorescence (top right) shows an area of hypoflourescence with punctate hyperfluorescence corresponding to the color photo lesion. EDI-OCT (lower portion) of the involved eye shows a healed heterogeneous hyperreflective mass partially obscuring the optic cup and limiting confirmation that deeper layers of the optic nerve were not affected secondary to shadowing from the lesion’s dense fibrous cap.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
REFERENCES
- Stewart JM, et al. Prevalence, clinical feature, and causes of vision loss among patients with ocular toxocariasis. Retina. 2005;25(8):1006–1013.
- Higashide T, et al. Optical coherence tomographic and agiographic findings of a case with subretinal Toxocara granuloma. Am J Ophthalmol. 2003;136(1):188–190.
- Lago A, et al. Optical coherence tomography in presumed subretinal Toxocara granuloma: case report. Arq Bras Oftalmol. 2006;69(3):403–405.
- Watzke RC, et al. Toxocara canisinfection of the eye: correlation of clinical observations with developing pathology in the primate model. Arch Ophthalmol. 1984;102:282–291.