Photoreceptor Recovery Following Laser Photocoagulation and Albendazole in Diffuse Unilateral Subacute Neuroretinitis

Diffuse unilateral subacute neuroretinitis is a rare condition that typically causes significant vision loss. Herein, we describe spectral-domain optical coherence tomographic (OCT) findings correlating with vision recovery following treatment of a patient with diffuse unilateral subacute neuroretinitis.

A 45-year-old man reported having progressive visual decline, floaters, and photopsias in the left eye for 2 months. One month prior, he was noted to have anterior segment inflammation. Treatment with topical and oral steroids did not halt his vision loss. He reported an unremarkable medical and ocular history. Review of systems revealed recent travel to Mexico and frequent outdoor activity in the northern United States.

Visual acuities measured 20/20 OD and 20/160 OS. A 1.2–log unit relative afferent pupillary defect was present in the left eye. Anterior segment examination findings were unremarkable. Dilated examination of the left eye demonstrated rare vitreous cells, optic nerve pallor, arteriolar attenuation, diffuse retinal pigment epithelial mottling, and a motile 1500-μm nematode in the papillomacular region (Figure 1A and B). Spectral-domain OCT demonstrated widespread outer retinal disruption, the nematode located in the inner retina, and an elevated epiretinal membrane (Figure 1C and D and Figure 2A). Photocoagulation of the worm was performed, avoiding the fovea (Figure 1E). The patient began treatment with a 30-day course of albendazole, 400 mg/d. Three days later, the worm had moved into the superior retina and was still motile. More aggressive photocoagulation was applied and the worm was successfully killed (Figure 1F).

The patient reported significant subjective improvement, and his visual acuity measured 20/40 OS 1 month and 20/25 OS 3 months following the initial visit. Spectral-domain OCT showed disruption of the photoreceptors in the papillomacular region secondary to prior photocoagulation but progressive restoration of the normal inner segment/outer segment junction and photoreceptor architecture in the fovea (Figure 2B and C).

Diffuse unilateral subacute neuroretinitis was initially characterized by Gass et al¹ and further described by Gass and Braunstein.² Typically, patients initially have unilateral ocular inflammation, optic disc swelling, and chorioretinitis. This condition is caused by at least 2 separate nematodes of different sizes. It has been suggested that the smaller nematode, measuring approximately 500 μm in length, is Ancylostoma caninum and the larger nematode, measuring 1500 to 2000 μm in length, is Baylisascaris procyonis.^2-4 Progression to optic atrophy, diffuse arteriolar attenuation, pigmentary degeneration, and significant vision loss occur if the nematode is not killed. The size of the nematode in this case is consistent with the larger worm.

Both antiparasitic medication and thermal laser photocoagulation can halt progression and may lead to visual improvement in some patients with diffuse unilateral subacute neuroretinitis.^5,6 The treatment of choice is photocoagulation if the worm can be identified. At the initial laser treatment, the worm demonstrated rapid movement across the macula, propelling itself with a whipping movement. It was presumed to have been killed when movement ceased. However, 3 days later the worm migrated to the superior retina. At the second photocoagulation, there was minimal movement and more aggressive laser was applied. It is possible that albendazole treatment resulted in impaired motility or that the initial laser injured the nematode.

Spectral-domain OCT demonstrated the initial inner retinal location of the nematode, associated diffuse disruption of the outer retinal architecture, and an elevated epiretinal membrane. Following treatment, progressive restoration of the inner segment/outer segment junction and outer retinal architecture suggests photoreceptor recovery. Persistent optic nerve pallor and visual field loss are likely the result of permanent damage to the ganglion cells, nerve fiber layer, and retinal pigment epithelium. The foveal epiretinal membrane was not seen on subsequent spectral-domain OCT and may have represented an inflammatory change that resolved. These findings coincided with improved visual acuity and support evidence that early killing of the nematode can allow visual improvement correlating with anatomical changes seen on spectral-domain OCT.

Correspondence: Dr Tarantola, Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa, 200 Hawkins Dr, Iowa City, IA 52242 (ryan-tarantola@uiowa.edu).

Financial Disclosure: None reported.

Funding/Support: This work was supported by Research to Prevent Blindness.

Role of the Sponsor: The sponsor had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.