Diffuse Unilateral Subacute Neuroretinitis (DUSN)

Diffuse unilateral subacute neuroretinitis (DUSN) is an infectious eye disease that, if not diagnosed and treated, can lead to severe visual loss or blindness. Conceptually, it is unilateral, affecting healthy children and young adults. The etiological agent is a nematode (presumably Ancylostoma caninum or Baylisascaris procyonis) that causes progressive toxic, inflammatory, and degenerative damage to neuroretinal tissue. The parasite is found in about 40–50% of cases and is most frequently observed in the early stage. The worm (white, mobile, with tapered ends) is generally subretinal. In the early stage, as the disease is almost always unilateral, the symptoms may not be noticed by the patient. For this reason, in their first evaluation, most patients are at an advanced stage of the disease, with a severe reduction in visual acuity (71% with VA < 20/200), extensive scotomas, and severe changes on retinal examination. In the late stage, extensive changes in the RPE and ILM reflex are observed, in addition to tracks and prints of the larva, which can be confused with the image of the larva itself, requiring greater persistence in identification. If undiagnosed and untreated, vision continues to deteriorate, with retinal arteriolar attenuation, sometimes with “sheathing,” increased vitreous cellularity, increased intensity and extension of RPE lesions, atrophy of the neuro-sensory retina (including the macula), and optic nerve atrophy. The most effective treatment is laser photocoagulation of the worm. Despite careful and persistent examination, the worm may not be located. In this situation, the use of oral anthelmintics is necessary.