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MD is a 32-year-old woman who presented with pain behind her left eye and loss of central vision. The pain worsened on looking horizontally in either direction. Examination revealed visual acuity in that eye of 20/200, a positive afferent pupil defect, and a normal-appearing optic disc. The presumed diagnosis of retrobulbar neuritis was made based on the clinical setting.

Echography was performed, and A-scan measured the right optic nerve to be 3.2 mm in greatest diameter and the left nerve 3.88 mm (Fig. 1). The 30° test was negative with a nonsignificant reduction to 3.74 mm on abduction of the left eye. B-scan showed mild echolucency of subtenon’s space posterior to the left globe. These findings were consistent with optic nerve edema secondary to retrobulbar neuritis.

Fig. 1
figure 00551

A-scan of mild optic nerve thickening in optic neuritis (vertical arrows)

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Most cases of optic neuritis are the result of demyelinating disease, but there are rarely other causes such as sarcoidosis. These patients usually present with a chronic course with fluctuating vision and low-grade pain over time. They may have other areas of ocular inflammation such as iritis, panuveitis, vitritis, and retinal vasculitis.