To report a case of acute zonal occult outer retinopathy (AZOOR), initially misdiagnosed as retrobulbar optic neuritis, which was responsive to an immunosuppressive agent.

A 28-year-old female with photopsia and a visual field defect in the left eye was referred to a hospital. There were no fundus abnormalities to explain her left visual field defect. Neurologic examination and brain MRI were normal. The patient was diagnosed with retrobulbar optic neuritis and treated with high-dose steroids. Four months after the onset of symptoms, she visited our hospital. Visual acuity was hand motion in the left eye. No relative afferent pupillary defect in the left eye and no anterior segment or fundus abnormalities were observed. A visual field examination of the right eye was normal and revealed field defect in the left eye. No abnormality was noted in the visual evoked potential test or fluorescein angiography. All examinations of the right eye were normal. In the left eye, fundus autofluorescence showed a hyperautofluorescent spot at the posterior pole, there was a decreased response in electroretinography and spectral domain optic coherence tomography showed that the junction between the photoreceptor inner and outer segments (IS/OS) was faintly visible only in the fovea. With the presumptive diagnosis of AZOOR, the patient was treated with an immunosuppressive agent. Visual acuity improved to 20/80 in the left eye at 10 months after the onset of symptoms.

Electroretinogaphy is essential to diagnose AZOOR in patients with photopsia, visual field defect and minimal or no fundus changes, especially in a young women. There is currently no proven standard treatment, however immunosuppressive agents may be helpful.