Case

A 48-year-old woman developed painless bilateral acute visual loss with a progressive visual field defect over 2 weeks. At the initial visit, her best-corrected visual acuity was 6/9 (right) and 6/15 (left). There was a left relative afferent pupillary defect. There was no ptosis, and ocular motility was full. Her retina appeared normal without papilloedema. Her critical flicker fusion frequency was 17 Hz in the right eye and 13 Hz in the left eye (normal range >37 Hz).1 On Humphrey visual field analysis, she had a complete bitemporal hemianopia (figure 1A). MR scan of orbit showed enhanced optic chiasm enlargement with slight extension to the right posterior optic nerve, suggesting a neoplasm or inflammatory process such as sarcoidosis (figure 2A–C).2–4 Her cerebrospinal fluid (CSF) was clear with normal pressure, containing 6 cells/µL (≤5), protein 1.2 g/L (0.15–0.45) and glucose of …