A 26-year-old Asian woman presented with a four day history of unilateral left-sided altitudinal visual loss associated with painful eye movements, headaches, nasal obstructive and catarrhal symptoms. She was asthmatic and had undergone endoscopic sinus surgery and nasal polypectomy for chronic sinusitis five months previously. On more detailed questioning, she described a three day history of gradual loss of sight occurring from the superior to the inferior aspect of her vision - 'like a shadow' falling over her left eye where she was able to see 'grey only' in the upper half of her left visual field with the lower half appearing 'blurry'. In addition, she had been concurrently experiencing dull pain around her left eye and on eye movements, especially left eye adduction. Over the next 24 hours her vision further deteriorated. She was now able to see 'grey only' in the whole left visual field at which point she presented to hospital. She had been suffering from a background of nasal congestive symptoms and intermittent headaches for the previous ten days. On admission, her visual acuity was 6/4 in her right eye and limited to perception of light in her left eye in all quadrants. In her left eye, there was a relative afferent pupillary defect and red desaturation. Eye movements were normal. Fundoscopy of her left eye revealed optic disc swelling but nothing else; the macula was normal, there was no vascular sheathing and spontaneous venous pulsation was present. Computed tomography of the brain showed normal intracranial appearances but opacfication of frontal, ethmoidal and sphenoidal sinuses. Magnetic resonance imaging showed an increased signal in the left optic nerve proximal to the optic chiasm suggestive of neuritis but no evidence of optic nerve compression. Blood tests revealed mild peripheral eosinophilia (absolute eosinophils = 0.8 × 109/L, normal interval: 0.0-0.4 × 109/L) though overall white cell count normal (8.8 × 109/L) and other white cell differential count unremarkable (absolute lymphocytes = 2.5 × 109/L, normal interval: 1-3.5 × 109/L; absolute monocytes = 0.4 × 109/L, normal interval: 0.3-1 × 109/L; absolute neutrophils = 5.1 × 109/L, normal interval: 2-7.5 × 109/L; absolute basophils = 0.1 × 109/L, normal interval: 0-0.1 × 109/L). Inflammatory markers showed slightly elevated ESR (14 mm/hour) and normal C-reactive protein (7 mg/L). Serum IgM 2.26 g/L (normal interval: 0.50-1.90 g/L) was raised though other antibodies were within normal ranges: serum IgG 14.2 g/L (normal interval: 5.4-16.1 g/L); serum immunoglobulin A 2.29 (normal interval: 0.8-2.80 g/L); and serum immunoglobulin E 99 kU/L. Other laboratory findings included: haemoglobin 13.4 g/dL, platelet count 378 × 109L, normal liver function and renal function, HIV status negative, syphilis serology negative and lyme serology negative. A lumbar puncture was performed which revealed a normal opening pressure (11 mmHg). Cerebrospinal fluid (CSF) protein electrophoresis showed no evidence of immunoglobulin G oligoclonal bands. CSF direct microscopy/culture showed no organisms on Gram stain and no growth at two days. Visual evoked potential testing showed absent P100 cortical responses to full field monocular stimulation of her left eye using both large and small check sizes consistent with a left optic neuropathy. The right eye studies were within the normal latency limits. She was treated with intravenous augmentin, amphotericin and methylprednisolone and four days later underwent radical sphenoethmoid disease clearance, revealing thick 'axle-grease' mucin. A sphenoethmoidectomy was completed to the level of the skull base, with wide sphenoidotomies and antrostomies fashioned. After the disease clearance, the walls of the sphenoid sinuses were inspected but no bony defect was found. The lamina papyracea were inspected on both sides but no defect was found. A histological analysis of the mucin and polypoid inflammatory tissue revealed abundant eosinophilic infiltrate and eosinophilic debris but no demonstrable fungal hyphae. Fungal cultures were negative. A diagnosis of EMRS was made. She was discharged ten days later on oral voriconazole and prednisolone. Visual acuity was to hand movements in her left eye and 6/4 in the right. At one month, there was gradual improvement to counting fingers in her left eye.