To report an extremely rare case of optic nerve involvement in Miller-Fisher syndrome.

A 74-year-old woman presented to our clinic with decreased visual acuity in both eyes. Such symptoms started 1 month prior to her visit, after sudden onset of left-side motor power weakness and dysphasia. Following the initial symptoms, our patient consecutively experienced worsening dysphagia, ptosis, and lateral gaze limitation. We confirmed the diagnosis as Miller Fischer syndrome with a positive anti-GQ1b antibody serology. She received immunoglobulin treatment for 5 days in other departement. She visited our clinic due to continuing diplopia, decrease of visual acuity and gait disturbance. On initial examination, the corrected visual acuity was 0.5 in both eyes. Ptosis of both eyelids, esodeviation, limitation in ocular movement was noted. The fundoscopic examinations revealed relatively pale optic disc. There was decrease in color vision in both eyes. The visual evoked potential test showed low amplitude and delayed latency in P₁₀₀ wave in both eyes. Two months after her initial visit to our department her symptoms started to improve, and after 4 months all the initial problems resolved completely and her corrected visual acuity checked out to be 0.8 in both eyes and VEP abnormality was recovered.

It is extremely uncommon for Miller Fisher syndrome to involve the optic nerve. We present such a case of a 74-year-old woman whose symptoms improved 4 months after its first attack with treatment.