Bilateral optic nerve sheath enlargement.

A 43-year-old man presented with progressive visual loss in each eye associated with bilateral optic nerve sheath enlargement. At surgery, the left optic nerve sheath was diffusely distended with clear fluid, but biopsy of the optic nerve and its sheath revealed only normal structures. Decompression of the right optic nerve prevented further deterioration of vision in this eye. The etiology of this condition and pathogenesis of visual loss is unknown.