The present invention provides a novel pharmaceutical use of 2-phenyl-1,2-benzisoselenazol-3(2H)-one or a salt thereof. 2-Phenyl-1,2-benzisoselenazol-3(2H)-one or a salt thereof exhibits an excellent suppressive effect on retinal ganglion cell death in a pharmacological test using rats, and is therefore useful as a prophylactic or therapeutic agent for an eye disease accompanied by optic nerve disorder.
