We confirmed that oral NR administration significantly increased NAD+ levels in the retina. ...Oral NR administration significantly prevented retinal ganglion cell (RGC) fiber loss in retinal flat mounts...Our findings suggest that oral NR administration protects against glaucomatous RGC axonal degeneration with the possible upregulation of p-AMPK...A recent study showed reductions in Nampt, Nmnat1, and Nmnat2 in RGCs in glaucoma patients, implying that not only the NAD+ level but also the NAD salvage pathway can be reduced in glaucoma.