&NA;Genetic, epigenetic, or disease‐related factors may change the morphology of the optic nerve. Ophthalmologists should consider the wide variation in the appearance of the optic discs when making a diagnosis. In several important morphometric studies on the optic nerve, aging and racial differences should be considered. Disc rim area decreases with age, with an annual loss of 4000 nerve fibers. Optic nerve aplasia and hypoplasia are not usually genetic but are developmental abnormalities. Neuroradiological evaluation is essential for detecting associated neurodevelopmental and endocrine abnormalities in patients with optic nerve hypoplasia, and photogrammetric evaluation is helpful for detecting mild cases. The extraordinary development of mitochondrial gene analysis in Leber's hereditary optic neuropathy has demonstrated surprisingly large clinical and relatively slight genetic variation in this disease and has revealed the possible contribution of extramitochondrial factors. These points are discussed along with comments on some reports dealing with another condition that bears Leber's name‐‐Leber's congenital amaurosis.Current Opinion in Ophthalmology 1993,4;VI:16‐21