This includes two major entities: maternally inherited Leber hereditary optic neuropathy (LHON), due to mtDNA point mutations affecting cI subunit genes, and autosomal dominant optic atrophy (DOA), which is prevalent due to heterozygous mutation in the nuclear gene OPA1, however also other genetic causes are also described for DOA, almost invariably related to mitochondrial function, in particular to the dynamic homeostatic properties that characterize mitochondria undergoing fusion and fission. The gene discussed is OPA1; the disease is Leber hereditary optic neuropathy.