Optical coherence tomography (OCT)Optical Coherence Tomography (OCT) has improved our understanding of hereditary mitochondrial optic neuropathiesOptic neuropathy like Leber’s hereditary optic neuropathyOptic neuropathy (LHON) and dominant optic atrophy (DOA). In LHON mutation carriers and in subacute stage, OCTOptical Coherence Tomography (OCT) shows a thickening of the temporal peripapillary retinal nerve fiber layerPeripapillary retinal nerve fiber layer (RNFLRetinal Nerve Fibre Layer (RNFL)), due to a preferential involvement of the papillo-macular bundle (PMB). In the early pre-symptomatic stage and in subacute stage, an early and progressive thinning of the ganglion cells layer (GCL) is also detectable, following a centrifugal and spiral pattern, reflecting the anatomic distribution of the PMB. A simultaneous thickening takes place in the inferior RNFLRetinal Nerve Fibre Layer (RNFL) sectors for the first 3 months, after which these fibers begin to thin. The superior and nasal sectors are involved later. Once the optic nerveOptic nerve is atrophic, all RNFLRetinal Nerve Fibre Layer (RNFL) and GCL sectors are thinner. Analysis of the optic nerveOptic nerve head (ONH) reveals that larger optic discs are associated with a better prognosis. In DOA, the RNFLRetinal Nerve Fibre Layer (RNFL) and GCL analysis reveals diffuse atrophy in all the sectors. The RNFLRetinal Nerve Fibre Layer (RNFL) thinning is more pronounced in the temporal and inferior quadrants and less evident in the superior and nasal ones. Analysis of the macular GCL suggests an earlier involvement of the macular area. The analysis of choroidal thickness and the introduction of the optical coherence tomography angiographyOptical coherence tomography angiography (OCTOptical Coherence Tomography (OCT)-A), studying the retinal, optic nerveOptic nerve head and choroidal microvascular circulations, show microvascular changes in LHON and DOA and could became useful biomarkersBiomarker to monitor the disease process, evaluate therapeutic efficacy and elucidate pathophysiology.