Leber hereditary optic neuropathy is a maternally inherited type of blindness caused by degeneration of the optic nerve. It is caused by point mutations in mitochondrial DNA. Like in other mitochondrial diseases, its penetrance and inheritance is complicated by heteroplasmy, tissue distribution, and the bottleneck phenomenon in oocyte maturation. On the cellular level, the mechanism of the disease development is still mysterious. Currently three theories of pathomechanism of LHON are considered: biochemical, ROS (reactive oxygen species) and apoptotic.