MT-ND4 and Leber hereditary optic neuropathy: Because retinal ganglion cells (RGCs) are the structural basis for the recovery of optic nerve function, the gene therapy approach is to transfect normal, non‐mutated ND4 into RGCs at the lesion site of the patient, in order to substitute the physiological function of mutated ND4 in the patient, thus providing treatment for LHON.8 LHON patients with better basal visual function have more functional RGCs, and more normal ND4 protein is expressed by the gene medicine reaching the target cells.