Thus, the investigators first carried out preliminary studies to verify the safety and efficacy of gene therapy for LHON by injecting a single vitreous cavity injection of recombinant Adeno-Associated Virus-NADH dehydrogenase, subunit 4 (complex I) to the worst-affected eye and noticed that six out of nine patients have vision improvement and no adverse events were observed [39]. This evidence concerns the gene MT-ND4 and Leber hereditary optic neuropathy.