Leber's hereditary optic neuropathy (LHON) is a maternally inherited 
mitochondrial disorder with bilateral loss of central vision primarily due to 
mitochondrial DNA (mtDNA) mutations in subunits of complex I in the respiratory 
chain (primary LHON mutations), while other mtDNA mutations can also be 
causative. Since the first description, it is known that LHON is not restricted 
to the eyes but is a multisystem disorder additionally involving the central 
nervous system, ears, endocrinological organs, heart, bone marrow, arteries, 
kidneys, or the peripheral nervous system. Multisystem involvement may start 
before or after the onset of visual impairment. Involvement of organs other than 
the eyes may be subclinical depending on age, ethnicity, and possibly the 
heteroplasmy rate of the responsible primary LHON mutation. Primary LHON 
mutations may rarely manifest without ocular compromise but with arterial 
hypertension, various neurodegenerative diseases, or Leigh syndrome. Patients 
with LHON need to be closely followed up to detect at which point organs other 
than the eyes become affected. Multiorgan disease in LHON often responds more 
favorably to symptomatic treatment than the ocular compromise.