Leber hereditary optic neuropathy (LHON) presents with sudden onset of visual 
loss mainly in young adult males. LHON is not uncommon in Australia, accounting 
for 2% of invalid blind pensions. We have identified 20 unrelated families 
carrying mitochondrial DNA mutations associated with LHON and 135 of 291 
individuals with documented LHON are currently alive in Australia. The mean age 
of onset of visual loss for males was 26 years and for females 27 years, with a 
range from six to 65 years. The mean risk of visual loss was 20% for males and 
4% for females. There are over 1750 male and female carriers living in Australia 
who have not yet lost vision; 600 carriers are under 24 years of age. The 
expected number of new cases of blindness from LHON is three to four per year.