Leber's hereditary optic neuropathy is a genetic defect, which can lead to optic nerve damage or neuropathy, is called by roughly one in every 9,000 people. Around 50 per cent of men and 80 per cent of women with the disorder will suffer no loss of vision. The main symptom is the sudden loss of vision, which is caused by a death of cells in the optic nerve responsible for relaying visual information from the eyes to the brain. Once cells start dying, affected eyes will begin seeing colours that appear more washed out. Within a period of eight weeks, it can lead to near or total blindness.