The disease was first described by the German eye specialist Theodore Leber in 1871.
The illness usually occurs in men, although some women can be affected.
There is no warning of the onset of the condition
Once a member of a family is diagnosed as having Leber's Hereditary Optic Neuropathy (LHON) then other members of the family are known to be potential sufferers or carriers.
There is no way of predicting whether or not an "at risk" person will develop symptons of LHON. Not every "at risk" individual becomes a sufferer.
Only women can pass the problem on to their children, men are not known to pass on the disease.
Eyesight can deteriorate over a period of hours to months. Both eyes are typically involved, although to varying degrees. Very rarely eyesight may improve or recover.
Most LHON sufferers are registered (legally) blind, although many retain enough useable eyesight to remain mobile, i.e. they can move around in familiar surroundings without any trouble but cannot drive a car or read without massive magnification.
Typically, sufferers cannot recognise people in the street, although they may be able to make out moving shapes as they approach. Ordinary eyeglasses or contact lenses are of no practical help as they alter focal length and not magnification. Low Visual Aids to help with reading are available from the National Health Service and some opticians.
There is no known cause or cure for the disease. Genetic defects have been identified in some sufferers, but this does not yet help to predict future sufferers as many people carry the genetic defect but do not lose their vision.
There is often no way to recognise a sufferer in public as the defect is in the optic nerve. The eyes appear perfectly normal.