On average people first notice symptoms around the ages of 25 to 35. Some cases have deteriorated slowly for up to two years.
Some people lose their sight suddenly and rapidly.
Both eyes can be affected at the same time, but usually one eye shows symptoms first. The average time interval between the first and second eye being affected is about 2 months. This means that they can see relatively large objects but only by not looking directly at them. Leber's is in my family. In most people, the eyesight damage caused by LHON takes a few months, but can sometimes happen slowly over a couple of years.