Leber's hereditary optic neuropathology (LHON) is an uncommon, hereditary mitochondrial disease. 1 in 50,000 individuals are estimated to have the disease in the Nordic region, and 1 in 9,000 are carriers. Only women can transmit the predisposition on to the next generation. Not all carriers develop symptoms, and in about 40% of those who fall ill there are no known cases on the maternal side of the family. The risk of developing symptoms is approx. 50% in men and 10% in women. LHON is caused by a change (mutation) in the mitochondria's own DNA, which leads to reduced energy-production in the cells. There are different mutations that can cause LHON and three of them are the most common. LHON patients are affected by selective damage and impaired function in certain cells in the eye's retina and optic nerve, which leads to loss of sight in the central field of vision. One eye is usually affected first and after a few weeks to months the other eye as well. In approximately one quarter of the patients, both eyes are affected at the same time. Loss of vision with LHON is usually pain-free. Onset of symptoms often takes place between the ages of 15 and 35, but can occur at all ages. The diagnosis is based on clinical findings and family history, and is confirmed via genetic testing. If genetic tests for the three most common mutations are normal, an in-depth analysis of mitochondrial DNA can be performed. The risk of developing symptoms, as well as the course of the disease, is affected by genetic, hormonal, life-style and environmental factors, among others. Spontaneous improvement can occur, but more than 90 % of patients develop severe vision loss within a year after onset of symptoms. Early diagnosis and deployment of treatment is important in order to maximise treatment results. For information about treatment, contact your doctor.