This study is meant to assess the effectiveness of idebenone on visual function measures in patients with Leber's Hereditary Optic Neuropathy over a 6 months period.

The study involves 6 clinic visits.

Inclusion Criteria:

• Age > or = 14 years and < 65 years
• Impaired visual acuity in at least one eye due to LHON
• Onset of visual loss due to LHON lies five years or less prior to Baseline
• Confirmation of either G11778A, T14484C or G3460A LHON mtDNA mutations at >60% in blood
• No explanation for the visual failure besides LHON
• Body weight ≥ 45 kg
• Negative urine pregnancy test at Screening and at Baseline (women of childbearing potential).

Exclusion Criteria:

• Treatment with Coenzyme Q10 or idebenone within 1 month prior to Baseline
• Pregnancy and/or breast-feeding
• Weekly alcohol intake 35 units (men) or 24 units (women)
• Current drug abuse
• Clinically significant abnormalities of clinical haematology or biochemistry including, but not limited to, elevations greater than 2 times the upper limit of normal of AST, ALT or creatinine
• Participation in another clinical trial of any investigational drug within 3 months prior to Baseline
• Other factor that, in the investigator's opinion, excludes the patient from entering the study