Optic atrophy describes a group of diseases of retinal ganglion cells and axons that eventually lead to loss of vision. Optic atrophy has both congenital and acquired causes, and its diagnosis (or differential diagnosis) is complicated. This case report describes a 20-year-old man who presented with a 1-year history of progressive vision loss in both eyes and no obvious systemic symptoms. Fundus examination revealed bilateral optic atrophy. Based on clinical characteristics, visual field analysis and pattern visual evoked potential examination, the presumptive diagnosis was Leber hereditary optic neuropathy (LHON). Analysis of mitochondrial DNA indicated the absence of all of three common mutations associated with LHON (m.3460G>A, m.11778G>A, m.14484T>C). Detailed questioning of the patient revealed a history of prolonged language development and poor balance. Neurological examination indicated abnormal co-ordination, suggesting the presence of inherited spinocerebellar ataxia (SCA). Analysis of the SCA7 gene revealed a high number of trinucleotide repeats [(CAG)n, n > 64], confirming the diagnosis of SCA. The aetiology of optic atrophies is complicated and the molecular genetic detection approach provides the best information for diagnosing these diseases.