Normal tension glaucoma and dominant optic atrophy share many overlapping clinical features, and differentiating between these two diseases is often difficult. The gene responsible for dominant optic atrophy is the OPA1 gene located on chromosome 3. This gene encodes for a protein product that is involved in mitochondrial metabolic function. Recent genetic linkage analysis of patients with normal tension glaucoma has shown an association with polymorphisms of the OPA1 gene. This association suggests that normal tension glaucoma may actually be a hereditary optic neuropathy with a pathophysiology based in mitochondrial dysfunction.