A young man with blurring of vision in right eye,followed by left eye after 3 months, showing disc hyperemia, edema, circumpapillary telangiectasia with normal pupillary response with centrocecal scotoma on perimetry, the cause is-

The characteristic presentation of Leber's hereditary optic neuropathy is blurring affecting the central visual field of one eye in young adult male; similar symptoms appear in the other eye an average of two to three months late. This sequential appearance of symptoms in young adult is quite characteristic for leber 's hereditary neuropathy. During acute phase fundus may show disc swelling and peripapillary telangiectasis. Pupillary reflex is normal. Toxic and nutritional deficiency optic neuropathies have similar manifestations to Leber's hereditary optic neuropathy. Differentiating features have been mentioned earlier, are:- Most patients of toxic optic neuropathy experience slowly progressive bilateral loss of central vision, in contrast to the sequential involvement in LHON. In toxic optic neuropathy, the fundus may appear normal initially, whereas in LHON, during acute phase fundus changes can be seen.