A 13-year-old boy developed sequential bilateral visual loss with inter-eye delay of 1 year. Mitochondrial DNA mutation at nucleotide position 11778 of Leber's hereditary optic neuropathy (LHON) was detected in the patient who had affected and unaffected maternal relatives. During the acute stage of visual loss in the right eye, the study of flash visual evoked potential was normal whereas pattern reversal visual evoked potential demonstrated prolonged P100 latency without any amplitude reduction which is unusual for LHON.
