Acute blindness.

A 15-year-old man presenting with cortical blindness as the initial symptom of mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) is reported. He showed fluctuating consciousness and severe occipital headache with nausea and vomiting. T2 and diffusion-weighted magnetic resonance imaging showed high signal intensity in the occipital lobes. Electroencephalography showed diffuse sharp waves with focal epileptic discharges over the posterior region. The nature of stroke-like episodes and seizure mechanisms is unexplained in MELAS. Consequently, the possible mechanisms of the cortical blindness in this case are discussed.