The purpose of this case report is to describe accompanying ocular findings, especially optic neuropathy, in a patient with MELAS syndrome.

A 10-year-old male patient who had lactic acidosis and neurological symptoms (loss of consciousness, vomiting, epilepsy, decreased vision, and constricted visual field), underwent a brain magnetic resonance imaging (MRI) scan and a molecular genetic analysis.

A diagnosis of cerebral infarction due to occlusion in the right posterior cerebral artery was made and confirmed by MRI scan. The diagnosis of MELAS syndrome was confirmed by performing molecular genetic analysis demonstrating the transformation of the mitochondrial tRNA^leu(UUR) gene (MTTL1) A to G⁽³²⁴³⁾. According to the ocular examinations, the patient's left eye showed decreased vision, hemianopsia, relative afferent pupillary defects, mild swelling of optic nerve, and decreased amplitude on visual evoked potential exam.

We encountered a case of MELAS syndrome involving optic neuropathy, which can (although rarely) occur with this syndrome. Therefore, in patients with an optic neuropathy of uncertain etiology, clinicians should consider performing comprehensive ocular exams and molecular genetic exams to rule out the possibility of genetic diseases.