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A 19-year-old man attended our neuromuscular clinic with bilateral ptosis and limited ocular movements present since birth. He had no relevant family history. He had been born at term to non-consanguineous parents and had age-appropriate developmental milestones. Previously, extensive investigation had been inconclusive, including normal serum creatine kinase and a muscle biopsy (when aged 3 years) with no relevant histological changes and normal analysis of the respiratory chain activity. On examination at age 19, he had bilateral ptosis with fixed infraduction, limited upgaze and severely restricted horizontal eye movements, without pupillary involvement. The remaining neurological examination was normal. His visual acuities were 6/7.5 (right) and 6/9 (left). The main differential diagnosis was a mitochondrial disease, and so we also looked for signs of mitochondrial retinopathies. There was no retinal dystrophy and no features resembling retinitis pigmentosa or maculopathy. The optic discs were normal on fundoscopy and optical coherence tomography and visual evoked potentials were normal.