Progressive External Ophthalmoplegia.

Progressive external ophthalmoplegia (PEO), marked by progressive bilateral ptosis and diffuse reduction in ocular motility, represents a finding of mitochondrial myopathy rather than a true diagnosis. PEO often occurs with other systemic features of mitochondrial dysfunction that can cause significant morbidity and mortality. Accurate and early recognition of PEO is paramount for the optimal care of these patients. We present an evidence-based review of the presenting neuro-ophthalmic features, differential diagnosis, diagnostic tools, systemic implications, and treatment options for isolated PEO and other PEO-associated mitochondrial syndromes.