Chronic progressive external ophthalmoplegia

Summary Chronic progressive external ophthalmoplegia (CPEO) is a slowly progressive extraocular muscle disorder characterized by bilateral, usually symmetrical, limitation of eye movements and ptosis. This classical manifestation of mitochondrial disease can develop either in isolation or more frequently, in association with other multisystemic features (CPEO plus). An expanding list of nuclear‐encoded mitochondrial genes is now known to cause CPEO phenotypes, predominantly in the context of multiple mitochondrial DNA (mtDNA) deletions, but also as part of mtDNA depletion syndromes. This genetic heterogeneity can result in diagnostic delays, which is further compounded by the clinical challenges inherent in distinguishing CPEO from other disorders that also present with external ophthalmoplegia and ptosis. Corrective ptosis surgery can be a highly effective treatment and alleviating symptoms of diplopia can make a significant difference to the patient's quality of life.