In conclusion, we have examined the EOM MRI appearance of patients with CPEO due to single mtDNA deletions and demonstrated atrophy of all EOMs, more frequent T1w hyperintensities in patients than controls and uniform prolongation of EOM T2 in patients. A correlation between EOM T2 and reduced ocular excursion facility suggests that this parameter might provide a valid, clinically relevant, objective measure of disease severity useful to monitor patients with established CPEO with possible value in future clinical trials.