Previous reports of EOM atrophy in CPEO are mixed and rather limited: Carlow et al. [4] examined MR, LR and IR volume in eight clinically diagnosed CPEO patients showing an overall 41 % reduction vs. controls. In a smaller series, EOM atrophy was reported on CT imaging of four clinically diagnosed CPEO patients [7]. Ortube et al. [6] detected isolated atrophy of SR and SO in five CPEO patients compared with controls. Finally, more recent work confirmed a primary myopathic rather than supranuclear pathway dysfunction aetiology for the limitation of eye movement in CPEO as evidenced by significant EOM atrophy in patients with single or multiple mtDNA deletions compared with controls [11]. Our EOM cross-sectional area results, incorporating SR and SO muscles in addition to MR, LR and IR, were consistent with these findings.