Abbreviations
CPEO Chronic progressive external ophthalmoplegia
EOM(s) Extra-ocular muscle(s)
IO Inferior oblique
IR Inferior rectus
KSS Kearn-Sayre syndrome
LR Lateral rectus
MR Medial rectus
mtDNA Mitochondrial DNA
ROEM Range of eye movement
ROI Region of interest
STIR Short-tau-inversion-recovery
SO Superior oblique
SR Superior rectus

The scientific guarantor of this publication is Robert D.S. Pitceathly (R.D.S.P.). The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article. No complex statistical methods were necessary for this paper. Institutional Review Board approval was obtained. Written informed consent was obtained from all subjects (patients and healthy controls) in this study.
R.D.S.P. is funded by MRC grant number G0800674. M.G.H., J.M.M. and C.D.J.S. are supported by an MRC Centre grant G0601943. S.R. is supported by Great Ormond Street Hospital Children’s Charity. This study was supported by the NIHR UCLH/UCL Comprehensive Biomedical Research Centre and undertaken at University College London Hospitals/University College London, which received a proportion of funding from the Department of Health's National Institute for Health Research Biomedical Research Centres funding scheme. Methodology: prospective, observational, performed at one institution.