• cytochrome oxidase-negative fibres;
  • fibre typing;
  • myosin heavy chain immunohistochemistry;
  • orbicularis oculi muscle;
  • ‘ragged-red’ fibres


Introduction:  Orbicularis oculi (OO) muscle has recently proposed as a suitable muscle for biopsy to diagnose mitochondrial cyopathy:

Methods:  Enzyme histochemical and immunohistochemical studies were performed on OO muscle obtained from 18 patients aged 37–87 years (median 64 years), 6 males, 12 females, who were undergoing routine upper blepharoplasty surgery.

Results:  We confirmed the marked type II fibre (fast myosin heavy chain) predominance (89%) but also noted a different proportion and distribution of mitochondria in these fibres with occasional pseudo-‘ragged-red’ fibres with prominent subsarcolemmal and cytoplasmic aggregation of mitochondria. Cytochrome oxidase-negative fibres and true ‘ragged-red’ fibres were found at all ages over 40 years at levels that approach those used for diagnosis of mitochondrial cytopathy in peripheral or limb skeletal muscles.

Conclusion:  We would therefore urge caution in the use of OO as muscle biopsy for diagnosis of mitochondrial cytopathy and advise concomitant biopsy of limb skeletal muscle and/or supplementary genetic studies.