Changes as the result of ageing in extraocular muscles: a post-mortem study

Background: Extraocular muscles differ from typical skeletal muscle in many respects such as smaller fibre size, high mitochondrial content, unusual c ontractile/innervation patterns and highly developed microvascular bed. Cha nges in typical skeletal muscle with ageing have been well documented yet t he reports on ageing changes in extraocular muscles is limited. The aim of this study was to examine these changes. Methods: The right inferior and medial rectus muscles were removed at post- mortem from patients with no history of prior ocular or neuromuscular disea se. These included 25 patients aged between 23 and 88 years (14 male, 11 fe male). The median age of the patients was 69 years and 72% of patients were aged older than 66 years. The median post-mortem interval was 28 h. Results: In young adults between 20 and 30 years of age, the muscle fibres were regular, of fairly uniform size with minimal endomysial connective tis sue and no lipofuscin was detected in fibres, in adults between 40 and 50 y ears of age, a small amount of subsarcolemmal lipofuscin was detected. Betw een 50 and 60 years of age, a few fibres with reduced density of myofibrils were noted. All patients over 65 years had definite changes of ageing and those between 70 and 80 years of age showed similar features to those betwe en 60 and 80 years of age. These changes included variation in fibre size, increased endomysial fibrous tissue and increased endomysial adipose tissue , and loss of myofibrils with some fibres devoid of fibrils and comprising 'bags' of mitochondria. There was increased lipofuscin in a number of fibre s; increased 'degenerative' changes such as vacuolation of fibres, scattere d 'eosinophilic intracytoplasmic bodies' and increased numbers of 'ringbind en'.