Muscle fiber types of human extraocular muscles: a histochemical and immunohistochemical study.
OBJECTIVE
To classify muscle fibers of human extraocular muscle (hEOM) and to compare them to previous studies on hEOM, as well as to nonhuman EOM classification schemes and skeletal muscle fiber types.


METHODS
Muscle fibers cut in different muscle planes were followed on consecutive cross sections and typed with regard to their oxidative profile in combination with their myosin-immunohistochemical characteristics.


RESULTS
Three zones were observed. In the global layer three muscle fiber types were observed: global layer singly innervated granular fibers, 79.4 +/- 8.1 microm (perimeter [values at midmuscle region] +/- SD); 59%; global layer singly innervated coarse fibers (80.3 +/- 10.8 microm; 21%); and global layer multiply innervated muscle fibers (4.1 +/- 9.7 microm; 21%). Two muscle fiber types were detected in the orbital layer: orbital layer singly innervated muscle fibers (54.1 +/- 8.5 microm; 83%) and orbital layer multiply innervated muscle fibers (53.5 +/- 7.6 microm; 17%). Three muscle fiber types were differed in the marginal zone: marginal zone singly innervated muscle fibers (83.1 +/- 15.8 microm; 56%), marginal zone multiply innervated low oxidative muscle fibers (84.4 +/- 23.3 microm; 7%), and marginal zone multiply innervated high oxidative muscle fibers (88.4 +/- 14.5 microm; 37%). Coexpressions of developmental myosin heavy chain isoforms and fast myosin heavy chain isoform were detected mainly in the marginal zone.


CONCLUSIONS
hEOMs resemble mammalian EOM with regard to their organization. However, in addition to an inner global layer and an orbital layer an external marginal zone was described for the first time in hEOM in the present study.
Wasicky
R
R
Institute of Anatomy, University of Vienna, Austria. richard.wasicky@univie.ac.at
Ziya-Ghazvini
F
F
Blumer
R
R
Lukas
J R
JR
Mayr
R
R
D000368:Aged; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D006651:Histocytochemistry; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000145:classification* / Q000166:cytology* / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D009246:NADH Tetrazolium Reductase / Q000378:metabolism; D009801:Oculomotor Muscles / Q000166:cytology* / Q000294:innervation / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000378:metabolism
D013385:Succinate Dehydrogenase; D009246:NADH Tetrazolium Reductase; D003576:Electron Transport Complex IV; D018995:Myosin Heavy Chains; D009218:Myosins