Study On The Morphology Of The Human Rectus Extraocular Muscle Pulley System

ObjectivesHistochemical and immunohistochemical techniques, entire orbit cut in the coronal plane with serially sectioned techniques, computer aided 3D reconstruction techniques were used to study the structure and three-dimensional distribution of the rectus extraocular muscle Pulley system in human orbit. To display histomorpgology of the pulley from multi-aspect and multi-angle, and to provide dissection and histology basis for discussion the function of the pulley. Methods(1)5 fresh cadaver right orbits without eye diseases were fixed in situ and serially sectioned at 4μm thickness. Every nearby section was stained through two special stains including Masson's trichrome stain, We igert'stain and immunohistochemical stain. After being stained, every section was examined through gross anatomy and light microscopy.(2)Selected sets of typical sections of pulley and pulley PB, stained with picrosiriusred method for collagen types. The content and distribution of collagen in the recti EOM pulley and pulley PB were observed with polarization microscopy combined with Mias-2000 image analyzer(3) The pictures of Masson stained adjacent coronal sections of a whole orbit were imaged by digital camera,which were inputted into computer continuously.arfter removing spottiness through photoshop 7.0 software,using 3D-Doctor software to registrate and split the image.finally three-dimensional computerized reconstructions of the rectus EOM pulley and eye ball, rectus muscles and orbit were finished. At thesame time using 3D-Doctor software measuring tools to measure and analyze pulleysystem structure.Results(1) Near the equator of the globe, rectus EOM Pulleys were at the points where rectus penetrate posterior Tenon's fascia, encircling the rectus orbit side by fiber ring sructure. There were Pulley Band among rectus EOM Pulleys. The main composition of the pulley and Pulley Band were collagen, elastic and smooth muscle. Each rectus EOM was consisted of a global layer contiguous with the tendon through pulley and inserting on the eyeball, an orbital layer inserting on the corresponding pulley.Under light microscopy,we found that the number of media rectus muscle fibers were the most, contrasting the other three recti extraocular muscle fibers there was statistically significant (p<0.05) .(2) There were most yellow-red dense collagen type I fibres and less green loose collagen type III fibres in the four rectus EOM pulley and pulley PB under Polarization microscopy. Collagen type I fibres of media rectus extraocular muscle arrayed regularly, as indicated by image analysis, the content of collagen type I fibres are the most among four rectus pulley (p<0.05) . Collagen type I and type III fibres of MR-IR PB were coarse, as indicated by image analysis, the content of collagen type III fibres were bigger than other groups' (p<0.05) .(3) Three-dimensional model of the rectus EOM pulley displayed directly the three-dimensional relationship of pulley and the eye , rectus EOM and orbit. This three-dimensional model could be rotated randomly, providing convenience for multi-angle observation.We could demonstrate the three-dimensional model selectively, providing convenience to get rid of disturbance and lock the aim for observation. Using 3D-Doctor software measuring tools to measure and analyze pulley system structure,we found media rectus pulley was thickest among four rectus pulley.The ratio between media rectus EOM pulley thickness and correspondingmedia rectus thickness could reach 1.11,which average thickness ratio exceeded that of other rectus greatly. The origin of the four rectus pulleys was 13.8—18.0mm from the corneoscleral limbus.The length of pulley was about 4.6—5.8mm. The distance from function spot of the four rectus pulleys to the corneoscleral limbus was: MR:16.8mm;IR: 17.4mm;SR:18.0mm;LR:19.8mm.The distance from the eye center to the function spot of every rectus pulley and tendon insertion were basic equal (7.43mm-8.43mm) . Conclusions:(1) Constitution and three-dimensional distribution in the orbit of Pulley provides histology and anatomic basis as the functional origins of the rectus EOM.(2) Collagen type I fibres and collagen type III fibres with close related mechanical character were main component of the collagen in pulley and pulley PB.Understanding the constitution of the collagen in pulley and pulley PB had an important meaning on representation the relationship of collagen shape, quantity,distribution and keeping binocular vision.(3) Three-dimensional model of the rectusEOM pulley provided direct picture for clinic doctors to understand the structure of pulley, at the same time which also provided three-dimensional anatomic basis for iconography research of the rectus EOM pulley. The data of pulley could be helpful to establish Chinese rectus EOM pulleys data bank.The analysis results of the pulley could be benefitial to represent ocular kinematics theory perfectly,which also could provide strong tool for design ocular kinematics model.