Preliminary Study On The Structure-function Relationships Of The Extraocular Muscles Connective Tissues In Different Mammals

ObjectivesTo study the structure of extraocular muscles (EOMs) connectivetissues in primate and other lower mammals. To analyze the differences ofits structure among different species, and identify the effects of thestructures on different species' eye movement, especially on high primateeye movement. And to research the role of EOMs connective tissues inhuman to eye movement and binocular vision.Methods1.2 adult rhesus, 5 adult rabbits, 5 adult cats and 5 adult Wistar ratswere anesthetized with ketamine hydrochloride. The gross anatomy of oneof the two orbits in each animal was observed. Meanwhile, the other orbitwas fixed in situ and serially sectioned. A murine monocolonal antibodyto smooth muscle (SM)-α-actin was used to show SM, while Massontrichrome stain was used to show muscles and collagens, and Wergeitstain to show elastin. Analyze the connective tissues around rectusextraocular muscles detail. Select the section of rhesus, rabbits andWistar rats, and abserve the connective tissues around oblique muscles.2. 1 adult rhesus, 4 adult cats and Wistar rats were anesthetized withketamine hydrochloride. Incise the inferointerior fornix conjunctiva withoperation microscope, expose the whole medial rectus tendon. Separatefascia around medial rectus(MR) muscle backward, and expose the whiteand hard connective tissue ring around it. Separate this hard connectivetissue downward, and expose the connective tissue. Take 1×1×1mm~3 block of this connective tissue near medial rectus that between medial rectusand inferior rectus muscle with microscissors. Immerse the specimen inglutaric dialdehyde immediately. Then processed them regularly to TEM,observe their ultrastructures. Take another specimen in the same site forMasson trichrome stain and Weigert stain.Results1. In all the four mammals, an encircling ring of connective tissuecircled each EOM, located near the globe equator in Tenon fascia, andcoupled to adjacent EOMs. But the tendency of connective tissues amongdifferent species was different. The connective tissue(collagen fiber andelastic fiber) ring around MR in rhesus is the most developed ring, andthe band between inferior rectus(IR) and MR is the most developed band.Similar to the elastic fiber, the SM cells were distributed by band betweenMR and IR, and were densest in orbit. The collagen rings were also seenin rabbit and cat. However, they were more thinner and crumblier. Theconnective tissues around MR and between MR and IR was not better thanthat around other EOMs, and SM cells only scattered around the MR withindividual cells. The connective tissue around MR was the mostdeveloped among which around four rectus in Wistar rat. But theconnective tissues band between inferior rectus muscle and MR was notbetter developed than the others.2. The connective tissue between MR and IR in rhesus was moretighter than which in cat and Wistar rat. Collagen matrix with alternatingbands of collagen fibers precisely arranged at right angles to one anotherin rhesus. Elastin fibrils were interspersed in the collagen matrix.Fibtoblasts scattered throughout the connective tissue. SM cells weredistributed in collagen, and did not connect with other SM cells. Therelated structure in cat and Wistar rat were mainly comprised of collagen.not arranged so tightly like that in rhesus. Elastin fibrils, Fibroblasts were scattered throughout the matrix. The alternating bands of collagen fiberswere arranged some angles to one another. There were no manifest SMcells were seen in the sample of cat.3. The orbital layers(OL) of any rectus extraocular muscles did notended at the most manifest connective tissues ring, but went forwards,present void between it and connective tissues ring.4. Both the superior oblique(SO) sheath and tendon pass through thetrochlea. Connective tissues around SO in rabbits and rats thickenedanteriorly, reflected in the trochlea along with the SO tendon, and becamecontiguous with the nasal aspect of the SR connective tissues ring.Rhesus SO OL inserts on a dense collagenous sheath, while globallayer(GL) becomes contiguous with the SO tendon. The SO sheath insertson the SR pulley, while the tendon thins and passes inferior to the SRpulley to insert on the sclera. The connective tissues around inferior oblique(IO) muscle in rhesus, rabbits and rats all connected with that around IRand lateral rectus(LR).5. The connective tissue around inferior oblique (IO) muscle in rhesus,rabbits and rats all connected with that around IR and lateral rectus(LR),but the arrangements among them were not entirely similar. Only theconnective tissue around IO in rhesus consisted of dense collagen,scattered elastic fiber, and connected closelyly with IR, LR Pulley. Theconnective tissues circling IO in rabbits and rats were crumbly, and wasnot connected closelyly with the connective tissues around IR.Conclusions1. The dense, density of connective tissues bands and SM cellsbetween EOMs in primate have some difference to that in other mammals,which suggested the difference of mechanism of eye movement betweenrat, cat, rabbit and primate. The organization of Pulley in primate mayplay a important role in the eye movement Listng raw, and be related to the developed binocular vision.2. The connective tissues between MR and IR in rhesus are tight,which provide great tenacity to MR Pulley and Pulley band in rhesus. Aabundant elastic fibers ensure MR Pulley fine elasticity and extensibility.The cytoarchitecture suggest that they are internally rigid structures.These characteristics make the connective tissues between MR and IR inrhesus more refined than which in cat and Wistar rat. More complicatedfunctions are suggested with these structures in rhesus.3. The OL of any rectus extraocular muscles did not ended at themost manifest connective tissues ring, but went forwards, present voidbetween it and connective tissues ring. This may suggest not all the EOMsOL fibers control the place of the connective tissues ring.4. The connective tissues around SO in three mammals all continueswith the connective tissues surrounding SR, and link with the OL of SOclosely, which shows the contraction of SO OL can cause SR shift nasally.The connective tissues around IO in rhesus, rat and rabbit linked with thatof LR and IR.This may explain the mechanism of vestibulo-ocularreflex(VOR) partly.5. The connective tissues in rhesus is not all similar to that in theother two mammals. In rhesus, it closely linked with OL of IO, IR, and LRPulley. Infer this structural continuation may make the movement of IO,IR and LR influence each other. IR Pulley moves to nasal side and makesextorsion when IO contracts, which shows IR Pulley has some mechanicslink with IO, and can explain the rectus pulley tilt temply in covergence.