Study On The Changes Of Ultrastructure And Fibronectin In The Resected Medial Rectus Muscles In Patients With Concomitant Exotropia

PurposeTo study on the changes of ultrastructure and fibronectin in the resected medialrectus muscles in patients with concomitant exotropia, and to have a betterunderstanding about the pathomorpholosical changes of extraocular muscles in thegenesis and development of concomitant exotropia.Materials and methodsTwelve concomitant exotropic patients were chosen as exotropic group and 7normals were selected as control group that were selected from cornea donatorsexcluded strabismus. All the resected tissues of the medial rectus muscles wereobtained from patients with concomitant exotropia during resection surgery andcornea donators. They all were cut into 1 mm~3 pieces,fixed in 3％glutaraldehyde,bufferred, postfixed 4 hours with 1％osmium tetroxide, bufferred, dehydratedgradually in ethyl carbinol, embed in ethoxyline 618. After semithin sectionlocalization, ultrathin-secti stages, stained with toluidine blue uranyl acetate andmedlar clavulanic acid alum,the sections were observed on JEM—1200EXtransmission electron microscope. Statistical comparison was performed on the casenumber that has pathological changes of muscle fiber such as myofibril andmitochondria, and the mean diameter, transverse area and density of collagen fibrilsbetween the control group and the exotropic group.Thirty-five concomitant exotropic patients were chosen as exotropic group and21 normals which were selected from cornea donators were selected as control groupExotropic patients were divided into intermittent s and constant exotropic groups. Allthe resected tissues of the medial rectus muscles were fixed 48 hours,embedded inparaffine and sliced to 3 micron,and then carried out immunohistochemistry study(sp).Fibronectin were measured its mean average Optical Density Value usingimage analyzer. The amounts of fibronectin of resected muscle of patients werecompared with normals, as well as correlated clinical data of patients such as differenttypes of exotropia, age, degree of deviation,gender and positive family history.Results On electron microscopy, various changes are found in both groups. Theseinclude①muscle fiber, myofibrils damages such as arrange disorderly sparse evendissolves, as well as the z belt is unclear or vanishes, presented in 10 cases ofexotropic group while 2 case of control group (P=0.0449). Mitochondriaabnormities, such as vacuole, increment or growing in quantity, presented in 11 casesof exotropic group while 2 case of control group (P=0.0095).②collagen fibrils,groups of collagen fibrils arranged irregularly in different orientations, forming athree-dimensional network in the rectus outside the muscle fibrils in both groups. Allfibrils had a round, regular contour. In the exotropic group, the collagen fibrils werethicker, as reflected by their significantly greater mean diameter: 54.23±6.865nm(mean±standard deviation) compared to 46.96±4.97nm in the control group.Also, significantly greater heterogeneity was found in the collagen fibril thickness ofeach individual in the exotropic group compared to the control group (Mean fibrilarea, nm~2) of the individual of the exotropic and control group were 2394.43±624.44and 1764.62±368.77 respectively(P=0.0272). Within-individual standard deviation offibril area was 651.46±301.13 and 330.99±45.55 respectively (P＜0.0500). However,the mean density of collagen fibrils in the exotropic group was 180.83±58.20 fibrilsper 106 nm~2 compared to 198.57±63.27 fibrils per 106 nm~2 in the control group,which has no statistic significance (P=0.5427).The amounts of fibronectin in the resected medial rectus muscles of patientswith concomitant exotropia (0.5228±0.0991) were significantly lower than those ofnormals (0.5914±0.0547) (P=0.0062). Patients with intermittent exotropia(0.5821±0.0792) showed significantly larger amounts of fibronectin than those withconstant exotropia (0.4729±0.0872) (P=0.0005), while the amounts of fibronectinhad no correction with age and degree of deviation. Neither gender nor positive familywas correlated with the amounts of fibronectin (P＞0.05).Conclusion1. Myofibrillar damage and mitochondrial abnormality suggest that EOMs fromindividuals with concomitant exotropia possess unique structural characteristicssuggestive of relationship with biomechanics that induces this diseases.2. Greater mean diameter of collagen fibrils, heterogeneity in the collagen fibril thickness of each individual and the lower amount of fibronectin in the exotropicgroup may shown abnormal mechanical stress and force conduction. Extracellularmatrix play an important role in the pathogenesis of concomitant exotropia.3. The pathomorpholosical changes of extraocular muscles may be importantfactors in the development of concomitant exotropia, which further research is neededto determine more definitely on.