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Tenon's Capsule: Ultrastructure of Collagen Fibrils in Normals and Infantile Esotropia

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Tenon's Capsule: Ultrastructure of Collagen Fibrils in Normals and Infantile Esotropia Investigative Ophthalmology & Visual Science, Vol. 33, No. 3, March 1992 Copyright © Association for Research in Vision and Ophthalmology Tenon's Capsule: Ultrastructure of Collagen Fibrils in Normals and Infantile Esotropia Yaacov Shouly,* Benjamin Miller,* Choim Lichrig,t Michaela Modan4 and Ewy Meyer* No detailed information about the ultrastructure of Tenon's capsule has been published. The purpose of the present study was to compare the ultrastructural features of collagen fibrils from Tenon's capsule in a nonstrabismic control group (seven children) to those in an infantile esotropic group (10 children). Small biopsy specimens from Tenon's capsule were taken during various operations to be examined by electron microscopy. On electron microscopy, the capsule was found to be composed of groups of collagen fibrils arranged irregularly in different orientations, forming a three-dimensional network that provides tissue resistance to stress. The cross-sectioned collagen fibrils were studied by an image analyzer. In both study groups, all fibrils had a round, regular contour. In the esotropic group, the Tenon's collagen fibrils were thicker, as reflected by their significantly greater mean diameter: 101 ± 5 nm (mean ± standard deviation) compared to 86 ± 5 nm in the control group. Also, significantly greater heterogeneity was found in the collagen fibril thickness of each individual in the esotropic group compared to the control group. Moreover, the mean number of collagen fibrils per unit area was significantly higher in the esotropic group: 98 ± 13 fibrils per 106 nm2 compared to 73 ± 5 fibrils per 106 nm2 in the control group. These ultrastructural changes may be stress-induced secondary alterations of the Tenon's collagen fibrils resulting from prolonged deviation of the eye in infantile esotropia. The significantly denser collagen fibrils may cause a decrease in the elasticity of Tenon's capsule in infantile esotropia. Invest Ophthalmol Vis Sci 33:651-656,1992 Tenon's capsule is a fascia made of dense connec- portant role in the physiology of ocular motility by tive tissue that covers the eyeball and the extraocular serving as a cavity within which the eyeball may muscles. This fascia was first described in 1806 by the move. Parisian ophthalmologist and anatomist Jacques Parks4 and other authors56 stress the importance of Rene Tenon.1 There are several synonyms for this fas- Tenon's capsule in squint surgery. An inadequate sur- cia, such as the fascia bulbi and the tunica vaginalis gical technique may cause restriction in ocular motil- oculi, but the most common name is Tenon's capsule. ity due to scarring and adhesions of the capsule to the The four extraocular rectus muscles penetrate extraocular muscles. Tenon's capsule posterior to the equator, whereas the We decided to study the ultrastructural features of two oblique muscles penetrate anterior to the equa- Tenon's capsule because, in reviewing the literature of tor.2 The anterior Tenon's capsule extends from the the last 20 years, we could not find one study on this four muscle penetrations to the limbus. The posterior topic. Long-standing deviation of the eye in one posi- Tenon's capsule lies between the four rectus muscle tion, such as in infantile esotropia, may cause shorten- penetrations and the optic nerve. Not only does ing and loss of elasticity of the conjunctiva and Tenon's capsule support and protect the globe, but it Tenon's capsule.7-8 Because, to the best of our knowl- also connects the eyeball to the orbit.3 It plays an im- edge, no data about the electron microscopic basis of these changes had been previously published, elucida- tion of the ultrastructural features of the capsule seemed appropriate. From the Departments of ""Ophthalmology and fPathology, The main purposes of this research were (1) to Rambam Medical Center and Bruce Rappaport Faculty of Medi- study the ultrastructural features of the collagen fibrils cine, Technion-Israel Institute of Technology, Haifa, and tthe De- of Tenon's capsule in children without strabismus partment of Clinical Epidemiology, Sheba Medical Center, Tel (control group); (2) to study the ultrastructural fea- Hashomer, and Sackler Faculty of Medicine, Tel Aviv University, tures of these collagen fibrils in children with infantile Tel Aviv, Israel. Submitted for publication: February 22, 1991; October 9, 1991. esotropia (esotropic group); and (3) to compare the Reprint requests: Ewy Meyer, MD, Department of Ophthalmol- ultrastructural features of these collagen fibrils in both ogy, Rambam Medical Center, POB 9602, 31096 Haifa, Israel. groups. 651 Downloaded from iovs.arvojournals.org on 09/29/2021 652 INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE / March 1992 Vol. 33 Materials and Methods In each case, a 2 X 2 mm biopsy specimen was taken from the anterior Tenon's capsule overlying the Subjects medial rectus muscle 8-10 mm from the limbus. On The study included 17 children in two study removal, the specimens were immediately cut into groups. small pieces and fixed with ice-cold 3% glutaralde- The control group included seven children without hyde in cacodylate buffer, pH 7.3, for 1 hr, postfixed strabismus who were operated on under general anes- with 2% osmium tetroxide, dehydrated through a se- thesia for congenital cataract (n = 3), traumatic cata- ries of graded alcohols (50-100%), and embedded in ract (n = 2), retinal detachment (n = 1), or intraocular epon. At least four blocks were cut from each biopsy foreign body (n = 1). Their mean age at operation was specimen. Sections 1 ^m thick were stained with tolu- 5.9 ± 5.6 yr (mean ± standard deviation; range, 1 mo idine blue and examined under the light microscope. to 12 yr). The mean refraction of four children in the Thin sections were stained with uranyl acetate and control group was +1.9 ± 1.75 diopters (mean ± SD; lead citrate and were examined with a Zeiss (Oberko- range, -2.0 to +3.25 D). chen, Germany) 9S electron microscope. Small biopsy specimens were taken from Tenon's capsule during the above-mentioned operations, Electron Microscopy and Individual Image Analysis which were associated with tenotomy as an integral part of the surgical procedure. Electron micrographs of Tenon's capsule, enlarged The esotropic group included 10 children operated 3800 times, were taken from areas away from blood on because of infantile esotropia. Their mean age at vessels. Micrographs of cross-sectioned and longitudi- operation was 2.9 ± 2.2 yr (range 1.5-8 yr). Their nally sectioned collagen fibrils, enlarged 56,000 times, mean refraction was +2.25 ± 2.0 D (range -1.5 to also were taken from these regions. For image analysis +5.5 diopters), and their mean angle of deviation was and morphometry, micrographs of the cross-sec- 54 ± 15 prism D (range 30-80 prism D). Five had tioned fibrils then were enlarged an additional 1.9881 dissociated vertical deviation, five had overaction of times (so the final enlargement was 111,333.6 times). inferior oblique muscles, four had amblyopia, two Image analysis was performed using the Stereology had nystagmus, and one had anomalous head pos- program of the Morphomat 30 image analyzer (Zeiss, ture. Oberkochen, Germany). A histologic window with a In all cases, the diagnosis of infantile esotropia was constant area of 2,420,297 nm2 was defined in each made by an ophthalmologist in the pediatric ophthal- electron micrograph. Each histologic window in- mology clinic of Rambam Medical Center. In all cluded 163-304 collagen fibrils. For each patient, cases, manifest esotropia was diagnosed prior to the image analysis of three histologic windows was per- age of 6 mo. The children were treated and followed formed. Final image analysis was based on the pooled up in our pediatric ophthalmology clinic. Only those data of the three histologic windows because prelimi- patients with clinical characteristics of essential infan- 9 nary analysis showed very little variability between tile esotropia were included in the study. the characteristics of the three windows of each indi- Seven patients underwent bilateral recession of the vidual. medial rectus muscles combined with bilateral reces- The pooled area of three windows is denoted as Ar. sion of the conjunctiva and Tenon's capsule over the For each pooled image (j), the number of fibrils (Nj) medial rectus muscles. Three patients underwent re- as well as the area (Aij) and the diameter (Dij) of each section of the lateral rectus muscle and recession of fibril (ij) was measured. Five individual summary fi- the medial rectus muscle combined with recession of bril characteristics were calculated for each pooled the conjunctiva and Tenon's capsule. Small biopsies image, as follows: from Tenon's capsule were taken during these opera- tions. All operations were performed under general 1. Point density (PDYj): The number of fibrils per 6 2 anesthesia. 10 nm of the tissue section, ie, The study was approved by the Helsinki Commit- PDYj = (Nj X 106)/Ar tee of Rambam Medical Center. In all subjects, preop- erative parental informed consent was obtained after 2. Mean fibril diameter (nm) of the individual (Dj): the nature of the biopsy procedure had been fully ex- plained. Qj = 2 DiJ/Nj u=i Tissue Processing 3. Mean fibril area (nm2) of the individual (Aj): Biopsies from Tenon's capsule always were taken during the same procedure and by the same surgeon Aj = 2 Aij/Nj (E.M.) during the various operations. ij Downloaded from iovs.arvojournals.org on 09/29/2021 No. 3 TENON'5 CAPSULE: ULTRASTRUCTURE OF COLLAGEN FIBRILS / Shouly er ol 653 4. Within-individual standard deviation (nm2) of fi- bril area (SD Aij): Zjjl, (Aij ~ Aj)2 SD Aij = Nj- 1 5. Volume density (VDYj): The fraction of the tissue volume occupied by the fibrils, ie, VDYj = 2 Aij/Ar Statistical Comparison Between the Study Groups Mean values ± SD (followed by ranges in parenthe- fmrn ses) pertaining to each of the five individual summary fibril characteristics were computed for each of the Fig.
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