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ERROR: type should be string, got "https://doi.org/10.1007/s00417-020-04939-7\nGraefe's Archive for Clinical and Experimental Ophthalmology (2021) 259:145–155 https://doi.org/10.1007/s00417-020-04939-7\nGraefe's Archive for Clinical and Experimental Ophthalmology (2021) 259:145–155 NEUROPHTHALMOLOGY * Andrea Hedergott\nandrea.hedergott@uk-koeln.de Abstract Background For some patients with complex ocular motility disorders, conventional strabismus surgery is insufficient. Surgery\nwith tendon elongation allows correction of larger angles and maintains a sufficient arc of contact for rectus muscles. This study\nreports results for tendon elongation with bovine pericardium (Tutopatch®) in indications other than Graves’ orbitopathy in\nwhich it is already widely used. Methods We reviewed the records of all patients who underwent surgery with Tutopatch® in our institution. Angles of squint\nand head postures were analyzed preoperatively, on the first postoperative day, and in the long term (median 9 weeks after the\noperation). Patients with Graves’ orbitopathy were excluded. Results From 2011 to 2018, the procedures on 58 eyes of 54 patients (35 females, median age 35 years (3–75)) met the inclusion\ncriteria. Horizontal rectus muscle surgery (53 eyes) was conducted on patients with residual strabismus (13), Duane’s retraction\nsyndrome with eso- (type I: 16)/exodeviation (type II: 2, type III: 1), 6th (7)/3rd nerve palsy (7), Möbius syndrome (2), congenital\nfibrosis of the extraocular muscles type 3A (CFEOM3A, TUBB3 mutation) (4), and orbital apex syndrome (1). Vertical rectus\nmuscle surgery (5 eyes) was conducted on patients with myasthenia (1), vertical tropia after orbital floor fracture (1), CFEOM1\n(2), and Parry-Romberg syndrome (1). 42 eyes had prior eye muscle surgery (1–5 procedures, median 1). Out of 45 patients with\npostoperative long-term data, 43 showed an angle reduction. Fifty-one percent had an angle of 10Δ (prism diopter) or less, one\nhad a significant over-effect, and 10 had revision surgery. For the heterogeneous group of residual eso- and exotropias, the\nmedian absolute horizontal angle was reduced from 35Δ (16 to 45Δ) to 9Δ (0 to 40Δ), for Duane’s retraction syndrome from\n27.5Δ (9 to 40Δ) to 7Δ (0 to 40Δ), and for sixth and third nerve palsies from 43Δ (20 to 75Δ) to 18Δ (4 to 40Δ). For 3 patients\nwith vertical rectus muscle surgery, the median absolute vertical angle was reduced from 30Δ (20 to 45Δ) to 4Δ (1 to 22Δ). The\nmotility range was shifted in the direction contrary to the elongated muscle in all subgroups. A considerable reduction of the\nexcursion into the field of action of the elongated muscle had to be registered. Conclusions Strabismus surgery with bovine pericardium introduces new surgical options for complicated revisions and for rare and\ncomplex oculomotor dysfunctions. 1\nDepartment of Ophthalmology, Faculty of Medicine and University\nHospital Cologne, University of Cologne, Kerpener Strasse 62,\n50937 Cologne, Germany Abstract Yet, it has to be recognized that this type of surgery aiming at maximum effects, despite preservation\nor restitution of the arc of contact, leads to reduction of the excursion into the field of action of the elongated muscle. Furthermore, dose\nfinding can be difficult depending on the underlying pathology and more than one intervention might be necessary for optimal results. Keywords Bovine pericardium . Tutopatch® . Strabismus surgery . Tendon elongation This study was presented at the annual meeting of the German Society of\nOphthalmology (DOG) 2019, 26.09. – 29.09., Berlin, Germany. Andrea Hedergott1\n& Ursula Pink-Theofylaktopoulos1 & Antje Neugebauer1 & Julia Fricke1 Received: 29 April 2020 /Revised: 18 August 2020 /Accepted: 10 September 2020\n# The Author(s) 2020\n/ Published online: 19 September 2020 Introduction Electronic supplementary material The online version of this article\n(https://doi.org/10.1007/s00417-020-04939-7) contains supplementary\nmaterial, which is available to authorized users. Primarily used in cardiothoracic, vascular, and neurosurgery,\nbovine pericardium has been introduced into ophthalmosurgery\naround the turn of the millennium [1, 2]. Its use was described\nfor coating hydroxyapatite implants in enucleation surgery, cov-\nering Ahmed implants in glaucoma surgery, or as a corneal\npatch in corneal ulcers [3–7]. In eye muscle surgery recessions are limited: the recessed\nmuscles should not be placed far behind the equator to Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 146 Key messages\nTendon elongation with bovine pericardium (Tutopatch®) is widely used in patients with Graves´ Orbitopathy. This study proofs that tendon elongation with Tutopatch® is a safe surgical method beyond this indication. Tutopatch® introduces new surgical options for complex and/or rare oculomotor dysfunctions, especially for \ncomplicated revisions, large angles of squint and residual head postures, where conventional eye muscle surgery has \nlimits. Key messages\nTendon elongation with bovine pericardium (Tutopatch®) is widely used in patients with Graves´ Orbitopathy. This study proofs that tendon elongation with Tutopatch® is a safe surgical method beyond this indication. Tutopatch® introduces new surgical options for complex and/or rare oculomotor dysfunctions, especially for \ncomplicated revisions, large angles of squint and residual head postures, where conventional eye muscle surgery has \nlimits. Tendon elongation with bovine pericardium (Tutopatch®) is widely used in patients with Graves´ Orbitopathy. This study proofs that tendon elongation with Tutopatch® is a safe surgical method beyond this indication. Tutopatch® introduces new surgical options for complex and/or rare oculomotor dysfunctions, especially for \ncomplicated revisions, large angles of squint and residual head postures, where conventional eye muscle surgery has \nlimits. Tutopatch® introduces new surgical options for complex and/or rare oculomotor dysfunctions, especially for \ncomplicated revisions, large angles of squint and residual head postures, where conventional eye muscle surgery has \nlimits. Orthoptic and ophthalmologic examination The motility of each eye was recorded with regard to\nover- or underactions in the main fields of action of all\nsix eye muscles (The patient was asked to follow a pen-\nlight with his eyes without moving the head. Monocular\nexcursions in the six main fields of action of the eye\nmuscles were estimated in degrees by an experienced\northoptist) The motility of each eye was recorded with regard to\nover- or underactions in the main fields of action of all\nsix eye muscles (The patient was asked to follow a pen-\nlight with his eyes without moving the head. Monocular\nexcursions in the six main fields of action of the eye\nmuscles were estimated in degrees by an experienced\northoptist) Within this study, we report results and experiences of\ntendon elongation with bovine pericardium (Tutopatch®) in\na large series with 58 eyes of 54 patients for various indica-\ntions beyond Graves’ orbitopathy. Measurement at the tangent screen of Harms was per-\nformed in the six fields of action of the eye whenever possible\n(especially patients with paresis and restrictive disorders). Due\nto young age and/or suppression of one eye, measurements\nwere not possible in all patients. Therefore, the values are not\ngiven within this study. Orthoptic and ophthalmologic examination preserve motility. The effect of rectus muscle recession is\ninitially linear, but increases with enlarging recession distance\nand approach to the equator. Yet if the muscle is placed behind\nthe equator, increasing duction limitations can be expected\n[8]. Surgery with tendon elongation allows correction of larg-\ner angles and maintains a sufficient arc of contact. Various\nmaterials were used for tendon elongation such as homolo-\ngous scleral grafts, polytetrafluoroethylene (Goretex), sili-\ncone, or fascia lata [9–12]. For this study the following pre- and postoperative measure-\nments have been considered from our medical records: –\nWhen a head posture was adopted: the head posture mea-\nsured with a hand-held goniometer with the patient fixing\nthe smallest age-appropriate target distinguishable for the\npatient at distance under binocular conditions with\nBCVA (best-corrected visual acuity) In 2011, Esser and Eckstein were the first to publish their\nexperiences (dating back to 1996) with bovine pericardium\n(Tutopatch®) in eye muscle surgery for tendon elongation in\npatients with Graves’ orbitopathy [13, 14]. They reported it to\nbe a safe surgical method which also showed satisfying long-\nterm results in correction of large angles of squint in this\nrestrictive disorder [14, 15]. Further, bovine pericardium was\nreported to be replaced by tendon-like tissue over time [13, 14,\n16]. Squint angles cannot be satisfactorily reduced by conven-\ntional eye muscle surgery not only in patients with Graves’\norbitopathy but also in other patients with secondary, com-\nplex, restrictive, and rare oculomotor dysfunctions. Van Rijn\net al. reported tendon elongation with Tutopatch® for 31 pa-\ntients with exotropia (two of them oculomotor nerve paresis/\npalsy), 7 patients with esotropia (two of them abducens nerve\npalsy), and one patient with hypotropia [16]. They showed\nsatisfactory results with fairly good alignment and high patient\nsatisfaction, but duction limitations in the direction of the\nelongated muscle. –\nTests for binocular function (Bagolini striated glasses test,\nLang I or II stereo test, Titmus stereo test) with the head\nposture adopted with BCVA Measurement of the full extent of deviation in primary\nposition by alternate prism and cover-uncover test at far\nfixation with BCVA (in setting of poor vision in one eye,\nthe angle was measured by Krimsky test). In restrictive\nand paralytic strabismus, measurement of the primary an-\ngle instead of the secondary angle is essential. This was\nachieved by strictly placing the prism in front of the eye\nwith worse motility. Patients’ characteristics From 2011 to 2018, 58 eyes of 54 patients (35 females, 19\nmales, median age 35 years (3 to 75 years)) underwent stra-\nbismus surgery with tendon elongation with bovine\npericardium. In all cases, the surgical procedure was performed by one\nof the authors (J.F.). Surgery was performed under general\nanesthesia. For tendon elongation, the affected muscle was\nheld by a muscle clamp and disinserted. Then, the posterior\nend of the implant (Tutopatch®) was sutured to the detached\nend of the muscle with non-absorbable sutures (Mersilene®\n5.0). In cases where the muscle was very tight and therefore\nthe use of a muscle clamp was not possible, the posterior end\nof the implant was attached by two sutures directly to the\nmuscle closely behind the insertion and then the muscle was\ndisinserted. In all cases, the anterior end of the implant was\nsutured to the sclera at a median distance of 3 mm behind the\nphysiological insertion (sutures should not be visible through\nthe conjunctiva). In early cases non-absorbable sutures\n(Mersilene® 5.0) were used for this step as well. Recently,\nwe switched to absorbable sutures (Resorba® 6.0). These\nwere only used in one patient within this study (patient 32). When a larger recession had already taken place on the muscle\nin question, the insertion of the elongated tendon thus was\n“advanced” while the original muscle tendon was recessed/\nelongated, as we aimed at weakening the muscle but enhanc-\ning the arc of contact. Indications involving the horizontal rectus muscles (53\neyes) were residual strabismus, Duane’s retraction syndrome\n(DRS) with eso- (type I)/exodeviation (type II, type III), par-\ntial abducens nerve palsy, partial oculomotor nerve palsy,\nMöbius syndrome, congenital fibrosis of the extraocular mus-\ncles type 3A (CFEOM3A, TUBB3 mutation), and orbital apex\nsyndrome (supplementary Table 1). Indications involving the\nvertical rectus muscles (5 eyes) comprised myasthenia gravis,\npersisting vertical tropia after orbital floor fracture, CFEOM1,\nand Parry-Romberg syndrome (supplementary Table 1). In 42\ncases, the procedure was performed on a muscle which al-\nready had been operated on, whereas in 16 cases it was a\nprimary procedure. The median number of previous proce-\ndures on the concerned eyes with previous surgery was 1\n(range 1–5). Results primary position, reduction of a head posture, elimination of\ndiplopia in primary position, and improvement of binocular\nfunctions. Therefore, the full extent of deviation in primary\nposition pre- and postoperatively was used to calculate the\ndose-effect. Statistical analysis Statistical analysis was performed using Excel (Microsoft\nExcel for Mac, Version 15.29.1, Microsoft, USA) and SPSS\n(IBM SPSS Statistics, Version 23.0.0.2, IBM, USA). For met-\nric data, median, minimum, and maximum values were calcu-\nlated. Differences between groups were evaluated with\nStudent’s paired t test for data with normal distribution, oth-\nerwise with the Wilcoxon test. Postoperative data Long-term data were available for 45 patients (83%), after a\nmedian of 9 weeks post operation (5 to 261 weeks). In 43\npatients the squint angle was reduced (96%); in 23 out of the\n43 patients the angle was reduced to 10Δ or less (51%). One\npatient had a significant over-effect. The patients’ binocular\nfunctions were either the same or better than before surgery\n(for detailed patients’ characteristics of all patients with long-\nterm data, see supplementary Table 1). Surgery In this single-center retrospective study, we reviewed the med-\nical records of all patients who underwent strabismus surgery\nwith tendon elongation with bovine pericardium in our insti-\ntution. Patients with Graves’ orbitopathy were excluded from\nthe study. Choice of procedure was made on an individual basis and\ndependent on the patients’ horizontal and vertical deviation,\nmotility, and head turn. The total amount of surgery was based\non the dosages used for each motility disorder for regular\nrevision surgery. Aim of surgery was ocular alignment in Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 147 Patients’ characteristics The tendon of the medial rectus muscle was elon-\ngated in 32 eyes (24 of them with previous surgery), of the\nlateral rectus muscle in 21 eyes (16 of them with previous\nsurgery), of the inferior rectus muscle in four eyes (1 of them\nwith previous surgery), and of the superior rectus muscle in\none eye (with previous surgery). Based on the surgical reports, the following data was de-\ntermined: length of the implant, amount of surgery in compar-\nison to preoperative localization of the muscle (“effective re-\ncession distance”), and insertion site of the implant. The dose-\neffect relation of the tendon elongation was calculated for\ngroups with at least 5 patients with the same preoperative\ndiagnosis and with long-term results. The groups had to be\nhomogeneous with regard to whether or not additional opera-\ntions were performed on other eye muscles. For calculation of\nthe dose-effect relation, the difference between largest preop-\nerative and long-term squint angle in primary position was\ncalculated (prism diopter Δ). This value was divided by the\ntotal amount of surgery (mm). For calculating the total amount\nof surgery in combined surgery, the effective recession dis-\ntance was added to the effective tucking/advancing distance of\nthe antagonist. Surgery Twenty-six patients had tendon elongation with bovine peri-\ncardium as single muscle surgery. Twenty-three patients had\nfurther procedures on the same eye, 3 had further procedures\non the partner eye, and 2 had further procedures on the same\nand on the partner eye. Patients with residual eso- and exotropia All of the 5 patients with long-term measurement showed an\nangle reduction with three showing an angle of ≤10Δ (60%). Median, minimum, and maximum squint angles are displayed\nin Table 1. Pre- and postoperative squint angles of each patient\nare shown in Fig. 1. For residual esotropia, the medial rectus muscle tendon was\nelongated with a median implant length of 12 mm (8 to 12\nmm). The median effective recession distance was 5 mm (3 to\n6 mm). In 3 eyes, the lateral rectus muscle was simultaneously\ntucked (patients 35, 36, 38). Thus, the median total amount of\nhorizontal eye muscle surgery for all eyes was 7.5 mm (4 to 11\nmm). In one case, the superior oblique muscle was additionally\nrecessed (patient 37). All patients with residual esotropia\nshowed a reduction in squint angle on the first day after surgery,\nbut in the long term, one of 5 patients showed angle enlarge-\nment nearly shifting back to the preoperative position. Three of\nthem had an angle of ≤10Δ (60%). Median, minimum, and\nmaximum squint angles are displayed in Table 1. Pre- and\npostoperative squint angles of each patient are shown in Fig. 1. The horizontal motility range has been narrowed. The me-\ndian preoperative abduction of the concerned eye was 35° (12\nto 40) with a median adduction of 50° (40 to 50). In the long The horizontal motility range was narrowed by the proce-\ndure. The median preoperative adduction of the concerned eye\nwas 50° (40 to 50) while the median abduction was 45° (30 to Table 1\nPatients with horizontal rectus muscle tendon elongation and\nlong-term follow-up: full extent of deviation in primary position (in prism\ndiopters) preoperatively, at the first postoperative day, in the long term\n(convergent angles are given in positive, divergent angles in negative values), and angle improvement for residual esotropia (5 patients), resid-\nual exotropia (5 patients), oculomotor nerve palsy (7 patients), abducens\nnerve palsy (5 patients), esotropic Duane’s retraction syndrome (13 pa-\ntients), exotropic Duane’s retraction syndrome (3 patients) Patients with long-term\nmeasurement\nHorizontal angle of squint (Δ)\nMedian (minimum to maximum)\nLong-term measurement\n(weeks)\nMedian (minimum\nto maximum)\nPreop. Postop. first day\nLong term\nDifference preop. -postop. Patients with residual eso- and exotropia Long-term data are available for 5 of the 6 patients with\nesotropia and for 5 of the 7 patients with exotropia. The squint\nangle showed statistically significant postoperative reduction Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 148 in the long term (Wilcoxon test p = 0.008). One patient with\ntendon elongation for secondary esotropia after traumatic in-\njury as a child had an enucleation of the painful and blind eye\n4 years after eye muscle surgery. Due to rubeotic glaucoma\nand PVR retinal detachment, the eye was enucleated after\nunsuccessful retinal surgery. The patient, one of two with\npostoperative over-effect after tendon elongation, was there-\nfore not available for long-term results. term, we measured a median abduction of 30° (20 to 50) and\nno median gain in abduction: −5° (−15 to 15). The median\nadduction was reduced to 30° (20 to 50) with a median loss in\nadduction of 10° (0 to 30). Up to date, the one patient (patient 38) without angle im-\nprovement in the long term and another patient (patient 36)\nwith residual esotropia and vertical tropia had a revision\nsurgery. All of the patients had previously had surgery. The esotropic\npatients had residual esotropia after esotropia surgery. The\nexotropic patients had residual exotropia after exotropia surgery\n(two of them initially had esotropia surgery). The median num-\nber of procedures on the concerned eye for residual esotropia\nwas 2 (1 to 5), for residual exotropia 1 (1 to 5). For residual exotropia, the lateral rectus muscle tendon was\nelongated with a median implant length of 10 mm (8 to 13\nmm). The median effective recession distance was 5 mm (1 to\n6 mm). In the case with an effective recession of only 1 mm,\nintraoperatively the lateral rectus muscle was found to insert in\na distance of 17 mm behind the limbus. Adhesions to the\nglobe over a longer section were solved before inserting the\ntendon elongation. The medial rectus muscle was simulta-\nneously tucked in four eyes respectively advanced in two eyes\nwith previous medial rectus muscle resection and insertion\nfound behind the original insertion (patients 1–3, 5–7). Thus, the median total amount of horizontal eye muscle sur-\ngery for all eyes was 9.5 mm (5 to 12 mm). All but one patient\nshowed a reduction in squint angle on the first day after sur-\ngery. The remaining patient showed a reduction after 8 weeks. Patients with oculomotor/abducens nerve palsy Up to date, one patient with bilateral oculomotor nerve\npalsy had a revision surgery. Long-term data are available for all 7 patients with oculomotor\nnerve palsy and for 5 of 7 patients with abducens nerve palsy. The squint angle showed statistically significant reduction in\nthe long term (Wilcoxon test p = 0.002). Two of the patients\nwith oculomotor nerve palsy had bilateral palsy. One of them\nas well as four of the unilateral palsies had prior surgery. One\nof the patients with abducens nerve palsy had bilateral palsy. This patient as well as 5 of the unilateral palsies had prior\nsurgery. For oculomotor nerve palsy, the lateral rectus muscle\nhad tendon elongation with a median implant length of 10 mm\n(8 to 14 mm); for abducens nerve palsy the medial rectus\nmuscle tendon was elongated with a median implant length\nof 9 mm (7 to 10 mm). In patients with abducens nerve palsy, the median absolute\nrecession distance was 6 mm (5 to 12 mm). In 4 eyes, the\nlateral rectus muscle was simultaneously tucked/resected (pa-\ntients 27–29, 33). Thus, the median total amount of horizontal\neye muscle surgery for all eyes was 11 mm (5 to 20 mm). In\none eye, the superior oblique muscle was tucked due to addi-\ntional trochlear nerve palsy (patient 32). Median, minimum,\nand maximum squint angles are displayed in Table 1, and pre-\nand postoperative squint angles of each patient in Fig. 2. All\npatients showed a reduction in squint angle postoperatively\n(first day and long term). In the long term, three of five had\nan angle ≤10Δ (60%). The horizontal motility has been shifted towards abduction\nand narrowed. The median abduction of the concerned eye\nwas 0° preoperatively (−15 to 40) while the median adduction\nwas 45° (40 to 50). In the long term, all except of one patient\nshowed an improved abduction with a median abduction of 7°\n(0 to 30) and a median improvement of abduction of 7° (−10\nto 15). The median adduction was reduced to 30° (10 to 50)\nwith a median loss in adduction of 15° (0 to 35). For patients with oculomotor nerve palsy, the median ef-\nfective recession distance was 6 mm (4 to 12 mm). In 6 eyes,\nthe medial rectus muscle was simultaneously tucked or\nresected (patients 41–46). Patients with residual eso- and exotropia first day\nDifference preop.-\nlong term\nResidual esotropia\n5/6 patients\n35\n(16 to 40)\n12\n(0 to 35)\n6\n(−8 to 40)\n16\n(0 to 23)\n19\n(0 to 43)\n188 (6 to 260)\nResidual exotropia\n5/7 patients\n−35\n(−18 to −45)\n−16\n(−4 to −18)\n−10\n(1 to −25)\n19\n(0 to 41)\n20\n(8 to 46)\n8 (8 to 261)\nOculomotor nerve palsy\n7/7 patients\n−45\n(−25 to −75)\n−10\n(0 to −50)\n−30\n(−8 to −40)\n31\n(19 to 40)\n15\n(5 to 42)\n16 (6 to 40)\nAbducens nerve palsy\n5/7 patients\n41\n(20 to 53)\n8\n(2 to 40)\n8\n(4 to 35)\n14\n(12 to 48)\n18\n(12 to 46)\n8 (7 to 16)\nEsotropic Duane’s retraction\nsyndrome 13/16 patients\n25\n(9 to 40)\n8\n(−2 to 20)\n2\n(−8 to 20)\n14\n(5 to 37)\n22\n(7 to 48)\n8 (5 to 260)\nExotropic Duane’s retraction\nsyndrome\n3/3 patients\n−30\n(−12 to −30)\n−12\n(−4 to −14)\n−19\n(−5 to −40)\n16\n(8 to 18)\n6\n(−10 to 11)\n11 (9 to 16) Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 149 -50\n-40\n-30\n-20\n-10\n0\n10\n20\n30\n40\n50\nPreop\npostop first day\npostop longterm\n1\n2\n3\n4\n5\n6\n7\n34\n35\n36\n37\n38\n39\nFig. 1 Pre- and postoperative full\nextent of deviation in primary\nposition for all patients with\nresidual esotropia and exotropia\n(prism diopters; esotropia is given\nin positive, exotropia in negative\nvalues). Patients with\nsimultaneous surgery on the\ncontralateral horizontal rectus\nmuscle: 1–3, 5–7, respectively 35,\n36, 38\n149\nGraefes Arch Clin Exp Ophthalmol (2021) 259:145–155 50). In the long term, one patient showed a gain in adduction\nwhile four showed no relevant change in adduction. The me-\ndian postoperative adduction was 50° (47.5 to 50) and the\nmedian gain in adduction 0 (0 to 7.5). The median abduction\nwas reduced to 30° (20 to 45), median loss in abduction of 15°\n(−15 to 30). minimum, and maximum squint angles are displayed in\nTable 1. Pre- and postoperative squint angles of each patient\nare shown in Fig. 2. The horizontal motility was shifted towards adduction. The\nmedian preoperative adduction of the concerned eye was 0° (−\n15 to 25) while the median abduction was 50° (40 to 50). Patients with residual eso- and exotropia In\nthe long-term course, all but one patient showed a gain in\nadduction with a median adduction of 10° (0 to 35) and a\nmedian gain in adduction of 5° (−10 to 35). The median\nabduction was reduced to 40° (5 to 50), median loss in abduc-\ntion 5° (0 to 40). Up to date, one patient (patient 6) with secondary exotropia\ndue to traumatic injury in childhood had two revision surger-\nies for remaining exotropia. Patients with Duane’s retraction syndrome dose-effect relation was 2.6Δ/mm (1.1 to 5.2Δ/mm; all 13\npatients with long-term data). Considering only patients with\nprevious medial rectus muscle surgery, the median effect was\n2.7Δ/mm (10 patients). Long-term data are available for 13 of 16 patients with\nesotropic DRS type I (the data of some of these patients\nhave already been published in a separate paper [17]),\nand for 3 of 3 patients with exotropic DRS (type II: 2;\ntype III: 1). Two patients had marked bilateral motility\nrestrictions. Eleven of 16 eyes with esotropic DRS and\ntwo out of three eyes with exotropic DRS had previous-\nly undergone surgery. The horizontal motility was shifted towards abduction and\nconsiderably narrowed. The median abduction of the con-\ncerned eye was 0° preoperatively (−3 to 30), the median\nadduction 50° (30 to 50). In the long term, 8 out of 13 patients\nshowed a gain in abduction. The median postoperative abduc-\ntion was 7° (0 to 30) and the median gain in abduction was 5°\n(0 to 20). The median adduction was reduced to 20° (7 to 45)\nwith a median loss in adduction of 25° (5 to 35°). For esotropic DRS, the medial rectus muscle tendon\nwas elongated with a median implant length of 10 mm\n(8 to 12 mm). The median absolute recession distance\nwas 6 mm (4 to 13 mm). None of the patients had\nsimultaneous surgery on another eye muscle. The abso-\nlute head turn (far distance) was reduced from median\n20° preoperatively (5 to 30°; turn to the left: 13; turn to\nthe right: 2; no head turn: 1) to 0° in the long term (−\n5 to 15°, negative value indicating over-effect). For exotropic DRS the lateral rectus muscle tendon was\nelongated with an implant length of 10 mm in all eyes. The\nhead turn was reduced from median 20° preoperatively (12 to\n25) to 12° in the long term (0 to 20). The median absolute\nrecession distance was 6 mm (6 to 10 mm). Median, minimum,\nand maximum squint angles are displayed in Table 1. Pre- and\npostoperative squint angles of each patient are shown in Fig. 3. All patients showed a reduction in squint angle on the first day\npostoperatively, but one patient showed no improvement in the\nlong term (patient 22). In the long term, one out of three patients\nwith exotropic DRS had an angle ≤10Δ (33%). Patients with oculomotor/abducens nerve palsy Thus, the median total amount of\nhorizontal eye muscle surgery for all eyes was 14 mm (5 to 22\nmm). In one eye, the superior rectus muscle was simulta-\nneously tucked (patient 40). All patients showed a reduction\nin squint angle postoperatively (first day and long term), but in\nthe long term, only one had an angle ≤10Δ (17%). Median, Up to date, one patient had a revision surgery. Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 150 -80\n-70\n-60\n-50\n-40\n-30\n-20\n-10\n0\n10\n20\n30\n40\n50\n60\nPreop\npostop first day\npostop longterm\n27\n28\n29\n30\n31\n32\n33\n40\n41\n42\n43\n44\n45\n46\nFig. 2 Pre- and postoperative full\nextent of deviation in primary\nposition for all patients with NIII\nand NVI palsy (prism diopters;\nesotropia is given in positive,\nexotropia in negative values),\nincluding patient 29 with bilateral\nNVI palsy and patients 43 and 44\nwith bilateral NIII palsy. Patients\nwith simultaneous surgery on the\ncontralateral horizontal rectus\nmuscle: 27–29, 33, respectively\n41–46 Other patients with horizontal rectus muscle tendon\nelongation Surgery on horizontal rectus muscles (4 patients, 7 eyes)\nwas conducted in patients with Mobius syndrome (pa-\ntient 48: bilateral medial rectus muscle tendon elonga-\ntion), congenital fibrosis of the extraocular muscles (pa-\ntients 50 and 51: bilateral lateral rectus muscle elonga-\ntion, patient 51 with previous surgery on the concerned\nmuscles), and orbital apex syndrome (patient 54: unilat-\neral medial rectus tendon elongation, previous surgery\non the concerned muscle). The median implant length\nwas 10 mm (6 to 10). The median absolute recession\ndistance was 10 mm (5 to 13 mm). Surgery on vertical rectus muscles (4 patients, 5 eyes) was\nconducted in patients with orbital floor fracture (patient 52:\nsuperior rectus muscle tendon elongation), myasthenia gravis,\nand Parry-Romberg syndrome (patients 47 and 53: inferior\nrectus muscle tendon elongation), furthermore in a patient\nwith a chin-up head posture due to congenital fibrosis of the\nextraocular muscles (patient 49: surgery on both inferior rec-\ntus muscles). Two patients had prior surgery of the affected\nmuscle (patients 52 and 53). The rectus muscle tendon was\nelongated with a median implant length of 8 mm (6 to 10). The\nmedian absolute recession distance was 10 mm (3.5 to 12\nmm). All patients showed a reduction in squint angle respec-\ntively head posture on the first postoperative day and in the\nlong term. Two out of three patients with unilateral vertical\nrectus muscle tendon elongation showed a maximum angle of\n10Δ in the long term. Median, minimum, and maximum\nsquint angles of the three patients are displayed in Table 2\n(due to the small and heterogeneous sample size, only descrip-\ntive statistics based on absolute values are provided). The\nvertical motility range was shifted to the direction contrary\nto the elongated muscle in all cases. In patients with inferior\nrectus muscle tendon elongation, the preoperative elevation of\nthe concerned eye was 15° below midline in patient 47 and\n10° above midline in patient 53. In the long term, the elevation\nwas almost to midline in patient 47 and almost without limi-\ntation in patient 53. In the patient with superior rectus muscle\ntendon elongation, the depression was possible only to 10°\nbefore midline in adduction and to midline in abduction before\nthe operation. Patients with Duane’s retraction syndrome Median, minimum, and maximum squint angles for all pa-\ntients with esotropic DRS are displayed in Table 1. Pre- and\npostoperative squint angles of each patient are shown in Fig. 3. Considering patients with esotropic DRS without previous\nsurgery only (patients 16, 18, 19, 21, 25), the median preop-\nerative squint angle was 40Δ (35 to 45Δ), the median abso-\nlute preoperative head turn was 25° (7 to 30°), and the abduc-\ntion was before or just up to midline (median abduction −5°,\nfrom −10 to 0°). The horizontal motility was shifted towards adduction. The\nmedian adduction of the concerned eye was 10° preoperative-\nly (−15 to 45) while the median abduction was 25° (20 to 45). In the long term, two patients showed improved adduction. The median postoperative adduction was 15° (−10 to 25) and\nthe median improvement in adduction was 5° (−30 to 15). The median abduction was reduced to 20° (20 to 40) while the\nmedian loss in abduction was 5° (0 to 5). All patients with esotropic DRS showed a reduction in\nsquint angle on the first day postoperatively and in the long-\nterm course (long term: Wilcoxon test p = 0.001, statistically\nsignificant reduction). In the long term, 9 of the 13 patients\nwith esotropic DRS (69%) had an angle ≤10Δ. The median Of all patients with DRS, two patients had a revision\nsurgery. Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 151 -40\n-30\n-20\n-10\n0\n10\n20\n30\n40\n50\nPreop\npostop first day\npostop longterm\n8\n9\n10\n11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n21\n25\n26\n22\n23\n24\nFig. 3 Pre- and postoperative full\nextent of deviation in primary\nposition for all patients with\nDuane’s retraction syndrome\n(prism diopters; esotropia is given\nin positive, exotropia in negative\nvalues)\n151\nGraefes Arch Clin Exp Ophthalmol (2021) 259:145 155 -40\n-30\n-20\n-10\n0\n10\n20\n30\n40\n50\nPreop\npostop first day\npostop longterm\n8\n9\n10\n11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n21\n25\n26\n22\n23\n24\nFig. 3 Pre- and postoperative full\nextent of deviation in primary\nposition for all patients with\nDuane’s retraction syndrome\n(prism diopters; esotropia is given\nin positive, exotropia in negative\nvalues) Patients with vertical rectus muscle tendon\nelongation Other patients with horizontal rectus muscle tendon\nelongation Surgical effect midline. Patient 53 (Parry-Romberg syndrome) had additional\neye lid surgery a few months later. Patients with complex, rare, restrictive, large, and residual\nstrabismus types, as well as paretic strabismus types with pre-\nvious surgery were selected for tendon elongation with bovine\npericardium. Results showed a reduction of squint angle in all\nexcept of two patients. In the postoperative long term, 51% of\npatients had a squint angle of 10Δ or less, before any kind of\nrevision surgery. Only one patient had a significant over-ef-\nfect. The effect of surgery showed a high variability, probably\ncaused by the very heterogeneous patient characteristics. Possible explanations for this are previous surgery of various\namounts, adherence of the affected muscle to the sclera, re-\nstriction of motility, paresis of various extents, or\ndysinnervation. Furthermore, some patients had a combined\nsurgery on both horizontal rectus muscles. Another patient (patient 49) with congenital fibrosis of the\nextraocular muscles had bilateral inferior rectus muscle reces-\nsion due to chin-up head posture. The head posture of 18°\npreoperatively (also due to bilateral ptosis) was reduced to\n15° on the first day after surgery. In the long term, after addi-\ntional eye lid surgery, the patient showed no longer chin-up or\nchin-down head posture. Preoperatively, the eye elevation was\nunder midline. Postoperatively, elevation was possible a short\ndistance above midline for both eyes. Adverse events and revision surgery One patient showed increasing conjunctival injection and\nchemosis 4 days after the operation. Patient was treated with\nsystemic antibiotics and steroids. Because of persistent swelling,\nwe decided to explore the surgical site 12 days after the tendon\nelongation. During revision surgery, there was no infection nor\nimplant rejection visible. Therefore, the implant was not\nexplanted but the surgical site was rinsed with antibiotics. Eventually the conjunctival chemosis and injection resolved un-\nder steroid therapy. Nine weeks post operation, the patient was\nfree of complaints and the postoperative site was unremarkable. As mentioned above, Esser et al. primarily published their\nexperience with tendon elongation with bovine pericardium\nfor eye muscle surgery in 2011 [13] (when dose-effects in\nstudies referred to in this discussion were given in °/mm, we\nconverted the numbers also into Δ/mm for better comparison\nas to be seen in brackets). For 10 patients with large vertical\nsquint angles due to Graves’ orbitopathy (GO), they reported\nan angle reduction of 2.0°/mm (3.5Δ/mm) using bovine peri-\ncardium for tendon elongation of the inferior rectus muscle. Good results were achieved for patients with/without previous\ninferior rectus muscle recession and with/without previous\norbital decompression. Up to now in 9 cases, a revision surgery was performed on\na muscle which had been elongated by bovine pericardium. The pericardium had been transformed into tendon-like mate-\nrial which could be picked up with a strabismus hook. Except\nfor the suture, the material usually showed no adhesion to the\nsclera. In 8 cases, the pseudo-tendon was recessed, and in one\ncase resected. The revisions could be performed without\ncomplications. Recently, the same study group reported results for medial\nrectus tendon elongation after orbital decompression surgery\nin GO patients. All patients showed lower dose effects com-\npared with medial rectus muscle recessions without prior de-\ncompression. Considering patients with unilateral and bilater-\nal tendon elongation of the medial rectus muscle, a median\ndose-effect of 1.8 ± 0.6Δ/mm was achieved [14]. Unilateral\nrecessions had a mean effect of 1.2 ± 0.4°/mm (2.1Δ/mm),\nbilateral of 1.0 ± 0.3°/mm (1.8Δ/mm). Unilateral medial rec-\ntus muscle tendon elongation with simultaneous simple reces-\nsion of the medial rectus muscle on the partner eye had a mean\neffect of 0.92 ± 0.3°/mm (1.6Δ/mm) and bilateral tendon\nelongation of 0.87 ± 0.3°/mm (1.5Δ/mm) [15]. Interestingly, Other patients with horizontal rectus muscle tendon\nelongation Postoperatively, the depression was 10° over The child with Mobius syndrome had a reduction of the\nhorizontal angle from 25Δ to 0Δ the first day after surgery,\nbut an over-effect of −25Δ in the long term which required a\nrevision surgery. In one child with congenital fibrosis of the extraocular\nmuscles (patient 51), the head turn was reduced from 30° to\n0° and the squint angle was reduced from −100Δ to −55Δ in\nthe long term; respectively in another child (patient 50), the\nhead turn was reduced from 35° to < 5° and the squint angle\nfrom −30° to −20° in the long term (Hirschberg test, near\nfixation). Patient 50 had further surgery to correct patient’s\nvertical head turn. One adult patient had an orbital apex syndrome due to\nmetastasis of a leiomyosarcoma at the side of her only seeing\neye. Patient’s head turn to the right of 40° preoperatively was\nreduced to 20° on the first day after surgery. The squint angle\nshowed a reduction from 75Δ to 40Δ. Patient was not avail-\nable for long-term results. Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 152 Table 2\nPatients with vertical rectus muscle surgery to improve a vertical angle of squint and long-term follow-up: full extent of deviation in primary\nposition (in prism diopters, absolute values) preoperatively, at the first postoperative day, in the long term, and improvement (3 patients)\nPatients with long-term\nmeasurement\nVertical angle of squint (Δ)\nMedian (minimum to maximum)\nLong-term measurement\n(weeks)\nMedian (minimum\nto maximum)\nPreop. Postop. first day\nLong term\nDifference\npreop.-postop. first day\nDifference\npreop.- long term\nVertical rectus muscle surgery to\nimprove a vertical angle of squint\n3/3 patients\n30 (20 to 45)\n8 (3 to 18)\n4 (1 to 22)\n22 (17 to 27)\n19 (8 to 41)\n12 (9 to 40) Discussion In this study tendon elongation with bovine pericardium was\nconsidered for a heterogeneous group of patients which was\nunlikely to show satisfying results with conventional eye mus-\ncle surgery only. Thereby the spectrum of indications for this\nspecial procedure has been broadened [13–18]. 153 Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 esotropic DRS (type I) preoperatively showed a median ad-\nduction of 50° with a very limited median abduction of 0°. Postoperatively, the abduction improved to median 7°, but the\nmedian postoperative adduction declined to 20°. A median\nloss of adduction of 25° was detected. None of the other\ngroups in our study showed a median loss of more than 15°\nin motility. the effect was stronger for inferior rectus muscle than for\nmedial rectus muscle tendon elongation. Wipf et al. reported a much higher dose-effect relation of\n3.6Δ/mm surgery. Within their study only five GO patients\nwith bilateral medial rectus muscle elongation but up to 10\nyears follow-up were described. Four out of the patients had\nprevious orbital decompression surgery [18]. In DRS, secondary structural muscle alterations occur. The\nhypo- or aplasia of the 6th nerve and its nucleus cause para-\ndoxical innervation of the lateral rectus muscle by the 3rd\nnerve. The cocontraction of medial and lateral rectus muscle\nleads to secondary fibrotic alterations in the medial rectus\nmuscle. Interestingly, a similar loss in adduction was found\nin patients with GO, another disease with fibrotic/alterated\nmuscle structure [14]. For patients with GO and decompres-\nsion surgery, Oeverhaus et al. reported a substantial narrowing\nof the horizontal motility after tendon elongation of the medial\nrectus muscle: abduction was improved by 12° in the unilat-\neral and 20° in the bilateral group, while adduction deteriorat-\ned by 20° in the unilateral and 40° in the bilateral group [14]. Especially for correction of exotropia, Van Rijn et al. also\nreported duction limitations in the direction of the involved\nmuscle. The duction limitations “had little effect on the cos-\nmetic appearance and patient satisfaction and decreased dur-\ning follow-up” [16]. This data might implicate that postoper-\native duction limitations are most pronounced in restrictive\nmotility disorders. Van Rijn et al. Biocompatibility Beside the otherwise mostly positive reports about bovine\npericardium in ophthalmic surgery, there is also one publica-\ntion with a critical view by De Vries et al. [21]. Following\nserious complications for 4 cases were described after using\nthis material as a wrap for acrylic implants in enucleation\nsurgery: orbital cellulitis, extrusion, and rapid resorption. It\nis unknown whether the acrylic material or bovine pericardi-\num caused these complications. However, beyond this publication the literature does not\nreport gross complications, especially not after rectus muscle\ntendon elongation with bovine pericardium [13, 14, 16, 17]. One of our patients showed a prolonged wound healing,\nbut no infection nor implant rejection was detected when re-\nvising the muscle. However, beyond this publication the literature does not\nreport gross complications, especially not after rectus muscle\ntendon elongation with bovine pericardium [13, 14, 16, 17]. One of our patients showed a prolonged wound healing,\nbut no infection nor implant rejection was detected when re-\nvising the muscle. Discussion performed tendon elongation with bovine\npericardium in a heterogeneous group of patients with second-\nary or consecutive eso- and exotropia (7 esotropic, respective-\nly 31 exotropic patients, also including two patients with N III\nand two with N VI palsy, and one patient with hypotropia). They described the dose-effect of muscle elongation as gen-\nerally stronger than in conventional recessions [16]. Angle\nreductions from −21.8 ± 5.7° to −3.3 ± 5.9° were reported\nfor correction of exotropia, from + 19.1 ± 5.4° to + 0.2 ± 0.5°\nfor correction of esotropia. For esotropic DRS, our study showed a median effect of\n2.6Δ/mm (respectively 2.7Δ/mm considering only patients with\nprevious medial rectus muscle surgery). This effect was stronger\nthan the effect described for medial rectus recession without\ntendon elongation as a primary procedure (2Δ/mm surgery)\n[19]. Altogether, the effect of tendon elongation with bovine\npericardium showed a high variability, probably depending\non the underlying pathology and muscle structure. The effect\ntends to be stronger than in conventional eye muscle surgery. Our study is limited by the short follow-up time of median\n9 weeks post operation. Oeverhaus et al. described excellent\nlong-term stability (up to 15 years) for patients with Graves’\norbitopathy and medial rectus tendon elongation [14]. In\nneuroparalytic strabismus though, the paretic muscle can fur-\nther stretch out. In fibrosis, muscles may remain tight and in\nother subgroups lack of fusion may destabilize the eye posi-\ntion [20]. Therefore, these patient groups may be more prone\nto recurrence of a squint angle. This is also reflected in the\nnumber of previous surgery for each subgroup of our study. Patients with residual strabismus (most of them without any\nbinocular functions) and patients with N. III/N. VI paresis had Altogether, the effect of tendon elongation with bovine\npericardium showed a high variability, probably depending\non the underlying pathology and muscle structure. The effect\ntends to be stronger than in conventional eye muscle surgery. tends to be stronger than in conventional eye muscle surgery. Our study is limited by the short follow-up time of median\n9 weeks post operation. Oeverhaus et al. described excellent\nlong-term stability (up to 15 years) for patients with Graves’\norbitopathy and medial rectus tendon elongation [14]. In\nneuroparalytic strabismus though, the paretic muscle can fur-\nther stretch out. In fibrosis, muscles may remain tight and in\nother subgroups lack of fusion may destabilize the eye posi-\ntion [20]. Discussion Therefore, these patient groups may be more prone\nto recurrence of a squint angle. This is also reflected in the\nnumber of previous surgery for each subgroup of our study. Patients with residual strabismus (most of them without any\nbinocular functions) and patients with N. III/N. VI paresis had\nthe highest number of previous surgery and thus the highest\nrisk of recurrence of the squint angle. References 1. Li X, Guo Y, Ziegler KR, Model LS, Eghbalieh SD, Brenes RA,\nKim ST, Shu C, Dardik A (2011) Current usage and future direc-\ntions for the bovine pericardial patch. Ann Vasc Surg 25(4):561–\n568. https://doi.org/10.1016/j.avsg.2010.11.007 2. Parizek J, Mericka P, Husek Z, Suba P, Spacek J, Nemecek S,\nNemeckova J, Sercl M, Elias P (1997) Detailed evaluation of\n2959 allogeneic and xenogeneic dense connective tissue grafts (fas-\ncia lata, pericardium, and dura mater) used in the course of 20 years\nfor duraplasty in neurosurgery. Acta Neurochir (Wien) 139(9):827–\n838 Although the arc of contact is preserved or restituted, this\ntype of surgery—aiming at maximum effects—reduces the\nexcursion into the field of action of the elongated muscle. Dose finding can be difficult depending on the underlying\npathology. Patients also have to know that more than one\nintervention might be necessary for optimal results. 3. Gupta M, Lyon F, Singh AD, Rundle PA, Rennie IG (2007) Bovine\npericardium (Tutopatch) wrap for hydroxyapatite implants. Eye\n(Lond) 21(4):476–479. https://doi.org/10.1038/sj.eye.6702227 Author contributions All authors contributed to the study conception and\ndesign. Material preparation and data collection and analysis were per-\nformed by Andrea Hedergott, Ursula Pink-Theofylaktopoulos, Antje\nNeugebauer, and Julia Fricke. The first draft of the manuscript was written\nby Andrea Hedergott and all authors commented on previous versions of\nthe manuscript. All authors have read and approved the final manuscript. 4. Gupta M, Puri P, Rennie IG (2002) Use of bovine pericardium as a\nwrapping material for hydroxyapatite orbital implants. Br J\nOphthalmol 86(3):288–289. https://doi.org/10.1136/bjo.86.3.288 5. Quaranta L, Riva I, Floriani IC (2013) Outcomes of using a\nsutureless bovine pericardial patch graft for Ahmed glaucoma valve\nimplantation. Eur J Ophthalmol 23(5):738–742. https://doi.org/10. 5301/ejo.5000260 Funding Open Access funding enabled and organized by Projekt DEAL. Funding Open Access funding enabled and organized by Projekt DEAL. 6. Gayre GS, Debacker C, Lipham W, Tawfik HA, Holck D, Dutton\nJJ (2001) Bovine pericardium as a wrapping for orbital implants. Ophthalmic Plast Reconstr Surg 17(5):381–387 Data availability The authors have full control of all primary data and\nthey agree to allow Graefes Archive for Clinical and Experimental\nOphthalmology to review their data upon request 7. Alio JL, Rodriguez AE, Martinez LM (2013) Bovine pericardium\nmembrane (tutopatch) combined with solid platelet-rich plasma for\nthe management of perforated corneal ulcers. Cornea 32(5):619–\n624. https://doi.org/10.1097/ICO.0b013e31825a6d9a Conclusions This study shows that tendon elongation with bovine pericar-\ndium is a safe surgical method not only in Graves’\norbitopathy. Strabismus surgery with bovine pericardium in-\ntroduces new surgical options for complex and/or rare oculo-\nmotor dysfunctions, especially for complicated revisions and\nlarge angles of squint and residual head postures, where con-\nventional eye muscle surgery has limits. Side effects Large recessions with placement of a muscle posterior to the\nequator lead to limited ocular ductions [8]. Maintaining the arc\nof contact by tendon elongation instead of large or repeated\nrecessions could have less effect on motility. In our patients,\nthe motility range was shifted in the direction contrary to the\nelongated muscle in all groups of indications. Yet, a consid-\nerable reduction of the excursion into the field of action of the\nelongated muscle had to be registered. This effect was most\nprominent for patients with esotropic DRS. Our patients with Oeverhaus et al. described the non-absorbable sutures of\nthe implant to penetrate the conjunctiva over time. Therefore,\nthey recommended using absorbable sutures [15]. Awadein\net al. reported a high incidence of over-effect for large hang-\nback medial rectus muscle recessions with absorbable sutures. This was due to inadequate anchoring of the medial rectus\nmuscle [22]. The problem did not occur with non-absorbable\nsutures. Nevertheless, we also switched to absorbable sutures\nfor anchoring of the implant recently, but only one patient Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 154 study, the Declaration of Helsinki and applicable national regulations and\nlaws were observed. with absorbable sutures was considered in this study. Seven\nweeks after surgery, the patient did not have an over-effect. Future studies will need to assess the safety of absorbable\nsutures in tendon elongation with bovine pericardium. Consent to participate\nNot applicable Consent to participate\nNot applicable Consent for publication\nNot applicable Consent for publication\nNot applicable Code availability\nVia corresponding author Code availability\nVia corresponding author Code availability\nVia corresponding author Open Access This article is licensed under a Creative Commons\nAttribution 4.0 International License, which permits use, sharing,\nadaptation, distribution and reproduction in any medium or format, as\nlong as you give appropriate credit to the original author(s) and the\nsource, provide a link to the Creative Commons licence, and indicate if\nchanges were made. The images or other third party material in this article\nare included in the article's Creative Commons licence, unless indicated\notherwise in a credit line to the material. If material is not included in the\narticle's Creative Commons licence and your intended use is not\npermitted by statutory regulation or exceeds the permitted use, you will\nneed to obtain permission directly from the copyright holder. To view a\ncopy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Like other study groups, we observed the bovine pericardium\nto be eventually replaced by tendon-like tissue. It usually\nshowed no adherence to the sclera behind the insertion\n[14–16]. Nevertheless, Oeverhaus reported one case with re-\nvision surgery where the implant was not distinguishable from\nsurrounding fibrotic scar tissue. In our study, revision surgery\nwas feasible in all cases. Compliance with ethical standards 8. Coats D, Olitsky SE (2017) Recession of the rectus muscle. In:\nLambert S, Lyons CJ (eds) Taylor & Hoyt’s Pediatric\nOphthalmology and Strabismus, vol 5. Elsevier, Edinburgh,\nLondon, New York, Oxford, Philadelphia, St. Louis, Sydney,\nTotonto, p 885 Conflict of interest\nThe authors declare that they have no conflict of\ninterest. Ethics approval\nAccording to regional medical regulations on retrospec-\ntive single-center clinical studies (§15 of the Professional code of con-\nduct, General Medical Council for the Northern Rhine in accordance with\nthe General Data Protection Regulation GDPR of the European Union),\nthe Ethics Committee of the University of Cologne ruled that approval\nwas not required for this retrospective analysis. Throughout the whole 9. Talebnejad MR, Eghtedari M, Owji N, Alavi A (2008) Super\noblique tendon elongation with fascia lata. J AAPOS 12(5):507–\n509. https://doi.org/10.1016/j.jaapos.2008.02.014 10. Wright KW (2000) Results of the superior oblique tendon elonga-\ntion procedure for severe Brown's syndrome. Trans Am\nOphthalmol Soc 98:41–48. discussion 48-50 Graefes Arch Clin Exp Ophthalmol (2021) 259:145–155 155 11. Langmann A, Lindner S, Wackernagel W, Koch M, Horantner R\n(2006) Polytetrafluoroethylene (Goretex) for muscle elongation in\nthe surgical treatment of strabismus with restricted motility. Acta\nOphthalmol Scand 84(2):250–253. https://doi.org/10.1111/j.1600-\n0420.2005.00578.x 17. Hedergott AM, Fricke J, Neugebauer A (2014) Medial rectus ten-\ndon elongation with bovine pericardium for type 1 Duane’s retrac-\ntion syndrome. Klin Monbl Augenheilkd 231(10):980–987. https://\ndoi.org/10.1055/s-0034-1383070 18. Wipf M, Berg BI, Palmowski-Wolfe A (2018) Medial rectus tendon\nelongation with bovine pericard (Tutopatch(R)) in thyroid-\nassociated orbitopathy: a long-term follow-up including\noculodynamic MRI. J Ophthalmol 2018:1294761. https://doi.org/\n10.1155/2018/1294761 12. Dyer JA (1976) The oculorotary muscles in Graves’ disease. Trans\nAm Ophthalmol Soc 74:425–456 13. Esser J, Schittkowski M, Eckstein A (2011) Graves’ orbitopaty:\ninferior rectus tendon elongation for large vertical squint angles that\ncannot be corrected by simple muscle recession. Klin Monbl\nAugenheilkd 228(10):880–886. https://doi.org/10.1055/s-0031-\n1281776 19. Fricke J, Neugebauer A, Russmann W (2006) Surgical options in\nretraction syndrome. Klin Monbl Augenheilkd 223(1):42–47. https://doi.org/10.1055/s-2005-858857 20. Guyton DL (2006) The 10th Bielschowsky Lecture. Changes in\nstrabismus over time: the roles of vergence tonus and muscle length\nadaptation. Binocul Vis Strabismus Q 21(2):81–92 14. Oeverhaus M, Fischer M, Hirche H, Schluter A, Esser J, Eckstein\nAK (2018) Tendon elongation with bovine pericardium in patients\nwith severe esotropia after decompression in Graves’ orbitopathy-\nefficacy and long-term stability. Strabismus 26(2):62–70. https://\ndoi.org/10.1080/09273972.2018.1450430 21. Publisher’s note Springer Nature remains neutral with regard to jurisdic-\ntional claims in published maps and institutional affiliations. Compliance with ethical standards De Vries FR, Notting IC, Marinkovic M, Schalij-Delfos NE,\nLuyten GP (2012) Complications due to bovine pericardium used\nto cover acrylic implants after enucleation and tubes of aqueous\ndevices. Eye (Lond) 26(2):336. https://doi.org/10.1038/eye.2011. 294 15. Oeverhaus M, Fischer M, Schluter A, Esser J, Eckstein A (2018)\nCorrective surgery of severe esotropia after decompression in pa-\ntients with Graves’ orbitopathy - comparison of tendon elongation\nand recession of the medial rectus muscle. Klin Monbl Augenheilkd\n235(10):1105–1114. https://doi.org/10.1055/a-0719-5354 22. Awadein A, Marsh JD, Guyton DL (2016) Nonabsorbable versus\nabsorbable sutures in large, hang-back medial rectus muscle reces-\nsions. J AAPOS 20(3):206–209. https://doi.org/10.1016/j.jaapos. 2016.03.009 16. van Rijn LJ, van De Ven SJ, Krijnen JS, Jansen SM, Bakels AJ,\nLangenhorst AM (2016) Tendon elongation with bovine pericardi-\num (Tutopatch(R)) when conventional strabismus surgery is not\npossible. Eur J Ophthalmol 26(3):193–202. https://doi.org/10. 5301/ejo.5000689 Publisher’s note Springer Nature remains neutral with regard to jurisdic-\ntional claims in published maps and institutional affiliations."