Evaluation of superior rectus muscle attachment following hang-back recession in rabbit eyes

PURPOSE: The hang-back suture technique has been advocated to decrease the risk of scleral perforation during strabismus surgery. In this study, we evaluated the muscle insertion site in rabbits 4 weeks after a hang-back recession was performed. METHODS: Twenty-five eyes of 13 rabbits underwent hang-back recessions of between 5 and 8 mm of the superior rectus muscle. Four weeks later, the attachment sites were examined. RESULTS: Four weeks following the surgery, 14 muscles (n=25, 56%) were anteriorly displaced. In the 5 mm recession group, one muscle was anteriorly displaced (n=7, 14.3%). In the 6 mm recession group, 50% of the muscles recessed were displaced anteriorly (n=8). The 7 mm hang-back recession group demonstrated forward displacement in five muscles operated (n=6, 83%) and in the 8 mm recession group, all four muscles (100%) were anteriorly displaced. The magnitude of displacement was positively correlated to the amount of the hang-back recession performed (Pearson correlation p<0.001). CONCLUSIONS: Anterior displacement of muscles using the hang-back technique in the rabbit eye is unacceptably high and occurred in 56% of the cases. A positive, statistically significant correlation exists between the amount of recession performed and the number of muscles displaced from their new insertion. Therefore, when performing large recessions using the hang-back technique displacement should be anticipated.     

Stability of Y-splitting procedure combined with hang-back recession of the rectus muscle in rabbit eyes

Background

The Y-splitting procedure has been used both to treat up-shoots and down-shoots in Duane syndrome, and as a substitute for posterior fixation suture. The Y-split is often performed in conjunction with a hang-back recession when a large amount of recession or an adjustable suture is necessary. Herein, we evaluated the stability of Y-splitting hang-back recession in the rectus muscle.

Methods

Under general anesthesia, a 5-mm hang-back recession of the superior rectus muscle (SR) with Y-splitting was performed in ten eyes from ten rabbits (hang-back group). A conventional recession was performed in the SR of the fellow eye (control group). Six weeks after the procedure, the distance between the original insertion and the recessed SR (recession amount) and the width between the nasal and temporal halves of the SR were measured. These values were compared to the measurements taken at the time of surgery.

Results

The hang-back group had a significantly larger forward displacement than the control group (P?<?0.001 for both the nasal and temporal halves). The width change between the nasal and temporal halves was also significantly larger in the hang-back group (4.94?±?1.32 mm) than in the control group (1.14?±?0.60 mm, P?<?0.001). Additionally, the Y-configuration appeared to be more collapsed in the hang-back group than in the control group.

Conclusion

Y-splitting of the rectus muscle may be unstable when it is combined with a hang-back recession. Surgeons should consider this possibility when performing Y-splitting procedures.     

Cytoplasmic inclusions in rabbit extraocular muscle

Cytoplasmic inclusion bodies, similar to those previously described in abnormal and normal human extraocular muscle, were observed in the orbital surface layer of the superior rectus muscle in rabbit. These inclusion bodies are composed of a flocculent material of low density studded with granular foci of increased density. In sequential samples of serially reconstructed muscle fibers visualized by electron microscopy, cytoplasmic inclusion bodies were seen in 4.5% of 1187 samples through multiply innervated fibers that vary systematically in diameter along their length; inclusion bodies were also seen in 0.8% of 354 samples through multiple innervated fibers of constant diameter. Cytoplasmic inclusion bodies were not seen in 1838 samples through singly innervated fibers. These data suggest that such inclusion bodies may occur preferentially in multiply innervated fibers. The present findings are not compatible with previous suggestions that such cytoplasmic inclusion bodies may be indicative of a pathologic or aging process. These findings are consistent with previous suggestions that such inclusion bodies are to be considered as normal structures in extraocular muscle.     

Changes in muscle fiber size and in the composition of myosin heavy chain isoforms of rabbit extraocular rectus muscle following recession surgery

Purpose

To assess the changes in the size of muscle fibers and the composition of myosin heavy chain (MyHC) isoforms in the global layer (GL) and the orbital layer (OL) of rabbit rectus extraocular muscle (EOM) after recession.

Methods

The right superior rectus muscles of two rabbits were harvested at 3 days or 1, 2, or 4 weeks after recession (eight rabbits in total). At each time point, one muscle was used for measuring the cross-sectional area of the muscle fibers and the other for identifying the composition of MyHC. The right superior rectus muscles of three additional naïve rabbits were used as controls.

Results

The mean cross-sectional area of the OL fibers did not change significantly. However, that of the GL fibers significantly decreased at 3 days (P < 0.001) and 1 week (P = 0.024) postoperatively, and increased thereafter to reach the control levels at 2 and 4 weeks postoperatively. Three days after surgery, the total MyHC content and the proportion of type IIb MyHC (MyHCIIb) plus EOM-specific MyHC (MyHCeom) decreased and remained at its lower level for 4 weeks.

Conclusions

Transient atrophy and regeneration were observed only in the GL, and the changes in the MyHCIIb plus MyHCeom appeared to be related to these changes.

     

Safety of bevacizumab on extraocular muscle in a rabbit model

Purpose

The purpose of this study was to investigate the myotoxicity of bevacizumab on extraocular muscles in a rabbit model.

Methods

Thirty New Zealand white rabbits were used for this study. The animals were evenly divided into two groups. In the first group, 15 rabbits were treated with intramuscular injections of bevacizumab (1.25 mg/0.05 mL) in the right superior rectus muscle and normal saline solution (0.05 mL) in the left superior rectus muscle. In the second group, 15 rabbits were treated with subconjunctival injections of bevacizumab (2.5 mg/0.1 mL) in the right superior subconjunctival area and normal saline solution (0.1 mL) in the left superior subconjunctival area. Five rabbits in each group were sacrificed at one day, two weeks and four weeks after the injections. Extraocular muscle samples were prepared for light microscopic (LM) and electron microscopic (EM) examination. Degrees of acute inflammation were evaluated via CD-11b immunohistochemistry, and global muscle change was investigated using hematoxylin and eosin stains. Intensity of fibrosis was evaluated using Masson trichrome stains, and ultrastructural changes were observed on EM.

Results

We observed no significant inflammatory cell infiltration, muscle necrosis or fibrotic change in treated and control eyes. EM findings revealed no significant damage to muscle or vascular tissue after bevacizumab injection.

Conclusions

We found no signs of extraocular muscle toxicity after LM and EM intramuscular and subconjunctival bevacizumab injections in a rabbit model.     

Cholinergic receptors in the extraocular rectus muscle of the rabbit

The cholinergic receptors in rabbit isolated rectus muscle preparations were characterized by means of cholinergic agonists and antagonists. The concentration-dependent contraction induced by acetylcholine, carbachol or oxotremorine remained uninfluenced by atropine (10(-5) M), whereas the nicotinic receptor antagonist hexamethonium caused a parallel shift of the concentration-response curve. The agonists pilocarpine, methacholine and aceclidine, which are selective muscarinic receptor stimulants, did not cause contraction of the muscle preparation. However, the nicotinic receptor stimulant 1,1-dimethyl-4-phenylpiperazine iodide (DMPP) caused contraction similar to that induced by acetylcholine. DMPP-induced contractions were inhibited by hexamethonium, causing a parallel rightward shift of the concentration-response curve. This shift could be quantified by means of a Schild plot, indicating competitive antagonism with a PA2 value of 4.63 for hexamethonium. Atropine when applied together with hexamethonium did not cause a further shift of the concentration-response curve. The present results clearly indicate that the cholinergic receptors which mediate contraction in the rabbit isolated extraocular muscle preparation belong to the nicotinic subtype.     

Evaluation of macular thickness change after inferior oblique muscle recession surgery

Purpose:

This study aimed to evaluate the changes in macular thickness following inferior oblique muscle recession surgery.

Materials and Methods:

Thirty-eight eyes from 21 patients undergoing ocular muscle surgery were included. Patients were grouped into three groups based on the type of surgical intervention: Group I (n = 12), inferior oblique recession surgery alone; Group II (n = 12), inferior oblique plus horizontal muscle surgery; Group III (n = 14), horizontal muscle surgery alone. Each eye was scanned using the optical coherence tomography (OCT) device preoperatively and on the first postoperative day to measure macular thickness.

Results:

Following surgery, a significant increase in foveal thickness occurred in Group I (P < 0.05) and Group II (P < 0.01). In addition, a statistically significant difference was observed between the groups with regard to the increase in foveal thickness (P = 0.016), with significantly lower changes in Group III.

Conclusion:

Our findings suggested that inferior oblique muscle recession surgery is associated with an increase in macular thickness.     

眼外肌注射A型肉毒毒素后神经萌芽及运动终板的变化

目的研究兔眼外肌注射A型肉毒毒素(BTXA)后3个月的神经末梢萌芽、运动终板及肌纤维的变化,从神经再生方面探讨BTX的作用规律。设计实验性研究。研究对象10只新西兰大白兔。方法10只白兔,在双眼8条眼外肌肌腹各注射BTXA 2．5U,在注射0、2、4、6、8、12周时各取一条眼外肌,共60条作乙酰胆碱酯酶(AchE)组化染色显示运动终板、肌纤维,用Bielschowsky银染法显示神经末梢萌芽。主要指标有萌芽终板数,总终板数；萌芽平均总长度/有萌芽终板数；运动终板的灰度值、面积；肌纤维直径。结果眼外肌的运动终板中,有萌芽终板数,总终板数、萌芽平均总长度/有萌芽终板数在2周(84．04±3．56．170．71±46．83)和4周(91．52±4．13,162．11±56．19)时达到最高峰,之后逐渐降低,到12周时降到最低(19．53±4．00,40．46±6．47),但仍稍高于正常值。运动终板的灰度值、面积及肌纤维直径亦出现此规律。结论注射BTXA后的神经末梢萌芽和运动终板的变化在2～4周时最为明显,之后逐渐降低,与临床上观察到的肉毒毒素作用规律相符,为研究肉毒毒素引起的肌麻痹的恢复过程提供一种新的观察途径。(眼科,2006．15：326-330)     

Pathologic findings after recession and resection of extraocular muscles in rabbits

A study on the pathologic findings after recession and resection of extraocular muscles in rabbits was performed. Fibrosis of the extraocular muscles increased with time, which showed no difference between the recessed and resected muscles. Inflammation and foreign body reaction decreased with time, which showed no difference between the recessed and resected muscles. Adhesions of extraocular muscles to the sclera were observed from one month after the operation. The resected muscles showed milder adhesion to the sclera than the recessed ones. The operated extraocular muscles showed atrophies at one month, which showed no difference between the recessed and resected muscles. According to our results, when reoperation is needed, fibrosis of the extraocular muscles after recession and resection should be considered when making a decision on the amount of muscle to be recessed and resected.     

The effect of mitomycin-C on the healing process in rabbit extraocular muscle surgery

BACKGROUND AND OBJECTIVE: One of the most serious complications following extraocular muscle surgery is formation of postoperative adhesions that may result in restrictive ocular motility dysfunction. The effect of mitomycin-C (MMC) on postoperative wound healing in extraocular muscle surgery was investigated. MATERIALS AND METHODS: Sixteen albino rabbits (24 eyes) were used and anesthetized with ketamine and xylazine. These rabbits were divided into 3 groups; (1) control group (balanced salt solution (BSS) exposure for 5 minutes), (2) Group 1 (0.5 mg/ml MMC exposure for 1 minute) and (3) Group 2 (0.5 mg/ml MMC exposure for 5 minutes). After 3 mm recession of superior rectus muscle, MMC or BSS was applied using Weck-Cel sponge (Solan, Jacksonville, FL). The reduction of fibroblast and collagen fiber proliferation were evaluated histopathologically with light microscope at 1, 2, 4 and 8 weeks after operation. We also evaluated the amount of basic fibroblast growth factor (bFGF) by immunohistochemical study at the same time. RESULTS: Histopathologically, there was a more significant reduction of fibroblast and collagen fiber proliferation in Group 1 and 2 than the control group. Immunohistochemically, Group 1 and 2 showed lesser expression of bFGF than the control group. But, there was no difference between Group 1 and 2. CONCLUSIONS: Topical intraoperative application of mitomycin C in extraocular muscle surgery may reduce postoperative adhesions.     

Change in proptosis following extraocular muscle surgery: effects of muscle recession in thyroid-associated orbitopathy.

PURPOSE: To evaluate the effect of strabismus surgery on proptosis in patients with thyroid-associated orbitopathy. METHODS: The medical records of 22 consecutive patients with thyroid-associated orbitopathy undergoing strabismus surgery were reviewed. Data pertaining to the number of muscles operated on, amount of muscle recession, prior orbital decompression, and exophthalmometry were evaluated. RESULTS: Thirty-eight eyes in 22 patients with thyroid-associated orbitopathy were studied before and after strabismus surgery. The mean change in exophthalmometry following strabismus surgery in all eyes was +0.6 mm (p < 0.01). Eyes with prior decompression averaged a 0.9 mm increase following strabismus surgery (p < 0.01); those without decompression averaged a 0.2 mm decrease (p = 0.658). In eyes that underwent two rectus muscle recessions the increase in Hertel measurements averaged 1.2 mm; when only one muscle was recessed, the average increase was 0.2 mm. In the eyes with muscle recession < or =5 mm, the mean exophthalmometric increase was 0.7 mm. When a muscle recession of more than 5 mm was performed, the exophthalmometry showed a mean increase of 0.5 mm. CONCLUSIONS: Strabismus surgery on patients with thyroid-associated orbitopathy can worsen proptosis, especially in those with prior decompression. When planning for orbital decompression, the surgeon should consider this effect. Moreover, patients should be made aware of the possible changes to their appearance.     

Latter reorganization of membrane-glycogen complexes in rabbit extraocular muscle

Characteristic modes of secondary reorganization were observed in membrane-glycogen complexes of rabbit extraocular muscle. These included (a) an irregular widening or narrowing of the intracisternal space, (b) a loss of the typical intracisternal flocculent densities, and (c) the acquisition of intercisternal flocculent densities. In irregularly widened cisternae, the membranes tended to remain closely adjacent to the intervening glycogen layer, thereby forming triads composed of a glycogen layer enclosed within the apposing membranes of adjacent cisternae. In the absence of glycogen particles from contiguous portions of several lamellae, the membranes became compacted to form myeloidlike figures. Degenerating complexes sometimes displayed distention of intercisternal spaces and layers of atypically small particles. The above modifications of membrane-glycogen complexes would be compatible with the notion that these structures are involved in the process of glycogen metabolism, as opposed to the previously suggested notion that these structures are transient vehicles for the accumulation of glycogen masses.     

The effect of resection on satellite cell activity in rabbit extraocular muscle

PURPOSE: A common treatment for motility disorders of the extraocular muscles (EOMs) is a resection procedure in which there is surgical shortening of the muscle. This procedure results in rotation of the globe toward the resected muscle, increased resting tension across the agonist-antagonist pair, and stretching of the elastic components of the muscles. In the rabbit, due to orbital constraints and limited rotation, resection results in more significant stretch of the surgically treated muscle than the antagonist. This surgical preparation allows for the examination of the effects of surgical shortening of one rectus muscle and passive stretch of its ipsilateral antagonist. METHODS: The insertional 6 mm of the superior rectus muscles of adult rabbits were resected and reattached to the original insertion site. After 7 and 14 days, the animals were injected intraperitoneally with bromodeoxyuridine (BrdU) every 2 hours for 12 hours, followed by a 24-hour BrdU-free period. All superior and inferior rectus muscles from both globes were examined for BrdU incorporation, MyoD expression, neonatal and developmental myosin heavy chain (MyHC) isoform expression, and myofiber cross-sectional area alterations. RESULTS: In the resected muscle and in the passively stretched antagonist muscle, there was a dramatic increase in the number of myofibers positive for neonatal MyHC and in the number of BrdU- and MyoD-positive satellite cells. The addition of BrdU-positive myonuclei increased from 1 per 1000 myofibers in cross sections of control muscles to 2 to 3 per 100 myofibers in the resected muscles. Single myofiber reconstructions showed that multiple BrdU-positive myonuclei were added to individual myofibers. Addition of new myonuclei occurred in random locations along the myofiber length of single fibers. There was no correlation between myofibers with BrdU-positive myonuclei and neonatal MyHC isoform expression. CONCLUSIONS: Both active and passive stretch of the rectus muscles produced by strabismus surgery dramatically upregulated the processes of satellite cell activation, integration of new myonuclei into existing myofibers, and concomitant upregulation of immature myosin heavy chain isoforms. Understanding the effects of strabismus surgery on muscle cell biological reactions and myofiber remodeling may suggest new approaches for improving surgical outcomes.     

青少年眼钝伤性房角后退的观察

目的本文观察282例眼钝位对房角损伤所致房角后退的各种状态,并探讨房角后退与前房出血及青光眼的关系.方法应用Goldmann前房角镜,检查282例眼钝伤的双眼前房角,观察房角后退的各种形态,根据Howard等的分类法将房角后退分成浅(Ⅰ度),中(Ⅱ度),深(Ⅲ度)三度,并以圆周0～360°范围作记录.结果各种原因所致282例钝伤眼中,267眼有房角后退占94.68%,其中Ⅰ度房角后退119眼(44.57%),Ⅱ度95眼(35.58%),Ⅲ度53眼(19.85%).有前房出血记录者198眼(70.21%),全部有房角后退.在房角后退的267眼中,41眼有眼压升高,其中17眼房角后退为唯一原因,眼压升高均发生在1年内,大部分在1周内.其中16眼经药物治疗后1年内眼压恢复正常,1眼手术治疗.结论眼钝伤做房角镜检查,有利于发现房角损伤,并综合各种损伤分析病情,指导临床治疗.若发现房角后退＞180°时,有可能发生青光眼,应定期随诊.     

The effects of bupivacaine injection and oral nitric oxide on extraocular muscle in the rabbit

Aim

Nitric oxide (NO) plays a key role in muscle regeneration, which is the primary response, observed during bupivacaine-induced extraocular muscle (EOM) hypertrophy. Our aims were to investigate the effects of bupivacaine injection into the rabbit EOM and the interaction with NO.

Materials and methods

Superior rectus (SR) muscles of 24 New Zealand albino rabbits were studied. Single muscle twitch tension (SMTT) and tetanic muscle tensions at 50, 75, and 100 Hz were recorded using a 15 V stimuli. The rabbits were equally allocated into three groups. Measurements were performed without any drug treatments in group 1. In groups 2 and 3, bupivacaine, 0.5 ml of a 0.50 % solution, was injected into the EOM, and after 21 days, measurements were performed. Oral isosorbide dinitrate (NO donor) at 20 mg/day was given each day prior to measurements in group 3.

Results

SMTTs were 69.9 (66.7–77.6), 187.7 (114.9–252.1) and 204.2 (135.3–311.6) mg in groups 1, 2, and 3 respectively. SMTTs for both groups 2 and 3 were significantly higher than that for group 1 (p?<?0.05). Compared with group 1, group 2 exhibited a 3.8–11.7 % increase in the tetanic tensions at 50, 75, and 100 Hz, but none of these differences were statistically significant. The increase was 47.5–137.5 % in group 3 relative to group 2, and the differences were statistically significant except at 100 Hz. The enlargement of the muscle fibers after bupivacaine injection was shown histopathologically.

Conclusion

Bupivacaine injection increased the EOM tension in rabbits to some extent. NO augmented the effect of bupivacaine.     

Presence and structure of innervated myotendinous cylinders in rabbit extraocular muscle

Innervated myotendinous cylinders (IMCs) in rabbit extraocular muscles (EOMs) were identified for the first time. The nature of IMC nerve terminals was demonstrated by means of electron microscopy and double fluorescent staining. The distal EOM portions of four rabbits of different age and sex were prepared for transmission electron microscopy and for double-fluorescent labelling. Antibody against neurofilament H and alpha-bungarotoxin were applied on longitudinal cryostat sections of distal myotendinous junction. IMCs were consistently and frequently observed at the distal myotendons of each EOM. More than 30 IMCs were counted in two medial recti of a 6 month and 3 year old rabbit. IMCs were enveloped by two to three layered capsules of fibrocytes. Each IMC contained the terminal portion of one multiply-innervated muscle fibre and its corresponding tendon. The tendon compartment of an IMC was entered by a single myelinated nerve fibre (2-3 microm in diameter). Inside the IMC, this nerve fibre ramified into up to four preterminal branches. Nerve terminals exclusively established contacts with the muscle fibre at its junction with the tendon fibrils. Nerve terminals contained mitochondria and a multitude of clear vesicles. Within the synaptic cleft a basal lamina was always present. alpha-Bungarotoxin labelled the muscle side of these myoneural contacts. Nerve terminals exhibited neither age nor sex differences. Among all species so far investigated, rabbit IMCs are unique by exhibiting exclusively myoneural terminal contacts. Based on fine structure and alpha-bungarotoxin binding, myoneural contacts in rabbit IMCs are almost certainly motor, as previously observed only in human IMCs. Thus, rabbit IMCs are supposed to have a predominant effector function.     

先天性麻痹性斜视眼外肌形态改变的研究

目的:研究先天性麻痹性斜视眼外肌的形态学改变,为麻痹性斜视病因学提供理论依据。方法:收集先天性麻痹性斜视16例20眼,将术中切下的弱侧肌6例8眼、强侧肌10例12眼以及正常组10例10眼分别行VG染色、光电镜观察,并测量肌细胞横截面积。结果:弱侧肌组肌纤维排列极其紊乱,絮状变性、溶解,肌纤维间隙大量胶原纤维增生,有的未见肌组织;强侧肌组肌纤维形态表现多样,部分肌纤维轻度肥大,走向欠规则,部分肌纤维排列紊乱,肌细胞内肌丝稀疏、溶解,线粒体水肿、空泡变,内质网扩张,甚至部分肌细胞内出现灶性絮状变性区。强侧肌组和对照组肌细胞截面积分别为758.31±163.55μm2,641.8±75.27μm2,两者差异无显著性意义;VG染色两组胶原纤维面积/肌纤维面积分别为19.27±2.73%,11.17±2.43%,差异有显著性意义。结论:先天性麻痹性斜视眼外肌均发生不同程度的改变,特别是强侧肌组形态改变的多样化是产生麻痹性斜视的重要原因。     

Cross-bridge kinetics of rabbit single extraocular and limb muscle fibers

PURPOSE: To gain insights into the functional significance of myosin heavy-chain (MyHC) heterogeneity by comparing the mechanical kinetic properties of single rabbit extraocular muscle (EOM) fibers with those of limb fibers. EOMs are known to contain developmental and EOM-specific MyHCs in addition to those present in limb muscles, and MyHCs profoundly influence muscle mechanics. METHODS: Isometric cross-bridge kinetics were analyzed in Ca(2+)-activated single glycerinated fibers from rabbit EOM and limb fast and slow muscles at 15 degrees C by means of mechanical perturbation analysis. The plots of stiffness and phase against frequency display a characteristic frequency, f(min), at which stiffness is minimum, and phase shift is zero. The value of f(min) is independent of Ca(2+) or force level but reflects the kinetics of cross-bridge cycling. RESULTS: Analysis of 121 limb fast fibers gave f(min) values ranging from 10 to 26 Hz. f(min) for the 10 slow soleus fibers was 0.5 Hz. Analysis of 170 EOM fibers gave f(min) values in the range for fast limb fibers, but in addition yielded f(min) values below (4-9 Hz) and above (27-33 Hz) this range. CONCLUSIONS: The wider range of mechanical kinetic characteristics in EOM fibers compared with limb fibers is likely due to the expression of developmental (low f(min)) and EOM-specific (high f(min)) MyHCs in addition to isoforms present in adult limb muscles. The considerable diversity of functional characteristics in EOM fibers is likely to be important for rotating the eyeball at various speeds during tracking and for executing saccades over a wide range of angles.