Three-dimensional location of human rectus pulleys by path inflections in secondary gaze positions

PURPOSE: Connective tissue pulleys serve as the functional mechanical origins of the extraocular muscles (EOMs). Anterior to these pulleys, EOM paths shift with gaze to follow the scleral insertions, whereas posterior EOM paths are stable in the orbit. Inflections in EOM paths produced by gaze shifts can be used to define the functional location of pulleys in three dimensions (3-D). METHODS: Contiguous magnetic resonance images in planes perpendicular to the orbital axis spanned the anteroposterior extents of 22 orbits of 11 normal adults with the eyes in central gaze, elevation, depression, abduction, and adduction. Mean EOM cross-sectional area centroids represented in a normalized, oculocentric coordinate system were plotted over the length of each EOM to determine paths. Path inflections were identified to define pulley locations in 3-D. RESULTS: All rectus EOM paths exhibited in secondary gaze positions distinct inflections 3 to 9 mm posterior to globe center, which were consistent across subjects. The globe center and the lateral rectus pulley translated systematically in the orbit with lateral gaze, whereas other pulleys remained stable relative to the orbit. CONCLUSIONS: Distinct inflections in rectus EOM paths in secondary gaze positions confirm the existence of pulleys and define their locations in 3-D. The globe and lateral rectus pulley translate systematically with gaze position. The EOM pulleys may simplify neural control of eye movements by implementing a commutative ocular motor plant in which commands for 3-D eye velocity are effectively independent of eye position.     

Magnetic resonance imaging of the arc of contact of extraocular muscles: implications regarding the incidence of slipped muscles.

BACKGROUND: Slipped muscles are complications of strabismus surgery that are encountered more frequently after recessions of the inferior and medial rectus muscles. METHODS: We obtained multipositional high-resolution magnetic resonance imaging of 10 orbits of 6 normal subjects, 9 orbits of 5 patients with thyroid-associated eye disease, and 4 orbits of 2 patients with thyroid-associated eye disease on the day after rectus muscle recessions using a suspension technique. The arc of contact and the distance between the insertion and the point of tangency of each of the extraocular muscles to the globe were measured in primary position as well as in the cardinal fields. RESULTS: The data confirm that the inferior and medial rectus muscles have a significantly smaller wraparound effect on the globe than the superior and lateral rectus muscles, respectively (P =.022 for the vertical rectus muscles; P =.05 for the horizontal rectus muscles, paired t test), and that their insertions may be found several millimeters posterior to their points of tangency in extreme rotation of the globe in their respective field of action. The appearance of the suspended recessed inferior rectus muscle on the first postoperative day and its decreased apposition to the globe raise concerns about the muscle losing contact with the globe in extreme downgaze. CONCLUSIONS: The small wraparound effect of the inferior and medial rectus muscles may explain one of the mechanisms accounting for the increased incidence of slipped muscles encountered after recessions of these muscles.     

Evidence for a pulley of the inferior oblique muscle

PURPOSE: This study was undertaken to investigate evidence for a connective tissue pulley constraining the path of the inferior oblique (IO) muscle. METHODS: From magnetic resonance images, the cross-sectional area, path, and orbital relationships of the human IO were determined in multiple gaze positions. Rectus pulleys were directly imaged with intravenous gadodiamide contrast. Images were compared with serial histologic sections of IO muscles of humans and monkeys. RESULTS: The IO path from origin to the lateral border of the inferior rectus (IR) muscle was straight. Lateral to the IR, the IO curved to follow the globe. At the point of IR crossing, the IO moved anteriorly from infraduction to supraduction by approximately 53% of the IR insertion's travel. Gaze-related change in IO cross section was demonstrable near the IR center. The gaze-related inflection in IO path corresponded to its encirclement by a pulley consisting of a dense ring of collagen, stiffened by elastin and smooth muscle, and united with the IR pulley. Orbital layer fibers of the IO inserted on its pulley, the lateral rectus (LR) pulley, and associated connective tissues. CONCLUSIONS: Like the rectus muscles, the human and monkey IO has a connective tissue pulley serving as its functional origin. The position of the IO pulley is influenced by its coupling to the actively moving IR pulley, whereas in turn the IO orbital layer inserts on and presumably shifts the IR and LR pulleys. These intercouplings facilitate implementation by rectus extraocular muscle suspensions of a commutative ocular motor plant.     

Magnetic resonance imaging of the effects of horizontal rectus extraocular muscle surgery on pulley and globe positions and stability

PURPOSE: Magnetic resonance imaging (MRI) was used to determine the effect of recessions and resections on horizontal extraocular muscle (EOM) paths and globe position. METHODS: Four adults with horizontal strabismus underwent contrast-enhanced, surface-coil MRI in central, secondary, and tertiary gazes, before and after horizontal EOM recessions and/or resections. EOM paths were determined from 2-mm thickness, quasicoronal MRI by analysis of cross-sectional area centroids in a normalized, oculocentric coordinate system. Globe displacement was determined by measuring the apparent shift of the bony orbit in eccentric gaze. RESULTS: In all subjects, the anteroposterior positions of the horizontal rectus pulleys shifted by less than 2 mm after surgery, indistinguishable from zero within measurement precision. In three subjects who underwent medial rectus (MR) recession or resection, postoperative globe position was similar in central gaze, but globe translation during vertical gaze shift changed markedly. There was no effect on globe translation in the subject who underwent only lateral rectus (LR) resection. CONCLUSIONS: Recessions and resections of horizontal EOMs have minimal effect on anteroposterior EOM pulley positions. Because the pulley does not shift appreciably despite large alterations in the EOM insertion, the proximity of a recessed EOM to its pulley would be expected to introduce torsional and vertical actions in tertiary gazes. Connective tissue dissection during MR surgery may destabilize the globe's vertical translational stability within the orbit, potentially changing the effective pulling directions of the rectus EOMs in vertical gazes. These changes may mimic oblique muscle dysfunction. LR surgery may avoid globe destabilization.     

Incomitant strabismus associated with instability of rectus pulleys

PURPOSE: Connective tissue pulleys serve as functional mechanical origins of the extraocular muscles (EOMs) and are normally stable relative to the orbit during gaze shifts. This study evaluated pulley stability in incomitant strabismus. METHODS: Contiguous 2- or 3-mm thick magnetic resonance images (MRIs) perpendicular to the orbital axis spanned the anteroposterior extents of 12 orbits of six patients with incomitant strabismus. Imaging was performed in central gaze, supraduction, infraduction, abduction, and adduction. Rectus EOM paths were defined by their area centroids and plotted in a normalized, oculocentric coordinate system. Paths of EOMs ran toward the pulleys. Sharp EOM path inflections in secondary gaze indicated pulley locations in three dimensions. RESULTS: MRI revealed substantial inferior shift of the lateral rectus (LR) pulley of up to 1 mm during vertical gaze shifts in patients with axial high myopia and a posterior shift from abduction to adduction in simulated Brown syndrome. There was substantial LR pulley shift opposite the direction of vertical gaze in a subject with X-pattern exotropia who had undergone repeated LR surgery. The medial rectus (MR) pulley shifted inferiorly with gaze elevation in Marfan syndrome. Pulley instability was associated with significantly increased globe translation during gaze shifts. CONCLUSIONS: Pulley instability, resulting in EOM sideslip during ductions, occurs in some cases of incomitant strabismus. Resultant patterns of strabismus may depend on static pulley positions, pulley instability, and coexisting globe translation that alters pulley locations relative to the globe. Translational instability of pulleys and the globe could produce abnormalities in actions of otherwise normal EOMs, and connective tissue disorders causing these instabilities should be considered as potential causes of strabismus.     

Anterior and nasal transposition of the inferior oblique muscles.

BACKGROUND: When performing anterior transposition of the inferior oblique (IO) muscle, placement of the posterior suture close to the lateral border of insertion of the inferior rectus (IR) muscle decreases the incidence of antielevation syndrome (AES). We hypothesized that placement of the suture nasal to the IR muscle insertion will convert the IO muscle into an intorter and depressor. Here we present the first series of results obtained with a new procedure for the treatment of elevation in adduction with extorsion and abnormal head postures. METHODS: Twenty patients with IO muscle overaction, superior oblique (SO) muscle palsy, absent SO muscles, AES, or Duane syndrome were studied. Before surgery, each patient showed at least one, but often more, of the following signs: elevation in adduction, exotropia (XT) in up gaze, abnormal head posture, and extorsion. Each underwent anterior and nasal transposition (ANT) of the IO muscle, with the new insertion typically 2 mm nasal and 2 mm posterior to the nasal border of the IR muscle insertion. RESULTS: Large improvements in ocular alignment, extorsion, and head posture were found in most patients. However, a poor result was noted in a patient with Y-pattern XT, who developed a mild amount of comitant XT after an extreme degree of ANT (4 mm nasal and 3 mm anterior to the nasal border of the IR muscle insertion). In Duane syndrome, ANT corrects upshoot, but downshoot may get worse. Mersilene permanent sutures, rather than dissolving suture materials, are recommended to avoid postoperative retraction of muscle fibers. CONCLUSIONS: ANT converts the IO muscle into an intorter and tonic depressor and can significantly improve elevation in adduction. This procedure seems particularly useful in patients with severe or recurrent congenital and acquired SO palsies, particularly as a secondary procedure. Extreme ANT may induce exotropia in the primary position.     

Rectus extraocular muscle pulley displacement after surgical transposition and posterior fixation for treatment of paralytic strabismus.

PURPOSE: To determine the effect of rectus extraocular muscle (EOM) transposition with posterior fixation (PF), we employed magnetic resonance imaging (MRI) to demonstrate pulley inflections in EOM paths before and after surgery in patients with paralytic strabismus. DESIGN: Consecutive interventional case series. METHODS: Five consecutive patients (three males and two females with a mean age 52 years, range 33 to 77 years) with paralytic strabismus were studied prospectively before and more than 6 weeks after EOM transposition and PF by means of contiguous cross-sectional MRI obtained in planes perpendicular to the long axis of the orbit. Muscle paths were determined in three dimensions (3-D) for each EOM by analysis of cross-sectional area centroids in normalized, oculocentric coordinate systems. RESULTS: Four patients underwent full tendon transposition with PF of the vertical rectus EOMs. One other patient underwent full tendon transposition without PF of the horizontal rectus EOMs superiorly. For transpositions with PF, there was a large displacement of EOM path in central (straight ahead) gaze beginning in the posterior orbit. After surgical transposition, clear inflections representing pulley locations of the superior, medial, and lateral rectus paths occurred in central gaze. There was no clear path inflection for the inferior rectus in central gaze, but there was a small inflection in adduction. After all transpositions, the globe center shifted away from the transposed insertions. CONCLUSIONS: Rectus EOM transpositions with PF shift EOM pulleys posteriorly and in the directions of the transposed EOM tendons, while translating the globe center. These changes may explain the superior effectiveness of PF in increasing duction towards the transposition.     

Normative measurements of Korean orbital structures revealed by computerized tomography

PURPOSE: The purposes of this study were to establish criteria for the diameters of normal extraocular muscles, the width of the optic nerve, and the globe position as revealed by CT, and to investigate the effects of age and sex on these parameters in the Korean population. SUBJECTS AND METHODS: Diameters of extraocular muscles (medial, lateral, superior complex, and inferior rectus), distance from the interzygomatic line to the posterior margin of the globe, width of the optic nerve-sheath complex, and length of the interzygomatic line were calculated for 214 patients on axial and direct coronal CT images, and the effects of age and sex were analyzed. RESULTS: Normal range for the diameters as given by mean+/-2SDs of extraocular muscles were medial rectus, 2.2--5.4 mm; lateral rectus, 2.1--4.9 mm; inferior rectus, 2.5--5.7 mm; and superior complex group, 2.6--6.4 mm. The mean optic nerve-sheath complex was 4.1 mm and the values ranged from 2.9 mm to 5.3 mm. The mean length of the interzygomatic line was 103.8 mm. The normal posterior position of the globe as here designed was 11.2 mm behind the interzygomatic line (range, 6.4--15.3 mm). All parameters under study were a little larger in males than females. Statistically, however, there was no significant difference between males' and females' results, nor between the various age groups (p>0.05). CONCLUSION: Our CT results may help clinical ophthalmologists to accurately assess enlargement of the extraocular muscles and the optic nerve as well as aiding in the evaluation of exophthalmos.     

Pre-operative variables affecting final vision outcome with a critical review of ocular trauma classification for posterior open globe (zone III) injury

Purpose:

To identify pre-operative variables affecting the outcome of posterior open globe (zone III) injuries. Secondary objective was to re-look at the definition or landmarks for zone III injury and its clinical significance for predicting visual prognosis following open globe injury.

Materials and Methods:

Retrospective review of medical records of all hospitalized patients with surgical repair of open globe injury over last 10 years at a tertiary referral eye care center in Singapore. Out of 172 eyes with open globe injury, 28 eyes (16.3%) with zone III injury was identified and reviewed further. Pre-operative visual acuity (VA) and other variables, extent of scleral wound in reference to rectus insertion, relative afferent pupillary defect (RAPD) and final vision outcome were recorded.

Results:

Median age was 37 years with male predilection (92.9%). Mean follow-up was 12.9 months. Pre-operative VA was no light perception (NLP) in 16 (57.1%) eyes. Final VA remained NLP in 14 eyes (50.0%). The factors contributing to poor post-operative vision based on univariate regression analysis were the presence of RAPD, poor pre-operative VA, blunt trauma, extent of trauma, associated traumatic cataract, hyphema, vitreous loss and associated vitreo-retinal trauma. Further on, zone III injuries with scleral wound limited anterior to rectus insertion (6 eyes) had better vision outcome than those with injuries extending beyond rectus insertion (22 eyes).

Conclusion:

Initial VA, blunt ocular trauma, visual axis involvement, loss of light perception, presence of RAPD, traumatic cataract, hyphema, vitreous loss were the important determinants for final visual outcome in patients with zone III injury. Wound extending posterior to rectus insertion has poorer outcome as those limited anterior to rectus insertion. We suggest that there may be a need to relook at zone III injuries with reference to rectus insertion for prognostic significance, and further studies are warranted.     

Posterior fixation sutures: a revised mechanical explanation for the fadenoperation based on rectus extraocular muscle pulleys

PURPOSE: To determine the effect of the rectus extraocular muscle pulleys on the fadenoperation, an operation designed to fixate the posterior muscle belly to the underlying retroequatorial sclera. METHODS: First, duction into the field of action of the operated-on muscle was quantified retrospectively after fadenoperation. Magnetic resonance imaging was then performed prospectively after surgery to verify anatomic changes. Forced duction testing was performed prospectively during surgery before and after faden placement. Finally, computed tomography in a cadaver containing radiographic markers was performed prospectively to determine the effect of fadenoperation on the position of the medial rectus insertion relative to its pulley. RESULTS: Mean maximum adduction after medial rectus fadenoperation was 18 degrees (range, 10 to 25 degrees; 13 eyes). Fadenoperations combined with large medial rectus recessions restricted adduction more than fadenoperations combined with smaller recessions (P = .019), but even fadenoperations without recessions substantially restricted adduction. Mean maximum abduction after lateral rectus fadenoperation was 40 degrees (range, 25 to 45 degrees; four eyes). Axial magnetic resonance imaging in two eyes demonstrated a smaller loss of muscle tangency to the globe during contraction than predicted by geometric models. Forced ductions in nine patients performed immediately after faden placement demonstrated a new mechanical restriction to duction toward the operated-on muscle. Cadaveric computed tomographic scans demonstrated posterior displacement of the medial rectus pulley during adduction after fadenoperation. CONCLUSIONS: Posterior fixation sutures do not significantly decrease muscle torque during contraction. Because posterior fixation sutures posteriorly displace the pulley sleeve during duction toward the operated-on muscle, the mechanical restriction after surgery probably represents the force deforming the pulley. This mechanical restriction may account for the limitation in duction seen after fadenoperation.     

间歇性外斜视眼外直肌磁共振成像研究

目的：利用磁共振成像（MRI）技术研究间歇性外斜视患者眼外直肌Pulley位置及其形态改变。方法：系列病例研究。收集2017年1-6月在天津市眼科医院确诊为间歇性外斜视的患者32例,平均年龄（15.4±1.8）岁。同时招募健康志愿者30例,平均年龄（16.1±1.6）岁,利用MRI技术对第一眼位眼外直肌行连续冠状扫描。采用线性回归和相关系数计算眼外直肌Pulley位置,独立样本t检验进行2组间比较;同时计算各MRI层面水平肌肉最大横截面积和体积的变化,2组间进行独立样本t检验。结果：间歇性外斜视患者眼外四条直肌Pulley位置与正常对照者相比差异无统计学意义。而间歇性外斜视患者各MRI扫描层面其内直肌横截面积均小于正常对照者,且其内直肌肌肉体积小于正常对照者（t=10.47,P=0.006）。对于外直肌而言,间歇性外斜视患者外直肌肌肉体积略大于正常对照者,但这种差异无统计学意义,但间歇性外斜视患者外直肌/内直肌肌肉体积比率（1.6±0.4）较正常对照者外直肌/内直肌肌肉体积比率（1.1±0.1）大,差异具有统计学意义（t=7.33,P=0.007）。结论：间歇性外斜视的发病与眼外直肌Pulley位置无关,而可能与水平直肌肌肉体积的变化有关,而这种改变可能会在术后继续影响眼位,从而导致斜视矫正术后远期复发率较高。     

Inferior oblique muscle recession

Surgical recession of the inferior oblique muscle is simpler to perform if the inferior rectus muscle, rather than either the lateral rectus muscle or the inferior oblique muscle insertion, is used as a landmark. We measured 200 consecutive autopsy eyes to determine the distance from the commonly used 8-mm recession site determined by the Fink technique to the lateral border of the inferior rectus muscle insertion. It was easier to reach this point by measuring 4.0 mm posterior and 4.4 mm superior to the lateral insertion of the inferior rectus muscle, or 2.9 mm superior (on a line parallel to the corneoscleral limbus) and 5.1 mm posterior (on the line perpendicular to the corneoscleral limbus) to the lateral insertion of the inferior rectus muscle. We made anatomical studies to grade the amount of inferior oblique muscle recession and to evaluate the proper placement of the posterior border of the recessed inferior oblique muscle.     

Evidence for active control of rectus extraocular muscle pulleys

PURPOSE: Connective tissue structures constrain paths of the rectus extraocular muscles (EOMs), acting as pulleys and serving as functional EOM origins. This study was conducted to investigate the relationship of orbital and global EOM layers to pulleys and kinematic implications of this anatomy. METHODS: High-resolution magnetic resonance imaging (MRI) was used to define the anterior paths of rectus EOMs, as influenced by gaze direction in living subjects. Pulley tissues were examined at cadaveric dissections and surgical exposures. Human and monkey orbits were step and serially sectioned for histologic staining to distinguish EOM fiber layers in relationship to pulleys. RESULTS: MRI consistently demonstrated gaze-related shifts in the anteroposterior locations of human EOM path inflections, as well as shifts in components of the pulleys themselves. Histologic studies of human and monkey orbits confirmed gross examinations and surgical exposures to indicate that the orbital layer of each rectus EOM inserts on its corresponding pulley, rather than on the globe. Only the global layer of the EOM inserts on the sclera. This dual insertion was visualized in vivo by MRI in human horizontal rectus EOMs. CONCLUSIONS: The authors propose the active-pulley hypothesis: By dual insertions the global layer of each rectus EOM rotates the globe while the orbital layer inserts on its pulley to position it linearly and thus influence the EOM's rotational axis. Pulley locations may also be altered in convergence. This overall arrangement is parsimoniously suited to account for numerous aspects of ocular dynamics and kinematics, including Listing's law.     

Periosteal fixation in third-nerve palsy.

PURPOSE: We present a new technique of anchoring the eyeball to the nasal periosteum using a nonabsorbable suture in acquired isolated third-nerve paresis. METHODS: This was a case series of 4 consecutive adult subjects with isolated third-nerve paresis. After a 12-mm lateral rectus muscle recession in all 4 subjects, we passed 5-O double-armed polyester (NW683 Ethibond; Ethicon, Division of Johnson and Johnson Ltd., Aurangabad, India) on spatulated needles through the periosteum overlying the anterior lacrimal crest (exposed as in a Dacryocystorhinostomy procedure) at its superior part. The needles were brought anterior to the medial rectus muscle insertion and tightened enough to align the eye in 8-10 prism diopters adducted position. RESULTS: Ocular alignment in the primary gaze was satisfactory at 6-12 months of follow up. CONCLUSIONS: The use of a nonabsorbable polyester suture to anchor the globe to the nasal periosteum is an additional technique that holds promise to align the eyes in the primary gaze.     

合并小度数垂直斜视的共同性外斜视眼外直肌MRI研究

目的观察共同性外斜视合并小度数垂直斜视患者眼外4条直肌Pulley位置、肌肉体积及水平直肌上、下两部分肌肉体积比值的特点。方法横断面研究。收集2018年1月至2019年12月在天津市眼科医院确诊为共同性外斜视患者,其中第一眼位不合并垂直斜视的患者为A组,第一眼位合并小角度垂直斜视(<5三棱镜度)的患者为B组;健康志愿者为C组。采用MRI冠状位扫描观察各组眼外4条直肌Pulley位置及体积的差异,同时计算比较水平直肌上、下两部分肌肉比值的差异。采用单因素方差分析及Kruskal-Wallis检验进行统计学分析。结果收集A组患者19例(38只眼),男性10例,女性9例,平均年龄30岁;B组患者10例(20只眼),男性4例,女性6例,平均年龄27岁;C组健康志愿者20名(40只眼),3个组间年龄和性别分布匹配(均P>0.05)。3个组间眼外4条直肌Pulley位置差异均无统计学意义(均P>0.05)。A组内直肌肌肉体积为(358.6±44.9)mm³,B组内直肌肌肉体积为(334.7±35.6)mm³,C组内直肌肌肉体积为(437.5±49.3)mm³,A组、B组内直肌肌肉体积均小于C组,差异均有统计学意义(t=6.405,6.025;均P<0.01);除内直肌外,其他直肌肌肉体积在3个组间差异均无统计学意义(均P>0.05)。3个组内直肌及外直肌上、下两部分肌肉体积比值差异均无统计学意义(均P>0.05);与A组和C组比,B组患者体积比值更分散。结论共同性外斜视合并小度数垂直斜视患者眼外4条直肌Pulley位置变化不明显,内直肌体积明显减小,水平直肌上、下两部分肌肉体积比值分布较分散可能与小度数垂直斜视有关。(中华眼科杂志,2021,57:223-227)     

Extraocular muscle sideslip and orbital geometry in monkeys

The belly of each extraocular muscle is elastically coupled to both the globe and orbit. The dependence of muscle planes on gaze angle must be determined experimentally. In monkeys, radio-opaque markers were implanted along the upper and lower margins of a lateral rectus. A scleral search coil was implanted in the other eye. With the eye in various gaze positions, X-ray images were made to show the LR in the lateral view. We found that as the eye rotates vertically over 50 deg (+/- 25 deg), the point of tangency of the LR with the globe slips an average of 5.1 mm vertically with respect to the globe, allowing this point--and so the muscle plane--to remain approximately fixed relative to the orbit. The results of quantitative orbital dissections are presented in support of the sideslip calculations.     

眼前节OCT技术对人眼水平直肌止端解剖结构的研究

背景眼外肌止端距离和厚度的测量对于眼外肌病变的诊断至关重要,但常用的影像学检测手段为接触性检查方法。眼前节光学相干断层扫描（OCT）可避免常规影像学检查的缺点,但尚未见到其用于眼外肌检测的报道。目的研究眼前节OCT（Visante OCT）在人眼外直肌止端解剖结构观察中的应用。方法收集不同屈光力受试者58例114眼,按照屈光力程度的不同分为低屈光力组（≤-3．00D）43眼,中屈光力组（〉-3．00D,≤-6．00D）49眼;高屈光力组（〉-6．00D）22眼,用Visante OCT测量水平直肌止端后沿到巩膜突的距离以及肌止端的厚度,对屈光力与直肌止端距离和及肌止端厚度的关系进行分析。结果外直肌、内直肌止端后沿到巩膜突的平均距离分别为（5．23±O．50）to／Y／和（3．81±0．46）mm。外直肌、内直肌止端平均厚度分别为（0．39±0．06）mm和（0．39±0．06）mm,与文献中超声生物显微镜（UBM）所测值比较差异无统计学意义（P=0．338;P=0．759）。低屈光力组的外直肌、内直肌止端距离分别为（5．25±0．45）mm和（3．74±0．53）mm,中屈光力组为（5．22±0．60）mm和（3．81±0．42）mm,高屈光力组为（5．20±0．35）mm和（3．904±0．42）mm,3组之间外直肌、内直肌止端距离的总体比较差异均无统计学意义（外直肌X^2=0．054,P=0．974;内直肌F=0．508,P=0．604）。外直肌、内直肌止端厚度低屈光力组分别为（0．41±0．06）mm、（0．40±0．06）mm,中屈光力组分别为（0．40±0．07）mm、（0．37±0．07）mm,高屈光力组分别为（0．36±0．05）mm、（0．39±0．05）mm,3组之间的外直肌止端厚度总体比较差异有统计学意义（,=4．922,P=0．009）,其中高屈光力组外直肌止端厚度较低屈光力组变薄（P〈0．05）,3组间内直肌止端厚度差异无统计学意义（F=2．152,P=0．125）。屈光力与外直肌止端的厚度呈正相关（r=0．284,P〈0．01）。结论Visante OCT是可用来观察人眼外直肌止端解剖结构的新方法,其测量值显示人眼水平直肌中,外直肌止端的厚度随着近视屈光力的增高有变薄趋势,高度近视组变薄明显。     

正常人眼球直肌Pulley功能位置的动态磁共振成像研究

目的研究正常人眼球运动动态磁共振成像（MRI）4条直肌Pulley（滑车）的功能性位置。方法采用西门子公司Sonata1.5T超导型MRI扫描仪,应用眼球运动动态MRI技术,获取20名正常人（20个眼眶）眼球原在位及上转、下转、内转、外转20度时垂直于眶轴的眼眶冠状位MRI图像。以眼球中心为原点建立三维坐标系,应用ScionImage医学图像测量软件分别测量各层面眼球垂直转动时水平直肌、眼球水平转动时垂直直肌的横截面质心。根据各层面直肌横截面质心的坐标值建立直线回归方程,分别求得眼球垂直转动时内、外直肌径路及眼球水平转动时上、下直肌径路直线回归曲线斜率变化最大的一点,即为该直肌Pulley的功能性位置。对4条直肌Pulley相对于眼球中心的坐标值（X、Y）进行统计。结果内直肌Pulley位于眼球中心后4mm,内14.7mm,下0.3mm;外直肌Pulley位于眼球中心后8mm,外9.8mm,下0.3mm;上直肌Pulley位于眼球中心后6mm,内1.6mm,上11.5mm;下直肌Pulley位于眼球中心后6mm,内4.4mm,下12.7mm。结论应用眼球运动动态MRI技术,分析眼球转动时直肌径路的变化,可证实4条直肌Pulley的存在并确定其功能位置。     

Prevention of suture knot exposure in posterior chamber intraocular lens implantation by 4-point scleral fixation technique.

BACKGROUND AND OBJECTIVE: The results and complications of posterior chamber intraocular lens (IOL) implantation by a 4-point scleral fixation technique are described. PATIENTS AND METHODS: Fifty eyes of 47 patients who underwent scleral-fixated IOL implantation were retrospectively evaluated. Twenty-one (42%) eyes had a history of trauma and 29 (58%) eyes had previously undergone cataract surgery. In all cases, IOL implantation by 4-point scleral fixation was performed and the knots of fixation sutures were rotated and buried in the globe. The IOL position was adjusted by suture rotation for best centration. RESULTS: The mean follow-up time was 7 +/- 4 months. Four (8%) eyes had minimal corneal edema preoperatively. Cystoid macular edema was noted in 2 (6.8%) eyes in the cataract surgery group and 8 (38%) eyes in the posttraumatic group. Two (9.5%) eyes in the posttraumatic group had atrophic macular changes and 1 (4.7%) had corneal scarring, which impaired vision. No complications such as knot exposure, tilting of the IOL, decentralization, or endophthalmitis were noted postoperatively. Postoperative mean corrected visual acuity was 0.4 +/- 0.3 in the posttraumatic group and 0.4 +/- 0.2 in the cataract surgery group. CONCLUSION: The 4-point scleral fixation technique resulted in no serious postoperative complications such as suture exposure and endophthalmitis. Because the knot can be rotated and buried in the globe, knot exposure is less likely to occur. This procedure is more effective than other techniques regarding IOL centralization.     

A case of congenital oblique retraction syndrome with upshoot in adduction

We treated a 27-year-old man who suffered from a congenital eye movement abnormality. The patient could not adduct the left eye, and showed exotropia, hypertropia and excyclotropia of the left eye. The range of abduction was also limited. The left eye showed marked upshoot on right gaze and eye globe retraction on right down gaze under conditions of right-eye viewing. The superior rectus muscle of the left eye was recessed and transposed nasally. The insertion of the superior oblique muscle was found to be defective. The upshoot and face turn improved after surgery. The globe retraction on right down gaze was no longer evident. We believe that the superior rectus muscle was innervated by an anomalous branch of the oculomotor nerve, which was originally destined to innervate the medial rectus, and that simultaneous contraction of the superior and inferior rectus muscles caused the globe retraction on right down gaze. This case also suggests the possibility that some part of the upshoot in adduction in Duane's syndrome is due to the co-contraction of the superior and medial rectus muscles due to this innervation anomaly.