用MRI测量正常人眼眶直肌坐标值及眼球动态直肌横截面积的研究

目的用MRI 研究正常人原在位4条直肌在眼眶中的静态位置及舒缩运动时的变化。方法应用眼球动态MRI 技术,获取20名正常人在原在位及眼球水平和垂直方向转动时的冠状位磁共振图像,应用计算机图像处理软件测量原在位时4条直肌横截面中心相对眼眶中心的坐标值及4条直肌收缩和松弛时横截面积的变化。在MRI 冠状位图像眼球-视神经连接平面上,规定直肌位于眼眶中心内侧及上方为正值。结果(1)原在位时, 相对于眼眶中心的坐标值分别为内直肌12.47mm,-2.24mm;外直肌-14.37mm,-2.87mm;上直肌1.87mm, 11.73mm;下直肌4.83mm,-11.31mm;(2)原在位及4条直肌收缩和松弛时,在MRI 图像上直肌最大横截面积所在层面位于眼球一视神经连接平面后约6mm 处;(3)直肌收缩和松弛时,MRI 图像上其横截面积变化幅度由大到小依次为上直肌、下直肌、内直肌、外直肌。结论正常人原在位MRI 图像4条直肌横截面中心在眼眶内坐标值及4条直肌收缩和松弛时横截面积变化的正常比值的建立,为眼外肌病的MRI 诊断及手术治疗提供了参考依据。     

轴性高度近视继发性内斜视的眼眶磁共振成像研究

目的用MRI研究轴性高度近视眼直肌位置变化,探讨轴性高度近视继发性眼球运动障碍的病因。设计前瞻性比较性病例系列。研究对象17~48岁轴性高度近视12例(22眼),年龄匹配的正常对照者20例(40眼)。方法高度近视者分为眼轴27~29mm、无眼球转动受限者(A组);眼轴>29mm、眼球外转及上转受限者(B组)。动态MRI技术获取眼球原在位及上转、下转、内转、外转位时的冠状MRI图像,图像处理软件测量原在位时眼球-视神经连接平面上4条直肌横截面中心相对眼眶中心的坐标值。主要指标直肌横截面中心相对眼眶中心的坐标值。结果 A组与正常对照组4条直肌的横截面中心相对眼眶中心的坐标值比较均无显著差异(P均>0.05);B组与正常对照组内直肌、上直肌、下直肌的横截面中心相对眼眶中心的坐标值比较无显著性差异(P均>0.05),但外直肌的横截面中心相对眼眶中心的坐标值较正常对照组向颞下移位(P<0.01);A组与B组内直肌、上直肌、下直肌的位点比较无显著性差异(P>0.05),B组较A组外直肌的位点向颞下移位(P<0.05)。结论外直肌止端向颞下移位可能是引起轴性高度近视继发性眼球运动障碍的重要原因。     

轴性高度近视眼直肌PULLY功能位置的动态磁共振成像研究

目的 用MRI研究轴性高度近视眼4条直肌pulley的功能位置,探讨轴性高度近视继发性眼球运动障碍的病因.方法 轴性高度近视12/例(22眼)根据眼屈光度、眼轴长度以及有无眼球运动受限分为A、B两组.A组无眼球运动受限;B组有眼球运动受限.应用动态MRI技术,获取眼球原在位及上转、下转、内转、外转位时的冠状位MRI图象.应用计算机图像处理软件测量各层面MRI图像眼球垂直方向转动时水平直肌、眼球水平方向转动时垂直直肌的横截面质心,根据其坐标值建立直线回归方程,统计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(直肌pulley的位点),将A组、B组、正常对照组进行比较.结果 A组与正常对照组4条直肌pulley的位点比较无显著差异(P＞0.05);B组与正常对照组内直肌、上直肌、下直肌pulley的位点比较无显著性差异P＞0.05);B组外直肌pulley的位点较正常对照组向颞下移位(P＜0.01);A组与B组内直肌、上直肌、下直肌pulley的位点比较无显著性差异(P＞0.05);B组较A组外直肌pulley位点向颞下移位(P＜0.05).结论 外直肌pulley的位点向颞下移位可能是引起轴性高度近视眼继发性眼球运动障碍的主要病因之一.     

轴性高度近视眼直肌PULLEY功能位置的动态磁共振成像研究

目的用MRI研究轴性高度近视眼4条直肌pulley的功能位置,探讨轴性高度近视继发性眼球运动障碍的病因。方法轴性高度近视12例(22眼)根据眼屈光度、眼轴长度以及有无眼球运动受限分为A、B两组。A组无眼球运动受限;B组有眼球运动受限。应用动态MRI技术,获取眼球原在位及上转、下转、内转、外转位时的冠状位MRI图象。应用计算机图像处理软件测量各层面MRI图像眼球垂直方向转动时水平直肌、眼球水平方向转动时垂直直肌的横截面质心,根据其坐标值建立直线回归方程,统计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(直肌pulley的位点),将A组、B组、正常对照组进行比较。结果A组与正常对照组4条直肌pulley的位点比较无显著差异(P>0.05);B组与正常对照组内直肌、上直肌、下直肌pulley的位点比较无显著性差异(P>0.05);B组外直肌pulley的位点较正常对照组向颞下移位(P<0.01);A组与B组内直肌、上直肌、下直肌pulley的位点比较无显著性差异(P>0.05);B组较A组外直肌pulley位点向颞下移位(P<0.05)。结论外直肌pulley的位点向颞下移位可能是引起轴性高度近视眼继发性眼球运动障碍的主要病因之一。     

共同性内斜视患者眼眶MRI成像中直肌坐标值及横截面积动态变化的研究

目的:用MRI研究共同性内斜视患者内外直肌在眼眶中的静态位置及舒缩运动时的变化,观察共同性内斜视患者中是否存在内外直肌的位置和功能异常。方法:应用眼球动态MRI技术,获取6例共同性内斜视患者在原在位及眼球水平方向转动时的冠状位磁共振图像,应用计算机图像测量软件对原在位时内外直肌横截面中心相对眼眶中心的坐标值;眼球内外转时,观察内外直肌最大横截面积所在平面面积的变化。同时设立正常对照组,将两组结果进行统计学比较。结果:共同性内斜视患者内外直肌在眼眶的位置较正常人无显著差异,共同性内斜视患者和正常人内外直肌最大横截面积位于眼球-视神经交接面后6mm,眼球内外转时,内外直肌最大横截面积的变化在两组无显著性差异。结论:内外直肌的位置和功能异常可能没有参与共同性内斜视的发生。     

人眼直肌Pulley系统胶原成分的实验研究

目的 研究人眼直肌Pulley系统胶原的组成成分及分布特点.方法 选取5个新鲜尸体眼眶,整体固定包埋,进行全眼眶连续冠状切片(4μm).相邻层面经苦味酸-天狼星红染色后,在偏振光显微镜下观察4条直肌Pulley及Pulley连接带(Pulley band,PB)的胶原组成及分布特点,并用MIAS-2000显微图像分析系统定量分析.结果 偏振光显微镜下可见4条直肌Pulley及PB中含有大量黄红色的I型胶原纤维及少量绿色的Ⅲ型胶原纤维.经图像分析,内直肌组Pulley中Ⅰ型胶原含量最高,内直肌-下直肌组PBⅢ型胶原含量最高,明显高于其他组,各组间差别有显著性(P＜0.05).结论 与力学特性密切相关的Ⅰ型胶原纤维及Ⅲ型胶原纤维作为眼直肌Pulley及PB胶原的主要组织成分,对眼球在功能眼位维持双眼视功能意义重大.     

猕猴眼外肌周围结缔组织结构及功能的研究

目的 研究灵长类动物眼外肌周围结缔组织形态特点,分析探讨眼外肌Pulley对眼球运动及高级视功能的作用.方法 分离成年猕猴眼眶;取新鲜内直肌与下直肌间结缔组织行电镜观察;完整眼眶行全眶冠状连续切片.以Masson、Weigert染色分别进行胶原、弹性纤维染色,以抗体标记平滑肌.结果 猕猴直肌眶层纤维与周围结缔组织相互移行.在赤道部稍后方,主要以胶原纤维组成的结缔组织包绕,连接眼外肌,弹性纤维、平滑肌散在其中.内直肌及其与下直肌间的结缔组织最发达;平滑肌与弹性纤维呈明显的带状分布.结论 猕猴眼外肌周围结缔组织的分布特征提示眼外肌Pulley对眼球运动具有重要作用.这一结构与人类同名结构的高度相似性,提示猕猴可以作为研究眼外肌Pulley的实验动物.     

眶内异常结构与垂直后退综合征

目的 探讨6例临床诊断为垂直后退综合征患儿的临床与MRI特征.方法 6例单眼垂直后退综合征患儿,年龄1岁3个月至8岁,平均(5.01±1.27)岁.斜视检查包括:屈光度、三棱镜、眼球运动、双眼视觉和眼底照相检查.眼球运动神经脑池段采用头线圈,3 D-FIESTA序列,层厚0.8 mm;眼眶段采用表面线圈,横断面+冠状面+矢状面,FSET1与T2加权扫描,层厚2.0mm,层间距0.3mm.结果 4例患儿表现为上斜视,下转受限,下转时伴轻度眼球后,且皆伴有患眼上睑迟落.MRI检查发现4例均有眼眶内异常结构位于肌锥内间隙上象限内直肌及上直肌群之间或上直肌水平.2例患儿表现为原在位间歇性外斜视,眼球上转受限伴轻度眼球后退睑裂缩小,侧转位时明显.MRI检查发现肌锥内间隙外下象限异常等信号影,1例可疑下直肌分出,1例靠近外直肌.结论 眼眶内异常结构是导致垂直后退综合征的主要原因之一.眼球运动检查结合MRI特征性表现是最重要诊断依据,出生早期发现上睑迟落提示眼眶内异常结构.     

人眼直肌Pulley与直肌肌肉纤维毗邻关系的研究

目的 研究人眼直肌Pulley与直肌肌肉纤维的毗邻关系.方法 选取5例新鲜尸体眼眶,整体固定包埋后行全眼眶连续冠状切片(4 μm).相邻层面经Masson特殊染色后,在光镜下观察每个层面Pulley及直肌肌肉纤维的组织结构,并用MIAS-2000显微图像分析系统定量.结果 各直肌肌肉纤维由眶层和球层组成,球层肌肉纤维穿过Pulley以肌腱的形式止于眼球,而眶层肌肉纤维则止于各自的Pulley.在光镜下,测得眼眶中部内直肌的肌肉纤维数目(15 813.0±386.8)最多,其他3组直肌肌肉纤维数目(分别为14 855.0±529.0,12 132.0±181.6,14 222.0±105.8)较少,差异有统计学意义(P＜0.05).结论 人眼直肌Pulley与眶层肌肉纤维的融合为其成为直肌的功能性起点提供了组织学和解剖学基础.     

副眼外肌畸形一例及文献复习

目的 手术探查一例伴随眼球运动受限及眼球后退现象的垂直非共同性斜视患者.方法 病例报告.运用MRI影像学检查了解该病例眼外肌结构特征,通过手术松解异常结构对眼球运动的限制并手术矫正斜视,组织病理学检查确定异常结构的组织学成分.结果 位于眼眶肌锥内间隙(外下象限),外直肌内下方、下直肌外上方,起自眶尖,附着于眼球后巩膜的类似眼外肌的异常结构是本例斜视患者的可能原因.通过手术松解其对眼球运动的限制并适当后退下直肌达到了矫正斜视的效果.眼球运动改善不明显.异常结构病理报告来源于肌肉组织.结论 本病例MRI检查发现的异常结构,术中发现与眼球运动限制有一定关系,该异常结构组织学检查为来源于肌肉组织,考虑为副眼外肌畸形.对伴随眼球运动受限及眼球后退现象的垂直非共同性斜视,要考虑到眼眶内异常结构的可能,有必要用MRI影像学检查,协助明确诊断.     

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.     

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.     

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 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.     

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)     

Quantitative analysis of the structure of the human extraocular muscle pulley system

PURPOSE: Extraocular muscle (EOM) paths are constrained by connective tissue pulleys serving as functional origins. The quantitative structural features of pulleys and their intercouplings and orbital suspensions remain undetermined. This study was designed to quantify the composition of EOM pulleys and suspensory tissues. METHODS: Five human orbits, ages 33 weeks gestation to 93 years, were imaged intact by magnetic resonance (MRI), serially sectioned at 10 micro m thickness, and stained for collagen, elastin, and smooth muscle (SM). With MRI used as a reference, digital images of sections were geometrically corrected for shrinkage and processing deformations, and normalized to standard normal adult globe diameter. EOM pulleys, interconnections, suspensory tissues, and entheses were quantitatively analyzed for collagen, elastin, and SM thickness and density. RESULTS: Rectus and inferior oblique pulleys had uniform structural features in all specimens, comprising a dense EOM encirclement by collagen 1 to 2 mm thick. Elastin distribution varied, but was greatest in the orbital suspension of the medial rectus pulley and in a band from it to the inferior rectus pulley. This region corresponded to maximum SM density. Structural features of pulleys, intercouplings, and entheses were similar among specimens. The major mechanical couplings to the osseous orbit were near the medial and lateral rectus pulleys. CONCLUSIONS: Quantitative analysis of structure and composition of EOM pulleys and their suspensions is consistent with in vivo MRI observations showing discrete inflections in EOM paths that shift predictably with gaze. Focal SM distributions in the suspensions suggest distinct roles in stiffening as well as shifting rectus pulleys.     

Active pulleys: magnetic resonance imaging of rectus muscle paths in tertiary gazes

PURPOSE: The orbital layer of each rectus extraocular muscle (EOM) inserts on connective tissue, and the global layer inserts on the eyeball. The active-pulley hypothesis (APH) proposes that a condensation of this connective tissue constitutes a pulley serving as the functional origin of the rectus EOM, and that this pulley makes coordinated, gaze-related translations along the EOM axis to implement a linear ocular motor plant. This study was designed to measure gaze-related shifts in EOM pulley locations. METHODS: Magnetic resonance imaging (MRI) was performed in eight normal volunteers in 2-mm thickness coronal planes perpendicular to the orbital axis for nine cardinal gaze directions. Intravenous gadodiamide contrast was administered to define EOM tendons anterior to the globe equator. Paths of EOMs, defined by their area centroids, were transformed into an oculocentric coordinate system. Sharp inflections in EOM paths in secondary and tertiary gaze positions defined pulley locations which were then correlated with gaze direction and compared with theoretical predictions. RESULTS: Rectus pulley positions were consistent with a central primary position. In tertiary gaze positions, each of the four rectus pulleys translated posteriorly with EOM contraction and anteriorly with EOM relaxation by a significant (P < 0.02) amount predicted by the APH, but more than 100 times greater than the translation predicted by a passive pulley model. CONCLUSIONS: The APH prediction of coordinated anteroposterior shifting of EOM pulleys with gaze is quantitatively supported by changes in EOM path inflections among tertiary-gaze positions. Human rectus pulleys move to shift the ocular rotational axis to attain commutative behavior of the ocular motor plant.     

Extraocular muscle insertions relative to the fovea and optic nerve: humans and rhesus macaque

PURPOSE: To identify extraocular anatomic relationships of muscle insertions relative to the fovea and the optic nerve. METHODS: Thirty-eight human eye bank eyes and 10 rhesus macaque (Macaca mulatta) eyes were measured. Ten human volunteers were used to determine the horizontal rectus muscle-to-globe apposition in primary, left, and right gaze. RESULTS: External globe measurements (human/rhesus; mm +/- SD) from the temporal border of the optic nerve (ON) to the center of the fovea (F) were 3.7 +/- 0.6 and 2.6 +/- 0.2; F to the posterior border of the inferior oblique (IO) insertion, 2.5 +/- 0.8 and 0.5 +/- 0.4; ON to the posterior border of the IO, 5.6 +/- 0.9 and 2.8 +/- 0.3; horizontal axial plane (H) of the eye, defined by the long posterior ciliary artery, to the IO, 2.0 +/- 0.8 and 0.5 +/- 0.4; and H to F, 1.0 +/- 0.6 and 0.4 +/- 0.3, respectively. The IO insertion formed an arc, inferior to H, with an anterior-to-posterior cord insertion width of 9.2 +/- 0.7 and 7.7 +/- 0.3. The IO angle of insertion (theta) was 30 degrees in 84% (32/38) and 0 degrees in 16% (6/38) of human eyes and 25 to 30 degrees in all rhesus. In 20 human volunteers, from the ON to the apex of lateral rectus globe apposition was 13.9 +/- 1.1 in primary, 17.2 +/- 1.9 in lateral, and 9.3 +/- 1.7 in medial gaze. CONCLUSIONS: The fovea is located mostly superior and slightly posterior to the posterior border of the IO insertion. Topographic relationships of the extraocular muscles relative to the fovea are essential for the design of extraocular drug delivery systems.