Fig. 1.1
Orbit anatomy: (a) pear-shaped 3D model of the orbit; (b, c) axial cross-sectional images of the orbits and the main parameters of the interorbital topographic and anatomic relationships: the medial orbital walls are almost parallel; the lateral orbital walls make a right angle. The interorbital distance is 25 mm; the angle between the optic nerves is 45°; the angle between the optic nerve and the optic axis is 22.5°
The axes of the orbital pyramids converge backward and diverge forward; the medial orbital walls are almost parallel, while the lateral ones make a right angle [1]. If the optic nerves are taken as the reference points, the normal divergence angle of the optical axes does not exceed 45°, which can be clearly seen in the computed axial tomography scans (Fig. 1.1b, c). The permanent adduction stimulus induced by divergence of the orbits (to maintain orthophoria) is responsible for the fact that the medial rectus is the strongest extraocular rectus muscle. Elimination of the convergence stimulus in individuals with a blind eye causes a noticeable temporal deviation of the blind eye (exotropia).
The divergence angle of the optical axes determines the interorbital distance (the distance between the anterior lacrimal crests). It is the crucial element of facial harmony. The normal interorbital distance in adults varies from 18.5 mm to 30.7 mm; the ideal value is 25 mm. Both decreased (stenopia) and increased (euryopia) interorbital distances are indicative of a severe craniofacial anomaly.
The average length of the anteroposterior axis (“depth”) of the orbit in adults is 45 mm. Hence, all orbital manipulations (retrobulbar injections, subperiosteal blunt dissection, and sizing of the grafts placed to repair bone defects) should not be performed more than 35 mm posterior from the bony orbital margin and 1 cm away from the optic canal (canalis opticus).
One should bear in mind that the orbital depth can vary in a rather broad range, the “deep and narrow” and “shallow and wide” orbits being the extreme variants. Attempts have been made to calculate the distance between the orbital margin and the apex that could serve as a reference to help plan for a safe surgical intervention. The results were so variable that they proved to be unreliable for surgical planning. Hence, interventions on the orbit must be preceded by obligatory axial and sagittal computed tomography followed by a thorough analysis of the images.
The volume of the orbital cavity (cavitas orbitalis) is somewhat smaller than it is generally believed to be (23–26 cm3), and the eyeball occupies only 6.5–7 cm3 [2]. The orbital volume in females is 10 % smaller than that in males. Ethnicity has a significant effect on orbital parameters.
The horizontal dimension (width) of the orbital opening (aditus orbitalis) is approximately 4 cm in adults; the vertical dimension (height) of the orbital opening does not exceed 3.5 cm.
1.1 Bones Forming the Orbit
The orbit is formed by seven bones: the maxilla, frontal, zygomatic, ethmoid, sphenoid, lacrimal, and palatine bones.
Each orbital wall is formed by several bones. If one uses the medial orbital wall as a reference point and follows a counterclockwise direction, the number of bones forming the orbital walls is represented by the mnemonic rule “4–3–2–2” (Table 1.1).
Table 1.1
Bones forming the orbit
Orbital walls | Bones forming the orbital walls | Adjacent structures |
|---|---|---|
Medial | Frontal process of the maxilla Lacrimal bone Orbital plate of the ethmoid bone Body of the sphenoid bone (The components of the medial wall are listed in the front–back direction) | Ethmoidal labyrinth Sphenoid sinus Nasal cavity |
Cribriform plate of the ethmoid bone at the level of the frontoethmoidal suture | ||
Inferior | Orbital surface of the body of the maxilla | Infraorbital canal |
Orbital surface of the zygomatic bone | Maxillary sinus | |
Orbital process of the palatine bone | ||
(The internal, external, and posterior portions, respectively) | ||
Lateral | Orbital surface of the zygomatic bone; orbital surface of the greater wing of the sphenoid bone | Temporal fossa |
Pterygopalatine fossa | ||
Middle cranial fossa | ||
Superior | Orbital portion of the frontal bone; lesser wing of the sphenoid bone | Anterior cranial fossa |
Frontal sinus |
Orbital Margins
The orbital margins (supraorbital, margo supraorbitalis; infraorbital, margo infraorbitalis; lateral, margo lateralis; and medial, margo medialis) form the so-called external orbital framework that ensures mechanical strength of the entire orbital complex and is a part of the complex system of facial counterforces or “stiffener plates” that reduce facial skeleton deformation during chewing and when one acquires a traumatic brain injury (Fig. 1.2a). Furthermore, the profile of the orbital margin plays the key role in formation of the contour of the upper and middle thirds of the face.
Fig. 1.2
Anatomy of the orbital margins and walls. (a) Involvement of the orbital opening in the system of midfacial pillars; (b) a spiral structure of the orbital opening [2]; (c) structure of the medial orbital margin and the lacrimal sac fossa; (d) bones forming the orbit: (1) frontal process of the maxilla (processus frontalis maxillae), (1a) orbital surface of the maxilla (facies orbitalis maxillae), (2) lacrimal bone (os lacrimale), (3) orbital plate of the ethmoid bone (lamina orbitalis ossis ethmoidalis), (4) orbital surface of the greater wing of the sphenoid bone (facies orbitalis alae majoris ossis sphenoidalis), (5) orbital surface of the orbital portion of the frontal bone (facies orbitalis ossis frontalis), (6) orbital process of the perpendicular plate of the palatine bone (processus orbitalis laminae perpendicularis ossis palatini), (7) orbital surface of the zygomatic bone (facies orbitalis ossis zygomatici) (Fig. 1.2a was taken from the website www.aofoundation.org)
The orbital margins lie in different planes: the lateral margin is posteriorly displaced as compared to the medial one, while the inferior margin is posteriorly displaced as compared to the superior one. Thus, a spiral structure with 90° angles is formed. This structure ensures a wide field of vision and downward/outward gaze but leaves the anterior half of the eyeball unprotected against an injuring agent moving from the same direction. The spiral structure of the orbital opening is broken near the medial margin where it forms the lacrimal sac fossa (fossa sacci lacrimalis) (Fig. 1.2b, c) [2].
The position of the orbital opening with respect to the frontal, horizontal, and sagittal planes is referred to as “the spatial architecture of the orbital opening” with its main parameters, inclination of the orbital opening and orbital openness. The average inclination of the orbital opening is 8–13° and is determined by the degree to which the supraorbital margin protrudes compared to the infraorbital one.
Orbital openness characterizes the position of the orbital opening with respect to the sagittal plane drawn through the medial margin. The average openness values are 104–108°.
The lateral and supraorbital margins (margo lateralis et supraorbitalis) formed by the thickened edges of the zygomatic and frontal bones are the strongest ones. As for the supraorbital margin, the well-developed frontal sinus is a very important factor of its mechanical strength as it dampens hits to this region.
The continuity of the supraorbital margin at the boundary between its middle and internal one-thirds is interrupted by the supraorbital notch (incisura supraorbitalis). The supraorbital artery, vein, and nerve (a., v., et n. supraorbitalis) pass through it. The shape of the notch can vary; it is approximately 4.6 mm wide and 1.8 mm high.
In 25 % of the population (and up to 40 % in the female population), there is a foramen (foramen supraorbitale), or a small bony canal, instead of the bony notch, through which the aforementioned neurovascular bundle passes. The foramen is usually smaller than the notch (3.0 × 0.6 mm).
The infraorbital margin (margo infraorbitalis) formed by the maxilla and the zygomatic bone is characterized by lower strength; hence, the orbit exposed to blunt trauma undergoes transient wavelike deformation that spreads to the inferior wall and causes an isolated (“blowout”) fracture with displacement of the muscles and adipose tissue inferior to the globe, into the maxillary sinus. The infraorbital margin typically remains intact.
The upper portion of the medial orbital margin (margo medialis) is formed by the nasal part of the frontal bone (pars nasalis ossis frontalis). The lower portion of the medial margin consists of the posterior lacrimal crest of the lacrimal bone and the anterior lacrimal crest of the maxilla (Fig. 1.2c).
Bony Orbital Walls
The lateral wall of the orbit (paries lateralis) is the thickest and strongest of the four walls. Its anterior portion is formed by the zygomatic bone, while the posterior portion is formed by the orbital surface of the greater wing of the sphenoid bone. The length of the lateral wall, measuring from the orbital margin to the superior orbital fissure, is 40 mm (Fig. 1.2d).
The frontozygomatic (sutura frontozygomatica) and zygomaticomaxillary (sutura zygomaticomaxillaris) sutures are the anterior borders of the lateral wall; the superior and inferior orbital fissures are the posterior borders (Fig. 1.3).
Fig. 1.3
Borders of the orbital walls. Oblique frontal (a) and parasagittal (b) views. The lateral wall is bordered anteriorly by the frontozygomatic (1) and zygomaticomaxillary (2) sutures and posteriorly by the inferior (3) and superior (4) orbital fissures. The medial wall is bordered superiorly by a line running along the frontoethmoidal suture (5) and inferiorly by the ethmoidomaxillary suture (6). The outer border of the upper wall is the superior orbital fissure (4); the inner border is the line continuing the frontoethmoidal suture (5) anteriad and posteriad. The inferior wall of the orbit (orbital floor) is bordered on its lateral side by the inferior orbital fissure (3) and, on its medial side, by the ethmoidomaxillary suture (6) continued anteriad and posteriad. The figure also shows the foramina: (7) zygomaticofacial foramen; (8) zygomaticotemporal foramen; (9) supraorbital foramen; (10) infraorbital foramen; (11 and 12) anterior and posterior ethmoidal foramina; (13) optic foramen; (14) lacrimal sac fossa connecting with the nasolacrimal duct (not shown); and (15) meningo-orbital foramen of the greater wing of the sphenoid bone. The oblique parasagittal slice of the orbit illustrates its topographic relationships with the pterygopalatine fossa (16) and cavernous sinus (17)
The orbital surface of the greater wing of the sphenoid bone (facies orbitalis alae majoris ossis sphenoidalis) has heterogeneous thickness. Its anterolateral one-third, which is connected to the orbital surface of the zygomatic bone by the sphenozygomatic suture (sutura sphenozygomatica), and the posteromedial one-third, which forms the lower border of the superior orbital fissure, are relatively thin. Therefore, the sphenozygomatic suture area is a convenient landmark for performing external orbitotomy.
The central one-third, trigone (or the sphenosquamous suture, sutura sphenosquamosa), is characterized by high strength. This triangular region separates the orbit from the middle cranial fossa, thus simultaneously forming both the lateral wall of the orbit and the skull base (Fig. 1.1b). This should be taken into account when performing external orbitotomy: one should bear in mind that the average distance between the lateral orbital margin and the middle cranial fossa is 31 mm [3].
The sphenofrontal foramen lies contiguously with the sphenofrontal suture (sutura sphenofrontalis) in the greater wing of the sphenoid bone, near the anterior margin of the superior orbital fissure. The sphenofrontal foramen contains a branch of the lacrimal artery, the recurrent meningeal artery (anastomosis between a. meningea media from the basin of the external carotid artery and the ophthalmic artery from the basin of the internal carotid artery).
The frontozygomatic suture (sutura frontozygomatica) provides rigid fixation of the zygomatic bone to the frontal bone. Due to its length and architecture, the sphenozygomatic suture plays a crucial role in zygomatic bone repositioning in patients with zygomatic fractures.
The zygomaticofacial (canalis zygomaticofacialis) and zygomaticotemporal (canalis zygomaticotemporalis) canals contain the corresponding homonymous arteries and nerves exiting the orbital cavity through its lateral wall and terminating in the zygomatic and temporal areas (Fig. 1.3a). Care should be taken when dissecting the temporal muscle during external orbitotomy so that the artery and nerve are not accidentally injured.
Whitnall’s orbital tubercle (tuberculum orbitale Whitnall), a small elevation on the orbital margin of the zygomatic bone that is found in 95 % of people, localizes 11 mm below the frontozygomatic suture and 4–5 mm behind the orbital margin [4]. This important anatomical landmark is connected to:
1.
Ligament attaching the lateral rectus muscle (lacertus musculi recti lateralis, “sentinel ligament”)
2.
Suspensory ligament of the lower eyelid (Lockwood’s inferior transverse ligament)
3.
Lateral palpebral ligament
4.
Lateral horn of the levator aponeurosis
5.
Orbital septum (tarso-orbital fascia)
6.
Lacrimal gland fascia
The lateral orbital wall separates the orbital contents from the temporal and the pterygopalatine fossae (and from the middle cranial fossa near the orbital apex).
The superior orbital wall (orbital roof, paries superior) is formed primarily by the frontal bone, its smooth and concave orbital surface, and in its posterior portion by the 1.5 cm long flat lesser wing of the sphenoid bone (ala minor ossis sphenoidalis). It is triangular in shape, just as the inferior and lateral walls.
The lacrimal fossa (fossa glandulae lacrimalis), a small impression where the homonymous gland resides, is found near the base of the zygomatic process of the frontal bone, immediately behind the supraorbital margin.
The trochlear fossa (fossa trochlearis) lies 4 mm medially to the supraorbital margin. It is usually adjacent to the trochlear spine (spina trochlearis), a small bony protrusion near the junction between the orbital roof and the medial wall. The tendinous portion of the superior oblique muscle passes through and abruptly changes direction as it passes through a tendinous (or cartilaginous) loop connected to the trochlear spine (Fig. 1.4) [5, 6].
Fig. 1.4
The anatomy of the trochlea
Damaged trochlea resulting from injuries or surgical intervention (in particular, frontal sinus surgeries) causes dysfunction of the superior oblique and persistent bothersome diplopia.
The aforementioned frontal sinus is located inside the superior orbital wall (orbital roof). The sinus occupies its anterointernal portion and spreads backward for up to a half or two-thirds of the depth of the orbit. In some cases, it may reach the posterior portions (i.e., the lesser wing of the sphenoid bone). In the posterior two-thirds of the orbit, the superior wall is much thinner compared to the anterior one-third. Nevertheless, it is rather deformity resistant due to the thickness of the frontal bone, the arc-shaped profile of the orbital surface, and the dampening effect of the frontal sinus.
As a result, fractures of the superior orbital wall are rare. However, the presence of these fractures is always indicative of a high-energy injury and suggests a high probability of open head injury and deserves the closest attention.
The longest (45 mm) orbital wall—the medial orbital wall (paries medialis)—is formed in its anteroposterior direction by the frontal process of the maxilla, the lacrimal, and the ethmoid bones and the body and the lesser wing of the sphenoid bone. It is bordered superiorly by the frontoethmoidal suture and inferiorly by the ethmoidomaxillary suture (Fig. 1.3). Unlike the other walls, it is rectangular in shape.
The medial wall is based on the orbital plate of the ethmoid bone, 3.5–5.0 × 1.5–2.5 cm in size and only 0.25 mm thick; it is also known as lamina papyracea (“paperlike sheet”). It is the largest but the weakest component of the medial wall. The orbital plate of the ethmoid has a slightly concave shape; hence, the maximum orbital width corresponds to a point 1.5 cm deeper from the plane of orbital opening. As a result, the transcutaneous and transconjunctival approaches to the medial wall of the orbit do not provide an adequate view of its entire area.
The orbital plate consists of approximately 10 honeycomb-shaped cells separated by septa into the anterior and posterior portions. The large and numerous small septa between the ethmoidal cells (cellulae ethmoidales) reinforce the medial wall from the direction of the nose. Hence, the medial wall is stronger than the inferior one, especially in case of a branched network of ethmoidal septa and a relatively small size of the orbital plate [7, 8].
In 50 % of orbits, the ethmoidal labyrinth reaches the posterior lacrimal crest; in other 40 % of cases, it reaches the frontal process of the maxilla [9].
The anterior portion of the orbital plate of the ethmoid bone is adjacent to the lacrimal bone and the frontal process of the maxilla. These form the medial orbital margin that is a part of the facial reinforcing structures and considerably strengthens the medial orbital wall. The body and lesser wing of the sphenoid bone, which is adjacent to the posterior surface of the ethmoid bone, forms the orbital apex near the optic canal.
The frontoethmoidal suture is an important landmark indicating the upper boundary of the ethmoidal labyrinth. Therefore, osteotomy above the frontoethmoidal suture is fraught with the danger of damaging the dura mater in the frontal lobe area.
At the level of the frontoethmoidal suture, 24 and 36 mm behind the anterior lacrimal crest, the medial orbital wall contains the anterior and posterior ethmoidal foramina (foramina ethmoidalia anterior et posterior). These foramina lead to the homonymous canals where the homonymous branches of the ophthalmic artery and the nasociliary nerve run from the orbit to the ethmoidal cells and the nasal cavity. It should be emphasized that the posterior ethmoidal foramen lies at the boundary between the superior and the medial orbital walls deep in the frontal bone only 6 mm away from the optic foramen (mnemonic rule: 24–12–6, where 24 is the distance (mm) between the anterior lacrimal crest and the anterior ethmoidal foramen, 12 is the distance between the anterior and posterior ethmoidal foramina, and 6 is the distance between the posterior ethmoidal foramen and the optic canal). The exposure of the posterior ethmoidal foramen during subperiosteal dissection of the orbital tissues absolutely indicates that any further interventions in this area should be terminated to avoid optic nerve damage.
The lacrimal sac fossa is the most important structure in the medial orbital wall. It is 13 × 7 mm in size and is formed by the anterior lacrimal crest of the frontal process of the maxilla and the lacrimal bone with its posterior lacrimal crest (Fig. 1.2b, c).
The lower portion of the fossa reaches the 10–12 mm long bony nasolacrimal canal (canalis nasolacrimalis) that runs deep in the maxilla and opens into the inferior nasal meatus 30–35 mm away from the external nasal opening.
The medial orbital wall separates the orbit from the nasal cavity, the ethmoidal labyrinth, and the sphenoid sinus. This fact is of great clinical significance as these sinuses are likely to be a source of acute or chronic inflammation which can spread to the contiguous orbital soft tissues. Both the insignificant thickness of the medial wall and the natural (anterior and posterior ethmoidal) foramina contribute to this possibility. Furthermore, congenital dehiscence occurs in the lacrimal bone and the orbital lamina of the ethmoid bone rather frequently. It is a variant of the norm but, when present, can act as an additional portal of infection.
The inferior orbital wall (orbital floor, paries inferior), the roof of the maxillary sinus, is primarily formed by the orbital surface of the body of maxilla, by the zygomatic bone in the antero-exterior portion, and by the small orbital process of the perpendicular plate of the palatine bone in the posterior portion. The inferior wall is the only orbital wall that is not partially formed by the sphenoid bone.
The inferior orbital wall is shaped like an equilateral triangle. It is the shortest (~20 mm long) wall. It does not reach the orbital apex and is adjacent to the inferior orbital fissure and the pterygopalatine fossa. The line running along the inferior orbital fissure forms the outer border of the orbital floor. The inner border is the continuation of the ethmoidomaxillary suture anteriad and posteriad (Fig. 1.3).
The area of the inferior orbital wall is ~6 cm2 [10] and is less than 0.5 mm thick. Thus, the inferior and medial walls are the thinnest of all the orbital walls; this anatomy explains well why the predominance of orbital fractures involves these two walls.
The infraorbital groove is the thinnest portion of the orbital floor. It divides the orbital floor into approximately equal parts and becomes a canal anteriorly. The posterior part of the internal half of the inferior wall is slightly stronger. The remaining portions of the inferior wall are rather resistant to mechanical impact. The junction between the medial and inferior orbital walls, which is supported by the medial wall of the maxillary sinus, is the thickest area.
The inferior wall has a characteristic S-shaped profile, which must be taken into account when shaping titanium implants used to repair orbital floor defects. If the reconstructed orbital wall has a flat profile, the orbital volume will increase, and enophthalmos will persist in the postoperative period (Fig. 1.5).
Fig. 1.5
Complex profile of the orbital walls. (a, b) Position of some areas of the inferior and medial walls of the so-called internal orbit (arrows ) ensuring the proper position of the eyeball in the orbit; (c) disappearance of the S-shaped profile of the inferior orbital wall (orbital floor) after its fracture; (d) incorrect and (e) the optimal contour of the implant used to repair the missing orbital wall
A 15° elevation of the inferior orbital wall toward the orbital apex and its complex profile prevent a surgeon from accidentally damaging the deeper orbital areas with a blunt instrument and make direct optic nerve damage during orbital floor reconstruction unlikely.
As mentioned above, the posteromedial portion of the inferior orbital wall is formed by the orbital process of the perpendicular plate of the palatine bone. It rests in a medial direction slightly above the crossing point between the infraorbital nerve and the inferior orbital fissure. Unlike the surrounding maxilla, the orbital process of the perpendicular plate of the palatine bone is inherently strong. Hence, it is rarely affected in individuals with orbital fractures and can be used as a landmark of the orbital apex. Furthermore, it plays a crucial role in repairing fractures involving the entire floor, and the orbital process of the perpendicular plate of the palatine bone is the only site where the posterior implant edge can be placed.
Another significant clinical aspect is the proximity of the maxillary sinus. This proximity allows for contiguous spread of inflammation in acute and chronic sinusitis.
Clinical Anatomy of the Orbital Apex
In terms of craniofacial surgery, the orbit is conventionally subdivided into three areas: the external orbit (consisting of the zygomatic bone and the nasoethmoidal complex, i.e., the frontal process of the maxilla, the nasal portion of the frontal bone, and nasal, lacrimal, and ethmoid bones), the internal orbit, and the deep orbit (its apex), which starts from the anterior edge of the inferior orbital fissure, is formed by the sphenoidal bone, and occupies 20 % of the orbital volume (Fig. 1.6) [11]. The landmarks (borders) of the orbital apex include the infraorbital nerve, the inferior orbital fissure, the orbital process of the perpendicular plate of the palatine bone, and the greater wing of the sphenoid bone. The area where the four anatomical landmarks listed above merge is known as the orbital confluence (confluens orbitae).
Fig. 1.6
Anatomy of the orbital apex. (a) Borders of the orbital apex follow the sphenozygomatic (1 sutura sphenozygomatica), sphenofrontal (2 sutura sphenofrontalis), and sphenoethmoidal (3 sutura sphenoethmoidalis) sutures, as well as the inferior orbital fissure (4). Thus, the bony structures of the orbital apex are formed by the sphenoid bone. (b) Topographic anatomy of the optic foramen and orbital fissures: (5) the greater wing of the sphenoid bone; (6) the lesser wing of the sphenoid bone; (7) the body of the sphenoid bone; (8) palatine bone; (9) maxilla; (10) optic foramen; (11) superior orbital fissure; (12) posterior ethmoidal foramen; (13) infraorbital groove; and (14) round foramen (According to [27, 60] with amendments)
Inferior Orbital Fissure (Fissura Orbitalis Inferior)
This fissure is the downward continuation of the superior orbital fissure. It separates the lateral and inferior walls. The anterior portions of the inferior orbital fissure open into the infratemporal fossa, while the posterior portions open into the pterygopalatine fossa localized behind the maxillary sinus. The fissure is bound superiorly by the orbital surface of the greater wing of the sphenoid bone and inferiorly by the orbital surface of the maxilla, zygomatic bone, and orbital process of the perpendicular plate of the palatine bone. The inferior orbital fissure is approximately 2 cm long; its width varies from 1 to 5 mm. The anterior edge of the fissure is 20 (sometimes even 6–15) mm away from the infraorbital margin and is the border of the inferior orbital wall. The lumen of the inferior orbital fissure is covered by a connective tissue septum with smooth muscle fibers interwoven: the so-called orbital muscle of Müller (m. orbitalis) which has sympathetic innervation. The possible proximity of the inferior orbital fissure to the orbital margin should be taken into account when reconstructing blowout fractures of the orbital floor. The appreciably dense periosteum adherent to the fissure edges can be mistaken for incarcerated soft tissues in the fracture area, while the club-shaped expansion of the anterior orbital edge observed in 42 % of individuals can be mistaken for the fracture area. Attempts to dissect the periosteum away from the edges of the inferior orbital fissure can cause severe hemorrhage from the infraorbital artery:
The maxillary nerve (n. maxillaris, V2)
The zygomatic nerve (n. zygomaticus) and its branches: the zygomaticofacial branch (r. zygomaticofacialis) and the zygomaticotemporal branch (r. zygomaticotemporalis) supplying the secretory fibers for the lacrimal gland through the anastomosis with the lacrimal nerve
Infraorbital nerve (n. infraorbitalis) and infraorbital artery (a. infraorbitalis)
Small orbital branches of the pterygopalatine ganglion (ganglion pterygopalatinum)
Branch or branches of the inferior orbital vein anastomosing with the pterygoid venous plexus and the deep facial vein. Thus, the venous network of the face, the pterygopalatine fossa, paranasal sinuses, and the cavernous sinus are all interconnected. It should be mentioned that in individuals with infectious cellulitis of the deep facial tissues, paranasal sinuses, and facial bones, infection may spread to the cavernous sinus through the inferior ophthalmic vein and cause its thrombosis.
An aperture with a regular circular shape, the foramen rotundum, is located behind the junction between the superior and inferior orbital fissures, on the external surface of the skull base. It connects the middle cranial fossa with the pterygopalatine fossa (near the orbit) and hosts the second branch of trigeminal nerve, the maxillary nerve (n. maxillaris).
The orbital apex contains two apertures: the optic foramen and the superior orbital fissure.
The optic foramen is found in the superomedial portion of the orbital apex along an imaginary horizontal line passing through the anterior and posterior ethmoidal foramina, approximately 6 mm behind the latter [12, 13]. The optic foramen is surrounded by the common tendinous ring (annulus tendineus communis Zinn) from where all the rectus extraocular muscles originate.
The optic canal (canalis opticus) is 6.5 mm in diameter and 8–10 mm long. It is oriented inward at an angle of 45º and upward at an angle of 15º. The lateral wall of the channel is formed by two roots of the lesser wing of the sphenoid bone and forms the internal wall of the superior orbital fissure. The medial wall of the optic canal is formed by the body of the sphenoid bone and is less than 1 mm thick. The 2–3 mm thick upper wall of the canal serves as a floor of the anterior cranial fossa. The orbital foramen in the canal is vertically oval shaped; the middle portion is round; the intracranial foramen is horizontally oval shaped. This gives the ophthalmic artery an arcuate path [14–20]. In addition to the optic nerve and the ophthalmic artery, the canal contains the sympathetic fibers of the carotid plexus.
The superior orbital fissure (fissura orbitalis superior) is a border between the superior and lateral orbital walls (Fig. 1.7). It is formed by the body and wings of the sphenoid bone, connects the orbital cavity and the middle cranial fossa, and is closed with a connective tissue membrane. Two portions can be distinguished: the inner or lower one (so-called intraconal; it is wider and has an oblique vertical orientation, i.e., opens into the muscular cone) and the outer one (upper; it is narrower, oriented obliquely horizontally, forward and upward extraconal). A border between these portions is the bony protrusion in the middle of the lower edge of the orbital fissure (spina recti lateralis) which is the origin of the lateral crus of the lateral rectus.
Fig. 1.7
Contents of the superior orbital fissure. (1) The common tendinous ring (annulus tendineus communis Zinn) surrounding the so-called oculomotor foramen, which is comprised of the optic foramen (2) and the lower (intraconal) compartment of the superior orbital fissure (3). The contents of the lower portion of the superior orbital fissure: (4) nasociliary nerve (n. nasociliaris), (N); (5) abducens nerve (n. abducens, n. VI) (A); (6) sympathetic and parasympathetic fibers (S); (7, 8) the superior and inferior branches of the oculomotor nerve (n. III) (O2). A mnemonic rule NASO2 (naso-squared) was proposed by Jordan and Anderson [29] to help memorize the topographic anatomy of the intraconal compartment of the superior orbital fissure. The content of the upper portion of the fissure in the lateral-to-medial direction: (9) lacrimal nerve (L); (10) recurrent branch of the middle meningeal artery (M); (11) superior ophthalmic vein (S); (12) frontal nerve (F); and (13) trochlear nerve (T). A mnemonic rule LMSFT (look: Michigan state football team) [29] (Cited by Zide and Jelks [60] with amendments) helps memorize the topographic anatomy of the extraconal compartment of the superior orbital fissure
The average length of the superior orbital fissure is 22 mm. Its width varies significantly, which is an anatomical factor for the development of superior orbital fissure syndrome [21].
The lumen of the superior orbital fissure contains a number of critical anatomical structures (Table 1.2):
Table 1.2
Orbital foramina and fissures
Anatomical structure | Topographic anatomy | Contents |
|---|---|---|
Supraorbital notch (foramen) | Separates the medial and middle thirds of the supraorbital margin | Supraorbital nerve (the branch of the frontal nerve from the ophthalmic nerve, V1) |
Anterior ethmoidal foramen | 24 mm away from the medial orbital margin at the level of the frontoethmoidal suture | Homonymous neurovascular bundle |
Posterior ethmoidal foramen | 12 mm behind the anterior ethmoidal foramen, 6 mm away from the optic foramen | Homonymous neurovascular bundle |
Foramina on the zygomatic bone | Zygomaticofacial and zygomaticotemporal neurovascular bundles | |
Nasolacrimal canal | Starts in the lacrimal sac fossa and opens into the inferior nasal meatus under the inferior nasal concha | Nasolacrimal duct |
Infraorbital foramen | Localizes 4–10 mm below the infraorbital margin | Infraorbital neurovascular bundle (from V2) |
Optic canal | 6.5 mm in diameter, 10 mm long | Optic nerve, ophthalmic artery, sympathetic fibers |
Superior orbital fissure | 22 mm long. The superior orbital fissure is confined to the greater and lesser wings of the sphenoid bone. Localizes below and laterally from the optic foramen and is separated into two (external and internal) portions by the crus of the lateral rectus muscle | External portion: superior ophthalmic vein; lacrimal, frontal, and trochlear nerves |
Internal portion: superior and inferior branches of the oculomotor nerve, nasociliary nerve, abducens nerve; sympathetic and parasympathetic fibers | ||
Inferior orbital fissure | Formed by the sphenoid, zygomatic, and palatine bones and the maxilla | Infraorbital and zygomatic nerves (V2), inferior ophthalmic vein |
Sphenofrontal foramen | Sphenofrontal suture | Recurrent meningeal artery anastomosing with the lacrimal artery |
1.
The ophthalmic nerve (n. ophthalmicus), the first branch of the trigeminal nerve, ensures sensory innervation of all the structures in the orbital complex. Usually within the superior orbital fissure, the ophthalmic nerve divides into three main branches: the lacrimal (n. lacrimalis), frontal (n. frontalis), and nasociliary (n. nasociliaris) nerves.
2.
All the oculomotor nerves of the orbit: oculomotor (n. oculomotorius), trochlear (n. trochlearis), and abducent (n. abducens) nerves.
3.
The superior ophthalmic vein (v. ophthalmica superior) or the ophthalmic venous sinus formed by connection of the superior and the inconstant inferior ophthalmic veins.
4.
The fissure sometimes contains the aforementioned recurrent meningeal artery (a. meningea recurrens), which frequently has the most lateral position. Even more rarely, the central retinal vein passes through the fissure (in cases when it anastomoses directly with the cavernous sinus instead of the superior ophthalmic vein).
The structures in the superior orbital fissure are found in the aforementioned extra- and intraconal compartments.
The upper (extraconal) compartment of the superior orbital fissure contains (in the lateral-to-medial direction) the following structures:
Lacrimal nerve (n. lacrimalis) from the first branch (n. ophthalmicus) of the trigeminal nerve.
A branch of the middle meningeal artery.
Superior ophthalmic vein.
Frontal nerve (n. frontalis) from the first branch (n. ophthalmicus) of the trigeminal nerve.
Trochlear nerve (n. trochlearis); the extraconal localization of the trochlear nerve explains why certain mobility of the eye is retained even after a perfectly performed retrobulbar block.
The lower (intraconal) compartment of the superior orbital fissure contains the following structures:
Nasociliary nerve (n. nasociliaris from n. ophthalmicus)
Abducent nerve (n. abducens, n. VI)
Sympathetic and parasympathetic fibers
Upper and lower branches of the oculomotor nerve (n. oculomotorius, n. III)
1.2 Soft Tissues of the Orbit
According to the International Anatomical Nomenclature, the soft tissues of the orbit include the structures localized inside bony walls and bounded anteriorly by the orbital septum (septum orbitale):
Orbital periosteum (periorbita)
Muscle fasciae (fasciae musculares)
Orbital fat body (corpus adiposum orbitae)
Levator palpebrae superioris (m. levator palpebrae superioris)
Orbital muscle and Müller’s tarsal muscles (m. orbitalis, m. tarsalis superior, m. tarsalis inferior)
Lacrimal gland
Extraocular muscles
Optic nerve and its sheaths
Eyeball
Nerves, arteries, veins, and lymphatic channels
The bony orbital walls are lined with thin but strong periosteum (periorbita). It is tightly adherent to the walls in the area of the orbital opening (the place where the orbital septum is attached to the bone, arcus marginalis, 6–10 mm wide), bone sutures, orbital foramina and fissures, and the posterior lacrimal crest. The periosteum spreads over the large openings (the superior and inferior orbital fissures), to interconnect with the connective tissue membranes and the dura mater in their lumen (Fig. 1.8). In other areas, the periosteum can be easily separated to form a subperiosteal space both by a blunt instrument used during a surgical intervention or by blood or an exudate in certain pathological conditions.
Fig. 1.8
Regions where the periosteum is tightly attached to the bone (hatched areas)
Posteriorly, near the orbital apex, the periosteum is interwoven with the perineural optic nerve sheath at the site where it enters the bony canal. Anteriorly, the periosteum spreads to the orbital septum and the frontal, buccal, and zygomatic areas. It spreads to the temporal and pterygopalatine fossae through the inferior orbital fissure. The periosteum lines the lacrimal sac fossa; its continuation, fascia of the lacrimal sac (diaphragma lacrimalis), surrounds the lacrimal sac.
The periosteum consists of two layers (the dense outer and loose inner layers) and mechanically hinders infection or tumor spreading from paranasal sinuses to the orbit.
The orbital periosteum receives abundant blood supply both from the bones and from the orbit. Two vascular systems anastomose with one another; thus, the periosteum cannot be considered a serious barrier for hematogenous dissemination of pathological agents [22]. Sensory innervation is ensured by small branches of the ophthalmic nerve (n. V1).
The periosteum on the side of the orbital cavity is lined with a thin loose fascia merging with muscle sheaths.
The orbital fasciae comprise a complex well-organized 3D structure, which includes the following [23–26]:
1.
Fascial sheath of eyeball (Tenon’s capsule, vagina bulbi).
2.
Sheaths of the extraocular muscles (and the intermuscular fascia connecting them).
3.
Trabeculae separating the adipose lobules of the orbit.
4.
Fibers that spread from the sheaths of extraocular muscles to orbital walls and eyelids (supporting ligaments and the tendinous expansion of the lateral rectus, lacertus musculi recti lateralis) and are components of a more sophisticated orbital suspensory system [27] (Figs. 1.9, 1.10, 1.11, 1.12, and 1.13). In turn, it is subdivided into the anterior and posterior suspensory systems:
Fig. 1.9
Schematic view of the anterior suspensory system of the orbit. (a) Anterior view, (b) dorsal view. (1) Orbicularis oculi muscle; (2) bulbar sheath (Tenon’s capsule); (3) lateral palpebral ligament; (4) retinaculum laterale; (5) supporting ligament system of the lateral rectus muscle; (6) lateral rectus muscle; (7) medial rectus muscle; (8) retinaculum mediale; (9) lacrimal sac fossa; (10) medial palpebral ligament; and (11) periosteum
Fig. 1.10
Anatomy of the fascial system of the orbit at the level of the eyeball equator. The oblique coronal view. The extensive adhesion of the lateral rectus muscle sheath (8) to retinaculum laterale (9) (supporting ligament of the lateral rectus muscle) is worth mentioning. Another feature is the dense adhesion of the inferior oblique muscle to the adjacent inferior rectus muscle, forming the inferior (10) muscle complex. (1) Supraorbital nerve; (2) Whitnall’s ligament; (3) ligament of the superior oblique muscle; (4) lacrimal vein; (5) lacrimal gland; (6) Sommering’s ligament attaching the lacrimal gland to the periosteum (7); (11) inferior branch of the oculomotor nerve; (12) Tenon’s capsule (According to Dutton [27] with amendments)
Fig. 1.11
Anatomy of the fascial system of the orbit at the level of the posterior pole of the eye. Oblique coronal view. Ligaments (1) attaching the superior muscle complex (2) to the orbital roof; (3) ophthalmic artery; (4) superior ophthalmic vein; (5) tendon of the superior oblique muscle; (6) supraorbital nerve; (7) superolateral area of the intermuscular fascia; (8) periosteum; (9) lacrimal nerve; (10) lacrimal gland; (11) zygomatic nerve; (12) zygomaticotemporal nerve; (13) retinaculum laterale; (14) inferior oblique muscle; (15) small branch of the oculomotor nerve innervating the inferior oblique muscle; (16) nasolacrimal canal; and (17) Tenon’s capsule (According to Dutton [27] with amendments)
Fig. 1.12
Anatomy of the fascial system of the orbit at the level of the posterior pole of the eye. Oblique coronal view. (1) Superior ophthalmic vein attached to the orbital roof by a ligament; (2) common fascial system of the superior rectus muscle and the levator palpebrae superioris muscle; (3) periosteum; (4) lacrimal vein; (5) supporting ligament of the lateral rectus muscle; (6) zygomatic nerve; (7) zygomaticofacial nerve; (8) small branch of the oculomotor nerve innervating the inferior oblique muscle; (9) supporting ligament of the inferior rectus muscle; (10) supporting ligament of the medial rectus muscle; (11) nasociliary nerve; (12) ophthalmic artery; (13) fascial system of the superior oblique muscle; and (14) frontal nerve. The adipose tissue is separated by connective tissue septa into appreciably large globules. The orbital veins lying between the septal sheets, which makes their spatial arrangement relatively constant. The arteries pass directly through the adipose globules, thus making their arrangement rather variable (According to Dutton [27] with amendments)
Fig. 1.13
Anatomy of the fascial system of the orbit behind the eyeball. Oblique coronal view. (1) Periosteum; (2) frontal nerve; (3) superior branch of the oculomotor nerve innervating the superior rectus muscle; (4) superior ophthalmic vein and the ligament fixing it; (5) lacrimal nerve; (6) abducens nerve; (7) inferior ophthalmic vein; (8) small branch of the oculomotor nerve connecting with the inferior oblique muscle; (9) zygomatic nerve; (10) small branch of the oculomotor nerve connecting with the inferior rectus muscle; (11) branch of the oculomotor nerve connecting with the medial rectus muscle; (12) nasociliary nerve; and (13) ophthalmic artery. It comes under notice that the structure of the ligament system of the orbit becomes simpler and results in elimination of the intraconal space (According to Dutton [27] with amendments)
A.
The anterior suspensory system of the orbit maintains the proper position of the eyeball and eyelids, suspends to the lacrimal gland (Sommering’s ligament), and ensures proper movements of the superior oblique tendon in the trochlear region. The system consists of three parts:
I.
Suspensory apparatus of the eyeball:
Lateral and medial supporting ligaments (tendinous expansions of the medial and lateral rectus muscles)
Lateral and medial palpebral ligaments
II.
Upper portion of the anterior suspensory system:
Whitnall’s superior transverse ligament
Adhesion of the fasciae of the levator palpebrae superioris and the superior rectus, forming in the so-called superior muscle complex
Sommering’s ligament attaching the lacrimal gland to the periosteum
Upper portion of Tenon’s capsule
III.
Lower portion of the anterior suspensory system:
Densified fascia around the inferior rectus (capsulopalpebral fascia)
Lockwood’s inferior transverse ligament
Lower portion of Tenon’s capsule (Fig. 1.9)
B.
Posterior suspensory system of the orbit consists of smaller anatomical structures, including:
Common tendinous ring of Zinn
Fascial adhesions between the superior orbital wall (orbital roof), the levator palpebrae superioris, and the superior rectus
Ligament suspending the superior ophthalmic vein
Orbital muscle of Müller
Tenon’s fascia of the eyeball (vagina bulbi) separates the retrobulbar adipose tissue from the eyeball. Anteriorly, it is tightly attached by the episclera directly behind the limbus. Posteriorly, Tenon’s fascia is attached to the sclera around the optic nerve by interweaving with its sheath. Along its remaining length, Tenon’s capsule is separated from the sclera by a slit-like episcleral space (spatium episclerale) intergrown with thin connective tissue septa. Tenon’s fascia of the eyeball is the thinnest in the area where the optic nerve passes and the thickest in the intermuscular space between the “tunnels” for extraocular muscles. Tenon’s capsule is interwoven with extrinsic (external) muscle sheaths (which, in turn, are connected with the (inter)muscular fascia) and layers separating the orbital adipose tissue into individual lobules (Fig. 1.14) [24–26, 28]. Thus, the eyeball, Tenon’s capsule, and the orbital fat are connected by elastic adhesions whose presumable function is to dampen the eye movements.
Fig. 1.14
Tenon’s fascia of the eyeball. Anterior view. (1) (inter)muscular fascia residing under Tenon’s capsule and connecting the sheaths of extraocular muscles into an integral system; (2) orbital portion of the lacrimal gland; (3) Lockwood’s ligament; (4) levator aponeurosis; (5) ligament supporting the medial rectus muscle; (6) muscle sheath; (7) Tenon’s fascia; (8) trochlea; (9) Whitnall’s ligament; (10) supraorbital neurovascular bundle; (11) supratrochlear nerve; and (12) medial palpebral ligament
Muscle Fascia (Fig. 1.14)
The muscle fascia interweaves with the anterior thirds of the sheaths of the rectus muscles (mostly at points where their ligaments are attached to the fibrous tunic of the eyeball) into an integral system and becomes noticeably thinner in its posterior portion near the common tendinous ring. As a result, the border between the central (intraconal) and peripheral (extraconal) surgical spaces is eliminated near the orbital apex. Thus, the conventional concept suggesting that there is a muscular funnel as a continuous cone formed by muscle fascia is not consistent with the reality [29].
A thinner inner wall of muscle sheaths is adherent to the septa separating the lobules of the intraconal (i.e., lying within the muscular cone) compartment of adipose tissue. The outer, considerably thicker portion of the sheaths is attached to the orbital walls with connective tissue cords. The thickest cords can be found in the anterior segments of the orbit, where they form supporting ligaments or tendinous expansions of muscles that control the amplitude of eye movements [30].
The supporting ligament of the medial rectus is attached to the bone at several points behind the posterior lacrimal crest and to the tarso-orbital fascia, the lacrimal caruncle, and the plica semilunaris (Fig. 1.15).
Fig. 1.15
Anatomy of the most well-developed supporting system of the medial rectus muscle that reaches the inferior wall, the inferior rectus muscle, and the superior muscle complex. (1) Ligament suspending the superior ophthalmic vein; (2) attachment of the muscle sheath to the orbital roof; (3, 4) fibers attaching the muscle to the orbital floor; (5) region of adhesion between the fascial sheaths of the inferior rectus and inferior oblique muscles; (6) supporting ligament of the medial rectus muscle; (7) points of fixation to the posterior pole of the eyeball; (8) medial horn of the levator aponeurosis; (9) its attachment to the orbit; (10) optic nerve; and (11) medial rectus muscle
The thickest ligament (the ligament of the lateral rectus) is attached to the posterior edge of Whitnall’s orbital tubercle, the lateral conjunctival fornix, the tarso-orbital fascia, and further the lateral orbital wall along the entire length of the ligament up to the common tendinous ring (Fig. 1.16). Efficient contraction of the belly of the lateral rectus passing round the sclera would probably be impossible if attachment of its sheath was not so extensive [27].
Fig. 1.16
Anatomy of the attaching system of the lateral rectus muscle. (1) Lateral rectus muscle; (2) numerous adhesions between its sheath and the lateral orbital wall; (3, 4) attachments to the sheaths of the inferior rectus and inferior oblique muscles; (5) delicate adhesions to the dura mater of the optic nerve (6); (7) point where the lateral rectus muscle is attached to the orbital floor; (8) ligament suspending the superior ophthalmic vein; (9) lateral horn of the levator aponeurosis; (10) periosteum; and (11) maxillary sinus
The medial palpebral ligament (lig. palpebrale mediale) consists of the anterior and posterior crura. The anterior crus is a wide fibrous structure attaching the eyelids to the anterior lacrimal crest of the frontal process of the maxilla. It gives rise to the superficial heads of the pretarsal and preseptal portions of the palpebral part of the orbicularis oculi muscle that is responsible for voluntary (winking) and involuntary (blinking) movements of the eyelids (Fig. 1.17a).
Fig. 1.17
Anatomy of the medial palpebral ligament. (a) Superficial and deep heads of the pretarsal (2) and preseptal (3) portions of the palpebral part of the orbicularis oculi muscle, which form the lacrimal pump together with the lacrimal sac fascia (1); (4) orbital portion of the orbicularis oculi muscle; (5) origination of the corrugator supercilii muscle (m. corrugator supercilii) (Adapted from Jones and Wobig [62]). (b) Sites where the portions of the palpebral part of the orbicularis oculi muscle are attached: (1) medial palpebral ligament; (2) deep head of the preseptal portion; (3) deep head of the pretarsal portion; (4) orbital portion of the orbicularis oculi muscle; (5) corrugator supercilii muscle (m. corrugator supercilii). (c) Axial section of retinaculum mediale: (1) lacrimal sac; (2) Jones’ muscle; (3) Horner’s muscle; (4) pretarsal portion of the palpebral part of the orbicularis oculi muscle; and (5) tarsus
The posterior crus of the medial palpebral ligament attached to the posterior lacrimal crest and the lacrimal sac fossa pulls the internal portions of the eyelid backward, thus providing their tight contact with the ocular surface. In addition, the deep heads of the pretarsal (m. tensor m. tarsalis Horner) and preseptal (L. Jones muscle) portions of the orbicularis oculi muscle, which originate from the posterior lacrimal crest and the surrounding fascia, merge with the posterior crus. Thus, the medial palpebral ligament plays a crucial role in lacrimal pump function by shortening the lacrimal canaliculi and displacing the lacrimal puncta inward (Fig. 1.17b).
Furthermore, the medial palpebral ligament is attached by the so-called superior supporting crus to the frontal bone and provides the medial angle profile of the palpebral fissure.
The combination of soft tissue structures attached to the periosteum of the posterior lacrimal crest forms the medial retinaculum (retinaculum mediale). These structures include the inferior and superior transverse (Lockwood’s and Whitnall’s) ligaments, the supporting ligament of the medial rectus, Horner’s muscle, the medial horn of the levator aponeurosis, and the tarso-orbital fascia.
Lateral palpebral ligament (lig. palpebrale laterale) is 10.5 mm long, 1 mm thick, and 3 mm wide. It continues in the tarsal plates and fibers of the orbicularis oculi muscle, ensuring attachment of the lateral canthal angle and tarsi to Whitnall’s orbital tubercle. Some fibers of the lateral palpebral ligament [31] are attached directly to the lateral orbital margin (Fig. 1.18).
Fig. 1.18
Anatomy of the lateral palpebral ligament. (a) Anterior view: (1) Eisler’s space filled with adipose tissue; (2) anterior crus of the lateral palpebral ligament or the superficial lateral canthal tendon; (3) posterior crus of the lateral palpebral ligament attached to Whitnall’s tubercle (4). (b) Axial section of the medial and lateral palpebral ligaments: (1) anterior crus; (2) posterior crus; and (3) Whitnall’s tubercle
The middle point of the lateral palpebral ligament is 10 mm inferior to the frontozygomatic suture and 2–3 mm superior to the middle point of the medial ligament.
As the lateral ligament approaches the tubercle, it becomes wider, up to 6–7 mm, due to its merging with the lateral horn of the levator aponeurosis, deep fibers of the pretarsal portion of the orbicularis oculi muscle, supporting ligament of the lateral rectus, as well as Lockwood’s and Whitnall’s ligaments. The combination of connective tissue structures attached to Whitnall’s tubercle forms the so-called lateral retinaculum (retinaculum laterale).
Adhesion of the supporting ligament of the lateral rectus to the palpebral ligament makes lateral displacement of the external canthal angle by 2 mm when maintaining an extreme sideward gaze possible in order to expand the peripheral field of view.
Flowers et al. [32] distinguish the so-called external tarsal strip, an independent anatomical structure connecting the inferior tarsus with the inferolateral orbital margin and being attached 3 mm below and 1 mm deeper the lateral ligament (i.e., ~4–5 mm posteriorly the orbital margin).
The anterior portions of the sheaths of the superior rectus and the levator palpebrae superioris muscle are connected by intermuscular fascia [33], forming the so-called superior muscle complex (Fig. 1.19). Whitnall’s superior transverse ligament acts as a supporting ligament that limits palpebral retraction during supraduction and enhances the efficiency of levator contraction [34, 35]. This horizontal whitish structure made of collagen and elastin lies in the upper eyelid 10 mm above the superior tarsus and is the compacted anterior sheet of the connective tissue tunic of the levator palpebrae superioris muscle. The medial edge of the ligament is attached to the trochlear fascia and the tendon of the superior rectus muscle, sharing its fibers with retinaculum mediale. The lateral edge of the ligament is attached to the fascia of the orbital portion of the lacrimal gland and the frontozygomatic suture by intertwining with retinaculum laterale (Fig. 1.20).
Fig. 1.19
Anatomy of the system supporting the superior rectus muscle, the levator palpebrae superioris muscle, and the superior oblique muscle. (1) Periosteum; (2) optic nerve; (3) superior oblique muscle; (4) lateral horn of the levator aponeurosis; (5, 6) its attachment to the ligaments of the lateral rectus muscle; (7) ligament suspending the superior ophthalmic vein; (8) connective tissue septa between the sheath of the superior oblique muscle and the posterior surface of the eyeball; (9) medial horn of the levator aponeurosis; (10) trochlear ligament system; (11) point where the levator palpebrae superioris muscle is attached to the tarsal plate and palpebral skin
Fig. 1.20
Whitnall’s superior transverse ligament. (a) Anterior view: (1) Whitnall’s ligament; (2) levator palpebrae superioris muscle; (3) levator aponeurosis; (4) trochlea; (5) frontozygomatic suture; (6) lacrimal gland; (7) lateral palpebral ligament; (8) medial palpebral ligament; (9) lateral horn of the levator aponeurosis; and (10) medial horn of the levator aponeurosis. (b) Dorsal view: (1) Whitnall’s ligament; (2) preaponeurotic fat pad of the upper eyelid; (3) levator palpebrae superioris muscle; (4) orbital portion of the lacrimal gland; (5) Whitnall’s tubercle; (6) supporting ligament of the lateral rectus muscle; and (7) supporting ligament of the medial rectus muscle
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