Structure and bony walls
The bony receptacle of the eye has the shape of a four-sided pyramid, with its base facing anteriorly (toward the entrance) and its apex directed toward the sella turcica. The orbital entrance (aditus orbitae) is bounded by dense bony margins. The cavity is isolated from adjacent anatomical regions by thin bone plates:
- Superior wall: serves as the boundary with the anterior cranial fossa.
- Inferior wall: separates the orbit from the maxillary sinus (sinus maxillaris).
- Medial wall: separates it from the nasal cavity.
- Lateral wall: acts as a barrier from the temporal fossa.
Communications with adjacent regions
The orbit has a developed system of fissures and foramina through which major vessels and nerves pass. The main pathways of communication are:
- With the cranial cavity: communication occurs via the optic canal (canalis opticus) and superior orbital fissure (fissura orbitalis superior).
- With the pterygopalatine fossa: via the medial part of the inferior orbital fissure.
- With the infratemporal fossa: via the lateral part of the inferior orbital fissure.
In addition to large fissures, there are several important foramina on the bony walls. On the lateral wall, the zygomaticofacial (foramen zygomaticofaciale) and zygomaticotemporal (foramen zygomaticotemporale) foramina transmit nerve branches from the second branch of the trigeminal nerve (n. maxillaris). On the medial wall lie the anterior and posterior ethmoidal foramina, through which neurovascular bundles pass toward the nasal cavity. On the inferior wall, anterior to the round foramen, run the infraorbital groove and canal.
Fascial apparatus and cavity compartments
The orbital space is divided by the sheath of the eyeball (vagina bulbi, or Tenon's capsule). This fascia divides the cavity into two isolated compartments: bulbar and retrobulbar.
- Externally, Tenon's capsule is fixed by strong connective tissue bands to the orbital margins. Anteriorly, it is pierced by the tendons of the extraocular muscles, and the capsule participates in the formation of their fascial sheaths.
- Internally, the capsule is completely smooth. A slit-like episcleral space remains between it and the sclera. It is filled with tissue fluid, which ensures free rotation of the eyeball.
In the posterior retrobulbar space lies the orbital fat body (corpus adiposum orbitae), surrounded by a fascial leaflet. This acts as a shock absorber for the eye. Overlying it are the supraorbital vessels (a. supraorbitalis), frontal artery (a. frontalis), as well as the supraorbital and supratrochlear nerves.
Topography of neurovascular bundles and muscles
The topography of structures within the orbit is complex and multi-layered. At the entrance lies the cartilaginous trochlea (trochlea), over which the tendon of the superior oblique muscle loops. The inferior oblique muscle originates on the inferior wall, and the infraorbital bundle (a., v. et n. infraorbitales) runs within the thickness of the wall.
In the upper tier, nerve trunks run from the apex to the superior margin: the frontal nerve divides into the supraorbital and supratrochlear nerves; lateral to them lie the vessels and nerve heading to the lacrimal gland; medially lies the nasociliary nerve (n. nasociliaris). Its branches (ethmoidal nerves) pass through the ethmoidal cells onto the cribriform plate to subsequently enter the nasal cavity as the anterior nasal nerves. Medial to the frontal nerve, resting on the levator palpebrae superioris muscle, lies the trochlear nerve (IV cranial nerve), which penetrates the middle of the superior oblique muscle.
Under the lateral margin of the superior oblique muscle runs the ophthalmic artery (a. ophthalmica). Medial to it lies the nasociliary nerve, and lateral to it lies the superior branch of the oculomotor nerve (n. oculomotorius, cranial nerve III).
In the middle and lower tiers, the inferior branch of cranial nerve III lies lateral to the optic nerve and supplies the inferior oblique, inferior rectus, and medial rectus muscles of the eye. The abducens nerve (cranial nerve VI) courses toward the lateral rectus muscle.
Briefly: answers to topical questions
What passes through the superior orbital fissure?
Cranial nerves, veins, and meningeal branches pass from the cranial cavity into the orbit through the superior orbital fissure.
- Ophthalmic nerve (n. ophthalmicus) — the first branch of CN V.
- Oculomotor nerve (n. oculomotorius) — cranial nerve III.
- Trochlear nerve (n. trochlearis) — cranial nerve IV.
- Abducens nerve (n. abducens) — cranial nerve VI.
- Superior ophthalmic vein (v. ophthalmica superior).
- Anterior meningeal branches — sometimes branch off from the ophthalmic artery (r. meningeus anterior ex a. ophthalmica).
Which anatomical structures pass through the inferior orbital fissure?
The inferior orbital fissure transmits vessels and nerves connecting the orbit with the pterygopalatine and infratemporal fossae.
- Infraorbital nerve (n. infraorbitalis) — a branch of n. maxillaris.
- Zygomatic nerve (n. zygomaticus) — a branch of n. maxillaris.
- Infraorbital vessels (a. et v. infraorbitales).
- Inferior ophthalmic vein (v. orbitalis inferior).
What passes through the optic canal?
The most important neurovascular structures pass from the cranial cavity into the orbit through the optic canal (canalis opticus).
- Optic nerve (n. opticus) — cranial nerve II.
- Ophthalmic artery (a. ophthalmica) — a branch of the internal carotid artery.
- Central retinal artery (a. centralis retinae) — a branch of the ophthalmic artery.
What branches does the ophthalmic artery give off within the orbital cavity?
Within the orbital cavity, the ophthalmic artery (a. ophthalmica) gives off a series of branches to the muscles and structures of the eye.
- Branches to the extraocular muscles.
- Ciliary arteries (aa. ciliares) — enter the eyeball around the entrance of the optic nerve.
- Lacrimal artery.
- Supraorbital artery.
The sheath of the eyeball (Tenon's capsule) is easily envisioned as a "sliding sleeve." The episcleral space is filled with fluid acting as a unique hinge lubricant, allowing the eye to rotate freely in the orbit without catching on the fat body.
Class and exam questions
What separates the orbital cavity from the eyelid region?
The boundary is formed by the orbital septum (septum orbitale), which stretches along the margins of the orbital entrance and completely closes it.
Where do the anterior and posterior ethmoidal foramina of the medial wall lead?
They transmit the corresponding vessels and nerves (branches of the nasociliary nerve) into the ethmoidal cells, from where they penetrate onto the cribriform plate and further into the nasal cavity.
Which muscles does the oculomotor nerve innervate in the orbit?
Its superior branch innervates the superior rectus and levator palpebrae superioris muscles. The inferior branch innervates the inferior oblique, inferior rectus, and medial rectus muscles.
What else to study on this topic
- Course and topography of the ophthalmic artery under the lateral margin of the superior oblique muscle.
- Topography of the lacrimal vessels and nerve in relation to the muscles.
- Location of the orbital fat body and its biomechanical function.
- Infraorbital neurovascular bundle on the inferior wall of the orbit.
- Anatomy and attachment sites of the extraocular muscles to the sclera and bones.
Master the complete topic in the "Topographic Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Topographic Anatomy of the Orbit" and 2,777 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 91 video lessons on the subject
Other topics in the section "Topographic Anatomy of the Head"
Free video lessons: topographic anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.