AAO Chapter 2

The orbital entrance averages approximately 35 mm in height and 45 mm in width.

The orbital roof is formed from the orbital plate of the frontal bone and the lesser wing of the sphenoid bone.

The spread of infection from the ethmoid sinus into the orbit.

Each orbit is pear-shaped.

It supplies blood to the inferior oblique muscle.

The inferior oblique muscle arises from the floor of the orbit just lateral to the opening of the nasolacrimal canal.

The nasolacrimal duct travels inferiorly within the bony nasolacrimal canal from the lacrimal sac fossa into the inferior meatus of the nose.

The spiral of Tillaux is an imaginary curve drawn through the insertions of the four rectus muscles on the sclera, which lie progressively farther from the limbus.

The trochlea is a structure made of hyaline cartilage attached to the trochlear fossa on the frontal bone, acting as a pulley for the superior oblique muscle.

The anterior fibers provide intorsion, while the posterior fibers provide depression and abduction.

The short ciliary nerves are formed by nonsynapsing sympathetic fibers, sensory fibers, and myelinated, fast-conducting postganglionic parasympathetic fibers.

Patients with retrobulbar optic neuritis may experience pain with extraocular movement due to the connection of the superior and medial rectus muscles to the optic nerve. Enlargement of these muscles can lead to compressive optic neuropathy in patients with thyroid eye disease.

The annulus of Zinn is a fibrotendinous ring that represents the origin of the 4 rectus muscles.

It is important when suturing to the sclera to avoid perforating the retina and when evaluating trauma patients with scleral lacerations that extend beyond the spiral of Tillaux, as this increases the risk of retinal incarceration and tractional retinal detachment.

The medial and superior rectus muscles are adjacent to the optic nerve sheath at their origin.

Approximately 1 cm in front of the annulus of Zinn, on the lateral side of the ophthalmic artery, between the optic nerve and the lateral rectus muscle.

The superior orbital fissure passes above and below the plane of the optic canal and is commonly mistaken for it.

Superior ophthalmic vein

Optic nerve

It is important to identify and avoid the fovea ethmoidalis to prevent inadvertent cerebral spinal fluid leakage and intracranial injury.

The bony orbit comprises 7 bones: ethmoid bone, frontal bone, lacrimal bone, maxillary bone, palatine bone, sphenoid bone (greater and lesser wings), and zygomatic bone.

Two groups of short ciliary nerves, totaling 6–10, arise from the ciliary ganglion.

The long ciliary nerves are sensory nerves that arise directly from the nasociliary branch of CN V1.

The vortex veins receive venous blood from the uveal tract.

Cranial nerves II to VII.

The circle connecting the ampullae corresponds roughly to the equator.

The three roots are the sensory root, sympathetic root, and motor root.

CN VI (abducens)

The check ligament of the lateral rectus muscle, suspensory ligament of the eyeball (Lockwood suspensory ligament), lateral canthal tendon, and lateral horn of the levator aponeurosis.

The orbital roof is composed of the orbital plate of the frontal bone and the lesser wing of the sphenoid bone.

Lesser wing of sphenoid bone

The medial orbital wall is formed by the maxillary bone, lacrimal bone, lesser wing of the sphenoid bone, and orbital plate of the ethmoid bone.

The angular artery.

The depth of the orbit varies from 40 to 45 mm.

The superior margin of the orbital margin is formed by the frontal bone.

The fossa for the lacrimal gland lies anterolaterally behind the zygomatic process of the frontal bone within the orbital roof.

The levator palpebrae superioris muscle is responsible for elevating the upper eyelid.

The vortex veins exit 14–25 mm from the limbus, between the rectus muscles.

The superior oblique muscle originates from the periosteum of the body of the sphenoid bone, above and medial to the optic foramen.

Each rectus muscle has 1–4 anterior ciliary arteries.

The annulus of Zinn is continuous with periorbita around the orbital apex, surrounding dura matter, and part of the optic nerve sheath.

Multiple sites of anastomoses between the external and internal carotid arteries.

The inferior tendon of the annulus of Zinn gives rise to the inferior rectus muscle and portions of the lateral and medial rectus muscles.

They enter through the superior orbital fissure within the tendinous ring, pass through the ciliary ganglion without synapsing, and innervate blood vessels of the eye and the dilator muscle of the pupil.

The anterior ethmoidal vessels and nerve.

The largest component of the medial wall is the lamina papyracea, which is the orbital plate of the ethmoid bone.

The annulus of Zinn consists of superior and inferior orbital tendons and serves as the origin of the 4 rectus muscles.

Each eye contains 4–7 (or more) vortex veins.

The lacrimal artery.

The short ciliary nerves supply the cornea, the ciliary body, and the iris.

The lateral orbital tubercle (Whitnall tubercle) is a small elevation of the orbital margin of the zygomatic bone, located approximately 11 mm below the frontozygomatic suture.

The ratio is very high, approximately 1:3 to 1:5.

The lamina papyracea is the orbital plate of the ethmoid bone, which is a paper-thin structure and the most common site of fracture following blunt trauma to the orbit.

The episcleral arterial circle runs on the surface of the sclera, connecting the anterior ciliary arteries.

Due to the thinness of the bone and the presence of emissary channels, ethmoid sinusitis is the most common cause of orbital cellulitis.

Levator muscle

The zygomatic bone and the greater wing of the sphenoid bone.

The fossa for the lacrimal sac is formed by both the maxillary and lacrimal bones.

It is located along the inferonasal orbit, where the orbital bones slope from the floor to the medial wall.

The anterior and posterior ethmoidal arteries.

The infraorbital canal exits 4 mm below the inferior orbital margin, opening into the infraorbital foramen.

Both oblique muscles insert posteriorly on the globe in the region of the macula.

There are 7 extraocular muscles.

The major arterial circle formed by the anterior ciliary arteries.

Internal carotid artery

Sensory fibers from the cornea, the iris, and the ciliary body.

Collagen, elastin, and smooth muscle.

At the medial third of the superior margin of the orbit.

The most direct path to the optic nerve is along the medial wall.

The medial margin is formed above by the frontal bone and below by the posterior lacrimal crest of the lacrimal bone and the anterior lacrimal crest of the maxillary bone.

The posterior ciliary vessels form the intramuscular circle of the iris.

Scleral buckling and orbital decompression.

Annulus of Zinn

The superior orbital fissure transmits the lacrimal nerve, frontal nerve, CN IV (trochlear nerve), superior ophthalmic vein, superior and inferior divisions of CN III, nasociliary branch of CN V1, and CN VI (abducens nerve).

The trochlea is a curved plate located medially within the orbital roof.

The lateral wall is formed by the zygomatic bone and the greater wing of the sphenoid bone.

Muscular branches of the ophthalmic artery, infraorbital artery, and lacrimal artery.

Inferior rectus muscle

The lateral wall of each orbit forms an angle of approximately 45° with the medial plane.

The lateral rectus muscle.

The orbital musculofibrous tissue stabilizes the movement of the extraocular muscles within the orbit and in relation to the globe and each other.

It is important to evaluate for numbness or tingling in the area of V2 distribution due to the infraorbital nerve being carried by the infraorbital groove in the maxillary bone.

The short posterior ciliary arteries are the major contributors to the pre-equatorial choroidal circulation.

The orbital floor slopes downward approximately 20° from posterior to anterior.

CN IV (the trochlear nerve) innervates the superior oblique muscle.

The long posterior ciliary arteries travel in the suprachoroidal space and terminate at the major arterial circle of the iris.

Inferiorly, in vertical meridian 6.5 mm from limbus

The extraocular muscles are encased in a fibrous sheath.

The annulus of Zinn is a fibrous ring formed by the origin of the 4 rectus muscles and trisects the superior orbital fissure.

The trochlear nerve (CN IV), lacrimal and frontal nerves (CN V1), and the superior ophthalmic vein are transmitted above the annulus of Zinn.

Superior oblique muscle

Fractures of the orbital floor involving the infraorbital groove.

The superior oblique muscle inserts onto the sclera superiorly, under the insertion of the superior rectus.

It is an uncommon variation that can supply the orbit.

The medial wall of the orbit is formed by the frontal process of the maxillary bone, lacrimal bone, orbital plate of the ethmoid bone, and lesser wing of the sphenoid bone.

The ora serrata internally.

Superior to the orbit are the anterior cranial fossa and the frontal sinus; inferiorly are the maxillary sinus and the palatine air cells.

41.8 mm long (tendon: length 5.8 mm, width 10.6 mm)

The optic canal conducts the optic nerve, the ophthalmic artery, and sympathetic fibers from the carotid plexus.

The inferior ophthalmic vein connects with the pterygoid plexus before draining into the cavernous sinus.

It is important because disinsertion of 2 or more rectus muscles can lead to anterior segment ischemia.

The iris vessels have a radial arrangement that is visible upon slit-lamp examination.

Annulus of Zinn

It is involved in the parasympathetic innervation of the eye.

The annulus of Zinn is a common fibrotendinous ring shared by the four rectus muscles, which is located at the orbital apex.

The optic canal is housed in the lesser wing of the sphenoid and transmits the optic nerve and ophthalmic artery.

The medial walls of the orbits border the nasal cavity anteriorly and the ethmoid and sphenoid sinuses posteriorly.

All extraocular muscles, except the inferior oblique, originate in the orbital apex.

The anterior ciliary arteries emerge from the surface of the rectus muscles.

The levator palpebrae superioris muscle arises from the lesser wing of the sphenoid bone, at the apex of the orbit, just superior to the annulus of Zinn.

The inferior oblique muscle originates anteriorly, from a shallow depression in the orbital plate of the maxillary bone, at the anteromedial corner of the orbital floor, near the fossa for the lacrimal sac.

The inferior oblique muscle inserts onto the sclera in the posterior inferotemporal quadrant.

A long sensory root from the nasociliary branch of CN V1, a short motor root from the inferior division of CN III, and a sympathetic root from the superior cervical ganglion.

The inferior oblique and inferior rectus muscles.

The spiral of Tillaux is formed by connecting the insertions of the tendons of the medial rectus, inferior rectus, lateral rectus, and superior rectus.

The inferior orbital fissure lies just below the superior fissure, between the lateral wall and the floor of the orbit.

The fibers are a mixture of slow, tonic-type fibers and fast, twitch-type fibers.

The medial wall contains the anterior and posterior ethmoidal foramina, which transmit the anterior and posterior ethmoidal arteries.

They supply the entire uvea, the cilioretinal arteries, the sclera, the margin of the cornea, and the adjacent conjunctiva.

It carries preganglionic parasympathetic fibers to supply the iris sphincter and the ciliary muscle.

The anatomical relationship between the anterior and posterior ciliary circulation can lead to anterior segment ischemia following strabismus surgery or scleral buckling procedures.

They usually supply the superior, medial, and inferior rectus muscles.

It produces tears.

The anterior and posterior foramina transmit the anterior and posterior ethmoidal arteries, respectively.

It may lead to anterior ischemic optic neuropathy.

Intermuscular septa and a pulley system.

Trigeminal (gasserian) ganglion

To trochlea, through pulley, just behind orbital rim, then hooking back under superior rectus, inserting posterior to center of rotation

Only the parasympathetic fibers.

The floor of the orbit is composed of the orbital plate of the maxillary bone, palatine bone, and orbital plate of the zygomatic bone.

The oculomotor nerve (CN III), nasociliary nerve (CN V1), abducens nerve (CN VI), and sympathetic fibers are transmitted through the oculomotor foramen.

The zygomaticotemporal and zygomaticofacial nerves and arteries.

Medial (inferior) muscular branch of ophthalmic artery and infraorbital artery

The sphenoid wing.

The supraorbital foramen/notch transmits the supraorbital nerve, a terminal branch of the frontal nerve of the ophthalmic division of cranial nerve V (CN V1).

The 'rule of twelves' helps guide the surgeon and reduce the risk of optic nerve damage, indicating distances of 24 mm from the anterior lacrimal crest to the anterior ethmoidal foramen, 12 mm from the anterior to posterior ethmoidal foramen, and 6 mm from the posterior ethmoidal foramen to the optic canal.

The infraorbital nerve, which is the maxillary division (V2) of the trigeminal nerve, is housed in the infraorbital groove and canal.