Orbit	Bones	Related structures/miscellaneous
Roof	Sphenoid (lesser wing)	Lacrimal gland fossa
	Frontal	Trochlea
		Supraorbital notch (medial)
Lateral wall	Sphenoid (greater wing)	Lateral orbital tubercle of Whitnall
	Zygomatic	Strongest orbital wall
		Lateral orbital rim at equator of globe
Floor	Maxilla	Contains infraorbital nerve and canal
	Palatine	Forms roof of maxillary sinus
	Zygomatic
Medial wall	Sphenoid	Lacrimal sac fossa
	Maxilla	Adjacent to ethmoid and sphenoid sinuses
	Ethmoid	Posterior ethmoidal foramen
	Lacrimal	Weakest orbital wall

Optic nerve

orbital length = 25–30 mm; length from globe to optic foramen = 18 mm; width = 1.5 mm in globe, 3.5 mm posterior to lamina cribrosa (due to myelin), 5.0 mm with the addition of the optic nerve sheath (see Figure 4-2)

Proptosis

measure with Hertel exophthalmometer (Table 6-2)

Table 6-2 Hertel exophthalmometry measurements

	Mean (mm)	Upper Limit of Normal (mm)
Caucasian male	16.5	21.7
Caucasian female	15.4	20
African American male	18.5	24.7
African American female	17.8	23.0

Apertures

(Figures 6-1 to 6-3)

Figure 6-1 Bony anatomy of the orbit in frontal view.

(From Dutton JJ: Atlas of Clinical and Surgical Orbital Anatomy, Philadelphia, WB Saunders, 1994.)

Figure 6-2 Orbital apex, superior and inferior orbital fissure. MR, medial rectus; IR, inferior rectus; LR, lateral rectus; SR, superior rectus; L, levator; SO, superior oblique. Note that the trochlear nerve lies outside the muscle cone.

Figure 6-3 Schematic representation of the landmarks, temporal view.

(From Bajandas FJ, Kline BK: Neuro-Ophthalmology Review Manual, Thorofare, NJ, Slack, 1988.)

(From Dutton JJ: Atlas of Clinical and Surgical Orbital Anatomy, Philadelphia, WB Saunders, 1994.)

Figure 6-5 Orbital veins. Venous drainage from the orbit, in coronal view.

(From Dutton JJ: Atlas of Clinical and Surgical Orbital Anatomy, Philadelphia, WB Saunders, 1994.)

Figure 6-6 Vascular supply to the eye. All arterial branches originate with the ophthalmic artery. Venous drainage is through the cavernous sinus and the pterygoid plexus.

Innervation of Eye

Sensory innervation provided by ophthalmic and maxillary division of trigeminal nerve (CN 5) (Figure 6-7)

Figure 6-7 Sensory nerves of the orbit, in lateral view.

(From Dutton JJ: Atlas of Clinical and Surgical Orbital Anatomy, Philadelphia, WB Saunders, 1994.)

Maxillary nerve (V₂)

Passes through foramen rotundum, then passes through inferior orbital fissure

Divides into infraorbital nerve, zygomatic nerve, and superior alveolar nerve

Parasympathetic innervation

Controls accommodation, pupillary constriction, and lacrimal gland stimulation

Enters eye as short posterior ciliary nerves after synapsing in the ciliary ganglion

Sympathetic innervation

Controls pupillary dilation, vasoconstriction, smooth muscle function of eyelids and orbit, and hidrosis

Dysfunction: Horner’s syndrome (ptosis, miosis, anhidrosis, and vasodilation)

Nerve fibers follow arterial supply as well as long ciliary nerves

Sinuses

(Figure 6-8)

Figure 6-8 Relationship of the orbits to the paranasal sinuses: FS, frontal sinus, ES, ethmoid sinus; MS, maxillary sinus; SS, sphenoid sinus.

(Reprinted with permission from Slamovits TL: Basic and Clinical Science Course, Section 7: Orbit, Eyelids and Lacrimal System. American Academy of Ophthalmology, San Francisco, 1993.)

Frontal

Not radiographically visible before age 6

Drains into anterior portion of the middle meatus

Ethmoid

Multiple thin-walled cavities

First sinus to aerate

Anterior and middle air cells drain into the middle meatus

Posterior air cells drain into the superior meatus

Ethmoidal sinusitis is the most common source of infection that leads to orbital cellulitis

Sphenoid

Rudimentary at birth

Reaches full size after puberty

Optic canal is superior and lateral to sphenoid sinus

Drains into sphenoethmoid recess of each nasal fossa

Maxillary

Largest sinus

Roof contains the infraorbital nerve

Drains into middle meatus

Soft Tissues

(Figure 6-9)

Figure 6-9 Sagittal section of orbital tissues through the vertical recti.

(Adapted from Parks MM: Extraocular muscles. In Duane TD Clinical Ophthalmology, Philadelphia, Harper and Row, 1982.)

Periorbita

Periosteum is attached firmly at the orbital rim and suture lines

Arcus marginalis: fusion of periosteum and orbital septum at orbital rim

Fuses with the dura covering the optic nerve

Annulus of Zinn

Fibrous tissue ring arising from periorbita that surrounds the optic canal

Origin of the 4 recti muscles

Fuses with dura covering ON at apex

Adipose tissue

Surrounds most of orbital contents; divided by fine fibrous septa

Preaponeurotic fat pads: lie immediately posterior to orbital septum

2 FAT PADS IN UPPER LID: anterior to levator aponeurosis; nasal pad smaller and paler than central pad; with aging, nasal pad moves anteriorly and may cause bulging of upper nasal orbit

3 FAT PADS IN LOWER LID: anterior to capsulopalpebral fascia; inferior oblique muscle separates the nasal and middle pads; lateral pad is small and more inferior

Lacrimal gland

2 lobes: orbital (larger) and palpebral, separated by levator aponeurosis

Ducts from both lobes pass though the palpebral lobe and empty into the superior fornix

Innervation: secretomotor from superior salivatory nucleus via CN 7; sensory from CN 5; sympathetic from superior cervical ganglion via deep petrosal nerve, pterygopalatine ganglion, and zygomatic nerve

Blood supply: lacrimal artery

Accessory lacrimal glands: glands of Wolfring located in tarsus and glands of Krause located in the conjunctival fornices (10% of production)

Eyelid

Lamellae of upper eyelid: (Figure 6-10)

Anterior: skin, orbicularis

Posterior: tarsus, levator aponeurosis, Müller’s muscle, palpebral conjunctiva

Figure 6-10 Cross section of upper eyelid. Note position of cilia, tarsal gland orifices, and mucocutaneous junction.

(Reprinted with permission from Grand MG: Basic and Clinical Science Course, Section 2: Fundamentals and Principles of Ophthalmology. American Academy of Ophthalmology, San Francisco, 1993.)

Orbicularis oculi: (Figure 6-11)

Main protractor of the eyelid; acts as lacrimal pump; innervated by CN 7

3 anatomic parts: palpebral portion (pretarsal and preseptal) involved with involuntary blinking; orbital portion involved with voluntary, forced lid closure

PRETARSAL: overlies tarsus, originates from lateral orbital tubercle, forms muscle of Riolan (seen as gray line at lid margin)

SUPERFICIAL HEAD: medially inserts into anterior lacrimal crest, contributes to medial canthal tendon, laterally inserts into zygomatic bone

DEEP HEAD: medially inserts into posterior lacrimal crest, called Horner’s muscle, surrounds canaliculi facilitating tear drainage, laterally inserts into lateral orbital tubercle, contributes to lateral canthal tendon

PRESEPTAL: overlies orbital septum

Originates from anterior limb of the medial canthal tendon, and from posterior lacrimal crest and lacrimal sac fascia

Forms lateral palpebral raphe overlying the lateral orbital rim

ORBITAL: lies beneath skin

Thickest portion of orbicularis

Inserts at medial canthal tendon

Interdigitates with the frontalis muscle superiorly at eyebrow

Figure 6-11 The orbicularis and frontalis muscles.

(From Dutton JJ: Atlas of Clinical and Surgical Orbital Anatomy, Philadelphia, WB Saunders, 1994.)

Other muscles of forehead and eyebrow

Frontalis: moves scalp anteriorly and posteriorly; raises eyebrows; innervated by CN 7

Corrugator: pulls medial eyebrow inferiorly and medially producing vertical glabellar wrinkle; originates from nasal process of frontal bone; inserts laterally into subcutaneous tissue; innervated by CN 7

Procerus: pulls forehead and medial eyebrow inferiorly producing horizontal lines in nose; interdigitates with inferior edge of frontalis; innervated by CN 7

Upper eyelid retractors

(Figure 6-13)

Whitnall’s ligament (superior transverse ligament): condensation of levator muscle sheath

Visible as horizontal white line 10 mm above superior edge of tarsus

Arises from the sheath of anterior portion of levator muscle

Medially attaches to trochlea

Laterally forms septa through stroma of lacrimal gland and attaches to inner aspect of lateral orbital wall at the frontozygomatic suture (10 mm above orbital tubercle [Whitnall’s tubercle]) and at the orbital tubercle

Acts to change direction of pull of levator and serves as check ligament to prevent excessive lid elevation

Müller’s muscle (superior tarsal muscle):

Posterior to levator aponeurosis

Sympathetic innervation

Originates from undersurface of levator approximately at level of Whitnall’s ligament

Inserts into upper border of tarsus

12–15 mm long; raises eyelid 2 mm

Peripheral arterial arcade found between aponeurosis and Müller’s muscle

Figure 6-13 The orbital septum inserts into the levator aponeurosis (arrows). The preaponeurotic fat pads are located posterior to the septum. In downgaze, the lid crease becomes attenuated (weakened), and in a normal young eyelid, the fold is absent.

(From Zide BW, Jelks BW: Surgical Anatomy of the Orbit. New York, Raven Press, 1985.)

Figure 6-14 The levator aponeurosis, and the medial and lateral canthal tendons.

(From Dutton JJ: Atlas of Clinical and Surgical Orbital Anatomy, Philadelphia, WB Saunders, 1994.)

Lower eyelid retractors

(Figure 6-15)

Capsulopalpebral fascia: analogous to levator aponeurosis

Originates from inferior rectus muscle sheath, divides as it encircles inferior oblique muscle, and then joins to form Lockwood’s ligament

Fuses with septum and inserts into inferior tarsus

Lockwood’s suspensory ligament: analogous to Whitnall’s ligament

Arises posteriorly from fibrous attachments to inferior side of the IR muscle and continues anteriorly as capsulopalpebral fascia

Medial and lateral horns attach to retinacula forming a suspensory hammock for the globe

Inferior tarsal muscle: analogous to Müller’s muscle

Sympathetic innervation

Arises from capsulopalpebral fascia

Figure 6-15 Anatomy of the lower eyelid retractors.

(Adapted from Hawes MJ, Dortzbach RK: The microscopic anatomy of the lower eyelid retractors, Arch Ophthalmol 100:1313-1318, 1982.)

Tarsus

Dense connective tissue plate in each eyelid; not cartilage

Contains meibomian glands

29 mm long and 1 mm thick; tapered at ends

Rigid attachments to periosteum medially and laterally

Superior tarsal plate: 10 mm in height

Inferior tarsal plate: 4 mm in height

Medial canthal tendon

Fusion of tendinous insertions of pretarsal and preseptal orbicularis muscles

Attaches to tarsal plates

Anterior limb: attaches to frontal process of maxillary bone and serves as origin of superficial head of pretarsal orbicularis; passes in front of lacrimal sac and attaches to anterior lacrimal crest

Posterior limb: attaches to posterior lacrimal crest; passes behind lacrimal sac. More important than anterior limb for normal medial canthal appearance and function (maintaining apposition of lids to globe)

Lateral canthal tendon

Broad band of connective tissue from lateral borders of upper and lower tarsal plates

Inserts onto lateral orbital tubercle of Whitnall; 3 mm superior to medial canthal tendon insertion

Eyelid margin

3 distinguishing landmarks

Lash line: 2–3 rows of lashes; 100 in upper lid, 50 in lower lid; 10-week growth, 5-month resting phase

Gray line: border of pretarsal orbicularis (muscle of Riolan); junction of anterior and posterior lamellae; vascular watershed

Meibomian gland orifices: 30 in upper lid, 20 in lower lid

Innervation

Sensory: CN V₁ (upper lid), CN V₂ (lower lid)

Motor: CN 3, CN 7, sympathetics

Lymphatic drainage

Submandibular nodes: drain medial

of upper lid, medial

of lower lid

Preauricular nodes: drain lateral

of upper lid, lateral

of lower lid

No lymphatic vessels or nodes are found within the orbit

Lymphatic vessels are found in the conjunctiva

Glands of the eyelids

(Table 6-3)

Eccrine: secretion by simple exocytosis

Holocrine: secretion by release of entire cellular contents (disruption of cell)

Apocrine: secretion by pinching or budding off of a portion of cellular cytoplasm

Table 6-3 Glands of the eyelids

Nasolacrimal System

(Figure 6-17)

Figure 6-17 Excretory lacrimal system.

(From Grand MG: Basic and Clinical Science Course, Section 2, Fundamentals and Principles of Ophthalmology, San Francisco, American Academy of Ophthalmology, 1993.)

Puncta

Upper and lower; 6 mm from medial canthus, lower is slightly more temporal

Slightly inverted against globe

Open into ampulla (2 mm long) oriented perpendicular to eyelid margin

Canaliculi

10 mm long (2 mm vertical segment [ampulla] and 8 mm horizontal portion parallel to lid margin)

Combine to form single common canaliculus in 90% of individuals

Valve of Rosenmüller prevents reflux from lacrimal sac into canaliculi

Nasolacrimal sac

10 mm long, occupies the lacrimal fossa

Lies between anterior and posterior crura of the medial canthal tendon, anterior to orbital septum

Lateral to middle meatus of nose

Nasolacrimal duct

15 mm long

Passes inferiorly, posteriorly, and laterally within canal formed by maxillary and lacrimal bones

Extends into inferior meatus, which opens under inferior turbinate (2.5 cm posterior to naris)

Partially covered by valve of Hasner

Lacrimal pump

Lids close: pretarsal orbicularis contracts, compresses ampulla, shortens canaliculus; punctum moves medially; lacrimal sac expands, creates negative pressure, draws fluid from canaliculus into sac

Lids open: muscles relax, lacrimal sac collapses, tears forced into nose, punctum moves laterally, tears enter canaliculus

Imaging

Ultrasound

Optimal sound wave frequency is 10 MHz

Higher frequencies give better resolution; lower frequencies provide better penetration (Table 6-4)

Table 6-4 Ultrasound characteristics of lesions

Good sound transmission	Poor sound transmission
Cavernous hemangioma	Metastatic cancer
Lymphangioma	Orbital pseudotumor
Mucocele	Glioma
Dermoid	Neurofibroma
High Reflectivity	Low Reflectivity
Neurofibroma	Metastatic cancer
Fresh hemorrhage	Orbital pseudotumor
Hemangioma	Cyst
Thyroid eye disease	Mucocele
	Varix
	Dermoid
	Lymphoma

MRI

Strong magnetic field results in alignment of nuclei of atoms with odd numbers of protons or neutrons

Radiofrequency pulse disturbs the alignment by energizing protons or neutrons

When pulse terminates, protons return to previous alignment and emit absorbed energy as radiofrequency signal, generating an image

Can provide axial, coronal, and sagittal views

Relaxation times

Longitudinal relaxation time (T1): time required for net bulk magnetization to realign itself along original axis

Blood, orbital fat, melanin, and mucus appear bright

Acute hemorrhage, vitreous, optic nerve sheath, and extraocular muscles appear dark

Most orbital tumors are hypointense to fat on T1-weighted images

EXCEPTIONS: mucinous lesions (orbital dermoid cyst, mucocele), lipoma, liposarcoma, melanoma, subacute hemorrhage

Gadolinium: bright white on T1-weighted images

Must perform fat suppression on T1-weighted images when gadolinium is used

Fat suppression renders orbital fat hypointense and permits better visualization of optic nerve and extraocular muscles

Transverse relaxation time (T2): mean relaxation time

Based on interaction of hydrogen nuclei within a given tissue

Provides more information about pathologic processes

Helps differentiate melanotic lesions from hemorrhagic process

Vitreous is bright on T2-weighted images

Blood and fat appear dark

Demyelinating plaques of MS are best seen with T2-weighted images (hyperintense foci, usually in periventricular white matter)

Table 6-5 CT and MRI characteristics of lesions

Most common orbital lesions with well-circumscribed appearance on CT and MRI	Most common orbital lesions with Ill-defined appearance on CT and MRI
Children:	Children:
Dermoid cyst	Capillary hemangioma
Lymphangioma	Orbital pseudotumor
Rhabdomyosarcoma	Plexiform neurofibroma
ON glioma	Leukemic infiltrate
	Eosinophilic granuloma
Adults:	Adults:
Cavernous hemangioma	Orbital pseudotumor
Neurofibroma	Metastasis
Neurilemmoma	Leukemic infiltrate
Fibrous histiocytoma	Primary malignant tumor
(Lymphoproliferative disorders)	Lymphoproliferative disorders