6 Orbit / Lids / Adnexa

Anatomy

Dimensions

Orbit

pear-shaped (widest diameter is 1 cm posterior to orbital rim); 40 mm wide, 35 mm high, 45 mm deep, volume = 30 cc (Table 6-1)

Table 6-1 Osteology

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

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

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

Eyelid

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.)

Upper eyelid retractors

(Figure 6-13)

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.)

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

Innervation

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

Motor: CN 3, CN 7, sympathetics

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

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

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

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