CHAPTER 2

Orbit, Eyelids, and Ocular Adnexa

Anatomy and Physiology

BONY ORBIT (Fig. 2–1) Average 30 cc volume (about that of a shot glass with a 6 cc globe inside), 35 mm height, 40 mm depth (22 mm globe and 18 mm from posterior globe to the orbital apex; thus, the 25 mm intraorbital optic nerve (ON) has 7 mm redundancy), and 45 mm width. Average interpupillary distance (IPD) ¼ 60 mm. Optic axis is 23 degrees lateral to anteroposterior axis. Maximum circumference is 1 cm behind rim (at the globe equator). All bones are of neural crest origin except superotemporal orbit (ectodermal); orbital growth completed by 7–9 years. Seven bones comprise the bony socket: frontal, zygomatic, greater and lesser wings of the sphenoid, maxillary, lacrimal, ethmoid, and palatine.

Two bones in the roof: frontal and lesser wing of the sphenoid. Bordered by anterior cranial fossa and frontal sinus. Trochlea is 4 mm behind rim. Houses the lacrimal gland fossa (postseptal). Optic canal travels through lesser sphenoid, 37 degrees off optic axis.

Two bones in the lateral wall: zygomatic and greater sphenoid wing. Bordered by temporal and pterygopalatine fossa. Lateral walls are perpendicular to each other, thickest (1.0–1.5 mm) and strongest orbital bones but least protective of globe.

Lateral orbital tubercle 4 mm posterior to the rim on the medial aspect of zygoma; also called Whitnall’s tubercle. The ‘‘4 L’s’’ attach here: lateral canthal (palpebral) tendon, Lateral rectus (LR) check ligament, lateral horn (aponeurosis) of the levator muscle, Lockwood’s suspensory ligament of eye (equivalent to Whitnall’s in upper lid).

Three bones in the floor: maxillary, palatine, and zygomatic bones. Bordered by infraorbital canal and maxillary sinus. The floor slopes upward from the inferior orbital rim toward the apex but does not reach the apex and ends at pterygopalatine fossa. It is the only wall without a sphenoid bone contribution.

Four bones in the medial wall (mnemonic: SMEL): sphenoid, maxillary, ethmoid, and lacrimal bones. Bordered by ethmoid and sphenoid sinuses, cribriform plate at frontoethmoidal suture (therefore stay below the ethmoidal neurovascular foramina during decompression surgery). Medial walls are parallel to each other and 25 mm apart

28

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Figure 2–1 Frontal view of the left orbit, showing the bones that contribute to the bony socket (palatine bone not shown).

between the medial canthi and are the thinnest walls ( 0.3 mm; called lamina papyracea because they are ‘‘paper thin’’). Houses the lacrimal sac fossa (preseptal).

Rule of halves (mnemonic: 24-12-6): anterior ethmoidal aperture (AEA) is 24 mm posterior to the anterior lacrimal crest, posterior ethmoidal aperture (PEA) is 12 mm posterior to the AEA, and the optic canal is 6 mm posterior to the PEA. Thus, total medial wall length is 42 mm long; remember this during medial orbitotomy.

FISSURES Two main fissures (Fig. 2–2 shows orbital apex anatomy and contents of the orbital fissures):

Inferior orbital fissure (IOF): ‘‘lower tier’’ of the apex opens into pterygopalatine fossa (behind maxillary fossa). Twice as long as the superior orbital fissure. Contents (mnemonic: PIMP): pterygoid nerve

of cranial nerve (CN) V2, inferior orbital vein, maxillary nerve (from CN V2), and the pterygopalatine ganglion nerve (postganglionic secretory innervation for the lacrimal gland).

Superior orbital fissure (SOF): ‘‘middle tier’’ of the apex opens into cavernous sinus. A pencil stuck through the middle of the globe would

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30 ORBIT, EYELIDS, AND OCULAR ADNEXA

Figure 2–2 The left orbital apex and associated structures.

go through the SOF into the cavernous sinus. The SOF is 22 mm long and separated by LR origin (and thus anulus of Zinn) into:

Superior division (mnemonic: ‘‘Look: Michigan State football

team’’): lacrimal nerve of CN V1 (most lateral structure at apex), middle meningeal artery recurrent branch, sympathetic nerves,

frontal nerve of CN V1, and trochlear nerve (CN IV, the least affected muscle from a retrobulbar block because it is outside the muscle cone)

Inferior division (mnemonic: NASO2): nasociliary branch of CN V1, abducens nerve (CN VI), sympathetic nerves, oculomotor nerve (CN III), and the superior orbital vein

FORAMINA Eight main orbital foramina (Fig. 2–3 shows skull base anatomy and openings):

Optic: the ‘‘upper tier’’ of the apex, located at the level of the anterior clinoid and opens into the middle cranial fossa (MCF). Contains the ON, ophthalmic artery, sympathetic nerves (also enter orbit with nasociliary nerve through SOF). It is 6.5 mm wide and 10 mm long. At the apex, the optic foramen is superior and nasal and points up and in toward the MCF.

Supraorbital: is a foramen in 20% of the population and a notch in80%. Protects the supraorbital vessels and nerve (branch of the frontal branch of CN V1, transmits sensation from forehead).

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Figure 2–3 Internal view of the right anterior skull base, showing the orbital roof and openings into the orbit.

Infraorbital: located 5–10 mm below rim and transmits the infraorbital

nerve (from CN V2) that provides sensation from midface, superior gums, and canine teeth.

Anterior and posterior ethmoidal: transmit vessels and nerves (from CN V1) at the junction of ethmoid and frontal bones.

Zygomatic: zygomaticofacial and zygomaticotemporal foramina house

their respective arteries and nerves (branches of CN V2, transmit sensation from the lateral face and temple).

Nasolacrimal fossa and duct: responsible for lacrimal drainage into the inferior meatus.

BLOOD SUPPLY TO THE ORBIT AND GLOBE First branch of the internal carotid artery is the ophthalmic artery, followed by the middle cerebral, posterior communicating, and anterior communicating arteries. The first branch of the ophthalmic artery is the central retinal artery (CRA). The CRA begins inferior and lateral to the ON, then sweeps over, crossing nasally (is also nasal to the medial rectus muscle. Its branches can be grouped into three circles: posterior (supplying globe: CRA, short and long

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32 ORBIT, EYELIDS, AND OCULAR ADNEXA

ciliaries); middle (supplying extraocular muscles and orbit: muscular, anterior ciliary, lacrimal); and anterior (terminal branches to skin: anterior and posterior ethmoidals, supraorbital, supraand infratrochlear, dorsal nasal).

BRANCHES OF THE OPHTHALMIC ARTERY

Central retinal: supplies the inner retina

Small meningeal/pial branch

Central collateral branch

Lacrimal

Lateral palpebral artery passes into the upper and lower eyelids, runs medially to anastomose with medial palpebral artery to form the palpebral arcades.

Zygomatic branches pass through zygomaticofacial and zygomaticotemporal foramina to anastomose with superficial temporal artery (from the ECA).

Muscular branch to LR (or variably from lacrimal artery)

Recurrent meningeal branch (may arise from the lacrimal artery): passes through the SOF, anastomoses with the middle meningeal artery (from the ECA)

Muscular branches to four rectus muscles: two branches to each muscle (except one to the LR). Gives rise to seven anterior ciliary arteries that supply the sclera and conjunctiva and terminate in the major arterial circle of iris, providing 50% of anterior segment blood (remainder is from the long posterior ciliary arteries). Vertical muscles contribute more to the anterior segment circulation than horizontal muscles.

Ciliary

Long posterior ciliary: two vessels pass through the suprachoroid space forward to supply the choroid anterior to the equator, ciliary body, and anastomose with the anterior ciliaries to form the major circle of the iris

Short posterior ciliary: usually about seven vessels that then divide into 10 to 20 branches; supply choroid posterior to the equator and form anastomotic ring of Zinn around the optic nerve head, and in 20% of the population give rise to a cilioretinal artery

Supraorbital: along medial aspect of the levator and superior rectus muscles through supraorbital foramen to the scalp, lying deep to the frontalis muscle, supplying the levator palpebrae muscle, frontal sinus, upper eyelid, and skin of forehead, and anastomoses with the superficial temporal artery (ECA)

Posterior ethmoid: through posterior ethmoid canal to posterior ethmoid air cells, anterior cranial dura, and upper nasal mucosa

Anterior ethmoid: through anterior ethmoid canal to anterior cranial fossa through cribriform plate into nose under nasal bone to face, supplying anterior and middle ethmoidal air cells, frontal sinus, meninges, anterior nasal mucous membranes, and skin of nose

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Meningeal: supplies meninges of middle cranial fossa

Medial palpebral (may also branch from dorsal nasal artery): usually two branches that travel below the trochlea, behind the lacrimal sac, through the septum, above and below the medial palpebral ligament, to pass laterally and enter the upper and lower eyelid and divide into the peripheral and marginal arcades between the orbicularis and tarsus, supplying eyelids and conjunctiva. Marginal arcade is 2 mm from the margin, and peripheral arcade in upper eyelid is 1 mm above the tarsus; both covered by levator (should not see during a blepharoplasty).

Supratrochlear: above trochlea through septum, supplying skin of forehead and scalp

Dorsal nasal: terminal branch of ophthalmic artery; lies within upper medial fat pad (beware during surgery) through septum above medial palpebral ligament, supplying lacrimal sac and anastomosing with facial artery (from the ECA) at the medial canthus

BRANCHES OF THE EXTERNAL CAROTID ARTERY

Superior thyroid

Ascending pharyngeal

Lingual

Occipital

Facial: becomes the angular artery, which anastomoses with the dorsal nasal artery (from the ICA)

Posterior auricular

Maxillary: gives rise to the infraorbital artery in the pterygopalatine fossa, through the IOF, down the infraorbital groove and canal, giving branches to the IR, IO, and lacrimal sac, then courses through the infraorbital foramen to supply the skin of the face, maxillary sinus, and upper teeth (upper superior alveolar artery)

Anterior tympanic

Middle meningeal: anastomoses with the recurrent meningeal (from the ICA)

Superficial temporal: anastomoses with the zygomaticotemporal (from the ICA). The artery lies on the superficial temporal fascia; thus, for a temporal artery biopsy, trace the vessel up from just anterior to the ear. If the cut is too deep, you will see the white glistening temporalis (temporal parietal) fascia that splits about 1 cm above the zygomatic arch into a deep and superficial layer.

ARTERIAL ANASTOMOSES BETWEEN THE ICA AND ECA (MNEMONIC: ZEBRAS RARELY SIP DOUBLE LATTES)

Zygomaticotemporal and superficial temporal

Recurrent meningeal and middle meningeal

Supraorbital and frontal (branch of superficial temporal)

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34ORBIT, EYELIDS, AND OCULAR ADNEXA

Dorsal nasal and angular

Lacrimal and palpebral

VENOUS SYSTEM Superior ophthalmic vein drains the orbit, travels beneath SR, and runs diagonally across the superior orbit from medial posterolaterally to the SOF. It is lateral to and larger than the ophthalmic artery. Because it is valveless and drains into the cavernous sinus, there is a risk of intracranial spread of infection from orbital cellulitis. The inferior orbital vein drains into the superior orbital vein and smaller branches into the pterygoid plexus. The angular vein of the facial plexus also contributes to venous drainage.

LYMPHATIC SYSTEM There are no orbital lymphatics (debatable but classic teaching; there are likely some lymph vessels present). The upper eyelid drains to the preauricular lymph nodes and the lower to submental nodes. The lateral lids drain into the preauricular nodes, and the medial lids drain into the submandibular nodes.

MUSCLES See Chapter 9 for EOM details.

Eyelid retractors

Capsulopalpebral fascia: retractor of the lower eyelid, analogous to the levator muscle, and arises from the IR sheath. After it splits around the IO muscle, it extends to Lockwood’s ligament, then takes a vertical course to the anterior tarsus. Thus, movement of the lower eyelid parallels the globe in downgaze.

Levator palpebrae superioris: originates superior to the SR at the orbital apex from the lesser wing of the sphenoid. Its 40 mm muscle belly extends to Whitnall’s ligament and is responsible for horizontal pull. Then the 12 mm tendon (aponeurosis) attaches to the lower half of tarsus and provides vertical pull. Gives attachments to the overlying orbicularis and skin (forms the eyelid crease). CN III innervation.

Mu¨ller’s (superior tarsal) muscle: originates from the undersurface of the levator muscle (is ‘‘posterior lamella’’ of the levator) and advances 10–12 mm to the superior tarsus. Gives 2–4 mm lift by sympathetic innervation (thus affected in Horner’s syndrome).

Select muscles of facial expression: CN VII (facial nerve) innervation.

Frontalis: part of the anterior scalp, elevates the forehead and brow.

Nasalis: lateral aspect of nose, to dilate or compress the nares.

Orbicularis oculi: primary protractor of eyelids; innervated by the temporal, zygomatic, and buccal (to a lesser extent) branches of the facial nerve. Its medial attachments contribute to lacrimal pump (thus, epiphora occurs with CN VII palsy from poor pump function in addition to corneal exposure and reflex tearing).

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Figure 2–4 The right ciliary ganglion, lateral view, and its tripartite contributions.

Involuntary lid closure (blink) is mostly from the pretarsal orbicularis and voluntary (wink) from the orbital fibers, with preseptal fibers contributing to both.

Procerus: attaches to frontalis muscle and inserts on the nasal bone; causes horizontal brow wrinkles.

Superciliary corrugator muscle: originates from the frontal bone, coursing laterally to insert in subcutaneous tissue; responsible for vertical brow wrinkles and rhytids (like a corrugated tin roof).

NERVES See Chapter 8 for cranial nerve details.

Ciliary ganglion (Fig. 2–4): three roots enter the ganglion, and fibers exit as the short ciliary nerves.

The motor root (parasympathetic fibers) arises from CN III branch to the IO muscle and synapse in the ganglion.

Sympathetic nerves from the carotid plexus pass through the ganglion without synapsing.

Sensory root derives from the nasociliary nerve (CN V1) and pass through the ciliary ganglion without synapse.

CN V1 (trigeminal nerve, ophthalmic division): lacrimal and frontal branches enter the orbit through the superior division of the SOF. The

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36 ORBIT, EYELIDS, AND OCULAR ADNEXA

lacrimal branch supplies the area around the lacrimal gland, and the frontal branch divides into the supraorbital and infratrochlear branches.

LACRIMAL GLAND The lacrimal gland has two lobes; excretory ducts from the larger orbital lobe pass into the palpebral lobe and continue into the conjunctival fornix. The two lobes are separated by the lateral horn of the levator aponeurosis. A salivatory-type gland with no true capsule, the lacrimal gland efferent innervation originates in the superior salivatory (lacrimal) nucleus ! nervus intermedius portion of CN VII ! greater petrosal nerve ! sphenopalatine (pterygopalatine) ganglion ! CN V2 infraorbital nerve ! zygomaticotemporal ! lacrimal nerve. (Afferent innervation is provided by CN V1 to the spinal trigeminal ganglion.)

EYELID GLANDS All aqueous glands are eccrine; all oil and mucous glands are holocrine except glands of Moll, which are apocrine.

Goblet cells: conjunctival glands that are apocrine for a time, then holocrine (gives ‘‘wholly’’ of itself, ruptures and extrudes contents)

Lacrimal: eccrine (modified sweat gland) and two types of accessory lacrimal glands are present in the conjunctiva:

Glands of Krause: present in the conjunctival fornices (glands of Krause are in the ‘‘crotch’’ of the lid); 20–42 in the upper fornix and 6–8 glands in the lower.

Glands of Wolfring: present in the ‘‘wall’’ of the palpebral

conjunctiva, about three glands near the upper border of the upper tarsus and two near the lower border of the lower tarsus.

Meibomian: holocrine glands that are hypertrophied sebaceous glands (unique because they are not associated with hairs) and lie within the tarsus

Zeis: holocrine glands that are rudimentary sebaceous glands connected to a lash follicle

Moll: apocrine glands that are atypical large sweat glands; loses cytoplasm with secretion and thus produces a thicker solution than sweat; empties into a lash follicle.

EYELID Functions primarily to protect the globe; also important in facial expression. The mucocutaneous junction is a critical eyelid structure because it functions to spread the tears and provides oxygen to the cornea. The mucocutaneous junction is posterior to the eyelashes near the meibomian gland openings; the gray line is anterior lamella and is the edge of the pretarsal orbicularis.

Eyelid layers (four basic layers near the eyelid margin):

Skin: thinnest skin in the body

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Epidermis has four layers: stratum corneum, granulosum, spinosum, and basale (germinativum). Melanocytes are present in about a 1:10 ratio with epidermal cells, and occasional Langerhans’ cells from monocyte precursors express immune antigen (contain Bierbeck granules).

Dermis contains hair, sebaceous, Zeis and meibomian glands, eccrine sweat glands, and apocrine glands of Moll. Subcutaneous areolar tissue is present beneath the dermis.

Orbicularis muscle: submuscular areolar tissue divides the anterior lamella of skin and orbicularis muscle with the posterior lamella of tarsus and conjunctiva.

Septum or tarsus: no cartilage in tarsus and is nonrenewable.

Conjunctiva

Layers of the eyelid that a penetrating wound would pass through:

Lower eyelid (Fig. 2–5) (mnemonic: 4-7 rule):

Figure 2–5 The lower eyelid and anterior orbit anatomy, sagittal section.

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38ORBIT, EYELIDS, AND OCULAR ADNEXA

The upper 5 mm has 4 layers: skin, orbicularis, tarsus, and conjunctiva.

The lower 5 mm has 7 layers: skin, orbicularis, septum, preCPF (capsulopalpebral fascia) fat, inferior sympathetic muscle (equivalent to Mu¨ller’s in the upper lid), CPF (equivalent to levator aponeurosis in upper lid), and conjunctiva.

Upper eyelid (Fig. 2–6) (mnemonic: 4-5-7 rule):

The lower 5 mm has 4 layers: skin, orbicularis, tarsus, and conjunctiva.

The middle 5 mm has 5 layers: skin, orbicularis, levator aponeurosis, tarsus, and conjunctiva.

Above 10 mm, the upper eyelid has 7 layers: skin, orbicularis, septum, preaponeurotic fat, levator aponeurosis, Mu¨ller’s muscle, and conjunctiva.

Figure 2–6 The upper eyelid and anterior orbit seen in cross-sectional anatomy.

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Vasculature: upper lid supplied by the marginal and peripheral vascular arcades. The lower lid usually has only a peripheral arcade. The peripheral vascular arcade lies along the peripheral border of the tarsus between the lid retractors and Mu¨ller’s (inferior tarsal) muscle. The marginal arcade lies anterior to the tarsus 2 mm above the eyelid margin. In eyelid surgery, visualizing these horizontally running vessels indicates that you are below the level of the aponeurosis.

ORBITAL CONNECTIVE AND SUPPORTING TISSUES Most of the orbit is

filled with fat.

Fat pads: removal of too much fat during surgery may result in sunken orbits, EOM restriction, and cicatricial eyelid changes.

Upper lid: two fat pads. The large, central, more yellow (higher lutein concentration) preaponeurotic fat pad protects the levator aponeurosis directly beneath it; it is contiguous with deep fat and is less vascular. The smaller, paler medial fat is more vascular and often migrates anteriorly with aging. There is no lateral fat pad in the upper lid because of the presence of the lacrimal gland in that position.

Lower lid: three fat pads. The medial and central pads are separated by the IO (essential to avoid the muscle in blepharoplasty) and communicate with deeper orbital fat; thus, excessive traction may lead to orbital hemorrhage. The smaller lateral fat pad is contiguous with the central pad and separated by the arcuate expansion of the IO.

Orbital septum: an extension of orbital bone periosteum (originates at the arcus marginalis); attaches to the levator aponeurosis 2–5 mm above the superior tarsus in upper lid (attaches lower in the Asian

eyelid and thus creates a lower to absent lid crease). Fuses with the lower lid retractors in the lower eyelid within 1–2 mm from the inferior border of tarsus. Is immediately deep to orbicularis muscle and superficial to preaponeurotic orbital fat.

Suspensory ‘‘ligamentous’’ system

Whitnall’s ligament (superior transverse ligament): condensation of levator aponeurosis suspended high in orbit, attached medially to the trochlea and laterally to the orbital lobe of the lacrimal gland and also attaches laterally to the orbital wall near the frontozygomatic suture (above but not at Whitnall’s tubercle). Acts to change the direction of pull of the levator muscle from horizontal to vertical and limits the extent of lid elevation.

Lockwood’s ligament: present in the lower lid and is analogous to Whitnall’s in the upper lid. Arises from inferior side of IR and continues anteriorly as the CPF (lower lid retractors) with contributions from intramuscular septae and Tenon’s capsule. It has medial and lateral horns that attach to the retinaculum, which

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40 ORBIT, EYELIDS, AND OCULAR ADNEXA

Figure 2–7 The left medial canthus anatomy and tendinous insertions of the orbicularis muscle.

attaches medially to the posterior lacrimal crest and laterally to the lateral orbital tubercle (Whitnall’s tubercle), forming a suspensory hammock for the globe.

Canthal ligaments (also known as tendons) (Fig. 2–7): lateral ligament has a superior and inferior crux. The anterior limb of the medial canthal tendon attaches to the frontal (nasal) process of the maxillary bone; the posterior portion (deep head of the pretarsal and preseptal orbicularis muscle) inserts onto the posterior lacrimal crest and fossa and is important in maintaining apposition of lids to the globe. The tarsus is like a knight’s visor that pivots at the canthal tendons.

CARUNCLE Modified lower lid margin composed of nonkeratinized stratified epithelium, with 15 to 20 fine hairs, sebaceous glands, lacrimal glands similar to Krause, and goblet cells. Blood is supplied from the superior medial palpebral artery, innervated from the infratrochlear nerve, and lymph drainage is into the submaxillary nodes.

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Figure 2–8 The right lacrimal drainage system, showing the soft tissue and bony components.

LACRIMAL DRAINAGE SYSTEM (Fig. 2–8) Begins at the punctum, which extends 2 mm to the ampulla (largest diameter of canalicular system), and into the canaliculus. Nearly 90% of the population has a common canaliculus (1 mm in diameter), which travels 8 mm through the valve of Rosenmu¨ller (Maier’s sinus) into the lacrimal sac. Drainage then proceeds through the valve of Krause and Arlt’s sinus that open from the sac to the nasolacrimal duct. The spiral valves of Hyrtl and Taillefer are present within the duct that opens through the valve of Hasner into the inferior meatus (1.5 cm up and in from the nasal opening).

Lacrimal drainage system forms at the 12 mm embryo stage from surface ectoderm (lacrimal gland forms at 25 mm). Nasolacrimal sac forms first, then canalization begins at 4 months (50 mm stage) and precedes bidirectionally (thus valve of Hasner opens last).

Amniocele and lacrimal sac mucocele are misnomers: they are really imperforate puncta and valve of Hasner with accumulation of lacrimal sac secretions (from goblet cells in the nonciliated pseudostratified columnar epithelium of the sac).

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