Upon completion of this session, the student will be able to:
- Identify the prominent bony features of the orbit with included foramina and fissures.
- Describe the components of the eyelids with associated muscles, tarsal glands, connective tissue fascia and conjunctiva.
- Identify the extraocular muscles, their function and innervation.
- Identify all sensory, motor and autonomic nerves of the orbit and trace their routes to and within the orbit.
- Identify branches of ophthalmic arteries and veins.
Learning Objectives and Explanations:
1. Identify the prominent bony featrues of the orbit with included
foramina and fissures. (N2, N11, TG7-03, TG7-57)
There are 7 bones that make up the orbit:
2. Describe components of eyelids with: muscles, tarsal glands, connective tissue fascia & conjunctiva. (N26, N81, N82, TG7-30, TG7-57, TG7-58A, TG7-58B, TG7-58C)
Orbit (bony): pyramidal-shaped space, formed by seven bones of the skull - four walls and an apex; medial walls are parallel and 2 cm apart, the space in between consists of the ethmoidal air cells and sphenoid sinus; the lateral walls diverge at 45 degrees from the medial walls, and left and right are 90 degrees apart; the margins of the orbital aperture are strong; the bone of the margins is much heavier than that of the walls within the cavity
- Frontal - entire roof of orbit. There are 3 prominent foramina to know in this region - the supraorbital notch
(superior margin) and the anterior and posterior ethmoidal
foramina (at junction of frontal/ethmoid bones). Nerves and vessels pass FROM the orbit TO the nasal cavity through these foramina
- Ethmoid bone - a very delicate bone in medial wall of orbit.
- Maxilla - medial wall and much of floor. Infraorbital groove is a deep groove on the orbital floor, where infraorbital n. lies. The
anterior lacrimal crest is on the medial margin. (note relation with sphenoid bone, info below)
- Lacrimal - very small bone; gives a crest - posterior lacrimal crest; between the post. and ant. crests is the fossa for the lacrimal sac (not to be confused with the lacrimal fossa of the roof of the orbit, where the gland is located under the frontal bone).
- Zygomatic - lateral margin and the rest of the floor
- Sphenoid - forms the apex;
there are a number of openings:
- medially: optic canal for optic n./ophthalmic a.
- laterally: superior orbital fissure for a number of nerves (III, IV, V1, VI) & superior ophthalmic v.; it separates the greater and lesser wings of this bone
- inferior orbital fissure between sphenoid and maxilla: through here brs. of maxillary nerve and artery pass; also veins from deep face region pass through here connecting with veins within orbit
- Palatine - not very important; however, note below under bony orbit, its small role in the floor of the orbit
Roof - orbital plate of frontal bone, and near the apex, lesser wing of the sphenoid bone; concave, especially laterally where the lacrimal fossa accommodates the lacrimal gland; the frontal sinus frequently extends over the roof of the orbit nearly to its apex
Lateral wall - formed in front by the zygomatic bone and behind by the greater wing of the sphenoid bone; the lateral wall, stronger, separates the orbit from the temporal fossa
Floor - slopes upward toward medial wall; formed by orbital surface of maxilla, supplemented laterally and anteriorly by the zygomatic bone and medially and posteriorly by the palatine bone; near the middle of the floor is the infraorbital groove extending forward from the inferior orbital fissure, ending in the infraorbital canal; the floor of the orbit is a bony separation between the orbit and the maxillary sinus
Medial wall - nearly vertical; consists of frontal process of the maxilla, the lacrimal bone and the orbital lamina of the ethmoid bone, and a small part of the body of the sphenoid bone; anteriorly the medial wall forms only a thin partition between the orbit and the ethmoidal air cells and sphenoid sinus
Openings - the principle openings of the orbit lie at the junction of its walls
Other features of the bony orbit
- Optic canal - junction of roof and medial wall; transmits ophthalmic artery and optic nerve (covered by meninges)
- Superior orbital fissure - upper lateral angle at apex of orbit; transmits CN III, IV, V1, VI, sympathetic fibers from cavernous plexus, and superior ophthalmic vein
- Inferior orbital fissure - junction of lateral wall and floor; from apex of the orbit 2/3rds distance to base; accommodates structures which have only an indirect relation to orbit, i.e., infraorbital nerve and artery, communication between inferior ophthalmic vein and pterygoid plexus, and infraorbital & zygomatic brs. of V2
- Other fissures/openings
- Supraorbital notch/foramen
- Zygomatico-orbital foramen for
zygomatico-orbital n. in lat wall
- Ant. & post. ethmoidal foramina
- Canal for nasolacrimal duct, leads inferiorly from lacrimal groove
- anterior lacrimal crest: see maxilla bone
- posterior lacrimal crest: see lacrimal bone
- lacrimal fossa: depression on roof laterally to accommodate the lacrimal gland
- anterior ethmoidal foramen: see frontal bone
- posterior ethmoidal foramen: see frontal bone
- optic canal: see sphenoid bone, and see below
- superior orbital fissure: see below
- inferior orbital fissure: see sphenoid bone, and see below
- periorbita (orbital periosteum): fascia surrounding the orbit and its contents
Orbicularis oculi m: sphincter m. of eyelids; the lacrimal portion of the orbicularis oculi m. is associated with the posterior offshoot of the medial palpebral ligament; a small fascicle of muscle fibers covers the deep surface of this band, arising from the posterior crest of the lacrimal bone; passing behind the lacrimal sac, the muscle divides into two slips for insertion into the medial parts of the tarsal plates of both lids ; fibers also attach to the lateral wall of the sac, creating a suction action when the lids are closed
3. Identify extraocular muscles, their function and associated innervation. (N84, N86, N121, TG7-59, TG7-61B, TG7-62A, TG7-62B, TG7-63A, TG7-63B)
Palpebral fissure: opening of eye itself; slit between two eyelids, a.k.a. palpebrae
- palpebral part: arises from the medial palpebral ligament, makes up the muscular layer of the eyelid; fibers run elliptically toward lateral palpebral raphe (where muscle bundles of the two lids intermingle)
- orbital part: surrounds the bony orbit
Lateral angle, canthus, commissure: lateral corner of eye
Medial angle, canthus, commissure: medial corner of eye; at this corner are the lacrimal caruncle, semilunar fold
Lateral palpebral ligament: attach the lateral portion of the tarsal plates to the zygomatic bone, deep to the raphe
Medial palpebral ligament: about 5mm long, arises from the frontal process of the maxilla, anterior to the lacrimal groove; extends lateralward into the eyelid in front of the lacrimal sac and divides; its parts continuous with the tarsal plates of the upper and lower eyelids; an offshoot of the ligament leaves its posterior surface lateral to the lacrimal sac and attaches to the posterior lacrimal crest of the lacrimal bone
Cornea: sclera, pupil, iris; the transparent cornea is dense, its surface is bulbar conjunctiva, is nonvascular and it is richly supplied with sensory nn from the ciliary nerves
- palpebral conjunctiva: the part of the conjuctiva that lines the inside of the lid
- bulbar conjunctiva: the part of the conjuctiva that covers the eyeball
- fornix: reflection of the conjunctiva from the eyeball to the eyelid; a potential space filled with nothing but tears; the lacrimal gland secretes tears and they fill this sac; superior fornix directly receives tears from the lacrimal gland through small ducts that empty from the deep lobe of the gland
Pupil: the central aperture of the iris; size is controlled by smooth muscle of the iris
Iris: thin, contractile membrane, having a central aperture, the pupil; within the loose stroma of the iris are two involuntary mm: sphincter pupillae m. (same parasympathetic innervation as the ciliary m.) and dilator pupillae muscle (sympathetic supply from superior cervical ganglion, reach the eye from the cavernous plexus through the short ciliary nn.); iris separates chambers of the eye, filled with aqueous humor
Lacrimal caruncle: mound of skin found at medial canthus (corner of eye)
Lacrimal lake: located in the medial canthus, collects tears as they distribute over eye through blinking
Semilunar fold: the edge of the lacrimal caruncle narrows out to form a thin fold of skin
Orbital septum: (the superior palpebral fascia in the upper lid and the inferior palpebral fascia in the lower lid), continuous with the periosteum of the bones of the superior and inferior margins of the orbit and ends in the anterior surfaces of the tarsal plates
- lacrimal papillae: slight elevations on the edge of the eyelids at the medial corner; in each of these is a little opening or punctum
- lacrimal puncta (pores): little openings in the lacrimal papillae; these openings drain fluid from the lacrimal lake by sucking the tears into the lacrimal canaliculi. The lacrimal fluid then passes through them into the lacrimal sac.
- lacrimal gland: produces tears, fills conjunctival sac; uppermost lateral part of the orbit, in the lacrimal fossa of the frontal bone; the gland is divided into superficial and deep parts by the levator palpebrae superioris m; on the deep lobe there are a number of small ducts that empty DIRECTLY into the superior conjunctival fornix
- lacrimal sac: tears sucked by lacrimal puncta from lake into canaliculi to the sac, where they drain on through the duct into the inferior meatus of the nasal cavity
- nasolacrimal duct: continuation of the lacrimal sac, extends downward and slightly lateralward and backward to the inferior meatus of the nose; occupies the nasolacrimal canal formed by the maxilla, the lacrimal bone and the inferior nasal concha, but traverses the mucous membrane of the nose obliquely, so that its opening is partially guarded by the lacrimal fold
Tarsal plates: dense fibrous plates of tarsofascial layer; inferior is narrower than superior; they give support and form to the eyelids; semilunar in shape; straight edge is at the lid margin; medially, tarsal plates are continuous with the bifurcated ends of the medial palpebral ligament; laterally they attach to the zygomatic bone by the lateral palpebral ligament, deep to the corresponding muscular raphe; embedded within, at the posterior surface, are the tarsal glands
Tarsal glands: embedded in the posterior surface of the tarsal plate in each lid; vertically arranged and parallel, they number ~30 in upper, a little less in lower; these glands secrete an oily substance that waterproofs the palpebral margins, so tears don't seep over the lid margins
Orbital sheath: when the optic nerve enters the orbit through the optic canal (sphenoid bone), it brings with it a meningeal coat of dura, arachnoid, and pia mater; these cover the nerve all the way to the back of the eyeball
Bulbar fascia: the fascia that covers the eye; forms a loose capsule within which the eyeball can move in all 3 axes of rotation; the sheath is continuous with the muscle sheaths that surround the various muscles of the eye; anchored to orbital margins via check ligaments
Muscle sheaths: the fascia covering the eye muscles, continuous with the bulbar fascia, and connects to the medial and lateral sides of orbit by check ligaments; this anchors the bulbar fascia to orbital margins by check ligaments
Check ligaments: connect muscle sheaths to sides of orbit; anchors bulbar fascia to orbital margins
Annulus: at apex of orbit, dense fascial ring, a.k.a. common ring tendon; surrounds both the optic canal and 1/2 superior orbital fissure; the four rectus mm. arise from it
Summary of eyelid:
- movable folds capable of closing in front of the eye, providing protection
- upper lid is larger, more movable (due to having an elevator muscle - levator palpebrae superioris)
- the eyelid is composed of five layers
- skin: thin
- subcutaneous tissue: lax, scanty, rarely contains fat; anterior edge of lid are cilia
(eyelashes); cutaneous nn. of eyelid = brs of V1 and brs. of infraorbital br. of V2; rich vascular supply
- muscular layer: mostly palpebral portion of orbicularis oculi m, arises from med palb lig
- tarsofascial layer: an important plane of division in the eyelid between a superficial
zone continuous with subcutaneous tissues of face/scalp and a deeper area
continuous with space of the orbit; this layer consists of:
- tarsus: dense fibrous plate; embedded within are the tarsal glands
- orbital septum: membrane
- conjunctiva: lines inner surface of each eyelid (palpebral) and is reflected over the
anterior portion of the sclera and cornea of the eyeball as the bulbar conjunctiva
There are 7 extraocular muscles - 6 that move the eyeball and 1 elevator of the upper eyelid.
All except inferior oblique muscle are at the apex of the orbit and pass forward at the sides of the eyeball. Of the 6 muscles that attach to the eyeball, 4 are straight (rectus) and 2 are oblique.
4. Identify nerves and trace them to and from cavernous sinus. (N86, N104, TG7-60A, TG7-60B)
Levator palpebrae superioris m.
As the uppermost extraocular muscle, it expands beneath the roof of the orbit and ends anteriorly in a wide aponeurosis
Origin: above and in front of optic canal
Insertion: superficial fibers - upper border of the superior tarsus (smooth muscle/ superior tarsal m.); deep layer of m. - ends in sup. fornix of conjunctiva
Innervation: III (sup. div.) Continuously active during waking hours except during closing of the lids
Simple lowering of the upper lid is accomplished by decrease of levator activity, but blinking is result of contraction of orbicularis oculi m.
Origin point for all 4 rectus muscles
Superior rectus m.
Elevates & Adducts (Up & In); rotates superior pole of eyeball medially
Inferior rectus m.
Insertion: sclera just posterior to cornea
Innervation: III (sup. div.)
Narrowest of rectus mm
Depresses & Adducts (Down & In) rotates superior pole of eyeball laterally
Medial rectus m.
Very inferior part of orbit
Innervation: III (inf. div.)
ADducts eye ONLY
Lateral rectus m.
Insertion: sclera just posterior to cornea
Innervation: III (inf. div.)
Broadest of rectus mm.
ABducts eye ONLY
Superior oblique m.
Origin: two heads - one on either side of sup orbital fissure; separated by the nerves and the ophthalmic vein that enter the orbit through the fissure
Insertion: tendinous expansion into sclera behind the margin of the cornea
Longest of rectus mm.
Depresses & Abducts (Down & Out); rotates superior pole of eyeball medially
Inferior oblique m.
Extreme medial upper part of orbit;
Origin: immediately above the optic canal, runs forward to trochlea, attached in the trochlear fovea of the frontal bone
Insertion: sclera behind the equator of eye
Runs forward, enters J-shaped ring of dense connective tissue: trochlea
Elevates & Abducts (Up & Out); rotates superior pole of eyeball laterally
Summary of Clinical Testing
Origin: near orbital margin
Innervation: III (inf. div.)
The only muscle that takes origin close to the orbital margin (the other 5 extraocular mm. take origin at apex); here it moves obliquely backward and inferior to attach to eyeball
Medial and lateral rectus can be tested by simply adducting and abducting the eye, respectively, looking for discrepancies in the degree of motion to one side or the other.
For the obliques and superior and inferior rectus, think of situps. People do bent-leg situps to prevent iliopsoas muscle from acting in trunk flexion, so that the six-pack muscles get a better workout. By flexing the hip, iliopsoas is prevented from doing its other action, trunk flexion.
Superior and inferior rectus can both adduct the eye in addition to elevating or depressing the gaze. So, prevent them from doing their second actions by doing the first - adduct the eye or turn the gaze inward toward the nose. Now the superior and inferior rectus are not able to do elevation or depression (just like bent-leg situps), so only superior oblique can depress the gaze, and only inferior oblique can elevate the gaze.
Turn the gaze outward, and now the oblique muscles are too short to do their other actions of elevation and depression. Ask the patient to look up or down to test superior or inferior rectus muscles.
The nerves of the orbit are the:
5. Identify branches of ophthalmic arteries and veins. (N85, N87, N70, TG7-62, TG7-73)
- 3 motor nn. to its muscles (CN III, IV, VI) [LR6, SO4, AO3]
- sensory ophthalmic division of CN V
- optic nerve arises in the retina of the eye, the other nn. enter the orbit through the sup. orbital fissure
- optic n. (CN II)
- ophthalmic n. (V1)
- frontal n. divides into the supraorbital n and supratrochlear n, which supply upper eyelid, forehead and scalp
- supraorbital n.
- supratrochlear n.
- nasocilliary n.: sensory nerve to the eye, supplies several brs. to the orbit
- anterior ethmoidal n. - terminal br. of nasocilliary, supply mucous membrane of the sphenoidal and ethmoidal sinuses and the nasal cavities, and the dura of the ant. cranial fossa
- long cilliary nn. - brs. of nasociliary n., transmit afferent fibers from the iris and cornea and some post-synaptic sympathetic fibers to dilator pupillae
- lacrimal n.: arises in lat wall of cavernous sinus, passes to the lacrimal gland, giving brs. to conjunctiva and skin of superior eyelid and providing secretomotor fibers from zygomatic n. (V2)
- oculomotor n. (CN III): aside from supplying most ocular mm., it supplies parasympathetic innervation to the sphincter pupillae m. of the iris and the ciliary m. of accommodation; it has 3 nerve components: somatic efferent (motor), general somatic afferent (to same mm), general visceral efferent (mm of iris and ciliary body with a synapse in the ciliary ganglion)
- superior division: sup. rectus/ levator palpebrae superioris m.
- inferior division: proceeds forward in orbit below optic n.; medial rectus, inferior rectus, inferior oblique & motor br. to ciliary ganglion
- trochlear n. (CN IV): smallest of CN's, supplies only one muscle - the sup. oblique; only CN that emerges from the dorsal aspect of the brainstem; most superior nerve entering in superior orbital fissure; in orbit it is medial to frontal nerve
- abducens n. (VI): like CN IV, it supplies only ONE muscle: the lat. rectus m.; enters the cavernous sinus by piercing the dura mater on the dorsum sellae of the sphenoid bone, turning over a notch in the bone below the posterior clinoid process; passing forward within sinus on lateral side of internal carotid a., enters orbit through the lower potion of the superior orbital fissure; at apex of orbit, passes between the two heads of origin of lateral rectus m., inferior to other nn. in this location
- preganglionics from oculomotor (III)
- cilliary ganglion: located between optic nerve and lat. rectus m, ~1cm from post limit of orbit; motor root from inf. br. of CN III, fibers contained in this root synapse in ciliary ganglion; the sensory root of ganglion is a br. of nasociliary n. of CN V1; the sympathetic root from the cavernous plexus passes to the ganglion adjacent to the sensory root; the nerve fibers of both the sensory and sympathetic roots pass through the ganglion WITHOUT synapsing; 6-10 short ciliary nn. leave ant. part of ganglion and course forward above and below optic nerve, to pierce the back of the eyeball
- short ciliary - postganglionic parasympathetics to sphincter pupillae and ciliary muscles of eyeball, postganglionic sympathetics to dilator pupillae
- postganglionic parasympathetics from pterygopalatine ganglion to lacrimal glands; preganglionics from facial, CN VII, via greater petrosal
Ophthalmic a.: branch of the intracranial portion of the internal carotid, as it emerges from the cavernous sinus; passes directly forward and enters orbit through optic canal, below and lateral to optic nerve; curves across optic nerve toward medial side of orbit, anteriorly; brs include:
Central artery of the retina,
Short posterior ciliary,
Long posterior ciliary,
Supratrochlear (terminal branch),
Doral nasal (terminal branch),
- central artery of retina (runs within optic nerve): is the first and one of the smallest branches; arises close to the optic canal and pierces optic near at the middle of its intraorbital course; accompanied central vein of retina; its brs on retina are: superior nasal, superior temporal, and inferior nasal and inferior temporal
- superior ophthalmic v.: begins in nasofrontal vein, enters orbit through supraorbital foramen (notch), after communicating with supraorbital vein; has tributaries which correspond to upper branches of ophthalmic a, usually joined by inf. ophthalmic vein at medial end of sup. orbital fissure; may leave head between two head of lat. rectus or above the muscular cone; ends in cavernous sinus; DOES NOT CONTAIN VALVES.
- cavernous sinuses: lie on either side of body of sphenoid, extend from sup. orbital fissure (in front) to the apex of petrous portion of temporal bone (in back); formed between the meningeal and periosteal layers of dura and trabeculae from each layer cross space, giving it a reticular (cavernous) structure; for more on this review item see page 325 in Woodburne and Burkel
- anterior cranial fossa: limited behind by post borders of lesser wings of sphenoid and groove for optic chiasma; floor is formed by orbital plates of frontal bone, cribriform plate of ethmoid and lesser wings and fore part of body of sphenoid; anterior midline is the crest of frontal bone leading to the foramen cecum, through which emissary vein passes from nasal cavity to beginning of sup. sagittal sinus; for more see page 319-320 WB.
Questions and Answers:
1. Define conjunctival sac. (N81, TG7-58)
See objective 2 above.
2. Define tarsal glands. (N81, TG7-58)
See objective 2 above.
3. What is the flow of lacrimal fluid across the eye? (N82, TG7-58)
Tears secreted from the lacrimal gland moves across eye via blinking, toward the medial canthus and lacrimal lake; drained off by lacrimal canaliculi; empty into lacrimal sac, then pass through nasolacrimal duct to inferior meatus of nasal cavity
4. Define orbicularis oculi m.: palpebral part vs. orbital part. What are differences? (N26, TG7-30, TG7-57, TG7-58)
*NOTE: when formed in normal amounts, the amount reaching nose evaporates; it is when the amount is increased (by emotion or other causes) that it flows from the nose
**NOTE: the parts of the lacrimal apparatus are: lacrimal gland; lacrimal canaliculi; lacrimal sac; nasolacrimal duct
The orbital part of orbicularis oculi surrounds the bony orbit, while the palpebral part extends into the lids.
5. What is the attachment of the medial palpebral ligament? (N81, TG7-57)
It attaches to the frontal process of the maxilla and extends into the eyelids to attach to both tarsal plates.
6. Define layers of superior lid. (N81, TG7-58)
Skin, subcutaneous tissue, palpebral part of orbicularis oculi, tarsofascial layer (tarsal plate attached to orbital septum, with tarsal glands embedded within plates), palpebral conjunctiva.
7. What is the relationship of lacrimal gland to eyelid? (N82, TG7-58B)
The lacrimal gland lies superolaterally in the bony orbit, deep to the conjunctival fornix.
8. Define tarsal plate and attachments. (N81, TG7-57, TG7-58)
The tarsal plates are attached to the medial and lateral palpebral ligaments and the orbital septum.
9. Define orbital septum. (N81, TG7-57)
The orbital septum is a fascial sheet extending from the orbital margins to the tarsal plates within the eyelids.
10. Where does the lacrimal part of orbicularis oculi attach? (N26, TG7-57)
The lacrimal part of orbicularis oculi arises from the lateral wall of the lacrimal sac and the bone posterior to it. It passes into the lids to insert on the tarsal plates.
10a. What is the action of the lacrimal portion of the orbicularis oculi muscle? (N26, TG7-57)
The lacrimal portion of the orbicularis oculi muscle pulls backward and holds the eyelids close against the eyeball. It also aids in dilating the lacrimal sac, creating a syphon-like action during blinking.
11. What is the drainage to the lacrimal sac? (N81, N82, TG7-43, TG7-58)
Lacrimal puncta drain the lacrimal fluid through lacrimal canaliculi into the lacrimal sac.
12. What muscles does the trochlear n. (CN IV) supply? (N86, N121, TG7-80)
Trochlear nerve innervates superior oblique muscle, which acts around a trochlea or pulley.
12a. How can you test the action of the superior oblique muscle? (N84, TG7-59)
To test the superior oblique muscle, the patient is asked, first, to direct the gaze medially and then down. By turning the gaze medially, the inferior rectus is shortened and prevented from performing its other action, turning the gaze down.
13. What is the distribution of anterior ethmoidal branch of the nasociliary nerve (V1)? (N86, N42, TG7-45, TG7-63)
Supplies twigs to ant. ethmoidal air cells; supplies internal nasal branches to mucosa of septum and nasal wall; ends as the external nasal br., supplies skin on lower half of the bridge of the nose (more pg 297 WB).
14. Define parts of lacrimal gland. (N82, TG7-58)
The orbital part of lacrimal gland lies in the lacrimal fossa of the orbital plate of the frontal bone. The palpebral part extends down into the lateral part of the upper lid by wrapping around the lateral margin of the levator palpebrae superioris.
15. What is the relation of lacrimal gland to levator palpebrae sup. aponeurosis? (N82, TG7-58)
The orbital part of the lacrimal gland lies superior to the aponeurosis, while the smaller palpebral part passes around the lateral edge of the aponeurosis and beneath it.
16.What is the innervation to the two heads of the lateral rectus m.? (N86, N121, TG7-63, TG7-86)
Abducens nerve (CN VI).
17. What are the relations of oculomotor and nasociliary nn. to optic n. and ciliary ganglion? (N86, N121, TG7-63)
The inferior division of the oculomotor nerve sends a short motor root up to the ciliary ganglion, which lies lateral to the optic nerve. The inferior division then passes anteriorly along the lateral edge of the inferior rectus. Nasociliary sends a branch to reach ciliary ganglion and then passes anteromedially superior to the optic nerve.
18. Define short ciliary nn. from ciliary ganglion to bulb. (N86, N121, TG7-62, TG7-79)
Short ciliary nerves carry postganglionic parasympathetics and sympathetics and sensory fibers from the ciliary ganglion to the back of the eyeball.
18b. What does the superior ophthalmic v. drain into? (N85, N104, TG7-61, TG7-73)
Cavernous sinus through the superior orbital fissure.
19. What are the actions of extraocular mm (ant. view?) (N84, TG7-59)
Superior oblique - turns pupil down and out (abducts & depresses)
20. With clinical testing of the mm., what are their actions and innervation? (N84, TG7-59)
Inferior oblique - up and out
Superior rectus - up and in
Inferior rectus - down and in
Medial rectus - in
Lateral rectus - out
See chart and explanation above.
21. How is the sheath (meninges) of optic n. formed? (N87, TG7-64)
The meninges pass through optic canal with the optic nerve.
22. How far does the subarachnoid space extend? (N87, TG7-64)
To the back of the eyeball.