Dissector Answers - Eye

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Identify the prominent bony features of the orbit with included foramina and fissures.
  2. Describe the components of the eyelids with associated muscles, tarsal glands, connective tissue fascia and conjunctiva.
  3. Identify the extraocular muscles, their function and innervation.
  4. Identify all sensory, motor and autonomic nerves of the orbit and trace their routes to and within the orbit.
  5. 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: 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
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
  • 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
Other features of the bony orbit
  • 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
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)
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 Palpebral fissure: opening of eye itself; slit between two eyelids, a.k.a. palpebrae

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

Conjunctival sac 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

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

Lacrimal apparatus 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

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:
3. Identify extraocular muscles, their function and associated innervation. (N84, N86, N121, TG7-59, TG7-61B, TG7-62A, TG7-62B, TG7-63A, TG7-63B)
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.

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.
Muscular annulus
Origin point for all 4 rectus muscles
Superior rectus m.
Elevates & Adducts (Up & In); rotates superior pole of eyeball medially
Origin: annulus
Insertion: sclera just posterior to cornea
Innervation: III (sup. div.)
Narrowest of rectus mm
Inferior rectus m.
Depresses & Adducts (Down & In) rotates superior pole of eyeball laterally
Very inferior part of orbit
Origin: annulus
Insertion: sclera
Innervation: III (inf. div.)
Medial rectus m.
ADducts eye ONLY
Origin: annulus
Insertion: sclera just posterior to cornea
Innervation: III (inf. div.)
Broadest of rectus mm.
Lateral rectus m.
ABducts eye ONLY
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
Innervation: VI
Longest of rectus mm.
Superior oblique m.
Depresses & Abducts (Down & Out); rotates superior pole of eyeball medially
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
Innervation: IV
Runs forward, enters J-shaped ring of dense connective tissue: trochlea
Inferior oblique m.
Elevates & Abducts (Up & Out); rotates superior pole of eyeball laterally
Origin: near orbital margin
Insertion: eyeball
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
Summary of Clinical Testing

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.
4. Identify nerves and trace them to and from cavernous sinus. (N86, N104, TG7-60A, TG7-60B)
The nerves of the orbit are the: Sensory Motor Autonomic
5. Identify branches of ophthalmic arteries and veins. (N85, N87, N70, TG7-62, TG7-73)
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, Lacrimal, Short posterior ciliary, Supraorbital, Long posterior ciliary, Posterior ethmoidal, Anterior ciliary, Anterior ethmoidal, Medial palpebral, Supratrochlear (terminal branch), Doral nasal (terminal branch), Muscular brs. Review:

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
*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
4. Define orbicularis oculi m.: palpebral part vs. orbital part. What are differences? (N26, TG7-30, TG7-57, TG7-58)
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)
Inferior oblique - up and out
Superior rectus - up and in
Inferior rectus - down and in
Medial rectus - in
Lateral rectus - out
20. With clinical testing of the mm., what are their actions and innervation? (N84, TG7-59)
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.