Clean the orbicularis oculi m., and examine the external eye and lacrimal apparatus - SUPERFICIAL

Find these structures:

• Orbicularis oculi m.

  • Palpebral part

  • Orbital part

• Palpebral fissure

  • Lateral angle (canthus) of eye

  • Medial angle (canthus) of eye

• Conjunctiva  

  • Palpebral conjunctiva

  • Bulbar conjunctiva

  • Conjunctival sac

  • Superior conjunctival fornix

  • Inferior conjunctival fornix

• Fibrous layer of eyeball

  • Sclera

  • Cornea

• Vascular layer of eyeball

  • Iris

    • Pupil

• Lacrimal apparatus

  • Lacrimal gland

  • Lacrimal canaliculi

  • Lacrimal papilla

  • Lacrimal puncta

  • Lacrimal sac

  • Lacrimal lake

  • Lacrimal caruncle

  • Nasolacrimal duct

1.) Clean the entirety of the orbicularis oculi m., if not previously completed. Skin both upper and lower eyelids. Distinguish the palpebral part from the orbital part of the muscle.

Note: The orbicularis oculi m. is a sphincteric, circumferential muscle of three parts (orbital, palpebral, and lacrimal), surrounding the orbit. The orbital part encircles the palpebral part. The palpebral part is typically involuntarily controlled (blinking), whereas the orbital part is typically voluntarily controlled (shutting the eyes tightly). The lacrimal part connects the posterior crest of the lacrimal bone and lacrimal sac to medial aspects of the tarsal plates of upper and lower eyelids. The orbicularis oculi m. is innervated by temporal and zygomatic brs. of the facial n. (CN VII).

Photo 1. Orbicularis oculi m.

2.) Examine the palpebral fissure and lateral and medial angles of the eye.

Note: The palpebral fissure is the opening between the eyelids (palpebrae). The margins of the palpebral fissure are the medial and lateral angles (canthi). The medial angle is the more significant of the two angles due to the lacrimal system.

Photo 2. Palpebral fissure, medial & lateral angles

3.) Make a mid-sagittal cut through the upper eyelid and lower eyelid. Reflect the four portions of the eyelids away from the eye, and use a blunt probe to investigate aspects of the conjunctiva and conjunctival fornices.

Photo 3. Procedural: cutting the eyelids

Note: The conjunctiva is a delicate mucous membrane that lines the eyelids and covers the anterior aspect of the eyeball (excepting the cornea and pupil). The bulbar conjunctiva covers the eyeball, and the palpebral conjunctiva lines the eyelids. The conjunctival fornices (superior and inferior) are the reflections of conjunctiva from bulbar to palpebral conjunctiva, and the conjunctival sac is the potential space between bulbar and palpebral conjunctiva.

Photo 4. Conjunctiva

4.) Distinguish the sclera and cornea of the fibrous layer of the eyeball. Identify the iris and the pupil of the vascular layer of the eyeball.

Note: The fibrous layer of the eye is important in providing structure and strength to the eyeball. The two main structures include the sclera and cornea. The sclera covers the majority of the eyeball, is often referred to as the “white of the eye,” and is the insertion site for extra-ocular and intrinsic eye muscles. The cornea covers the anterior portion of the eye (approximately ⅙th of the anterior eye - Moore et al., 7th edition), is completely avascular, and sensitive to touch.

Note: The vascular layer of the eye (uvea) is composed of 3 structures: choroid, ciliary body, and iris. The iris is a diaphragm located on the anterior surface of the lens. The pupil, an aperture important in transmitting light, is located centrally in the iris. The iris is can appear various colors, while the pupil is black. The pupil is controlled by two muscles: sphincter pupillae (contracts pupil, parasympathetically-controlled) and dilator pupillae (dilates pupil, sympathetically-controlled).

Photo 5. Eye features

5.) Locate the lacrimal gland in the superolateral portion of the orbit. Visualize the route of lacrimal fluid to the medial portion of the eye, and identify the lacrimal caruncle, lacrimal lake, and lacrimal papilla and puncta.

Photo 6. Lacrimal gland, caruncle, papilla/puncta, and lake

Photo 7. Lacrimal caruncle and lake

6.) Remove the medial palpebral ligament from its attachment point on the maxilla, and expose the lacrimal canaliculi (very small and difficult to identify) and lacrimal sac. Open the lacrimal sac to expose the nasolacrimal duct.

Note: The lacrimal system begins with the lacrimal gland, located in the superolateral margin of the orbit. The lacrimal gland rests in the lacrimal fossa of the frontal bone, and sits between the aponeurosis for levator palpebrae superioris m. (medial to the gland) and the lateral rectus m. (inferior to the gland). The lacrimal gland secretes into the conjunctival sac along the lateral margin of the superior fornix. Tear fluid is conducted across the conjunctiva and accumulates in the lacrimal lake in the medial canthus. Deep to the lacrimal lake is a mound of skin, the lacrimal caruncle. Superior and inferior to the lacrimal lake are lacrimal papillae, which host small lacrimal puncta (pores) into which tear fluid flows. Fluid is conducted from the puncta via superior and inferior canaliculi into the lacrimal sac, the superior dilation of the nasolacrimal duct. The lacrimal sac lies in the lacrimal groove of the lacrimal bone. The nasolacrimal duct conducts tear fluid into the inferior nasal meatus.

Note: Route of lacrimal fluid: lacrimal gland → conjunctival sac → lacrimal lake → lacrimal papillae → lacrimal puncta → lacrimal canaliculi (superior & inferior) → lacrimal sac → nasolacrimal duct → inferior nasal meatus

Photo 8. Lacrimal canaliculi, sac, nasolacrimal duct

Remove the orbicularis oculi m., and examine the tarso-fascial layer - DEEP

Find these structures:

• Lateral palpebral ligament

• Medial palpebral ligament

• Tarso-fascial layer of eyelids

  • Orbital septum

  • Superior tarsus (tarsal plate)

  • Inferior tarsus (tarsal plate)

  • Tarsal glands

• Extra-ocular muscle

  • Levator palpebrae superioris m.

    • Superior tarsal m.

7.) On the opposite side of the face, remove the orbicularis oculi m., and gently clear the subcutaneous connective tissue to reveal the insertion of levator palpebrae superioris m. and the tarso-fascial layer of the eyelids.

Note: The eyelids, layered from superficial-to-deep, include: skin, subcutaneous tissue, palpebral fibers of orbicularis oculi m. and associated connective tissues, a tarso-fascial layer, and palpebral conjunctiva (which rests upon the orbital conjunctiva of the eye). The edge of the eyelids host eyelashes and associated glands.

Note: The tarso-fascial layer of the eye consists of: tarsal plates, associated (tarsal) glands & ligaments, the orbital septum, and the insertion for the levator palpebrae superioris m. on the superior tarsal plate. The medial and lateral palpebral ligaments attach the upper and lower eyelids to the medial and lateral margins of the orbit.

Note: The levator palpebrae superioris m. attaches the apex of the orbit to the superior tarsal plate and tarso-fascial layer of the eyelid. Innervated by the oculomotor n. (CN III), when active, the muscle elevates the upper eyelid to open the eye. The levator palpebrae superioris m. is supplied by the ophthalmic a.

Note: A small layer of smooth muscle, the superior tarsal m., is located deep to the levator palpebrae superioris m. and inserts on the superior tarsal plate. Sympathetic fibers derived from perivascular plexuses of the ICA are typically transmitted to the superior tarsal mm. by the oculomotor n. (CN III).

Photo 9. Tarso-fascial layer of the eyelid

Examine the contents of the middle cranial fossa - BOTH

Find these structures:

• Cavernous sinus

• Internal carotid a.

• Cranial nerves

  • Optic n. (CN II)

  • Oculomotor n. (CN III)

  • Trochlear n. (CN IV)

  • Trigeminal n. (CN V)

    • Ophthalmic n. (V1)

    • Maxillary n. (V2)

    • Mandibular n. (V3)

  • Abducens n. (CN VI)

8.) Carefully strip away the dura mater in the middle cranial fossa. Take care to only remove the meningeal layer of the dura covering the cavernous sinus, and do not interrupt cranial nerves: III, IV, V1, and V2.

Note: The cavernous sinuses are relatively expansive dural venous sinuses lateral to the sella turcica, extending between the superior orbital fissures (anteriorly) and the apices of the petrous part of the temporal bones (posteriorly). Tributaries of these sinuses include ophthalmic vv., sphenoparietal sinuses, and superficial middle cerebral vv. The cavernous sinuses drain into the petrosal sinuses. Structures traversing the cavernous sinus include: the internal carotid a., abducens n. (CN VI), and internal carotid plexus of sympathetic nn. The oculomotor (CN III), trochlear (CN IV), and the ophthalmic (V1) and maxillary (V2) divisions of the trigeminal n. (CN V) are located in the lateral walls (meningeal layer of dura mater) of the cavernous sinuses. Cavernous sinus thromboses may endanger these structures.

9.) Remove any coagulated blood from the cavernous sinus to locate the abducens n. (CN VI) and the internal carotid a. Investigate the neurovasculature located in the lateral wall of the cavernous sinus: oculomotor n. (CN III), trochlear n. (CN IV), ophthalmic n. (V1), and maxillary n. (V2). The mandibular n. (V3) is located in the vicinity, exiting through the foramen ovale.

Photo 10. Middle cranial fossa

Examine the contents of the orbit from a superior approach - DEEP

Find these structures:

• Nerves:

  • Optic n. (II)

  • Oculomotor n. (CN III)

    • Superior branch

    • Inferior branch

    • Branch to ciliary ganglion

  • Ciliary ganglion

    • Short ciliary nn.

  • Trochlear n. (CN IV)

  • Ophthalmic n. (V1)

    • Lacrimal n.

      • Communicating br. with zygomatic n.

    • Frontal n.

      • Supra-orbital n.

        • Lateral branch

        • Medial branch

      • Supratrochlear n.

    • Nasociliary n.

      • Long ciliary nn.

      • Posterior ethmoidal n.

      • Anterior ethmoidal n.

        • External nasal n.

      • Infratrochlear n.

    • Abducens n. (CN VI)

• Muscles

  • Levator palpebrae superioris m.

  • Common anular tendon (common tendinous ring)

  • Superior rectus m.

  • Inferior rectus m.

  • Medial rectus m.

  • Lateral rectus m.

  • Superior oblique m.

    • Trochlea

• Vasculature

  • Ophthalmic a.

    • Central retinal a.

    • Posterior ethmoidal a.

    • Anterior ethmoidal a.

  • Superior ophthalmic v.

  • Inferior ophthalmic v.

10.) If not done previously, remove the scalp from the frontal bone.

Photo 11. Procedural: preparing the cranium

11.) To visualize the contents of the orbit, strip the dura mater from the anterior cranial fossa, then remove the roof of the orbit (the orbital surface of the frontal bone). Using bone shears, make two cuts in the frontal bone, as demonstrated in the visuals below. BE SURE TO WEAR APPROPRIATE EYE PROTECTION WHEN CUTTING AND REMOVING BONE.

Photo 12. Procedural: cutting the frontal bone

12.) With firm pressure, gently reflect the portion of the frontal bone between the cuts anteroinferiorly. If necessary, you may make a third cut midway between the two cuts. Be aware that you want to preserve the supra-orbital neurovasculature (located near the medial-most cut) and the lacrimal gland (located near the lateral-most cut). The goal is to fracture the frontal bone at the junction of the orbital plate and the facial portion of the bone.

Photo 13. Procedural: reflecting the frontal bone fragment

13.) It is impossible to predict exactly how the frontal bone will fracture, so further dissection is opportunistic. Using a combination of forceps, hemostats, and small bone shears, remove portions of the orbital surface until the entire orbit is exposed superiorly. Continue to remove bone to uncover the superior orbital fissure.

Photo 14. Superior view of orbit

14.) Using fine forceps, remove the orbital adipose connective tissue to uncover the most superior layer of neurovasculature and muscles: frontal n. (with branches supratrochlear n. and supra-orbital n.), trochlear n. (CN IV), lacrimal n., levator palpebrae superioris m., and superior oblique m.

Note: The frontal nerve is the largest branch of V1. It afferently serves the medial upper eyelid (skin & conjunctiva), skin of the forehead, and frontal sinus mucosa. A prominent feature of the superior orbit, the frontal n. may be found superior to the levator palpebrae superioris m.

Note: The frontal n. divides about midway through the orbit into the supra-orbital (lateral) and supratrochlear (medial) nn. The supratrochlear n. passes superior to the trochlea of the superior oblique m. to afferently serve the skin of the medial forehead, and skin and conjunctiva of the medial superior eye. The supra-orbital n. further divides into medial and lateral branches, which afferently serve the mucosa of the frontal sinus, skin of the lateral forehead, and skin and conjunctiva of the lateral superior eye. Branches of the supra-orbital n. may be seen exiting the cranium via the supra-orbital foramen or notch.

Note: The levator palpebrae superioris m. attaches the apex of the orbit to the superior tarsal plate and tarso-fascial layer of the eyelid. Innervated by the superior division of oculomotor n. (CN III), when active, the muscle elevates the upper eyelid to open the eye. The levator palpebrae superioris m. is supplied by the ophthalmic a.

Photo 15. Superior view of orbit

Note: The superior oblique m. originates on the sphenoid bone at the apex of the orbit, above the origin of the superior rectus m. The body of the superior oblique m. is one of the most superomedial structures in the orbit. The distal tendon of the superior oblique m. runs through the trochlea, a fibrocartilaginous loop (pulley) that attaches to the trochlear fossa of the frontal bone, before inserting on the posterosuperior sclera of the eye. This muscle is innervated by the trochlear n. (CN IV), and plays a role in abduction, depression, and intorsion (medial rotation) of the eye.

Note: The trochlear n. (CN IV) is the smallest cranial nerve and the only nerve to arise from the dorsal aspect of the brainstem. The trochlear n. travels within the lateral wall of the cavernous sinus, enters the orbit through the superior orbital fissure, and travels along the medial wall of the orbit to innervate the superior oblique m. This nerve is generally easiest to locate running deep to the posterior-most aspect of the superior oblique m.

Photo 16. Superior view of orbit

Note: The lacrimal n. (V1) is the smallest branch of the frontal n. The lacrimal n. enters the orbit through the superior orbital fissure, and may be found superior to the lateral rectus m., en route to the lacrimal gland.

Note: Anatomists have classically understood (and taught) that the secretomotor postganglionic fibers to the lacrimal gland were conducted by the lacrimal n. from fibers transmitted from the pterygopalatine ganglion via the zygomaticotemporal brs. (i.e. pterygopalatine ganglion → zygomaticotemporal brs. → lacrimal n. → lacrimal gland). Recent studies show considerable variation in the course of these fibers, with the majority of cases demonstrating secretomotor postganglionic fibers from the pterygopalatine ganglion directly innervating the lacrimal gland via the zygomaticotemporal brs. Variants do exist that reflect the ‘classical condition.’

Photo 17. Superior view of orbit

15.) Cut the levator palpebrae superioris m. approximately at its midpoint, and reflect the bulk of the body of the muscle anteriorly and posteriorly to better reveal the superior rectus m.

Note: The superior rectus m., like the other rectus muscles, originates from the common anular tendon (common tendinous ring), and inserts on the sclera of the superior eye. The common anular tendon surrounds the optic n. (CN II), oculomotor n. (CN III), and abducens n. (CN VI). The superior rectus m. is innervated by the superior division of the oculomotor n. (CN III). The superior rectus m. elevates and adducts the eye. The superior rectus m. also produces intorsion of the eye.

Note: The orbit is not a symmetric cone, nor does the eye gaze perfectly outward from the apex of the cone. As such, extra-ocular mm. may exert additional, rotational forces upon the eye. As an example, the superior rectus m. both elevates and adducts the eye. This adduction demonstrates such a rotational force.

Photo 18. Superior view of orbit

16.) Cut the superior rectus m. near its insertion on the sclera, and reflect the bulk of the body posteriorly. Locate the lateral rectus m. and the abducens n. (CN VI).

Note: The lateral rectus m. originates from the common anular tendon, and inserts on the sclera of the lateral eye. The lateral rectus m. is innervated by the abducens n. (CN VI). The lateral rectus m. abducts the eye.

Note: The abducens n. (CN VI) arises from the brainstem, travels through the cavernous sinus, and enters the orbit through the superior orbital fissure (and also through the common anular tendon). The abducens n. innervates the lateral rectus m. (i.e. the ABDUCens ABDUCts the eye).

Photo 19. Superior view of orbit

17.) Move the superior oblique m. as medially as possible in order to better view the medial rectus m. If needed, the superior oblique m. may be reflected while preserving the surrounding neurovasculature.

Note: The medial rectus m. originates from the common anular tendon, and inserts on the sclera of the medial eye. The medial rectus m. is innervated by the inferior division of the oculomotor n. (CN III). The medial rectus m. adducts the eye.

Photo 20. Superior view of orbit

18.) Clean the neurovasculature deep to the superior oblique m. This includes: ophthalmic a. (and its branches - anterior and posterior ethmoidal aa.) and vv (superior & inferior)., and nasociliary and its branches (anterior and posterior ethmoidal nn., infratrochlear n., long ciliary nn.).

Note: The ophthalmic a. branches from the internal carotid a. after the ICA emerges from the cavernous sinus. The ophthalmic a. enters the orbit through the optic canal and branches to supply the structures of the orbit. The bulk of the ophthalmic a. may be found between the superior oblique m. and the medial rectus m., along the medial border of the orbit, and the many smaller branches typically accompany their namesake V1 branches (e.g. lacrimal, ant./post. ethmoidal, supra-orbital, supratrochlear, etc.). The ophthalmic a. gives rise to the central artery of the retina, which is bundled with the optic n. (CN II).

Note: The superior ophthalmic v. drains blood from the eye, superior orbit, ethmoidal cells, forehead, and the angular v. of the face. The inferior ophthalmic v. collects blood from the face and inferior orbit. Both the superior and inferior ophthalmic vv. may be valveless (there are instances of these vv. having valves), and may transport blood from the face to the cavernous sinus.

Photo 21. Superior view of orbit

Note: The nasociliary n. branches from V1 in the superior orbital fissure. The nasociliary n. gives rise to:

• long ciliary nn.,

• anterior & posterior ethmoidal nn.,

• infratrochlear n., and

• a communicating branch to the ciliary ganglion transmitting afferent fibers from the eye via short ciliary nn.

Note: The long ciliary nerves arise from the nasociliary n. (V1) in the vicinity of the optic n. (CN II). These branches carry afferent fibers from the eye and postganglionic sympathetic fibers to the dilator pupillae muscle of the eye.

Note: The anterior and posterior ethmoidal nn. exit through the anterior and posterior ethmoidal foramina, respectively.

Note: The infratrochlear n. provides sensory innervation to conjunctiva, skin of eyelids, lacrimal caruncle and sac, and side of nose. This nerve can be seen exiting the orbit below the trochlea of the superior oblique m.

Photo 22. Superior view of orbit

19.) Locate the optic n. (CN II), ciliary ganglion, and short ciliary nn. The ophthalmic v. will need to be moved or reflected to locate these structures.

Note: Optic n. (CN II) travels through the optic canal to enter the orbit and pierce the sclera. This is the most obvious structure in this area. This cranial nerve is special somatic afferent and functions in vision.

Note: The ciliary ganglion is a peripheral parasympathetic ganglion for intra-ocular muscles, typically located on the lateral aspect of the optic n. (CN II) near the apex of the orbit. The ciliary ganglion has three conduits to/from the remainder of the PNS:

• nasociliary n. (of V1) - transmits afferent fibers from the eye through the ganglion to the nasociliary n.,

• oculomotor n. (CN III) - transmits preganglionic parasympathetic fibers to the ciliary ganglion, and

• sympathetic - postganglionic sympathetic fibers are transmitted to (and through) the ciliary ganglion from perivascular plexuses of the internal carotid a. These fibers may also associate with the oculomotor n.

The ciliary ganglion communicates with the eye via the short ciliary nn.

Note: The short ciliary nn. transmit three types of fibers between the eye and the ciliary ganglion:

• afferent fibers from the eye, through the ganglion, to the nasociliary n. (V1),

• postganglionic parasympathetic fibers from the ganglion (preganglionics from oculomotor) to the ciliary muscles and sphincter pupillae muscles, and

• postganglionic sympathetic fibers (from perivascular plexuses) to the intra-ocular vessels.

Photo 23. Superior view of orbit

20.) Distinguish between the superior and inferior divisions of the oculomotor n. (CN III).

Note: The oculomotor n. (CN III) arises from the midbrain, travels within the lateral wall of the cavernous sinus, divides into superior and inferior divisions, and these divisions enter the orbit through the superior orbital fissure (and also through the common anular tendon). The superior and inferior divisions are typically separated by the nasociliary n. (of V1) and the optic n. (CN II).

The superior division of oculomotor n. efferently innervates:

• levator palpebrae superioris m., and

• superior rectus m.

The inferior division of oculomotor n. efferently innervates:

• medial rectus m.,

• inferior rectus m.,

• inferior oblique m., and

• transmits preganglionic parasympathetic fibers to:

  • ciliary ganglion (for sphincter pupillae muscles and ciliary muscles).

Photo 24. Superior view of orbit

21.) Cut a short (<1 cm) section of the optic n. Examine the optic n. in cross section to see the central artery of the retina.

Note: The central artery of the retina is the first branch of the ophthalmic a. The central artery of the retina enters the dural sheath of the optic n. (CN II) and travels within the nerve to the retina.

Photo 25. Procedural: excising a piece of the optic n.

Photo 26. Transverse section of the optic n.

22.) Move neurovasculature to locate and clean the inferior rectus m. The inferior oblique m. is often difficult to see in the superior view.

Note: The inferior rectus m. originates from the common anular tendon (common tendinous ring), and inserts on the sclera of the inferior eye. The inferior rectus m. is innervated by the inferior division of the oculomotor n. (CN III). The inferior rectus m. depresses, adducts, and produces extorsion (lateral rotation) the eye.

Note: The inferior oblique m. originates from the orbital surface of the maxilla on the floor of the orbit, and inserts on the sclera of the inferior eye. The inferior oblique m. is innervated by the inferior division of the oculomotor n. (CN III). The inferior oblique m. elevates, abducts, and produces extorsion (lateral rotation) the eye.

Photo 27. Superior view of orbit

Examine the contents of the orbit from an anterior (surgical) approach - SUPERFICIAL

Find these structures:

• Lacrimal gland

• Muscles

  • Levator palpebrae superioris m.

  • Common anular tendon

  • Superior rectus m.

  • Inferior rectus m.

  • Medial rectus m.

  • Lateral rectus m.

  • Superior oblique m.

  • Inferior oblique m.

23.) On the side of the head with an intact orbital roof, remove the orbicularis oculi m. and the tarso-fascial layer of the eye. Cut the levator palpebrae superioris m. at its attachment to the superior tarsal plate. Cut both (medial and lateral) palpebral ligaments, and bluntly separate the orbital septum. As necessary, incise around the conjunctiva, and remove any palpebral conjunctiva.

24.) Clean the extra-ocular eye mm.: the recti and oblique muscles.

Photo 28. Orbit

25.) Enucleate (remove) the eye. Locate the insertions for the four rectus muscles and two oblique muscles on the eye, and using a combination of forceps and scissors, cut each insertion as near to the eye as possible. Finally, using scissors, cut the optic n. (CN II) near the eye.

Photo 29. Orbit post-enucleation

Photo 30. Orbit post-enucleation

26.) Using forceps, carefully remove orbital adipose to best visualize and appreciate the muscles and neurovasculature of the orbit. In particular, locate the common anular tendon. Note the relationships of the extra-ocular muscles to the common anular tendon and the elements of neurovasculature that pass through the tendon.

Note: The common anular tendon (common tendinous ring) is the origin site for the rectus muscles. The ring encircles the optic nerve (CN II), superior and inferior divisions of the oculomotor n. (CN III), and abducens n. (CN VI).

Photo 31. Posterior orbit