Lab Manual - 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. (explanation)
  2. Describe the components of the eyelids with associated muscles, tarsal glands, connective tissue fascia and conjunctiva. (explanation)
  3. Identify the extraocular muscles, their function and innervation. (explanation)
  4. Identify all sensory, motor and autonomic nerves of the orbit and trace their routes to and within the orbit. (explanation)
  5. Identify branches of ophthalmic arteries and veins. (explanation)

Readings and Modules:

Procedure:

1. Review the osteology of the bony orbit. (Play movie; View images: N 2A, 2B, 11, 81B, 81C, 82, 83, 87, TG 7-03, 7-04, -07, 7-57B, 7-57C, 7-58A, 7-58B, 7-58C, 7-64)

On a skull identify the orbital rim and orbit. Note the contribution from each of the following bones: frontal, zygomatic, maxillary, sphenoid, ethmoid, and lacrimal. Identify anterior lacrimal crest, lacrimal fossa and the fossa for the lacrimal sac, posterior lacrimal crest, anterior and posterior ethmoidal foramina, optic canal, superior and inferior orbital fissures. Consider shape and orientation of orbits.

Observe the following characteristics on the eyes of your partners: palpebral fissure, lateral angle (canthus, commissure) medial angle (canthus, commissure), lacrimal caruncle, lacrimal lake, semilunar fold, upper and lower lacrimal papillae and lacrimal puncta (pores), cornea, pupil, iris. On the cadaver pull the lids away from the bulb and define palpebral and bulbar conjunctiva and the fornices formed. Define conjunctival sac. Define tarsal glands and locate orifices and glands on the cadaver and your partner. Consider the flow of lacrimal fluid across the eye.

Surface anatomy of the eye

2. Skin the eyelid, exposing the orbicularis oculi muscle and its parts. (Play movie; View images: N 26, 81, TG 7-30, 7-57)

Skin the eyelids; note that the superficial fascia consists only of loose connective tissue with no fat. Define orbicularis oculi and its palpebral and orbital parts, differences? Clean the medial palpebral ligament. What is its attachment?

3. On one eyelid make a vertical incision in the superior lid to expose the tarsal plate and its relation to the conjunctiva and levator apparatus, and the lacrimal gland. (Play movie; View images: N 81B, 81C, 82, TG 7-57, 7-58B, 7-58C)

In one eyelid (one half of your specimen), cut vertically through the mid-point of the full thickness of the superior lid; on the cut surface, define its layers: muscular, tarsofascial layer (tarsal plate and orbital septum), insertion of levator palpebrae superioris muscle and its smooth (tarsal) muscle part, and the conjunctiva. In the lateral half locate the lacrimal gland; note its relation to the eyelid.

4. On the other half head reflect the orbicularis oculi down to expose the palpebral ligaments, lacrimal sac and nasolacrimal duct. (Play movie; View images: N 2, 26, 37, 81B, 81C, 82, TG 7-30, 7-43, 7-57B, 7-57C, 7-58B, 7-58C)

In the other half of your cadaver remove the orbicularis oculi muscle from the lid, turning it downward from the orbital rim to the palpebral fissure. With the muscle removed, define the tarsal plate and its attachments (the medial palpebral ligament and the lateral palpebral ligament) and the orbital septum. Demonstrate the levator palpebrae superioris. Cut through the tarsal plate of both lids and pull the medial half toward the nose. Strip the conjunctiva from their deep surfaces. Identify the small lacrimal part of orbicularis oculi. Where does it attach? What is the action of the lacrimal portion of the orbicularis oculi muscle? Return the lid to its normal position and cut through the medial palpebral ligament. Locate the lacrimal sac in the fossa for the lacrimal sac. Consider the lacrimal canaliculi and drainage to the lacrimal sac. Understand that the lacrimal sac drains into the lower portion of the nasal cavity via the nasolacrimal duct.

5. Remove the dura from the middle cranial fossa to expose the contents and lateral wall of the cavernous sinus. (Play movie; View images: N 11, 104A, 104B, TG 7-07, 7-47, 7-51, 7-60A, 7-60B)

Examine the cavernous sinus by carefully stripping the dura from the middle cranial fossa. Note the middle meningeal artery, its position in dura, its course and entrance through the foramen spinosum. Carefully remove the meningeal layer from the cavernous sinus and examine oculomotor nerve (III), trochlear nerve (IV), ophthalmic and maxillary divisions of trigeminal nerve (V1 and V2) in this layer. Also note the trigeminal ganglion and the mandibular division of the trigeminal nerve (V3) contained within a cleft of the dura. Remove the blood from the cavernous sinus and note trabeculae. Expose the internal carotid artery and, lying across it, the abducens nerve (VI).

6. Remove the roof and lateral wall of the orbit and cavernous sinus to expose the contents of the orbit and follow the nerves and vessels into it. (Play movie; View images: N 45, 70, 83, 85, 86A, 86B, 104A, 104B, 121, TG 7-29, 7-60A, 7-60B, 7-61A, 7-61B, 7-62, 7-73, 7-80)

Remove the dura from the anterior cranial fossa. Break a hole through the roof of the orbit. The bone is usually thin and you may find a mucosa-lined lateral extension of the frontal sinus and/or ethmoidal air cells within the roof. Gently push away the lining periosteum; remove the roof and lateral walls of the orbit and the bone from the boundaries of the optic canal and the superior orbital fissure. This will leave the orbital contents encased within the orbital periosteum (periorbita). Carefully remove the periorbita in all areas except the optic canal. Identify the frontal nerve (from V1) and its supraorbital and supratrochlear branches, lacrimal nerve (from V1), trochlear nerve (IV) (to what muscle?). Trace these nerves posteriorly through the superior orbital fissure to their source in the lateral wall of the cavernous sinus. Identify the superior ophthalmic vein.

7. Reflect the levator palpebrae superioris and superior rectus muscle and remove orbital fat to expose the orbital nerves and vessels. (Play movie; View images: N 41, 42, 82, 84A, 84C, 85, 86A, 86B, 121, TG 7-45AB, 7-45CD, 7-57, 7-59A, 7-59C, 7-61, 7-62A, 7-62B, 7-63A, 7-63B, 7-79C, 7-79D, 7-80)

Dissect the levator palpebrae superioris and superior rectus muscles. Cut them at their mid-point and reflect. Locate the nerve to both (superior division of oculomotor nerve (III)).

Dissect the superior oblique muscle. Locate the trochlear (IV) nerve. How can you test the action of the superior oblique muscle? Locate the nasociliary nerve (from V1) and its anterior ethmoidal branch (distribution?). Identify medial rectus. Now trace the nasociliary nerve backward, noting its relation to the optic nerve and looking for long ciliary nerves. Note the accompanying ciliary and ethmoidal branches of the ophthalmic artery.

Follow the lacrimal nerve forward to the lacrimal gland. Define the parts of the gland and show its relation to levator palpebrae superioris aponeurosis. Dissect the lateral rectus muscle to the muscular anulus. Note its two heads of origin. Cut through the upper one and locate the abducens nerve (VI). Trace it into the cavernous sinus. Pick up the nasociliary nerve and the superior division of the oculomotor nerve; trace them through the muscular anulus to the ophthalmic division of the trigeminal nerve and the oculomotor nerve, respectively. Now locate the inferior division of the oculomotor nerve and trace into the orbit. Note the relations of all of these nerves to the optic nerve and ciliary ganglion. Trace and define short ciliary nerves from ciliary ganglion to the bulb. Trace the ophthalmic artery through the orbit, noting course and relations. Into what does the superior ophthalmic vein drain?

8. Transect the optic nerve to reveal the central artery and relationships of the nerve sheaths. (Play movie; View images: N 70, 85A, 85C, 86, 87, 104A, 104B, TG 7-60A, 7-60B, 7-61B, 7-62, 7-64, 7-73)

Return to the optic canal, trace the optic nerve and the ophthalmic artery into the orbit. Cut the optic nerve; examine its sheath (meninges) and the central artery of the retina. How is the sheath formed? How far does the subarachnoid space extend? Now trace the remaining fibers of the inferior division of the oculomotor nerve to the medial rectus, inferior rectus, and inferior oblique muscles. The inferior oblique muscle can be located easily by cutting through the inferior lid near the lower border of the anterior lacrimal crest.

MRI of the eyeball and optic nerve
CT of the eyeball and optic nerve
MRI of eye muscles

Review the actions of the extraocular muscles from an anterior view of the bulb. Consider the actions of the muscles in reference to clinical testing and review their innervation.

Actions of the extraocular muscles