S10 Dissection Summary

S10 Dissection Summary

Part 1

    • Clean the entirety of the orbicularis oculi m., if not previously completed
    • Examine the palpebral fissure and lateral and medial angles of the eye
    • Reflect the four portions of the eyelids away from the eye
        • investigate aspects of the conjunctiva and conjunctival fornices
            • blunt dissection
    • 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
    • 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
            • lacrimal papilla and puncta
    • Remove the medial palpebral ligament from its attachment point on the maxilla

Part 2

    • On the opposite side of the face, remove the orbicularis oculi m.

Part 3

    • 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:
        • Oculomotor nn. (CN III)
        • Trochlear nn. (CN IV)
        • Trigeminal nn. (V1, and V2)
    • 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)
        • maxillary n. (V2).
        • The mandibular n. (V3) is located in the vicinity, exiting through the foramen ovale

Part 4

    • If not done previously, remove the scalp from the frontal bone
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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).
    • 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.
    • 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 n. and its branches (anterior and posterior ethmoidal nn., infratrochlear n., long ciliary nn.).
    • 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.
    • Distinguish between the superior and inferior divisions of the oculomotor n. (CN III).
    • 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.
    • Move neurovasculature to locate and clean the inferior rectus m. The inferior oblique m. is often difficult to see in the superior view.

Part 5

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