Prelab Images - Eye

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Review the osteology of the bony orbit. (Play movie)

Plate N2 or TG7-03 and TG7-57 shows the bony rim and orbit and the bones that form it (frontal, zygomatic, maxillary, sphenoid, ethmoid, and lacrimal). The fossa for the lacrimal sac (labeled in plate N2 or TG7-04) is formed by the anterior and posterior lacrimal crests (can be seen in plate N2 or TG7-04). Plate N11 or TG7-57 labels the anterior and posterior ethmoidal foramina and identifies the structures that pass through them. The optic canal is seen in plate N2 or TG7-57 and N11 or TG-07. The superior and inferior orbital fissures can be seen in plates N2 or TG7-57, N11 or TG7-03, and N83. The palpebral fissure is the line that is formed when upper and lower eyelids are closed (shown, but not labeled in plate N81 or TG7-57, bottom). The lateral and medial canthi are essentially the lateral and medial corners where the eyelids come together when the eye is open (plate N81 or TG7-58, top unlabeled). The lacrimal caruncle, lacrimal lake, and semilunar fold (plica semilunaris) are labeled in plates N81 or TG7-58 (top) and N82. Plate N81 or TG7-58 labels upper and lower lacrimal papillae and punctae. The cornea, pupil, and iris are seen in plate N81 or TG7-58 and N87 or TG7-64. Plate N81 or TG7-58C (middle) shows the palpebral conjuctiva reflecting onto the eyeball to become bulbar conjunctiva and form a fornix in the process. Looking at the conjunctiva in plate N81 or TG7-58C (middle) you can see that it forms a sac. Tarsal glands are identified in plate N81 or TG7-58C. Plate N82 or TG7-58B traces lacrimal fluid across the eye from lacrimal gland to the nasolacrimal duct.

Step 2. Skin the eyelid, exposing the orbicularis oculi muscle and its parts. (Play movie)

Remove the skin from the eyelids carefully because there is no fat beneath it. Plate N26 or TG7-30 defines the orbicularis oculi muscle and its palpebral and orbital parts. Plate N81 or TG7-57 labels the medial palpebral ligament.

Step 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)

In one eyelid, cut fully through the mid-point of the superior lid vertically. Plate N81 or TG7-58 shows the layers of the eyelid: skin, orbicularis oculi muscular layer, tarsofascial layer (composed of tarsal plate and orbital septum seen in plate N81 or TG7-57, bottom), insertion of levator palpebrae superioris and its smooth tarsal muscle part (plate N81 or TG7-58C), and conjunctiva. Plate N81 or TG7-57 labels the superior and inferior tarsal plates. Plate N82 or TG7-58B shows the location of the lacrimal gland.

Step 4. On the other half head reflect the orbicularis oculi down to expose the palpebral ligaments, lacrimal sac and nasolacrimal duct. (Play movie)

On the other eyelid remove the orbiculis oris muscle from the rim of the orbit and reflect it downward toward the palpebral fissure (N26 or TG7-30). This should expose the superior tarsal plate and orbital septum (plate N81 or TG7-57). Plate N81 or TG7-57 identifies the tarsal plate, medial and lateral palpebral ligaments, and the insertion of levator palpebrae superioris into the eyelid. Cut through the tarsal plate of both lids and pull the medial half towards the nose. Strip the conjunctiva off of the deep side of the tarsal plate (N81 or TG7-58). Now identify a part of the orbicularis oculi muscle that attaches to the lacrimal sac (you can see these muscle fibers if you look closely at plate N26 or TG7-57). Next, cut through the medial palpebral ligament (N81 or TG7-57) to locate the lacrimal sac. Plate N82 or TG7-58B labels the nasolacrimal duct and lacrimal sac. The lacrimal sac resides in the fossa for the lacrimal sac (N2 or TG7-57). Plate N37 or TG7-43 and N82 shows the opening of the nasolacrimal duct into the nose just into the inferior meatus.

Step 5. Remove the dura from the middle cranial fossa to expose the contents and lateral wall of the cavernous sinus. (Play movie)

Plate N104 or TG7-51 shows the location of the middle meningeal artery as it comes through the foramen spinosum (N11 or TG7-07). This plate also shows the oculomotor nerve (III), trochlear nerve (IV), ophthalmic division of the trigeminal nerve (V1), maxillary division of the trigeminal nerve (V2), mandibular division of the trigeminal nerve (V3), and trigeminal ganglion in the vicinity of the cavernous sinus. Remove blood from the cavernous sinus and identify the internal carotid artery and the abducens nerve (VI) lying next to it (N104 or TG7-47). It is important to note that the abducens nerve (VI) and internal carotid artery travel through the center of the cavernous sinus while cranial nerves III, IV, V1, and V2 all line the lateral walls of the sinus (see plate N104 or TG7-60A and TG7-60B).

Step 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)

Next, you must break through the roof of the orbit and remove the bone of the roof and the lateral wall of the orbit (the bone is very thin and easy to chip away at). Also, remove the bone from the boundaries of the optic canal and superior orbital fissure. When all of this is done you should have a view similar to plate N86 or TG7-61A. Remove the orbital periosteum in all areas except for the orbital canal. Plates N86 or TG7-61B and N45 or TG7-62 identify the frontal nerve and lacrimal nerve branches of the ophthalmic nerve (V1). The frontal nerve has supraorbital and supratrochlear branches (N86 or TG7-61, N45 or TG7-29). Plates N86 and N121 or TG7-80 show the trochlear nerve (IV) innervating the superior oblique muscle. Plate N104 once again shows the position of the nerves (III, IV, V, and VI) traced back to the cavernous sinus. Plate N83 or TG7-60A or TG7-60B shows the relationships of the nerves to each other as they pass through the superior orbital fissure. Plates N70, N85 , and N104 or TG7-61B or TG7-73 identify the superior ophthalmic vein.

Step 7. Reflect the levator palpebrae superioris and superior rectus muscle and remove orbital fat to expose the orbital nerves and vessels. (Play movie)

Plates N84 or TG7-62 and N86 identify the levator palpebrae superioris and superior rectus muscles. Cut through the muscles at their midpoint and reflect. These two muscles are innervated by the superior division of the oculomotor nerve (see plates N86 and N121 or TG7-62). Plates N86 and N121 or TG7-80 shows the superior oblique muscle being innervated by the trochlear nerve. Plate N84 or TG7-59 shows the actions of the superior oblique muscle (and the other extrinsic muscles of the eye as well). Plate N86 or TG7-63 shows the nasociliary nerve (branch of V1) and its anterior ethmoidal branch. The distribution of the anterior ethmoidal nerve is shown in plate N42 or TG7-45. Plate N86 or TG7-63 shows the nasociliary nerve laying on the medial rectus muscle and sending long ciliary nerves to the back of the eyeball. Plate N85 or TG7-62 shows the ciliary and ethmoidal branches of the ophthalmic artery (the distribution of the ethmoidal branches is shown in plate N41 or TG7-45). Plate N86 or TG7-63 shows the lacrimal nerve. The levator palpebrae aponeurosis is shown (unlabeled) in plate N82 or TG7-57 dividing the lacrimal gland into palpebral and orbital parts. The muscular anulus is labeled as the common tendinous ring in plate N86 or TG7-59 and TG7-61. The lateral rectus muscle is shown being innervated by the abducens nerve in plate N86 or TG7-63. Plate N86 or TG7-63 traces the nasociliary nerve and superior division of the oculomotor nerve back to the ophthalmic nerve and oculomotor nerve, respectively. Plates N86 or TG7-63 and N121 or TG7-79 show the inferior branch of the oculomotor nerve sending fibers to the ciliary ganglion, medial rectus muscle, inferior rectus muscle, and inferior oblique muscle. Plates N86 or TG7-63 and N121 or TG7-79 also identify short ciliary nerves running from ciliary ganglion to the back of the eye. Plate N84 or TG7-63 shows the position of the inferior oblique muscle and how it relates to the lower eyelid.

Step 8. Transect the optic nerve to reveal the central artery and relationships of the nerve sheaths. (Play movie)

Plate N86 or TG7-62 traces the course of the optic nerve. Plate N87 or TG7-64 shows the optic nerve sheath (meninges), central artery of the retina, and the subarachnoid space extending to the back of the eye. Plate N85 or TG7-62 shows the ophthalmic artery giving off the central retinal artery, which then travels inside the optic nerve (N87 or TG7-64). Plate N85, N70, and N104 or TG7-61B or TG7-73 all identify the superior ophthalmic vein, which drains into the cavernous sinus (N104 or TG7-60A or TG7-60B).