Lab 4: Orbit and Cavernous Sinus Review ”The Basics” and ”The Details” for the following cranial nerves in the Cranial Nerve PowerPoint Handout. • Oculomotor n. (CN III) • Trochlear n. (CN IV) • Ophthalmic division trigeminal (CN V1) • Maxillary division trigeminal (CN V2) • Abducens n. (CN VI) Slide Title Slide Number Slide Title Slide Number Osseous Orbit Slide 3 Optic Disc and Optic Nerve Slide 21 Osseous Orbit (Continued) Slide4 Central Artery of Retina Slide 22 Osseous Orbit (Continued) Slide 5 Macula Lutea and Fovea Centralis Slide 23 Palpebrae Slide 6 Papilledema Slide 24 Palpebrae: Tarsi, Glands, and Muscles Slide 7 Extraocular Eye Muscles: Optical Axis versus Orbital Axis Slide 25 Palpebrae: Muscles Slide 8 Extraocular Eye Muscles: Axes of Movement Slide 26 Palpebrae: Orbital Septum Slide 9 Conjunctiva Slide 10 Extraocular Eye Muscles: Muscles that Move the Eyes Slide 27 Lacrimal Apparatus Slide 11 Extraocular Eye Muscles: Complete Anatomy Slide 28 Lacrimal Apparatus (Continued) Slide 12 Extraocular Eye Muscles: Actions Slide 29 Lacrimal Gland Innervation Slide 13 H Eye Exam Slide 30 The Eye: Major Layers Slide 14 Extraocular Eye Muscles: Muscles That Move Eyelids Slide 31 Fibrous Tunic Slide 15 Extraocular & Eyelid Cranial Nerve Mnemonics Slide 32 Uvea (Vascular Tunic): Choroid, Ciliary Body, Ciliary Slide 16 Processes, and Ciliary Muscles Cavernous Sinus & Associated Cranial Nerves Slide 33 Lens Accommodation Slide 17 Cavernous Sinus & Venous Blood Slide 34 Uvea (Vascular Tunic): Iris Slide 18 Cavernous Sinus & Venous Blood (Continued) Slide 35 Autonomic Innervation to Pupillae and Ciliary Muscles Slide 19 Cavernous Sinus & Thrombosis Slide 36 Review: Oculomotor Nerve (CN III): The Details Slide 20 Osseous Orbit The following bones form the walls of the the bony orbit (Figure 3). • Frontal • Ethmoid • The lamina papyracea (orbital lamina) is a thin, delicate layer of ethmoidal bone separating the orbit from the ethmoid air cells (sinuses) • Lacrimal • Maxilla • A thin layer of maxillary bone separates the floor of the orbit from the maxillary sinus. • Zygomatic • Sphenoid • Palatine Review the structures that pass through the the following apertures to enter and exit the posterior bony orbit. • Optic canal: Optic n. (CN II) and Ophthalmic a. • Superior orbital fissure: Ophthalmic n. (CN V1), Oculomotor n. (CN III), Trochlear n. (CN IV), Abducens n. (CN VI), Sympathetic fibers, Ophthalmic veins • Inferior orbital fissure: Infraorbital n. branch of Maxillary Zygomatic Infraorbital n., Zygomatic branch of of Maxillary n., Infraorbital vessels nerve nerve Osseous Orbit (Continued) Figure 5 Review the structures pass through the the following apertures to exit the anterior bony orbit. • Supraorbital notch/foramen: Supraorbital n. branch of Ophthalmic n. (CN V1) & Supraorbital Supraorbital vessels foramen/notch • Infraorbital foramen: Infraorbital n. branch of Maxillary n. (CNV2) Infraorbital foramen Osseous Orbit (Continued) Figure 3 The medial (lamina papyracea) and inferior walls of the orbit are quite thin. These thin regions of the bony orbit separate the orbit from the ethmoid sinuses (air cells) medially and the maxillary sinuses inferiorly (Figure 1). CLINICAL ANATOMY: Because the margins of the orbit are significantly stronger than its walls, trauma to the orbit may result in either a separation and displacement of bones at sutures, or a fracture of one or more of its walls (“blowout” fracture) (Figures 2, 3, and 4). Fractures of the medial wall may involve the ethmoid or sphenoid sinuses; fractures of the inferior wall may affect the maxillary sinus and infraorbital nerve. • Diplopia and heterotropia (abnormal eye alignment) can result from from a muscle becoming entrapped at the fracture site or from swelling that alters the function of an eye muscle. The muscle most often affected in a blowout fracture is the inferior rectus muscle because of its position along the thin, inferior floor of the orbit. Figure 1 Figure 2 Figure 4 Palpebrae • The palpebra (Pl. = palpebrae) is the anatomical term for eyelid. • The opening between the superior and inferior eyelids is the palpebral fissure. • Closing of the palpebral fissure is controlled by the facial nerve (CN VII) • Opening of the palpebral fissure is controlled by the oculomotor nerve (CN III) and sympathetic fibers. Palpebrae Palpebral Fissure Palpebrae: Tarsi, Glands, and Muscles The tarsi (superior and inferior tarsal plates) are elongated plates of dense connective tissue forming the inner core of each eyelid. • The tarsal (meibomian) glands are embedded within each tarsus. The glands are a modified sebaceous gland that secretes a lipid substance onto free edge of the eyelid at the posterior border. The secreted lipid prevents evaporation and forms a barrier that prevents spilling of lacrimal fluid out of the eyelids. • Associated with the eyelashes projecting from the anterior border of the eyelid's free edge are sebaceous glands called ciliary glands. CLINICAL ANATOMY: Blockage and inflammation of a ciliary gland leads to the formation of a stye on the edge of the eyelid. Muscles that open palpebral fissure • The levator palpebrae superioris muscle has a deep insertion on the tarsus and a superficial attachment to the the skin of the eyelid. This muscle elevates the upper eyelid and opens the palpebral fissure. It is innervated by the oculomotor n. (CN III). • The superior tarsal muscle is a short slip of smooth muscle that extends from the levator palpebrae superioris to the superior margin of the tarsus. This small slip of smooth muscle assists the levator palpebrae superioris in elevating the upper eyelid. This muscle is innervated by the sympathetic nervous system. CLINICAL ANATOMY: Loss of function of the superior tarsal muscle (via loss of sympathetic innervation) results in a partial ptosis of the upper eyelid. In addition, loss of sympathetic innervation will result in a pin-point pupil due to a lack of innervation to the dilator pupillae muscle (parasympathetic innervation still intact). Partial ptosis can also the result of a partial third nerve palsy, but in this condition the pupil will be dilated. Palpebrae: Muscles Muscles that close the palpebral fissure (Figure 1) • The orbicularis oculi muscle consists of two parts, which are both innervated by the facial nerve (temporal and zygomatic branches). • The palpebral portion of the muscle gently closes the palpebral fissure, as in normal blinking. • The orbital portion of the muscle tightly closes the palpebral fissure. CLINICAL ANATOMY: Injury to the facial nerve or its branches resulting in loss of tonus to the orbicularis oculi muscle causes superior eyelid retraction and the inferior eyelid to fall away from the surface of the eye (ectropion) (Figure 2). The inability to blink results in lacrimal fluid not being spread across the surface of the cornea. This can lead to inadequate lubrication, hydration and flushing of the corneal surface, which renders it vulnerable to ulceration. A corneal scar as a result of ulceration can permanently impair vision. Figure 1 Figure 2 Palpebrae: Orbital Septum The orbital septum is a fibrous membrane that spans the distance between the tarsal plates and the bony margins of the orbit, where it is continuous with the periosteum of the bone. CLINICAL ANATOMY: The orbital septum is clinically important because it can limit the spread of infection to and from the orbit. However, it can also confine an infection within the orbit. Conjunctiva The covering of the eyelid not in contact with the eye (external covering) differs from the covering of the eyelid that is in contact with the eye (internal covering). • The external eyelids are covered by thin skin, which consists of a thin stratum corneum relative to skin in other areas of the body. • The internal eyelid is covered by a transparent mucous membrane, called the palpebral conjunctiva (Figure 3A). The palpebral conjunctiva reflects onto the anterior surface of the eye (white sclera and transparent cornea) to become the the bulbar conjunctiva at the superior and inferior conjunctival fornices. • The bulbar conjunctiva covering the sclera contains small blood vessels, which are visible when viewing someone's eye. However, the cornea itself is avascular. • When the eyelids are closed the palpebral and bulbar conjunctiva form the closed conjunctival sac. The conjunctival sac is a specialized form of mucosal “bursa” that enables the eyelids to move freely (frictionless) over the surface of the eye as they open and close. CLINICAL ANATOMY: Inflammation of the conjunctiva, (conjunctivitis, or “pink eye” to patients), is quite common. It is caused by a variety of bacteria and viruses, allergic reactions, or by toxins or irritants (e.g. dust). In most cases, conjunctivitis is not dangerous. However, certain bacteria, especially N. gonorrhoeae and C. trachomatis, can cause severe damage or even blindness. Conjunctival fornix Lacrimal Apparatus The lacrimal gland is located in the superolateral aspect of the orbit and is divided into a superior (orbital) part and a palpebral (inferior) part by the lateral tendon of the levator Tendon levator palpebrae superioris muscle. palpebrae superioris Lacrimal fluids secreted by the lacrimal gland are swept across the cornea and conjunctiva of the eye during blinking. At the medial angle (medial canthus) of the eye the lacrimal fluid is removed from the surface of the eye by passing through the following structures. • Fluid drains into the lacrimal puncta, which are small openings