Orbit & Contents PDF

Orbit and Contents DPM Program Learning Objectives: 1. Describe the extraocular muscles, in terms of their attachments, innervations, and actions. 3.0 2. Describe the muscles responsible for opening and closing the palpebral fissure. 3.0 3. Describe the intrinsic muscles of the eye, as well as their...

Orbit and Contents DPM Program Learning Objectives: 1. Describe the extraocular muscles, in terms of their attachments, innervations, and actions. 3.0 2. Describe the muscles responsible for opening and closing the palpebral fissure. 3.0 3. Describe the intrinsic muscles of the eye, as well as their actions and innervation. 3.0 4. Describe the arterial supply and venous drainage of the orbit. 3.0 5. Describe the parasympathetic and/or sympathetic innervation of the orbit and its contents. 3.0 6. Define Horner’s syndrome. 4.0 1 Overview of the Orbit Each orbit is a pyramidal-shaped cavity whose boundaries are formed by seven bones (frontal, sphenoid, zygomatic, maxilla, palatine, ethmoid, and lacrimal) of the skull. Each orbit possesses four walls (roof [superior wall], lateral wall, floor [inferior wall], and medial wall), an apex posteriorly, and a base anteriorly. The orbital cavities contain the eyes, together with their associated muscles, nerves, blood vessels, fat, and much of the lacrimal apparatus. These bones are relatively thin and easily fractured by penetrating objects. Such trauma may cause damage to the: maxillary sinus, ethmoidal & sphenoidal sinus, or frontal lobe of the brain. Boundaries: Roof: Frontal bone and Sphenoid Bone Apex: Located at the optic canal Lateral Wall: Zygomatic bone and sphenoid bone Medial Wall: Ethmoid, Frontal, Sphenoid and Lacrimal Bone Floor: Maxilla, Zygomatic bone, Palatine bone Posterior Wall: Wall of the orbit-Sphenoid bone Openings: Optic canal (optic nerve (CN II) and ophthalmic artery) Superior orbital fissure (ophthalmic vein, oculomotor nerve (CN III) trochlear nerve (CN IV), abducens nerve (CN VI), branches of the ophthalmic division of the trigeminal nerve (CNV) Inferior orbital fissure (maxillary division of the trigeminal nerve (CNV), zygomatic nerve, infraorbital artery 2 and vein) The Orbit Posterior ethmoidal foramen Orbital surface of frontal bone Anterior ethmoidal foramen Orbital surface of lesser wing of sphenoid bone Orbital plate of ethmoid bone Lacrimal bone Superior orbital fissure Fossa for lacrimal sac Optic canal (foramen) Orbital process of palatine bone Orbital surface of greater wind of sphenoid bone Orbital surface of zygomatic bone Orbital surface of maxilla Inferior orbital fissure Infraorbital groove Anterior View Right Orbit: Frontal and Slightly Lateral View 3 The Eyeball Layers The eyeball is a durable fluid-filled sphere which possesses a three-layered wall. Going from external to internal, the three layers are: Outer Fibrous Tunic (coat) Sclera: white of the eye Cornea: transparent; avascular but richly supplied with sensory nerves; principal refractor of the eye Middle Vascular Tunic Choroid: thin, highly vascular; brown in color as a result of the pigment cells in its outermost layer Ciliary Body: anterior continuation of the choroid layer, suspends the lens by a suspensory ligament, primary component is the ciliary muscle Iris: thin contractile layer that possess a central opening the Pupil (“eye color”) Inner Layer Retina thin, delicate membrane which is an outgrowth of the diencephalic portion of the brain has a multilaminated layer that contains photosensitive transducer cells which transform photic information into electrical impulses conveyed to the brain via the optic nerve Other components: Aqueous humor: clear, watery fluid which fills the anterior and posterior chambers of the eye; helps maintain intraocular pressure and nourishes the lens and cornea which are both avascular. Undergoes constant replacement Lens: transparent, biconvex, elastic structure composed of highly ordered connective tissue. Shape is altered by the ciliary body (discussed in next slides) Vitreous Body (Humor): transparent semigelatinous material fills the cavity between the lens and retina. Formed early in development and cannot be replaced. 4 5 Smooth Muscle of the Orbit (Intrinsic Muscles Of The Eye) CILIARY MUSCLE 1) Situated within the ciliary body 2) The normal elastic tension exerted on the lens by the ciliary body tends to flatten the lens—the shape most conducive for viewing distant objects. 3)Contraction of the ciliary muscle acts to narrow the diameter of the ring formed by the ciliary body, thus releasing tension on the zonular fibers. This increases the curvature of the lens for near vision. NOTE: All of the above components of accommodation are controlled by the Oculomotor Nerve. Innervated by postganglionic parasympathetic fibers SPHINCTER PUPILLAE 1) Consists of myoepithelial cells circularly arranged in the iris around the pupil 2) Consequently, contraction results in a decrease in the diameter of the papillary opening (e.g., in response to increased illumination). This action is referred to as PUPILLARY CONSTRICTION OR PUPILLARY LIGHT REFLEX. 3) Innervation provided by postganglionic parasympathetic fibers. DILATOR PUPILLAE 1) Consists of myoepithelial cells radially arranged in the iris around the pupil 2) As a result, contraction results in an increase in the diameter of the papillary opening (e.g., in response to decreased illumination). This action is referred to as PUPILLARY DILATATION. 3) Innervation provided by postganglionic sympathetic fibers 6 7 Lacrimal Apparatus -lacrimal glands secrete lacrimal fluid. -The glands sit in the superolateral aspect of the orbit inside a fossa in the frontal bone - lacrimal ducts – convey fluid from the glands into the conjunctival sac on the surface of the eye - lacrimal canaliculi – convey fluid from the medial angle of the eye to the lacrimal sac - The lacrimal sac is the dilated superior portion of the nasolacrimal duct 8 Superior and Inferior Tarsal Muscles The tarsal muscles are thin sheets of smooth muscle found in the upper (Superior tarsal muscle) and lower (Inferior tarsal muscle) eyelids. The Superior tarsal muscle connects the levator aponeurosis to the tarsal plate in the upper lid and is considered to be part of the Levator palepbrae superioris. The Inferior tarsal muscle is poorly developed. Innervation: -sympathetic fibers Function is to: - widen the palpebral fissure. - Superior tarsal muscle assists in keeping the upper lid elevated during our waking hours without our having to think about it (i.e., involuntary) Superior Tarsal Muscle Clinical Correlation: -When sympathetic nerve supply to the face and eye is damaged a collection of symptoms is referred as Horner’s Syndrome. -One symptom is PTOSIS (drooping of the upper eyelid) -result of the paralysis of the superior tarsal muscle 9 Orbicularis Oculi Muscle Innervation Orbicularis oculi Function Closes the palpebral fissure 1) Palpebral part Facial nerve [VII] Closes the eyelid gently and some wrinkling of the forehead 2) Orbital part Facial nerve [VII] Closes the eyelid forcefully 10 Axes of the Eyeball Horizontal Movement Abduction Adduction Vertical Movement Elevation Depression Pivotal Movement Intorsion Extorsion 11 The Extraocular Muscles The extraocular muscles are located between the eye and the orbit. There are seven extraocular muscles, one of which does not attach to the eye and thus does not elicit movement of the eye. Trochlea Levator palpebrae superioris (does not attach to the eye) Superior oblique Superior rectus Medial rectus Superior oblique Medial rectus Superior rectus Lateral rectus Inferior oblique Lateral rectus Inferior rectus 12 Lateral Rectus Muscle Muscle at rest Muscle Contraction 13 Medial Rectus Muscle Muscle at rest Muscle Contraction 14 **Note medial and lateral rectus are the only 2 extraocular muscles that act in the X-axis. Important for clinical testing of the eye discussed later. Orientation of the Extraocular Muscles The axis of the eyeball and axis of the orbit are not the same. As a result, this affects the movements that the extraocular muscles have on the eyeball acting on the Y-axis. 15 Superior Rectus Muscle Muscle at rest Muscle Contraction 16 Inferior Oblique Muscle Muscle at rest Muscle Contraction 17 Superior Oblique Muscle Muscle at rest Muscle Contraction 18 Inferior Rectus Muscle Muscle at rest Muscle Contraction 19 Muscle Innervation Function Levator palpebrae superioris Oculomotor nerve [III] Elevation of upper eyelid Superior rectus Oculomotor nerve [III] Primary Action: Elevation Secondary Action: Adduction, medial rotation of eyeball Inferior rectus Oculomotor nerve [III] Primary Action: Depression Secondary Action: Adduction, lateral rotation of eyeball Medial rectus Oculomotor nerve [III] Adduction of eyeball Lateral rectus Abducent nerve [VI] Abduction of eyeball Superior oblique Trochlear nerve [IV] Primary Action: Depression Secondary Action: Abduction, medial rotation of eyeball Inferior oblique Oculomotor nerve [III] Primary Action: Elevation Secondary Action: Abduction, lateral rotation of eyeball Mnemonic for innervation of extraocular muscles: LR6 SO4 AO3 20 Clinical Testing of Muscles of the Eye 21 Clinical Testing of the Medial and Lateral Rectus Muscles The medial and lateral rectus are the only 2 extraocular muscles that act in the X-axis. 22 Clinical Testing of the Superior Rectus and Inferior Oblique Muscles The Superior Rectus and Inferior oblique muscles are the only 2 extraocular muscles that act in the Y-axis to elevate the eye (look up). Therefore to test these muscles they must be isolated from one another. In order to isolate the SR from the IO muscle the vector pull of the muscle (solid arrow) must be placed in parallel with the gaze of the orbit (dotted arrow). In order to isolate the IO from the SR muscle the vector pull of the muscle (solid arrow) must be placed in parallel with the gaze of the orbit (dotted arrow). To accomplish this, you would have the patient abduct their eye and then look up. To accomplish this, you would have the patient adduct their eye then look up. 23 Clinical Testing of the Superior Oblique and Inferior Rectus Muscles The Superior Oblique and Inferior Rectus muscle are the only 2 extraocular muscles that act in the Y-axis to depress the eye (look down). Therefore to test these muscles they must be isolated from one another. The action necessary to put the vector of the SO muscle (solid arrow) in parallel with the gaze of the orbit (dotted) arrow would be adduction. Then you would have the patient look down. The action necessary to put the vector of the SO muscle (solid arrow) in parallel with the gaze of the orbit (dotted) arrow would be abduction. Then you would have the patient look down. 24 Sensory Nerves Optic (CN II) – SA - through optic canal -special sensory for sight Ophthalmic Division of Trigeminal (CN V1) - GSA – through superior orbital fissure to be sensory to the eyeball and skin of the surface of the nose, part of nasal cavity, upper eyelid and forehead. Three main branches: a. Frontal supratrochlear supraorbital b. Nasociliary long/short ciliary nerves (to eyeball) anterior ethmoidal external nasal (to tip of nose) c. Lacrimal 25 Optic Nerve 26 Ophthalmic Division of Trigeminal (CN V1) Superficial Superior View Deep Superior View 27 Motor Nerves Oculomotor (CN III) (GVEp and GSE). -through superior orbital fissure -motor to levator palpebrae superiorus, superior, inferior and medial rectus, & inferior oblique. -carries presynaptic parasympathetics to the ciliary ganglion -Short ciliary nerves (CN V1) carry postsynaptic parasympathetics from the ciliary ganglion to supply the -ciliary and sphincter pupillae muscles. They will also carry postsynaptic sympathetics to the dilator pupillae m. Oculomotor nerve palsy: ptosis, dilated and nonreactive pupil, fully abducted and depressed pupil Trochlear (CN IV) (GSE) -through superior orbital fissure to innervate the superior oblique muscle. Trochlear nerve palsy: The characteristic sign of trochlear nerve injury is dipoplia (double vision) when looking down. Abducens (CN VI) (GSE) -through superior orbital fissure to innervate the lateral rectus muscle. In abducens nerve palsy the affected eye is permanently adducted due to the unopposed action of the medial rectus muscle. 28 Motor Nerves of the Eyes SO4 LR6 AO3 Superficial Superior View Deep Superior View 29 Arteries of the Eye The arterial supply to the structures in the orbit, including the eyeball, is by the ophthalmic artery. This vessel is a branch of the internal carotid artery, given off immediately after the internal carotid artery leaves the cavernous sinus. The ophthalmic artery passes into the orbit through the optic canal with the optic nerve. Ophthalmic artery -branch of internal carotid artery (in the neck), enters orbit through optic canal and passes into the orbit through the optic canal with the optic nerve. It gives off the: Central artery of the retina enters the optic nerve, proceeds down the center of the nerve to the retina, and is clearly seen when viewing the retina with an ophthalmoscope—occlusion of this vessel or of the parent artery leads to blindness 30 Veins of the Eye There are two venous channels in the orbit, the superior and inferior ophthalmic veins. Superior Ophthalmic vein: communicates with the facial vein passing through superior orbital fissure and terminates into the cavernous sinus Inferior Ophthalmic vein: drains to superior ophthalmic vein; also connects to the pterygoid plexus (in the infratemporal fossa) draining into cavernous sinus Central vein of the retina: inside the optic nerve, drains to cavernous sinus (blockage causes blindness) NOTE: recall that blood from the face may drain into cavernous sinus via ophthalmic veins forming a possible route for the spread of infection from the face into the cranial cavity 31 The Ciliary muscle and Sphincter pupillae are innervated by the parasympathetic system. a) Preganglionic parasympathetic nerve cell bodies are found in the EDINGER-WESTPHAL NUCLEUS (ACCESSORY OCULOMOTOR NUCLEUS) located in the MESENCEPHALON. b) The axons of these neurons then join the OCULOMOTOR NERVE (CN III) as it leaves the brainstem. c) The preganglionic parasympathetic fibers terminate by synapsing with postganglionic nerve cell bodies located in the CILIARY GANGLION which is found in the orbit between the optic nerve and the lateral rectus muscle approximately 1 cm from the posterior limit of the orbit. d) The postganglionic parasympathetic fibers leave the ciliary ganglion and gain access to the eyeball (i.e., Ciliary muscle 32 and Sphincter pupillae) by travelling in a number of SHORT CILIARY NERVES. The Dilator pupillae (and Superior tarsal muscle) are innervated by the sympathetic system. a) Preganglionic sympathetic nerve cell bodies are located in the INTERMEDIOLATERAL CELL COLUMN and their axons leave the spinal cord through the upper thoracic spinal nerves, particularly T1. b) The preganglionic sympathetic fibers terminate by synapsing with postganglionic nerve cell bodies in the SUPERIOR CERVICAL GANGLION. c) The postganglionic fibers from the superior cervical ganglion join the internal carotid plexus (network of sympathetic fibers from the superior cervical ganglion traveling along the internal carotid artery to structures in the head and neck) and reach the iris (Dilator pupillae—remember? I know it has been a while!) either by: (1) traveling along the vessels to the eyeball (i.e., branches of the ophthalmic artery), (2) joining the ophthalmic division of the trigeminal nerve and traveling in the nasociliary nerve and its long ciliary branches, or 33 (3) by passing through the ciliary ganglion and mingling with other fibers of short ciliary nerves 34 Abducent Nerve Palsy If there is damage to the abducens nerve (CN VI), then the lateral rectus muscle will be paralysed. Therefore, the medial rectus muscle will be unopposed and the affected eye will be permanently adducted (as in the picture). In order to prevent diplopia (double vision) the patient will need to abduct the unaffected eye so that both eyes are oriented in the same direction. 35 Horner’s Syndrome A lesion to the cervical sympathetic trunk results in the interruption of sympathetic innervation to the head on the ipsilateral side. This leads to a collection of manifestations referred to as HORNER’S SYNDROME. One of the symptoms is a PTOSIS (i.e., drooping of the upper eyelid) which results from the paralysis of the Superior tarsal muscle. Often referred to as a PSEUDOPTOSIS to distinguish it from a lesion of the Oculomotor nerve (CN III) which also results in a PTOSIS (more pronounced than that resulting from a lesion of the sympathetic trunk) caused by the paralysis of Levator palpebrae superioris. The other manifestations of Horner‘s syndrome include: papillary constriction (miosis, from a paralysis of the Dilator pupillae muscle), vasodilatation, and lack of sweating on one side of the head and neck (anihidrosis). 36 Oculomotor Nerve Palsy Full assessment of oculomotor nerve function involves testing of movement, reaction to light (testing sphincter pupillae), and accommodation (testing the ciliary body). Eye is abducted Eye is depressed Ptosis Dilated/nonreactive pupil 37