Final Exam Study Guide PDF

Final Exam Study Guide 1. All cornea, cornea physiology and sclera 2. Lens development The eyes begin to form from the wall of the diencephalon. During the 3rd week of embryonic development, the embryonic plate has been formed by the three primary germ layers (Ectoderm, mesoderm, and endoderm). The...

Final Exam Study Guide 1. All cornea, cornea physiology and sclera 2. Lens development The eyes begin to form from the wall of the diencephalon. During the 3rd week of embryonic development, the embryonic plate has been formed by the three primary germ layers (Ectoderm, mesoderm, and endoderm). The lens is formed by the surface ectoderm. On approximately the 18th day, two neural folds develop in the ectoderm, grow towards each other and fuse, forming the neural tube by the 22nd day. On the 25th day the eyes start forming, beginning as optic pits. Each optic vesicle invaginates to form a two-layered optic cup with an optic stalk and a fetal fissure for the hyaloid artery/vein. The embryonic fetal fissure is the last structure to close during the formation of the optic cup, which allows the mesenchyme to migrate into this region to develop the hyaloid plexus. • The hyaloid plexus eventually disintegrates but the hyaloid artery persists as the central retinal artery. 3. Hyaloid artery development During the 5th week of development, a branch of the internal carotid artery enters the optic cup through the fetal fissure and becomes the hyaloid artery. This artery forms a network that fills the primary vitreous cavity and forms the posterior vascular tunic of the lens. During the 2nd month of development, the primary vitreous reaches its greatest extent, forming Cloquet’s canal. During the 4th month, the vessels of the hyaloid system begin atrophying while the zonular fibers begin to stretch from the ciliary region to the lens capsule. 4. Short ciliary arteries Arise as 1-2 branches and then form 10-20 branches. They enter the sclera in a ring around the optic nerve and form the arterial network within the choroidal stroma. They divide to form the Posterior Choriocapillaris which nourishes the outer layers of the retina. Other branches form the circle of Zinn which encircles the optic nerve at the choroid and supplies the nerve head. 5. Perfusion pressure The perfusion pressure is a numeric value that indicates how easily blood can pass through a tissue. Approximately 50mmHg Diastolic BP – IOP = Ocular perfusion Patients with low ocular perfusion pressure are 1.5x more likely to develop progressive nerve damage from ischemia. 6. Oculomotor nerve innervation Innervated by superior division of Oculomotor nerve – Superior rectus, levator palpebrae Innervated by inferior division of Oculomotor nerve – Medial rectus, Inferior rectus, Inferior oblique 7. Muscle that retract and close the eyelids Orbicularis oculi – orbital portion is used for forced closure of the eyelids while the palpebral portion is used for spontaneous/reflex blinking. Superior levator palpebrae – originates from the lesser wing of the sphenoid and is the main retractor of the upper eyelid. Muscle of Muller – smooth muscle, innervated by the sympathetic nervous system and originates on the levator and provides 2-3mm of upper eyelid lift (minor retractor). 8. Components of Tear film and layers Lipid layer – 1% of the thickness of the tear film, consists of waxy esters, cholesterol and fatty acids. It functions to retard evaporation and provide lubrication for smooth eyelid movement; they also provide stability. Aqueous layer – 60-70% of the tear film, contains water, electrolytes, inorganic salts, glucose, urea, enzymes, immunoglobulins, cytokines, proteins, peptide growth factors, glycoproteins, antibacterial substances and vitamins. Mucous layer – 30-40% of total tear film, composed of the glycocalyx of the ocular surface epithelium and mucin. It acts as an interphase that facilitates adhesion of the aqueous layer to the ocular surface. Mucin also binds and entraps bacteria by blocking binding sites on microbes, preventing them from penetrating the ocular surface. 9. Glands functions for tear film layers Lipid layer – formed by Meibomian and Zeis glands. Aqueous layer – formed by main and accessory lacrimal glands Mucous layer – secreted by conjunctival goblet cells. 10. Nasolacrimal valves Valve of Rosenmuller – where the common canaliculus enters into the sac. Valve of Krause – constrictions at the junctions of the sac in the nasolacrimal duct. Valve of Hyrtl and Tallefer – within the nasolacrimal duct Valve of Hasner – at the end of the nasolacrimal duct, under the inferior turbinate. 11. Lacrimal gland The lacrimal gland is located in the temporal fossa of the orbital plate of the frontal bone, posterior to the superior orbital margin. It is divided into by the aponeurosis of the levator muscle: • Orbital portion - larger and almond shaped. Superior surface lies against the periorbita of the lacrimal fossa, interior surface lies against the aponeurosis, medial edge lies against the levator muscle and the lateral edge lies the lateral rectus muscle. • Palpebral portion - ⅓ to ½ the size of the orbital lobe, subdivided in 2-3 sections. o The lacrimal glands can be seen when you evert the upper eyelid. o Ducts from both portions of the lacrimal gland exit through the palpebral lobe. 12. Connective tissues of orbit functions Periorbita – covers the bones of the orbit and serves as an attachment site for muscles, tendons and ligaments. • It is a support structure for the blood supply to the orbital bones. • It is loosely attached to the underlying bone except at the orbital margins, sutures, edges of fissures and foramina. Orbital septum – serves as a strong barrier to prevent facial infections from entering the orbit and also maintains orbital fat in place. Tenon’s capsule – encases the globe and forms sleeve-like sheaths at muscle insertions that cover the tendons. Acts as a barrier to prevent the spread of orbital infections into the globe. Suspensory ligament of Lockwood – helps to support the globe, particularly in absence of orbital floor bones. Muscle of Muller – only eyelid muscle with sympathetic innervation, elevates the lid 3mm. Orbital septal system – organizes the orbital space surrounding the globe into radial compartments. Anchors and supports EOMs and blood vessels, attaching them to adjacent orbital walls. Orbital fat – surrounds the optic nerve, separating it from the EOMS and separates the muscles from the walls of the orbit. 13. Edinger Westphal nucleus The oculomotor nerve originates at the level of the midbrain at the superior colliculi from two nuclei: Edwinger-Westphal nucleus - contains general visceral efferent preganglionic fibers to the ciliary region. Oculomotor nucleus - contains general somatic efferent fibers to the SR, MR, IR, IO and levator palpebrae. Found in the midbrain. 14. Horner’s and Riolan muscles Muscle of Riolan – most superficial portion, keeps kid margin tightly applied to the globe during eye movements and may contribute to rotating eyelashes toward the eye during eye closure. Muscle of Horner – fibers of the orbicularis which help drain tears into the lacrimal sac 15. Muller muscle 16. CN VII innervation (Facial) Its upper two branches (temporal and zygomatic) supply the frontalis, procerus, corrugator and orbicularis muscles. Its lower branches supply the remaining facial muscles. Large motor root - innervates facial muscles Smaller motor root - contains sensory fibers which carry taste from the tongue and parasympathetic fibers that supply secretomotor fibers to the lacrimal, parotid and sublingual glands. 17. CN IV innervation (Trochlear) Innervates the superior oblique muscle. 18. CN VI innervation (Abducens) Innervates the lateral rectus muscle. 19. Nasociliary nerve Formed by the joining of the Infratrochlear n., Anterior/Posterior Ethmoid n., 2 Long Ciliary n. and the sensory root of the ciliary ganglion. It exits the orbit by passing through the common tendinous ring and the superior orbital fissure into the cranial cavity. 20. Optic foramen Gap between the lesser wing and the sphenoid body (NOT the greater wing). It provides communication between the orbital cavity and the middle cranial fossa, an exit for the optic nerve and an entry for the opthalmic artery. 21. Superior orbital fissure Is the gap between the lesser wing and greater wing of the sphenoid bone providing communication between the orbital cavity and middle cranial fossa. It has a sharp spur that serves as the attachment for the lateral rectus muscle. Passing above the circular tendon: Lacrimal nerve, Frontal nerve, Trochlear nerve and Superior Ophthalmic vein. Passing through the superior orbital fissure and ring tendon: Superior/Inferior Oculomotor nerve, Nasociliary nerve and Abducens nerve. Passing through the optic canal and the tendinous ring: Optic nerve and Ophthalmic artery.