EYE ANATOMY & PHYSIOLOGY Dr. Cesar Carrillo [email protected] Sight For All **Disclaimer** The images contained in this presentaon are not my own, they can be found on the web Eye Anatomy and Physiology A thorough understanding of the anatomy and physiology of the eye, orbit, visual pathways, upper cranial nerves, and central pathways for the control of eye movements is a prerequisite for proper interpretaon of diseases having ocular manifestaons. Furthermore, such anatomic knowledge is essen;al to the proper planning and safe execu;on of ocular and orbital surgery Eye Anatomy and Physiology Objecves: Brief overview of eye anatomy and relevant physiology — Embriology — The Orbit, Cranial Nerves, Blood supply and Venous drainage — The Ocular Adnexa — The Extraocular muscles — The Conjunc;va, Sclera and Cornea — The Uveal tract — The Lens — The Re;na, Vitreous and Op;c Nerve — The Visual Pathway Embryology The eye is derived from three of the primi;ve embryonic layers: — Surface ectoderm, including its derivave the neural crest — Neural ectoderm — Mesoderm — Endoderm does not enter into the formaon of the eye — Mesenchyme is the term for embryonic connecve ssue. Ocular and adnexal connec;ve ;ssues previously were thought to be derived from mesoderm, but it has now been shown that most of the mesenchyme of all of the head and neck region is derived from the cranial neural crest Embryology Development of the structures of the head and neck occurs between 3-8 weeks of gestation — Eye develops as an ectodermal diverticulum from the lateral aspect of the forebrain — Diverticulum grows out laterally from the side of the head, and becomes the optic vesicle Embryology — Proximal bit becomes the optic stalk — Week 3: organogenesis — Day 22 : optic groove appears Embryology — 3rd month: differentiation of precursors of rods and cones — 4th month: formation of retinal vasculature/lamina cribrosa/ physiologic cup of optic disc — 5th month: eyelid separation Embryology — 6th month: cones differentiate, nasolacrimal system becomes patent — 7th month: rods differentiate, myelination of optic nerve — After birth: macula develops Embryology — Surface ectoderm: lens, lacrimal gland, cornea epithelium, conjunc;va, adnexal glands, eyelid epidermis — Neural crest: corneal keratocytes, endothelium, trabecular meshwork, iris and choroid stroma, ciliary muscle, sclera fibroblast, vitreous, op;c nerve meninges, orbital car;lage and bone, orbital connec;ve ;ssue and nerves, EOM, eyelids subepidermis — Neural ectoderm: op;c vesicle and cup, re;na, RPE, ciliary epithelium pigmented and non-pigmented layers, iris posterior epithelium and muscles, op;c nerve fibers — Mesoderm: EOM, orbital & ocular vascular endothelium Embryology of specific structures STRUCTURE EMBRYONIC LAYER SIZE/STAGE Lids and Lacrimal Apparatus Mesenchyme 16mm/6 w – 5th m Sclera and Extra-ocular Muscles Mesenchyme/Mesoderm 20mm /7w – 4th m Anterior Segment Neural crest 12mm/5w – 6th m Lens Surface ectoderm 13mm/ 7th m Ciliary Body and Choroid Neural ectoderm/Mesenchyme 6mm/3 .5w – 3rd m Re;na Neural ectoderm 10mm/5w – 6m aer birth Vitreous Neural crest/Mesenchyme 4.5mm/3mm – 4m Opc Nerve Neural ectoderm 26mm/8w - 3m aer birth Blood Vessels Mesenchyme/Mesoderm 16mm/6w – 8m The Orbit — Pyramid of four walls that converge posteriorly — The medial walls are parallel and separated by the nose — The lateral and medial walls form an angle of 45 degrees, which results in a right angle between the two lateral walls — Volume of the adult orbit :30 mL — Eyeball occupies only about one- fi_h of the space — Anterior limit of the orbital cavity: orbital septum The Orbital Walls — The roof : frontal bone Posteriorly, the lesser wing of the sphenoid bone containing the op;c canal, the lacrimal fossa in the anterior lateral aspect — The lateral wall: separated from the roof by the superior orbital fissure, which divides the lesser from the greater wing of the sphenoid bone. The anterior por;on of the lateral wall is formed by the orbital surface of the zygomac (malar) bone (strongest part of the bony orbit) The Orbital Walls — The orbital floor: separated from the lateral wall by the inferior orbital fissure. The orbital plate of the maxilla forms the large central area and is the region where blowout fractures most frequently occur. The zygomac bone laterally complete the inferior orbital rim. The orbital process of the palane bone forms a small triangular area in the posterior floor The Orbital Walls — The medial wall : ethmoid bone; lacrimal bone; The body of the sphenoid ( most posterior aspect of the medial wall). The angular process of the frontal bone forms the upper part of the posterior lacrimal crest. — The anterior lacrimal crest is easily palpated through the lid and is composed of the frontal process of the maxilla. The lacrimal groove lies between the two crests and contains the lacrimal sac The Orbital Walls WALLS BONY STGRUCTURES FORMING THE WALLS Roof Orbital plate of frontal bone, and lesser wing of sphenoid Floor Orbital plate of maxilla, orbital surface of Zygomac, orbital process of Palane Lateral wall Zygomac, and greater wing of Sphenoid Medial wall Frontal process of Maxilla, lacrimal bone, orbital plate of ethmoid, and body of sphenoid The Apex Region — Entry portal for all nerves and vessels to the eye and the site of origin of all extraocular muscles except the inferior oblique — The superior ophthalmic vein and the lacrimal, frontal, and trochlear nerves pass through the lateral por;on of the fissure that lies outside the annulus of Zinn. The Apex Region — The superior and inferior divisions of the oculomotor nerve and the abducens and nasociliary nerves pass through the medial por;on of the fissure within the annulus of Zinn — The opc nerve and ophthalmic artery pass through the op;c canal, which also lies within the annulus of Zinn Cranial Nerves — CN II Opc – Vision — CN III Oculomotor – 4 muscles – Sympathe;cs to pupil — CN IV Trochlear – Superior oblique — CN V Trigeminal – Ocular sensaon — CN VI Abducens – Lateral rectus — CN VII Facial – Orbicularis oculi Oculomotor Nerve — Runs along the lateral wall of the cavernous sinus — Two nuclei: oculomotor - EW — Two branches: • Superior: Superior rectus and levator palpebrae superioris • Inferior: medial rectus, inferior rectus, inferior oblique • A short thick branch is given to the lower part of the ciliary ganglion, and forms its short root (short ciliary nerves: sphinter pupillae and ciliaris muscle) Trochlear Nerve Motor nerve (general somac efferent for SOM) Unique cranial nerve: — Thinnest (less axons) — Greatest intracranial length — Only that exists from the dorsal aspect of the brainstem (nucleus lesion → affects contralateral eye) — Runs along the lateral wall of the cavernous sinus (with Caro;d artery, III & V nerves) — Enter SOF, travel over the levator — Ends in a tendon (Trochlea) Trigeminal Nerve — Face sensaon and motor func;ons (bi;ng and chewing) — The largest CN — 3 mayor branches: 1. Ophthalmic V1 (sensory): Nasociliary, Lacrimal , & frontal 2. Maxillary V2(sensory) 3. Mandibular V3 (sensory and motor) Trigeminal Nerve Ophthalmic nerve V1: (sensory) ! Scalp, forehead ! Upper eyelid ! Conjunc;va ! Cornea ! Nose, frontal sinuses ! Part of meninges (Dura) Maxillary nerve V2: (sensory) ! Lower eyelid ! Cheek, nares and upper lip ! Upper teeth and gums ! Maxillary, ethmoid and sphenoid sinuses,nand part of meninges Abducens Nerve — Somac efferent for LRM — Runs alongside the internal caro;d in the cavernous sinus — Enters the orbit SOF — Long course → vulnerable to injure at many levels (i.e. petrous temporal bone Fx, aneurysms, mass lesions) — Other problems can damage: stroke (infac;ons), demyelinaon, infec;ons (meningi;s),neuropathies (DR) — Rare: Wernicke-korsakoff syndrome (thiamine↓), Tolosa –Hunt syndrome Orbit Blood Supply — Ophthalmic artery: is the first major branch of the intracranial por;on of the internal caro;d artery. It passes beneath the op;c nerve and accompanies it through the op;c canal into the orbit — Central renal artery: is the first intraorbital branch, which enters the opc nerve — Lacrimal artery, supplying the lacrimal gland and upper eyelid — Long and short posterior ciliary arteries Orbit Blood Supply — Muscular branches to the various muscles of the orbit — Medial palpebral arteries to both eyelids — Supraorbital and supratrochlear arteries Lids Blood Supply — Arterial arcades of the eyelids: Formed by the most anterior branches of the ophthalmic artery (lateral and medial palpebral branches), which make an anastomosis with the external caro;d circulaon via the facial artery Eye Blood Supply — Short posterior ciliary arteries: supply the choroid & parts of the opc nerve — Long posterior ciliary arteries:supply the ciliary body and form the major arterial circle of the iris — Anterior ciliary arteries: derived from the muscular branches to the rectus muscles. They supply the anterior sclera, episclera, limbus, and conjunc;va and contribute to the major arterial circle of the iris Venous Drainage — Superior and inferior ophthalmic veins: drain the vortex veins, the anterior ciliary veins, and the central re;nal vein. Communicate with the cavernous sinus via the superior orbital fissure and the pterygoid venous plexus via the inferior orbital fissure Ocular Adnexa — Eyebrows: prevent sweat, water, and other debris from falling down into the eye socket, also important to human communicaon and facial expression — Eyelids: is a thin fold of skin that covers and protects the eye — Lacrimal