Ocular Anatomy & Physiology. Learning Objectives: Let s get oriented first. 3 Major Layers (Tunics) of EYE. Topics to be covered: FIBROUS TUNIC

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1 Lecturer: Ocular Anatomy & Physiology M. Patrick COLEMAN, ABOC, COT Kerrville, TX Learning Objectives: 1. Correctly identify ocular structures around or within the eye 2. List the key functions of various ocular structures 3. Accurately point out key external landmarks on, or around the eye 4. Name major bones of the orbit that surround the eye 5. List the six extraocular muscles that control eye movement 6. Accurately identify key ocular structures that compose the visual pathway Topics to be covered: 3 Major Layers (Tunics) of the Eye Ocular Media Ocular Adnexa The Bony Orbit Extraocular Muscles (EOMs) Visual Pathway Let s get oriented first Superior = UPWARD (or TOP) Inferior = DOWNWARD (or BOTTOM) Nasal / Medial = TOWARD NOSE Temporal / Lateral = TOWARD TEMPLE Posterior = BEHIND (or Toward the BACK) Anterior = IN FRONT (or Toward the Front) 3 Major Layers (Tunics) of EYE FIBROUS TUNIC UVEAL TRACT or (Vascular Tunic) NERVOUS TUNIC Protective layer of eye Tough & fibrous Two parts: Cornea Sclera FIBROUS TUNIC 1

2 Fibrous Tunic: Cornea Anterior 1/6 th of the fibrous tunic Clear; Avascular; approx D power 5 layers: Just remember ABCs Epithelium ( A pithelium?) Bowman's Membrane Stroma ( C troma? Like ceiling )» Dua s Layer (Sixth layer? Reported in May 2013) Descemets Membrane Endothelium Fibrous Tunic (cont.): Layers of the Cornea Fibrous Tunic (cont.): Sclera White in color (appears bluish in infants) Avascular (without blood vessels; (what look like blood vessels in the sclera are really in the EPISCLERA which lays on top of the sclera) Makes up posterior 5/6 th of fibrous tunic Very tough! Cornea & sclera are the same material! UVEAL TRACT (Vascular Tunic) IRIS (colored part of eye) CILIARY BODY (behind iris) CHOROID (can see it on retinal photos, and OCT scans of the retina!) UVEAL TRACT (cont.): Iris, Ciliary Body, Choroid UVEAL TRACT (cont.): IRIS Color of iris dependent on amount of pigment Very little pigment = BLUE EYE Medium amount of pigment = HAZEL EYE Heavy amount of pigment = BROWN EYE Hole in center of iris regulates amount of light entering the eye what s it called? Dilator muscles vs. Sphincter muscles 2

3 UVEAL TRACT (cont.): Ciliary Body Located just behind the iris, at its base UVEAL TRACT (cont.): Ciliary Body Ciliary Processes produces aqueous humor constantly (keeps our eye filled with fluid so it remains inflated ) Ciliary Muscles control the focusing of the lens When the ciliary muscles RELAX, they pull the zonules tight, making the lens thinner, so we can see FAR clearly. When the ciliary muscles CONTRACT, they release the tension on the zonules so the lens can grow thicker, (causing us to focus, or accommodate); this allows us to see clearly at NEAR distances. The CILIARY BODY (processes & muscles) UVEAL TRACT (cont.): CHOROID UVEAL TRACT (cont.): CHOROID Supplies blood to the iris, ciliary body, inner retina & inner sclera The CHOW HALL of the eye - brings nourishment & oxygen Sandwiched between the SCLERA and the RETINA NERVOUS TUNIC The Retina that s it! Retina lines the back 2/3 rds of eye 10 layers thick; all the layers are transparent except the RPE (retinal pigment epithelial) layer Retina lies on top of the choroid It s in contact with the vitreous humor (fluid) Contains cells that respond to light (photoreceptors); two (2) types CONES & RODS It is a NEURAL CONNECTION TO THE BRAIN; often considered an extension of the brain! (It s directly connected to the II CN, which is the Optic Nerve.) 3

4 Nervous Tunic (i.e., the RETINA) Sandwiched between the VITREOUS & CHOROID Retina has 10 layers; key layers? Nerve Fiber Layer (NFL) Photoreceptor (Rods & Cones) Retinal Pigment Epithelium (RPE) Nervous Tunic: The Retina (cont.) The photoreceptor layer contains RODS & CONES Rods & Cones convert light to an electro-chemical impulse, which gets passed along the ganglion cells, to the nerve fiber layer (NFL) Then it goes to the brain via the Optic Nerve (II CN) Rods & Cones only sense wavelengths in the visible electromagnetic spectrum (ROY G. BIV) which is between: 400nm (VIOLET) to 700nm (RED). CONES are for bright (photopic) conditions; can see color & fine detail There are approximately 6 million cones in the retina The fovea centralis (center of Macula) contains ONLY CONES! Cones emit a chemical called IODOPSIN Trivia Question: What percentage of MEN are colorblind? What percentage of WOMEN are colorblind? RODS are for dim (scotopic) conditions; They provide a poor image but have a great ability to sense movement There are approximately 120 million rods in the retina. Rods emit a chemical called RHODOPSIN TRIVIA QUESTION: * When entering a dark movie theater, whose eyes will dark adapt the quickest: A young person or an elderly person? 4

5 The retina is CLEAR, with the exception of the Retinal Pigment Epithelium (RPE) layer which, like the iris, contains pigment The RPE layer is the garbage man : It absorbs excess light AND It must remove the chemicals emitted by the rods (rhodopsin) and cones (iodopsin) as these chemicals are TOXIC TO THE RETINA. The layer closest to the vitreous humor is the RETINAL NERVE FIBER LAYER (NFL) This layer contains the nerves coming from every part of the retina At the optic nerve, the nerve fiber bundles are most concentrated superiorly & inferiorly Ever do an OCT scan of the area around the optic nerve head (ONH) of a glaucoma patient? Why? Zeiss OCT scan of optic nerve head (ONH) of both eyes: Green = GOOD Yellow = BORDERLINE Red = BAD (glaucoma?!) As the nerve fibers approach the optic disk, they start to bundle closer together and form the cable to the brain we call the OPTIC NERVE (II CN) In GLAUCOMA, these nerve fibers die off 9/10ths of the Retinal blood supply comes from the CENTRAL RETINAL ARTERY (CRA) So that s it, right? HARDLY! The TUNICS of the eye are just layers of the main functional components. There are many other parts that make up the eye and help it work correctly. Time to look at the rest of the eye 5

6 OCULAR MEDIA These are the clear structures of the eye light must pass through to get to the retina. They are the: CORNEA AQUEOUS HUMOR LENS VITREOUS HUMOR OCULAR MEDIA - Cornea (cont.) Cornea Needs a good tear layer to transmit light well Good quality tears have three parts: Lipid (oil) layer (top/outermost layer) - keeps aqueous layer from evaporating away too quickly Aqueous layer (middle layer) - water portion of tear (thickest layer!) Mucin (mucous) layer (innermost/against cornea) - keeps tears stuck against cornea OCULAR MEDIA (cont.): TEAR FILM OCULAR MEDIA Aqueous Humor (cont.) AQUEOUS HUMOR Produced by the CILIARY BODY in posterior chamber of the eye Flows thru the pupil into anterior chamber Provides nourishment to Endothelial layer of the cornea & maintains pressure in the eye Drains thru the TRABECULAR MESHWORK and into the CANAL OF SCHLEMM, dissipating into the layers of the sclera OCULAR MEDIA Aqueous Humor (cont.) OCULAR MEDIA Lens (cont.) Lens (sometimes called the Crystalline Lens ) Three parts: CAPSULE CORTEX NUCLEUS Changes shape to focus images on retina Soft & flexible in the young; harder as we age Cataracts form in this structure (BUMMER!) Approximately D to D of power 6

7 OCULAR MEDIA Lens (cont.) OCULAR MEDIA Vitreous (cont.) VITREOUS HUMOR Fills the posterior 5/6ths of the eye When we are young, it is thick & jello-like As we age, it breaks down and becomes more watery. It also tends to shrink a bit causing PVDs (post-vitreous detachments) When we see floaters it is usually debris in the vitreous that s moving around What you have is all you get. If you lose vitreous, the body will NOT make more! OCULAR MEDIA - Vitreous (cont.) So is that it? As they say on TV, But wait! There s More!!! Ocular Adnexa The Bony Orbit Extraocular Muscles (EOMs) Eyelids & Landmarks Muscles of the eyelids Tarsal Plate & Glands Conjunctiva & Lacrimal System OCULAR ADNEXA EYELIDS & LANDMARKS Eyelids are the folds of tissue that cover the eye itself. Their primary purpose is PROTECTION!!! Limit amount of light entering the eye (giving the pupil an times) Keep dust & dirt out of the eye (& fingers & racquetballs & fish hooks & well, you get the idea!) Eyelashes = early warning sensors (Which lid has MORE lashes? UPPER or lower?) 7

8 LANDMARKS of the EYELIDS EYELIDS & LANDMARKS (cont.) MUSCLES of the EYELIDS Muscles open & close the lids (duh!) To OPEN the lids, we use the: LEVATOR PALPEBRAE SUPERIORIS (let s just go with LEVATOR!) & the MUSCLE OF MUELLER The III CN (Oculomotor nerve) operates these nerves (Which muscle is the PRIMARY worker here?) LEVATOR PALPEBRAE SUPERIORIS (LEVATOR)! A way to remember? Mueller gets on the LEVATOR to go UP & fix the oculomotor on the 3 rd (III) floor Levator OPENS the eyelids Mueller helps III CN (Oculomotor nerve) controls them both EYELIDS & LANDMARKS (cont.) MUSCLES of the EYELIDS (cont.): To CLOSE the lids, we use the: ORBICULARIS OCULI muscle & the RIOLAN S muscle The VII CN (Facial nerve) operates these two muscles QUESTION: Which is the PRIMARY muscle for closing the lids? ORBICULARIS OCULI EYELIDS & LANDMARKS (cont.) It is the primary muscle for closing the eyelid Just remember: Orbicularis Oculi CLOSES the eye! 8

9 EYELIDS & LANDMARKS (cont.) TARSAL PLATE IN THE LID TARSAL PLATE: Levator & Mueller s muscles attach here It is considered the skeleton of the lid as it s made up of tough, fibrous tissue When the doctor everts the lid to look for a foreign body (FB) or wayward contact, they are pushing at the top of the TARSAL PLATE to get the lid to flip inside out OCULAR ADNEXA (cont.) - GLANDS OCULAR ADNEXA (cont.) - Glands GLANDS The adnexa (eyelids & surrounding structures) contain GLANDS that secrete OIL or AQUEOUS SEBACEOUS GLANDS secrete OIL LACRIMAL GLANDS secrete AQUEOUS OCULAR ADNEXA (cont.) - Conjunctiva OCULAR ADNEXA (cont.) - Conjunctiva CONJUNCTIVA Thin, saran-wrap-like layer on the surface of your sclera and inner eye lids TWO PARTS: PALPEBRAL & BULBAR Where the two parts meet is called the FORNIX Protection; barrier to infection; keeps things from getting behind the eye Contains GOBLET CELLS that secrete MUCIN 9

10 OCULAR ADNEXA (cont.)-lacrimal System LACRIMAL SYSTEM Seven (7) distinct structures involved in the production, distribution, & disposal of tears 1) Lacrimal Gland 2) Lacrimal Canal (Ducts) 3) Conjunctival Sac 4) Puncta (upper & lower) 5) Canaliculi 6) Lacrimal Sac 7) NasoLacrimal Duct OCULAR ADNEXA (cont.) LACRIMAL SYSTEM: THE BONY ORBIT Additus Orbitae (the opening of the bony orbit) The bony orbit is composed of seven (7) bones that surround the eye to protect it & provide passage or attachment points for various structures (like the eye muscles, nerves, fat, lacrimal gland and vascular supply) Bony orbit is comprised of a: ROOF (lesser wing of SPHENOID & FRONTAL) FLOOR (MAXILLA, PALATINE, & ZYGOMATIC) LATERAL WALL (ZYGOMATIC & greater wing of SPHENOID) MEDIAL WALL (MAXILLA, ETHMOID, LACRIMAL & lesser wing of SPHENOID) THE BONY ORBIT (cont.) THE BONY ORBIT (cont.) ROOF: (Light Shines From the roof) Lesser wing of Sphenoid (foramina for optic nerve [II CN] to pass through!) Frontal bone (fossa for lacrimal gland) FLOOR: (MoP Zee floor) Maxilla (blow out fractures!) Palatine (smallest bone) Zygomatic (strongest bone) THE BONY ORBIT (cont.) LATERAL WALL: (Zee Great Side!) Zygomatic (strongest) Greater wing of Sphenoid MEDIAL WALL: M E L L S) Maxilla (blow out fractures!) Ethmoid (thinnest bone) Lacrimal (fossa for the lacrimal sac) Lesser wing of Sphenoid (foramina for optic nerve [II CN] to pass through!) 10

11 THE BONY ORBIT (cont.) THE BONY ORBIT (cont.) Cracks, Holes, & Depressions Fissures = cracks in bones (the Superior Orbital Fissure allows the III, IV, V, & VI cranial nerves [CN] access to the bony orbit) Foramina/Foramen = holes in bones (the Optic Foramina is a hole in lesser wing of Sphenoid that the optic nerve [IICN] passes through) Fossa/Fossae = depressions ( dents ) in bones (Lacrimal Fossa is a dent in the lacrimal bone where the lacrimal sac sits) EXTRAOCULAR MUSCLES EXTRAOCULAR MUSCLES (cont.) SIX (6) muscles on each eye They attach to the sclera of the eye Job is to move the eyes to keep objects of interest lined up with the macula of each eye Goal is: Single Binocular Vision (SBV) Want to avoid: diplopia or suppression resulting in monocular vision. Primary Position of Gaze = Straight Ahead EXTRAOCULAR MUSCLES (cont.) Rectus Muscles There are four Rectus muscles for each eye: Lateral Rectus (LR), Medial Rectus (MR), Superior Rectus (SR), & Inferior Rectus (IR) Rectus muscles attach ANTERIOR to the equator; so they pull the eye in the direction they say : Lateral Rectus (LR) pulls eye laterally (OUT), or ABDUCTION Medial Rectus (MR) pulls eye medially (IN), or ADDUCTION Superior Rectus (SR) pulls eye superiorly (UP), or ELEVATION Inferior Rectus (IR) pulls eye inferiorly (DOWN), or DEPRESSION 11

12 EXTRAOCULAR MUSCLES (cont.) OBLIQUE MUSCLES There are two (2) OBLIQUES muscles for each eye. OBLIQUES are unique ; they move the eyes OPPOSITE of what they say SUPERIOR OBLIQUE (SO) makes the eye look inferiorly (Depression) and across the nose (intorsion) INFERIOR OBLIQUE (IO) makes the eye look superiorly (Elevation) and across the nose (extorsion) EXTRAOCULAR MUSCLES (cont.) ExtraOcular Muscles (EOMs) are innervated by cranial nerves (nerves make the muscles work!) Which nerves operate which muscles? What!? LR6 SO4 3 Lateral Rectus = VI (6 th ) CN (Abducens) Superior Oblique = IV (4 th ) CN (Trochlear) All the rest = III (3 rd ) CN (Oculomotor) EXTRAOCULAR MUSCLES (cont.) Our eyes are YOKED together. The OD can t look up while the OS looks down! Where one eye goes, the other follows IS YOUR BRAIN FULL YET? So far, we have covered The three layers (or Tunics) of the eye: FIBROUS TUNIC, UVEAL TRACT or (Vascular Tunic), & the NERVOUS TUNIC The Ocular Media: CORNEA, AQUEOUS HUMOR, CRYSTALLINE LENS, & VITREOUS HUMOR And then the Ocular Adnexa, The Bony Orbit, & the Extraocular Muscles Next, the Visual Pathway The body has AFFERENT neurons (nerves); they carry sensory messages to the brain (like sight!) 12

13 The Visual Pathway: AFFERENT The visual pathway is carrying an afferent message to the brain: 1. RETINA 2. OPTIC NERVE (II Cranial Nerve) 3. OPTIC CHIASM ( chiasm = crossing ) 4. OPTIC TRACT (50% from OD; 50% from OS) 5. LATERAL GENICULATE BODY (LGB) 6. OPTIC RADIATIONS (fibers start to spread out) 7. VISUAL CORTEX (brain interprets visual message here!) Here is another way to look at the Afferent (visual) pathway Notice how 50% of the visual message crosses over to the other side of the head at the OPTIC CHIASM! Images that hit the retina are upside down & backwards AFFERENT (visual) pathway (cont.) Why do you care? Think about the tests you run on patients: Visual Acuity (VAs) Visual Fields (VFs) Cover Testing (CT) Extra Ocular Motility (EOMs) Pupillary Response These all rely on an intact & functioning AFFERENT (Visual) Pathway! In conclusion, we covered the 3 Major Layers (Tunics) of the Eye Ocular Media Ocular Adnexa The Bony Orbit Extraocular Muscles (EOMs) Visual Pathway Lecturer: Thank You for your TIME! M. Patrick COLEMAN, ABOC, COT Kerrville, TX 13