Ocular Anatomy & Physiology 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 Lecturer: M. Patrick COLEMAN, ABOC, COT 6. Accurately identify key ocular structures that Kerrville, TX compose the visual pathway Topics to be covered: Let’s get oriented first… • 3 Major Layers (Tunics) of the Eye • Superior = UPWARD (or TOP) • Ocular Media • Inferior = DOWNWARD (or BOTTOM) • Ocular Adnexa • Nasal / Medial = TOWARD NOSE • The Bony Orbit • Temporal / Lateral = TOWARD TEMPLE • Posterior = BEHIND (or Toward the BACK) • Extraocular Muscles (EOMs) • Anterior = IN FRONT (or Toward the Front) • Visual Pathway FIBROUS TUNIC 3 Major Layers (Tunics) of EYE • FIBROUS TUNIC • Protective layer of eye • Tough & fibrous • UVEAL TRACT or (Vascular Tunic) • Two parts: – Cornea – Sclera • NERVOUS TUNIC 1 Fibrous Tunic (cont.): Layers of the Cornea Fibrous Tunic: Cornea • Anterior 1/6th of the fibrous tunic • Clear; Avascular; approx. +40.00D 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.): Sclera UVEAL TRACT (Vascular Tunic) • White in color (appears bluish in infants) • IRIS (colored part of eye) • Avascular (without blood vessels; (what look like blood vessels in the sclera are really in the EPISCLERA which lays on top of the • CILIARY BODY (behind iris) sclera) • Makes up posterior 5/6th of fibrous tunic • CHOROID (can see it on retinal photos, • Very tough! and OCT scans of the retina!) • Cornea & sclera are the “same” material! UVEAL TRACT (cont.): UVEAL TRACT (cont.): IRIS Iris, Ciliary Body, Choroid… • 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 UVEAL TRACT (cont.): Ciliary Body UVEAL TRACT (cont.): Ciliary Body • Located just behind the iris, at its base • 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 UVEAL TRACT (cont.): CHOROID (processes & muscles) UVEAL TRACT (cont.): CHOROID NERVOUS TUNIC • Supplies blood to the iris, The Retina…that’s it! ciliary body, inner retina & • Retina ‘lines’ the back 2/3rds of eye inner sclera • 10 layers thick; all the layers are transparent except • The “CHOW HALL” of the the RPE (retinal pigment epithelial) layer eye - brings nourishment • Retina lies on top of the choroid & oxygen • It’s in contact with the vitreous humor (fluid) • Contains cells that respond to light (photoreceptors); –“Sandwiched” between the two (2) types – CONES & RODS SCLERA and the RETINA • 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 Nervous Tunic (i.e., the RETINA) Nervous Tunic (i.e. RETINA) cont. • ‘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.) Nervous Tunic (i.e. 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). Nervous Tunic (i.e. RETINA) cont. Nervous Tunic (i.e. RETINA) cont. • CONES are for bright (photopic) • RODS are for dim conditions; can see color & fine (scotopic) conditions; detail They provide a poor – There are approximately 6 million cones in the retina image but have a great – The fovea centralis (center of ability to sense Macula) contains ONLY movement CONES! – There are – Cones emit a chemical called approximately 120 IODOPSIN TRIVIA QUESTION: million rods in the Trivia Question: * When entering a dark retina. • What percentage of MEN are movie theater, whose eyes “colorblind”? – Rods emit a chemical will ‘dark adapt” the • What percentage of WOMEN called RHODOPSIN quickest: A young person are “colorblind”? or an elderly person? 4 Nervous Tunic (i.e. RETINA) cont. Nervous Tunic (i.e. RETINA) cont. • The layer closest to the • The retina is CLEAR, with the vitreous humor is the exception of the Retinal Pigment RETINAL NERVE Epithelium (RPE) layer which, like FIBER LAYER (NFL) the iris, contains pigment • This layer contains the – The RPE layer is the “garbage nerves coming from man”: every part of the retina • It absorbs excess light • At the optic nerve, the –AND nerve fiber bundles are most concentrated • It must remove the chemicals superiorly & inferiorly emitted by the rods (rhodopsin) and cones • Ever do an OCT scan of (iodopsin) as these chemicals the area around the optic nerve head (ONH) of a are TOXIC TO THE RETINA. glaucoma patient? Why? Nervous Tunic (i.e. RETINA) cont. Zeiss OCT scan • As the nerve fibers of optic nerve approach the optic head (ONH) of disk, they start to both eyes: bundle closer Green = GOOD together and form the cable to the brain Yellow = we call the OPTIC BORDERLINE NERVE (II CN) Red = BAD • In GLAUCOMA, these (glaucoma?!) nerve fibers die off Nervous Tunic (i.e. RETINA) cont. So that’s it, right? HARDLY! • 9/10ths of the Retinal blood • The TUNICS of the eye are supply comes just “layers” of the main from the functional components. CENTRAL • There are many other RETINAL “parts” that make up the eye ARTERY (CRA) and help it work correctly. • Time to look at the “rest of the eye”… 5 OCULAR MEDIA OCULAR MEDIA - Cornea (cont.) • These are the clear structures of the • Cornea eye light must – Needs a good tear layer to transmit light well pass through to – Good quality tears have three parts: get to the retina. • Lipid (oil) layer (top/outermost layer) - • They are the: keeps aqueous layer from evaporating – CORNEA away too quickly – AQUEOUS • Aqueous layer (middle layer) - water HUMOR portion of tear (thickest layer!) – LENS • Mucin (mucous) layer (innermost/against – VITREOUS cornea) - keeps tears ‘stuck’ against HUMOR cornea OCULAR MEDIA OCULAR MEDIA – Aqueous Humor (cont.) (cont.): TEAR FILM 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 +18.00D to +21.00D of power 6 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 OCULAR ADNEXA • Eyelids are the folds of tissue that cover the eye itself. Their primary purpose is… • Eyelids & – PROTECTION!!! Landmarks – Limit amount of light entering the eye • Muscles of the (giving the pupil an “assist” @ times) eyelids –Keep dust & dirt out of the eye (& fingers & • Tarsal Plate & racquetballs & fish hooks &…well, you get Glands the idea!) • Conjunctiva & Lacrimal System – Eyelashes = ‘early warning’ sensors • (Which lid has MORE lashes? UPPER or lower?) 7 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 EYELIDS & LANDMARKS (cont.) SUPERIORIS (LEVATOR)! • MUSCLES of the EYELIDS (cont.): –To CLOSE the lids, we use the: • A way to remember? • ORBICULARIS OCULI muscle & the… • Mueller gets on the LEVATOR to go UP & fix the oculoMOTOR on the 3rd (III) floor • RIOLAN’S muscle –The VII CN (Facial nerve) “operates” these • Levator OPENS the eyelids two muscles – Mueller