The eye is a 23 mm organ...how difficult can this be? OCULAR ANATOMY AND DISSECTION JEFFREY M. GAMBLE, OD COLUMBIA EYE CONSULTANTS OPTOMETRY & UNIVERSITY OF MISSOURI DEPARTMENT OF OPHTHALMOLOGY CLINICAL INSTRUCTOR The orbit The outer coats of the eye The middle coats of the eye The internal ocular media The retina Structures external to the eye The lacrimal apparatus The extraocular muscles The orbital blood vessels The nerve supply of the orbit Bones of the orbit The maxillary The palatine The frontal The sphenoid The zygomatic The ethmoid The lacrimal The Orbit Openings in the orbit Superior orbital fissure Oculomotor nerve Trochlear nerve Trigeminal nerve Various sympathetic nerves Superior ophthalmic vein Inferior orbital fissure Infraorbital nerve Zygomatic nerve Infraorbital artery Ethmoidal foramen Connects orbit and ethmoid sinus Optic canal Optic nerve Ophthalmic artery The Orbit 1
The Outer Coats The Middle Coats The Sclera (the white of the eye) Episcleral layer Stromal layer Lamina fusca The Cornea Epithelium - six layers thick attached to a basement membrane Bowman s membrane - any injury that breaks through this layer will scar Stroma - makes up 90% of the corneal thickness. Descemet s membrane - elastic membrane attaches to the endothelium Endothelium - works like a pump to keep the cornea the appropriate thickness The Limbus The junction of the cornea and sclera The Uvea - Purpose is to supply blood and drain blood. Also pigmented to reduce stray light The Choroid Vascular supply of the eye Acts like the radiator of the eye The Ciliary Body Makes the aqueous humor and has some role in accommodation The Iris Primary role is to adjust the amount of light entering the eye Internal Ocular Media Anterior and posterior chambers Anterior segment: in front of the lens Posterior segment: behind the lens The crystalline lens - works like the zoom of a camera Receives nutrients from aqueous humor With age, the lens yellows, hardens, loses elasticity and the ciliary muscle weakens = presbyopia The aqueous humor Fills the anterior segment Nourishes the cornea and lens (both are avascular) The vitreous humor Fills the posterior segment Attached at the ora serrata of the retina and the optic disc The Retina 2 Functions: Detect light and movement through the rods Transmit color vision and form through the cones Multiple layers Pigment epithelial layer Photoreceptors External limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Nerve fiber layer Internal limiting membrane 2
The Retina The Fovea The most sensitive portion of the retina Contains only cones Accounts for a dime-sized area of vision at arms length The Retinal Pigmented Epithelium (RPE) Restricts material from the choroid entering the eye (blood-retina) barrier Reduces stray light to protect photoreceptors Provide photorecepters with nourishment Digest spent photoreceptor lamellae discs Reservoirs for Vitamin A (eat your carrots) The Retina Photoreceptors Responsible for the conversion of light signals into electricity The signal is then conducted by the optic nerve to the brain Long and thin cells with an outer and inner segment Outer segment contains disc lamellae (camera film) Rods Rods respond to monochromatic light and compile small pieces of information over a large area Very sensitive to movement 120 million in the eye Cones Respond to only wavelengths of light in the color spectrum Located primarily in the fovea 6.5 million in the eye Structures External to the Eye Eyebrow Primary role is protection of the eye Functions to keep sweat out of the eye Can serve to limit opportunities for a mate (unless you re making 40 million as an NBA star) Eyelids Protect the eye Limit light Spread the tear film over the eye and push tears out the punctum Conjunctiva - Tarsal and Bulbar Thin layer of epithelium that covers the globe and inner lids Turns from the lid back to the globe at the conjunctival fornix ( no that bug that flew in your eye cannot lay eggs behind your eye ) The Lacrimal Apparatus The Lacrimal Gland Innervated by both sympathetic and parasympathetic system 10-12 openings into the eye Reflex tearing will accompany irritation to the cornea (dryness), coughing, sneezing, taste or smell. Tear Film 3 Layers Lipid (secreted by the meibomian glands) Aqueous (secreted by the lacrimal gland) Mucous (secreted by conjunctival goblet cells) All three layers contain Lysozyme, a natural bacteriocidal 3
The Extraocular Muscles Superior Rectus - 1) Elevates 2) adducts 3) intorts Inferior Rectus - 1) Depresses 2) adducts 3) extorts Medial Rectus - 1) Adducts Lateral Rectus - 1) Abducts Superior Oblique - 1) Intorts 2) Depresses 3) Abducts Inferior Oblique - 1) Extorts 2) Elevates 3) Abducts Levator - Raises the upper lid. Orbital Blood Vessels The internal carotid branches into the ophthalmic artery and then separates into the following branches: Central retinal artery Short posterior ciliary arteries Long posterior ciliaries Anterior ciliary arteries Lacrimal artery Muscular branches Supraorbital artery Posterior ethmoidal artery Anterior ethmoidal artery Medial palpebral arteries Nasal artery Supratrochlear artery Ocular Nerves Cow Eye Dissection Optic Nerve (II) - Carries vision to the brain Oculomotor Nerve (III) - Innervates the superior rectus, levator, inferior rectus, inferior oblique and finally the iris Trochlear Nerve (IV) - Innervates the superior oblique Trigeminal Nerve (V) - Sensory innervation to cornea Abducens Nerve (VI) - Innervates the lateral rectus Facial Nerve (VII) - Closes the upper lid 4
5
6
jmgamble@socket.net 26 7