The Eye - PDF

The Eye Dr. Jessa Mayet Sumatra-Mabalot M.P.H Overview of the Orbit Orbit Pyramid-shaped bony recess in the anterior part of the skull lined by the periosteum called the periorbital fascia Contents: eye, extrinsic muscles, optic nerve,oculomotor nerve,ciliary ganglion,...

The Eye Dr. Jessa Mayet Sumatra-Mabalot M.P.H Overview of the Orbit Orbit Pyramid-shaped bony recess in the anterior part of the skull lined by the periosteum called the periorbital fascia Contents: eye, extrinsic muscles, optic nerve,oculomotor nerve,ciliary ganglion, trochlear nerve, CN V1, abducens nerve, ophthalmic artery, superior and inferior ophthalmic veins, lacrimal apparatus, fatty tissue Walls of the Orbit Openings in the Orbit Structures Opening Bony boundaries passing through Optic Lesser wing of the Optic nerve and foramen sphenoid ophthalmic artery Openings in the Orbit Bony Opening Structures passing through boundaries CN V lacrimal ,frontal,nasociliary Superior Greater and branch Orbital Lesser wing of CN III,IV,VI Fissure the sphenoid Superior and inferior ophthalmic veins Openings in the Orbit Bony Opening Structures passing through boundaries Greater wing of Inferior Infraorbital nerve and vessels the sphenoid Orbital Zygomatic nerve Fissure Branch of ophthalmc vein Maxilla Openings in the Orbit Bony Opening Structures passing through boundaries Supraorbital Supraorbital nerve and vessels Foramen/ Frontal Supratrochlear nerve and vessels notch Openings in the Orbit Bony Opening Structures passing through boundaries Infraorbital groove and Maxilla Infraorbital nerve and vessels canal Openings in the Orbit Bony Opening Structures passing through boundaries Zygomatic Zygomatic Branches of the zygomatic foramen Openings in the Orbit Bony Opening Structures passing through boundaries Nasolacrimal Lacrimal Nasolacrimal duct canal Eye Eye A spherical globe with a diameter of approx. 2.5cm that lies in the orbit’s anterior portion Surrounded by a thin capsule- fascia bulbi (Tenon’s capsule) Has 3 coats: fibrous coat, vascular pigmented coat, and the nervous coat Tenon’s Capsule  3 coats: Fibrous Sclera,cornea Vascular pigmented Choroid, ciliary body, iris & pupil Nervous Retina Sclera Outermost layer Very fibrous White along the periphery Opaque Posteriorly, it is pierced by the optic nerve and is fused with the dural sheath of that nerve Anterior portion is transparent (cornea) Fibrous Coat of the Eye Sclera Lamina cribrosa- area pierced by the nerve fibers of the optic nerve Also pierced by the ciliary arteries and nerves and their assoc veins , venae vorticosae Directly continuous in front with the cornea at the corneoscleral junction or limbus Cornea Transparent Largely responsible for the refraction of light entering the eye In contact posteriorly with the aqueous humor Avascular, no lymphatic drainage Nourished by diffusion from the aqueous humor and from the capillaries at its edge Cornea Most important refractive medium of the eye Refractive power occurs on the anterior surface of the cornea where refractive index of the cornea differs greatly from that of the air Tear film in the cornea important in maintaining the normal environment for the corneal epithelial cells Vascular Pigmented Coat of the Eye Vascular Pigmented Coat “Uveal tract” Composed of the choroid layer ciliary body iris Choroid Vascular Pigmented Coat Pigmented (outer) vascular (inner) layer between sclera and retina Extends from the region of the optic nerve then anteriorly where it is continuous with the ciliary body near the ora serrata Ciliary Body Vascular Pigmented Coat Located between the choroid and the iris Ring-shaped Has a series of transparent fibers that form the suspensory ligament of the lens Within it is the ciliary muscle which changes the shape of the lens Ciliary body Vascular Pigmented Coat Also contains ciliary processes that are radially arranged in folds or ridges that are connected to the suspensory ligaments of the lens Ciliary Muscle Vascular Pigmented Coat Supplied by the parasympathetic fibers from CN III (oculomotor) Contraction of the ciliary muscle pulls the ciliary body forward which relieves the tension in the suspensory ligament resulting in lens becoming more convex Iris Vascular Pigmented Coat A thin disclike structure with a central opening - the pupil Suspended in the aqueous humor between the cornea and the lens Separates the aquaeous humor into the anterior chamber (anterior to the iris) posterior chamber (between the iris and the lens) Iris Vascular Pigmented Coat Muscle fibers are involuntary and consist of circular and radiating fibers sphincter pupillae muscle (circular) dilator pupillae muscle (radial) Iris Vascular Pigmented Coat sphincter pupillae muscle Circular fibers that are arranged around the margin of the pupil Supplied by the parasympathetic fibers from the CN III Bright light & accommodation= pupil constriction Iris Vascular Pigmented Coat dilator pupillae muscle Radial fibers that lie close to the posterior surface Supplied by the sympathetic fibers (superior cervical ganglion) Low intensity light& excessive sympathetic activity= Pupil dilation Nervous Coat of the Eye Retina Nervous Coat Innermost coat of the eye Thin and highly vascular Consist of an outer pigmented layer In contact with the choroid inner nervous layer In contact with the vitreous body Retina Nervous Coat its anterior edge forms a wavy ring, the ora serrata, and the nervous tissues end here anterior part nonreceptive consists merely of pigment cells Covers the ciliary processes and the back of the iris Posterior 3 quarters Receptor organ Retina Three areas located on the retina’s posterior portion Optic disc Macula lutea Fovea centralis Optic Disc Marks the beginning of the optic nerve Where the retina’s central artery enters and divides into superior and inferior branches Complete absence of rods and cones- “blind spot” Seen as pale pink in color, paler that surrounding retina (ophthalmoscope) Macula Lutea Located lateral to the optic disc A depressed, yellow-appearing area that contains the fovea centralis in its center Area of the retina for the most distinct vision Contents of the Eyeball Contents of the Eyeball Refractive media Aqueous humor Vitreous body Lens Aqueous Humor Is a clear fluid that fills the anterior and posterior chambers of the eyeball Believed to be a secretion from the ciliary process from which it enters the posterior chamber and then flows into the anterior chamber through the pupil Aqueous Humor Canal of Schlemm Where the fluid from the anterior chamber is drained from the iridocorneal angle Obstruction in flow= increase intraocular pressure (glaucoma) Aqueous Humor Functions mainly to support the wall of the eyeball by exerting internal pressure maintaining optical shape Nourishes the cornea and the lens Removes products of metabolism Vitreous Body A transparent gel that fills the eyeball behind the lens Contribute slightly to the magnifying power of the eye Supports the posterior surface of the lens Assists in holding the neural part of the retina against its pigmented part  hyaloid canal a narrow channel that runs through the vitreous body from the optic disc to the posterior surface of the lens in the fetus, it is filled by the hyaloid artery, which disappears before birth Lens Located posterior to the iris Encircled by the ciliary process Transparent biconvex structure enclosed in a transparent capsule responsible for focusing Lens Connected to the ciliary body by the suspensory ligaments Pull of the radiating fibers of the suspensory ligament tends to keep the elastic lens flattened to enable focus on distant objects Lens Lens fibers Formed from the cuboidal epithelium at the equator of the lens Make up the bulk of the lens Clinical Correlate Accommodation of the Eye Refers to the ability of the eye to change its focus from distant to near objects (and vice versa) to maintain a clear image of an object To accommodate the eye for close objects, the ciliary muscle contracts and pulls the ciliary body forward and inward so that the radiating fibers of the suspensory ligament are relaxed. This allows the elastic lens to assume a more globular shape. Accommodation of the Eye Constriction of the Pupil during Accommodation of the Eye sphincter pupillae muscle contracts so the pupil becomes smaller to ensure that the light rays pass through the central part of the lens Accommodation of the Eye Convergence of the Eyes during Accommodation of the Lens Retina focus only on one set of objects When an object moves closer, eyes converge so that a single object (not two) is seen Convergence results from coordinated contraction of the medial rectus muscles Movements of the Eyeball Terms Used in Describing Eye Movements All movements of the eyeball are related to direction of the movement of the anterior pole (center of the cornea/pupil) as it rotates on any of the 3 axes- horizontal, vertical and sagittal Terms Used in Describing Eye Movements Elevation Rotation of the eye upward Depression Rotation of the eye downward Abduction Rotation of the eye laterally Adduction Rotation of the eye medially Extrinsic Muscles of the Eye Six voluntary muscles that run from the posterior wall of the orbital cavity to the eyeball superior rectus muscle inferior rectus muscle medial rectus muscle lateral rectus muscle superior oblique muscle Inferior oblique muscle Right Eye Superior Rectus Muscle Origin: Common tendinous ring on sphenoid Insertion: superior sclera Action:elevation, adduction, intorsion Nerve:superior division CN III * a check ligament attaches it to the levator palpebrae superioris muscle to help elevate the upper eyelid Superior Rectus Muscle Levator palpebrae muscle right Superior rectus muscle  Levator palpebrae superioris Origin: root of the orbit Insertion: skin of the upper eyelid Levator palpebrae muscle right Actions: raises the upper eyelid Nerve:superior division of CN III, sympathetic fibers to the smooth muscle *lesion of the sympathetics will lead to drooping of the upper eyelid-ptosis Inferior Rectus Muscle Origin: Common tendinous ring on sphenoid Insertion: inferior sclera Action: depression, adduction, extorsion Nerve: inferior division CN III Attached to the inferior tarsal plate via a check ligament to help depress lower eyelid Medial Rectus Muscle Origin: Common tendinous ring on sphenoid Insertion: medial sclera Action: adduction Nerve: inferior division CN III Most medial of all the extraocular muscles Lateral Rectus Muscle Origin: Common tendinous ring on sphenoid Insertion: lateral sclera Action: abduction Nerve: CN IV (trochlear) Superior Oblique Muscle Origin: body of the sphenoid Insertion: superior portion of the posterolateral sclera Action: depression,abduction, intorsion Nerve: CN VI (abducens) Its tendon passes through a trochlea which serves as a pulley Inferior Oblique Muscle Origin: maxilla (lateral to the lacrimal groove) Insertion: inferior portion of the posterolateral sclera Action:elevation, abduction, extorsion Nerve:inferior division of CN III (oculomotor) Only EOM that attaches to the maxilla Extraocular Muscles Extraocular Muscles Extraocular Muscles Extraocular Muscles Innervation of the Eye Sensory Vision- special somatic afferent via the optic nerve General sensation -ophthalmic division of trigeminal (some V2) nerve Motor Oculomotor, trochlear, abducens nerves Autonomics- parasympathetic(ciliary ganglion), sympathetic (superior cervical ganglion) Innervation of the Eye Cranial nerves II- vision III- extraocular motor and autonomics to the intrinsic muscle of the eye IV- extraocular motor V-general sensation VI- extraocular motor