The Eye 2023 PDF

The Eye Images from Human Anatomy 8th ed., © 2015, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. 1 The Orbit • a pyramidal space • base located anteriorly • apex located posteromedially at the optic foramen...

The Eye Images from Human Anatomy 8th ed., © 2015, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. 1 The Orbit • a pyramidal space • base located anteriorly • apex located posteromedially at the optic foramen • contains eyeballs, muscles, Ns, BVs, lacrimal apparatus and orbital fat Orbits, superolateral view The medial walls are parallel. Orbits, superior view 2 The Orbit: Bones Roof A. frontal bone B. sphenoid bone C. fossa for lacrimal gland A J C Medial wall I D. ethmoid bone E. lacrimal bone F. fossa for lacrimal sac B Lateral wall D E G. zygoma F G B. sphenoid bone Floor H. maxilla K H G. zygoma Orbital openings I. optic canal J. superior orbital fissure Ma6.15 K. inferior orbital fissure 3 Surface Anatomy of the Eye A. palpebral fissure C B. medial and lateral angles H C. palpebrae superioris and inferioris G D. pupil B E. iris F F. sclera covered by conjunctiva; conjunctivitis E G. eyelashes with sebaceous and apocrine glands D C’ Ma18.19 covered by cornea A B’ H. in medial angle, the lacrimal lake 4 The Eye & Eyelids A. orbicularis oculi B. sup., inf. tarsal plates F D C’ E C G A B – tarsal glands are large sebaceous glands – often implicated in styes C. medial, lateral palpebral ligaments D. levator palpebrae superioris C. orbital fat D. lacrimal gland Ma18.19 E. lacrimal sac 5 The Eye in Sagittal Section Ma18.21 D C B. palpebral conjunctiva B A C. conjunctival sac D. conjunctival fornix E K J G F I A. orbital conjunctiva H E. sclera F. cornea G. iris H. pupil I. lens J. suspensory ligaments K. ciliary body 6 The Lacrimal Apparatus A B E C F D G H Ma18.19 • fossa for lacrimal gland (A) in superolateral orbit • gland secretes lacrimal fluid into conjunctival sac via ~12 lacrimal ducts (B) that open into the superior conjunctival fornix • lacrimal fluid collects in lacrimal lake (C) • drains via lacrimal puncta (D), lacrimal canaliculi (E) to the lacrimal sac (F) • drains via nasolacrimal duct (G) into nasal cavity (H) 7 The Globe Consists of Three Layers Fibrous Vascular Neural tunic tunic tunic (sclera) (choroid) (retina) The three layers, or tunics, of the eye Ma18.21 The Fibrous Layer: The Sclera & Cornea Visual axis A. opaque sclera covers post. 5/6 of eyeball D B C C B. ant. portion visible through orbital conjunctiva C. insertion of the six extraocular eye muscles, which position the eye in the orbit A D. transparent cornea covers ant. 1/6 of eyeball, bends light to focus it on the fovea (E) Ma18.21 E 9 G The Extraocular Eye Muscles Trochlea A D II B E C • insert into the sclera • position the eye in the orbit F A. Superior rectus B. Inferior rectus C. Medial rectus D. Lateral rectus E. Superior oblique F. Inferior oblique G. LPS Why two muscles elevate, and two muscles depress? Balance out unwanted mvts ELEVATION A Trochlea E Frontal bone LPS E Trochlea Optic nerve A C D ABDUCTION D ADDUCTION B F Ma10.5 B DEPRESSION F Maxilla Lateral view 10 Movements of the Eye are Balanced In the neutral position the eye is adducted relative to the orbital axis: Depression: • superior oblique: depression (and intorsion & abduction) • inferior rectus: depression (and extortion & adduction Elevation: • inferior oblique: elevation (and extorsion & abduction) • superior rectus: elevation (and intorsion & adduction) ELEVATION A Trochlea E C D ABDUCTION F Orbits, superior view ADDUCTION B DEPRESSION Ma10.5 From Moore’s Essential Clinical Anatomy, 7e, © 2023 by Wolters Kluwer 11 Clinical Testing of Extraocular Muscles • abduction aligns angle of gaze with pull of sup., inf. rectus • adduction aligns angle of gaze with pull of sup., inf. oblique From Moore’s Essential Clinical Anatomy, 7e, © 2023 by Wolters Kluwer 12 Innervation: LR6, SO4, AO3 IV III G A D II B F VI E C A. Superior rectus B. Inferior rectus C. Medial rectus D. Lateral rectus E. Superior oblique F. Inferior oblique G. Levator palpebrae superioris Ma10.5 13 Nerve Palsies Oculomotor nerve palsy • only lateral rectus, inferior oblique spared • inc. paralysis of levator palpebrae superioris • inc. paralysis of sphincter pupillae • Presentation: – eye “down and out” – ptosis (droopy eyelid) – mydriasis (large pupil) Abducens nerve palsy • paralysis of lateral rectus • eye adducted at rest due to unopposed medial rectus • when asked to look toward lesioned side, only contralateral (unaffected) eye moves 14 The Pigmented (Vascular) Layer Fornix Levator palpebrae superioris Upper eyelid muscle Posterior cavity Retina Ethmoidal labyrinth Sclera Lacrimal gland Medial rectus muscle Optic nerve (N II) Trochlear nerve (N IV) Lateral rectus muscle Ma18.21 Horizontal section, superior view A The Pigmented (Vascular) Layer Ma18.22 A H F B Ma18.21 G A. choroid ends anteriorly as the: ciliary body (B) & iris (C) C C. iris a contractile diaphragm extending anterior to lens with a central aperture, the pupil • size of pupil controlled by constrictor (D) & dilator (E) pupillae muscles within the iris… D F. ciliary processes secrete aqueous humor, provide attachment for suspensory ligaments of lens (G) H. ciliary muscle, within ciliary body, adjusts thickness of lens to further refract light • controlled by the accommodation reflex... E B 16 Control of Pupillary Size Constrictor pupillae (circular) Pupil Constrictors contract with PSy input Dilator pupillae (radial) Ma18.22 Ma18.21 Dilators contract with Sy input 17 The Accommodation Reflex: Far and Near Vision • lens transparent, biconvex • enclosed in a highly elastic capsule – isolated lens spherical • held in place by suspensory ligaments • ciliary muscle relaxed • suspensory ligaments taut • lens flattened • less refraction of light • tension in suspensory ligaments adjusts shape, convexity of lens The eye accommodates for close vision by tightening the ciliary muscles, allowing the pliable crystalline lens to become more rounded. • ciliary muscle contracted • suspensory ligaments slack • lens rounded • more refraction of light – controlled by ciliary muscle • convexity of lens varies continuously to fine-tune focus of objects on retina Light rays from distant objects are nearly parallel and don’t need as much refraction to bring them into focus. Light rays from close objects diverge and require more refraction to bring them into focus. 18 The Lens and Chambers of the Eye Ma18.22 Vascular tunic Choroid Ciliary body Iris Posterior cavity Neural tunic (retina) Neural layer Pigmented layer Anterior cavity Fibrous tunic Cornea Sclera The lens is suspended between the posterior cavity and the anterior cavity. The Circulation of Aqueous Humour Ciliary process • anterior cavity divided into anterior and posterior chambers, separated by the iris Suspensory ligaments • epithelial cells covering the ciliary body secrete aqueous humor into the Anterior cavity: Posterior chamber posterior chamber Anterior chamber Posterior cavity (vitreous chamber) Pupil Cornea Lens Body of iris Ciliary body Canal of Schlemm Conjunctiva Sclera Choroid Retina Ma18.22 • aqueous humor flows from the posterior chamber through the pupil, into the anterior chamber • nourishes the avascular cornea • at the iridocorneal angle aqueous humor drains through the trabecular meshwork into the scleral venous sinus (canal of Schlemm) and is thus returned to venous blood • glaucoma occurs with increased intraocular pressure • usually caused by decreased 20 Glaucoma • aqueous humor produced / removed at same rate to maintain intraocular pressure, IOP • in glaucoma, IOP rises due to accumulation of aqueous humor • increased pressure on retina, optic nerve inhibits blood flow • causes ischemic damage of retina Open-angle glaucoma most common • slowly developing • age-related changes in the trabecular meshwork increases resistance to aqueous humor outflow • initially peripheral vision loss, eventually blindness • screening for glaucoma part of eye exam • tx medication, laser trabeculoplasty 21 The Inner (Neural) Layer A. the retina B. the ora serrata separates the visual and nonvisual parts of the retina B C. macula lutea A D. fovea centralis E. optic disc: the “blind spot” E F. optic nerve C G. central A & V Ma18.21 F G D 22 Macula Fovea lutea Ma18.23 Optic disc Central retinal artery (blind spot) and vein emerging from center of optic disc A photograph taken through the pupil showing the retinal blood vessels, the origin of the optic nerve, and the optic disc The Retina Has Four Cell Layers 1. ganglion cells: axons form optic N 2. horizontal, bipolar & amacrine cells process visual signal 3. photoreceptors (rods & cones) transduce light energy into a change in membrane potential 4. pigmented layer absorbs XS light Horizontal cell Cone Rod Choroid Pigmented layer of retina Rods and cones Amacrine cell Bipolar cells Ganglion cells Nuclei of Nuclei of rods Nuclei of ganglion cells and cones bipolar cells LM x 75 Ma18.23 LIGHT The retina 24 Why is Resolution Highest in the Fovea? 1. types of photoreceptors • there are two kinds of photoreceptors: rods and cones • cones are specialized for: – high temporal resolution due to fast response time – low sensitivity ∴ only saturate in intense light – colour vision due to the presence of three types of cones with different pigments • rods are specialized for: – low temporal resolution due to slow response time – high sensitivity saturates in daylight – achromatic as there is only one kind of rod pigment • cones are concentrated at the fovea, rods in the periphery of the retina 25 Why is Resolution Highest in the Fovea? cont. 2. ratio of photoreceptors to ganglion cells • average for entire retina 137:1 • in periphery 1000:1 ∴pixel size large • at the fovea 1:1 ∴pixel size small 3. anatomically adapted for light sensitivity • light passes through fewer cell layers to reach photoreceptor cells Rods and cones Fovea Bipolar cells Ganglion cells 26 The End Ma18.23