Eye and Visual Pathways 2 PDF

EYE AND VISUAL PATHWAYS 2 By: Dr. Shahnaz Sabetkam Assistant professor of Anatomical sciences Kyrenia University  Vessels Arteries. ❖ The arterial supply t...

EYE AND VISUAL PATHWAYS 2 By: Dr. Shahnaz Sabetkam Assistant professor of Anatomical sciences Kyrenia University  Vessels Arteries. ❖ The arterial supply to the structures in the orbit, including the eyeball, is by the ophthalmic artery. ❖ Is a branch of the internal carotid artery, given off immediately after the internal carotid artery leaves the cavernous sinus. ❖ The ophthalmic artery passes into the orbit through the optic canal with the optic nerve. ❖ In the orbit the ophthalmic artery initially lies inferior and lateral to the optic nerve. ❖ As it passes forward in the orbit, it crosses superior to the optic nerve and proceeds anteriorly on the medial side of the orbit. ❖ In the orbit the ophthalmic artery gives off numerous branches as follows: 1-The lacrimal artery ❖ On the lateral side of the optic nerve ❖ Supplying the lacrimal gland, muscles ❖ The anterior ciliary branch ❖ The lateral palpebral branches ❖ Zygomatic (zygomaticofascial and zygomaticotemporal) 2-The central retinal artery The center of the nerve to the retina Is clearly seen when viewing the retina with an ophthalmoscope—occlusion of this vessel or of the parent artery leads to blindness. 3-The long and short posterior ciliary arteries Are branches that enter the eyeball posteriorly Piercing the sclera, and supplying structures inside the eyeball. The central artery of the retina is an end artery. It does not have effective anastomoses with other arteries. Occlusion of the artery results in blindness. The intraocular part of the artery can be seen, in the living, through an ophthalmoscope. 4-The muscular arteries 5-The supraorbital artery Arises from the ophthalmic artery Exits the orbit through the supraorbital foramen with nerve. 6-The posterior ethmoidal artery Exits the orbit through the posterior ethmoidal foramen Supply the ethmoidal cells and nasal cavity 7-The anterior ethmoidal artery ❖ Exits the orbit through the anterior ethmoidal foramen ❖ Giving off the anterior meningeal branch ❖ Into the nasal cavity 8-The medial palpebral arteries, ✓Small branches ✓The upper and lower eyelids 9-The dorsal nasal artery, oOne of the two terminal branches of the ophthalmic artery oLeaves the orbit to supply the upper surface of the nose 10-The supratrochlear artery ❑ The other terminal branch of the ophthalmic artery ❑ Leaves the orbit with the supratrochlear nerve ❑ Supplying the forehead  Veins There are two venous: the superior ophthalmic vein The inferior ophthalmic vein The superior ophthalmic vein: ▪ Begins by connecting veins from the supraorbital vein and the angular ▪ It passes across the superior part of the orbit, receiving tributaries from The companion veins to the branches of the ophthalmic artery and veins draining the posterior part of the eyeball. ▪ Posteriorly, it leaves the orbit through the superior orbital fissure and enters the cavernous sinus. The inferior ophthalmic vein : ✓ Is smaller than ✓ Begins anteriorly, and passes across the inferior part of the orbit. ✓ It receives various tributaries from muscles and the posterior part of the eyeball as it crosses the orbit. The inferior ophthalmic vein: 3 routes to leave the orbit posteriorly by: A-joining with the superior ophthalmic vein B-passing through the superior orbital fissure on its own to join the cavernous sinus C-Passing through the inferior orbital fissure to join with the pterygoid plexus of veins in the infratemporal fossa. Because the ophthalmic veins communicate with the cavernous sinus, they act as a route by which infections can spread from outside to inside the cranial cavity.  Innervation Numerous nerves pass into the orbit and innervate structures within its bony walls. They include: ❑ Optic nerve ❑ The oculomotor nerve ❑ The trochlear nerve ❑ The abducent nerve ❑ Autonomic nerves ❑ Other nerves such as the ophthalmic nerve [V1] innervate orbital structures and then travel out of the orbit to innervate other regions.  Optic nerve The optic nerve [II] is not a true cranial nerve, but rather an extension of the brain carrying afferent fibers from the retina of the eyeball to the visual centers of the brain. Clinical anatomy The optic nerve is surrounded by the cranial meninges, including the subarachnoid space, which extends as far forward as the eyeball. Any increase in intracranial pressure therefore results in increased pressure in the subarachnoid space surrounding the optic nerve. This may prevent venous return along the retinal veins, causing edema of the optic disc (papilledema), which can be seen when the retina is examined using an ophthalmoscope. The optic nerve leaves the orbit through the optic canal. It is accompanied in the optic canal by the ophthalmic artery. ❖ Leaves the anterior surface of the brainstem between the midbrain Oculomotor nerve and the pons. ❖ Passes forward in the. lateral wall of the cavernous sinus ❖ Just before entering the orbit divides into superior and inferior branches. ❖ Enter the orbit through the superior orbital fissure ❖ Lying within the common tendinous ring ❖ The small superior branch passes over the lateral side of the optic nerve to innervate the superior rectus and levator palpebrae superioris muscles ❖ The large inferior branch divides into three branches: One passing below the optic nerve as it passes to the medial side of the orbit to innervate the medial rectus muscle A second descending to innervate the inferior rectus muscle The third descending as it runs forward along the floor of the orbit to innervate the inferior oblique muscle  Oculomotor nerve As the third branch descends, it gives off the branch to the ciliary ganglion. To the ciliary ganglion and carries preganglionic parasympathetic fibers. The postganglionic fibers are distributed to the eyeball through short ciliary nerves and innervate the sphincter pupillae and ciliary muscles.  Trochlear nerve Arises from the posterior surface of the midbrain Passes around the midbrain Passing through the lateral wall of the cavernous sinus just below the oculomotor nerve Through the superior orbital fissure Above the common tendinous ring Enter the superior oblique muscle  Abducent nerve The abducent nerve [VI] arises from the brainstem between the pons and medulla. It enters the dura, continues in a dural canal until it reaches the cavernous sinus. Enters the cavernous sinus runs through lateral to the internal carotid artery. Enters the orbit through the superior orbital fissure within the common tendinous ring. Supply the lateral rectus muscle  Postganglionic sympathetic fibers ❑ Preganglionic sympathetic fibers arise from the upper segments of the thoracic spinal cord, mainly T1. ❑ They enter the sympathetic chain through white rami commu- nicantes ❑ Ascend to the superior cervical ganglion where they synapse with postganglionic sympathetic fibers. ❑ The postganglionic fibers are distributed along the internal carotid artery and its branches. ❑ The postganglionic sympathetic fibers travel with the ophthalmic artery. ❑ Once in the orbit the fibers are distributed to the eyeball either by: A. Passing through the ciliary ganglion, without synapsing, and joining the short ciliary nerves B. Or passing through long ciliary nerves to reach the eyeball. ❑ In the eyeball postganglionic sympathetic fibers innervate the dilator pupillae muscle.  Ophthalmic nerve [V1] ❑ Is the smallest and most superior of the three divisions of the trigeminal nerve. ❑ This purely sensory nerve receives input from structures in the orbit and from additional branches on the face and scalp. ❑ Leaving the trigeminal ganglion ❑ Passes forward in the lateral wall of the cavernous sinus inferior to the trochlear and oculomotor nerves. ❑ Just before it enters the orbit it divides into three branches: 1. Nasociliary 2. Lacrimal 3. Frontal These branches enter the orbit through the superior orbital fissure with the frontal and lacrimal nerves outside the common tendinous ring, and the nasociliary nerve within the common tendinous ring Lacrimal nerve ❖ The lacrimal nerve is the smallest of the three branches of the ophthalmic nerve [V1]. ❖ Passes forward along the upper border of the lateral rectus muscle. ❖ It receives a branch from the zygomaticotemporal nerve, which carries parasympathetic and sympathetic postganglionic fibers for distribution to the lacrimal gland. The lacrimal nerve supplies: a) The lacrimal gland b) Conjunctiva c) Lateral part of the upper eyelid  Frontal nerve ❑ The frontal nerve is the largest branch ❑ Receives sensory input from areas outside the orbit ❑ Exiting the superior orbital fissure ❑ Above of the levator palpebrae superioris ❑ It divides into its two terminal branches: a. Supraorbital nerves b. Supratrochlear nerves  Terminal branches of Frontal nerve The supratrochlear nerve continues forward in an anteromedial direction, passing above the trochlea, exits the orbit medial to the supraorbital foramen, and supplies the conjunctiva and skin of the upper eyelid and the skin on the lower medial part of the forehead. The supraorbital nerve is the larger of the two branches, continues forward, passing between the levator palpebrae superioris muscle and the periorbita covering the roof of the orbit, exits the orbit through the supra-orbital notch and ascends across the forehead and scalp supplying the upper eyelid and conjunctiva, the forehead, and as far posteriorly as the middle of the scalp.  Nasociliary nerve The nasociliary nerve is intermediate in size between the frontal and lacrimal nerves and is usually the first branch from the ophthalmic nerve. It is most deeply placed in the orbit, entering the area within the common tendinous ring between the superior and inferior branches of the oculomotor nerve.  Nasociliary nerve crosses the superior surface of the optic nerve as it passes in a medial direction below the superior rectus muscle. Its first branch, the communicating branch with the ciliary ganglion (sensory root to the ciliary ganglion continues forward along the medial wall of the orbit, between the superior oblique and the medial rectus muscles, giving off several branches. Several branches include: ❑ The long ciliary nerves, which are sensory to the eyeball but may also contain sympathetic fibers for Nasociliary nerve pupillary dilation. ❑ The posterior ethmoidal nerve, which exits the orbit through the posterior ethmoidal foramen to supply posterior ethmoidal cells and the sphenoidal sinus. ❑ The infratrochlear nerve, which distributes to the medial part of the upper and lower eyelids, the lacrimal sac, and skin of the upper half of the nose. ❑ The anterior ethmoidal nerve, which exits the orbit through the anterior ethmoidal foramen to supply the anterior cranial fossa, nasal cavity, and skin of the lower half of the nose.  Ciliary ganglion The ciliary ganglion is a parasympathetic ganglion of the oculomotor nerve [III]. The ciliary ganglion is a very small ganglion, in the posterior part of the orbit immediately lateral to the optic nerve and between the optic nerve and the lateral rectus muscle. Fıbers: 1. It is associated with the nasociliary branch of the ophthalmic nerve (sensory fibers). 2. Is the site where preganglionic and postganglionic parasympathetic neurons synapse as fibers from this part of the autonomic division of the PNS make their way to the eyeball. 3. The ciliary ganglion is also traversed by postganglionic sympathetic fibers and sensory fibers as they travel to the eyeball. THE EYEBALL  THE PERIPHERAL ORGAN OF VISION Located in the orbit- embedded in orbital fat The fascial sheath (bulbar sheath) or Tenon capsule: Suspensory ligament Investing fascia surrounding each muscle (Tubular sheath) Check ligaments (medial and lateral rectus muscles) LAYERS (TUNICS) OF EYEBALL  LAYERS (TUNICS) of Eyeball I-FIBROUS LAYER II- VASCULAR LAYER (uveal tract) III-NERVOUS LAYER (retina) Walls of the eyeball Surrounding the internal components of the eyeball are the walls of the eyeball. They consist of three layers: ✓ The outer fibrous layer consists of the sclera posteriorly and the cornea anteriorly. ✓ The middle vascular layer consists of the choroid posteriorly and is continuous with the ciliary body and iris anteriorly. ✓ The inner layer consists of the optic part of the retina posteriorly and the nonvisual retina that covers the internal surface of the ciliary body and iris anteriorly. 30  I-FIBROUS LAYER Two spheres - anterior segment, transparent, 1/6 - posterior segment, opaque,5/6  FIBROUS LAYER- FUNCTIONS A place for the attachment of muscles. Maintain a constant intraocular pressure. Protect the deeply located structures.  FIBROUS LAYER. CORNEA -1/6 ANTERIOR PART Transparent SCLERA -5/6 POSTERIOR PART White  FIBROUS LAYER SCLERA ( characteristics ) -5/6 -It composed of dense fibrous tissue -Opaque, white in colour (conjunctiva covers as the “white of the eye) -Thickest behind -Posteriorly it is pierced by the nerve fibers of optic nerve  I-1.SCLERA Tenon’s capsule (Fascial Sheath-Vagina Bulbi) Episcleral space SCLERA Perichoroidal space- delicate cellular tiss. (suprachoroid lamina) VASCULAR LAYER  SCLERA IS POSTERIORLY PIERCED BY – Fibers of the optic nerve-LAMINA CRIBROSA SCLERAE – Ciliary vessels and nerves – Central vessels of retina – Venae vorticosae (4-5 in number)  SCLERA Meets the CORNEA at the SCLEROCORNEAL JUNCTION ( LIMBUS CORNEA ) – SINUS VENOSUS SCLERAE ( SCHLEMM’S CANAL ) at the sclerocorneal junction.  SCLERA Vessels ----- few. Nerves-------- ciliary nerves  I-2.CORNEA The major site of refraction of light entering the eye. More convex , 1/6 anterior part. Transparent. Avascular. Rich in nerves-opthalmic n.(long ciliary nn) Does not have lymph vessels.  II-VASCULAR LAYER (UVEAL TRACT ) (Pigmented layer) It consists from behind forward: 1.CHOROID 2. CILIARY BODY 3. IRIS  II-1.CHOROID Is composed of an outer pigmented layer and an inner Thin, highly vascular membrane. Color– dark brown Extends as far as the ora serrata. Outer surface is related to— suprachoroid lamina Inner surface—pigmented layer of retina  II-1.CHOROID The choroid is posterior and represents approximately two thirds of the vascular layer. It is a thin, highly vascular, pigmented layer consisting of smaller vessels adjacent to the retina and larger vessels more peripherally. Firmly attached to the retina, loosely to the sclera  II-2.CILIARY BODY THE DIRECT ANTERIOR CONTINUATION OF THE CHOROID  CILIARY BODY Ciliary body – Ciliary ring (This triangular-shaped structure, between the choroid and the iris, forms a complete ring around the eyeball) – Ciliary process – Ciliary muscles  CILIARY BODY Is continuous posteriorly with the choroid It lies behind the peripheral margin of the iris  CILIARY BODY-FUNCTIONS SUSPENSION OF LENS PRODUCTION OF AQUEOUS HUMOUR CHANGING THE ANTEROPOSTERIOR DISTANCE OF LENS (FOR THE MECHANISM OF ACCOMODATION )  CILIARY BODY-INTERNAL ASPECT May be divided into two parts 1-Anterior plicated part (corona ciliaris) 2-posterior smooth part (ciliary ring)  CILIARY BODY Rich in blood supply -Anterior ciliary arteries -Long posterior ciliary arteries -Short posterior ciliary arteries  ANTERIOR PLICATED PART 70- 80 CILIARY PROCESSES- secretion *AQUEOUS HUMOUR SUSPENSORY LIGAMENTS- towards the lens - Zonular fibers- *accomodation- CILIARY ZONULE  POSTERIOR SMOOTH PART CILIARY RING  CILIARY MUSCLE Smooth muscle- longitudinal,circular,oblique fibers Nerves- OCULOMOTOR- postganglionic fibers from ciliary ganglion-in short ciliary nerves Function-changes in anteroposterior distance of lens. ---contract-susp. lig. relax.-thickness of lens increases. (or opposite)  CILIARY MUSCLE Nerve: the parasymphatetic fibers from the ‘’oculomotor nerve’’ After synapsing the ciliary gang, the postganglionic fibers pass forward to the eyeball in the ‘’short ciliary nerve’’  CILIARY MUSCLE Action:Contraction of the ciliary muscle pulls the ciliary body forward. This relieves the tension in the suspensory ligament, and the elastic lens becomes more convex. This increases the refractive power of the lens  CILIARY MUSCLE The nervous impulses pass from the retina via the optic nerve, the optic chiasma, the optic tract, the lateral geniculate body, optic radiation and the cerebral cortex, occipital lobe The visual cortex is connected to the eye field of the frontal cortex.  CILIARY MUSCLE The visual cortex is connected to the eye field of the frontal cortex. From here the efferent impulses reach the constrictor pupilla via the 3. CN, ciliary gang., and the short ciliary nerves.  II-3.IRIS Coloured (blue- dark brown ) Surrounds the pupil Adjustable diaphragm Has two margins - CILIARY - PUPILLARY Attached to cornea by --pectinate ligaments  IRIS Somewhat suspended in aqueous humour and divides the area between cornea and lens into two chambers: 1. ANTERIOR CHAMBER 2. POSTERIOR CHAMBER Cornea – iris meet at: ‘’IRIDOCORNEAL ANGLE’’  AQUEOUS HUMOUR CILIARY PROCESSES -> POSTERIOR CHAMBER - > PUPIL –> ANTERIOR CHAMBER –> SINUS VENOSUS SCLERAE (at the iridocorneal angle) –> ANTERIOR CILIARY VEINS- > OPHTHALMIC VEINS –> CAVERNOUS SINUS  MUSCLES OF THE IRIS SPHINCTER PUPILLA MUSCLE— smooth muscle-meiosis—innervated by parasymp.-short ciliary nn. (oculomotor n.) DILATOR PUPILLA MUSCLE— smooth muscle- midriasis- innervated by symp.—sup. cervical symp. gang.-int. car. a.- long cili. nn.(nasocil.n.) –(OR short cil.nn.)  ARTERIES OF IRIS Long posterior ciliary aa. Anterior ciliary aa. Arteries of ciliary process --MAJOR ARTERIAL CIRCLE—(at the ciliary margin) --MINOR ARTERIAL CIRCLE (at the pupillar margin)  Inner layer of the The inner layer of the eyeball is the retina. It consists of two parts: eyeball A- Posteriorly and laterally is the optic part of the retina, which is sensitive to light B-anteriorly is the nonvisual part, which covers the internal surface of the ciliary body and the iris. The junction between these parts is an irregular line (the ora serrata). Optic part of the retina The optic part of the retina consists of two layers: 1- an outer pigmented layer 2- an inner neural layer The pigmented layer is firmly attached to the choroid and continues anteriorly over the internal surface of the ciliary body and iris. The neural layer, which can be further subdivided into its various neural components, is only attached to the pigmented layer around the optic nerve and at the ora serrata.  III. 3-NERVOUS LAYER (RETINA) Innermost layer of the eyeball. The neural- sensory layer Composed of 2 layers ----Outer—PIGMENTED LAYER ----Inner---NERVOUS LAYER  ORA SERRATA The place where nervous layer of retina ends. But the pigmented layer continues anteriorly over the back of the ciliary processes and the iris— – ciliary part – iridial part  Neural Tunic (Retina) Retina from optic disk to ora serrata composed of 10 layers, that contains photoreceptor cells known as rods and cones, from outside to inside where they are continuous with optic nerve are as follows: 1- Pigmented epithelium 2- Layer of rods and cones 3- Outer limiting membrane 4- Outer nuclear layer 5- Outer plexiform layer 6- Inner nuclear layer 7- Inner plexiform layer 8- Ganglion cell layer 9- Optic nerve fiber layer 10- Inner limiting membrane  PARTS OF RETINA OPTIC PART From optic disc-to ora serrata pigmented+ nervous layers present here. Pars caeca PARS CAECA RETINA-’’Blind part’’ from ora serrata anteriorly. optic Only pigmented layer present.  MACULA LUTEA-FOVEA CENTRALIS MACULA LUTEA=YELLOW SPOT Oval yellowish area near the the centre of posterior part of retina. FOVEA CENTRALIS---is the central depression located in the macula lutea---where VISUAL RESOLUTION IS HIGH. HAS ONLY CONES.  OPTIC DISC OPTIC DISC Localization: 3mm. nasal to macula lutea. Point where optic nerve Enters the eyeball: lamina cribrosa Optic disc is the elevation on the lamina cribrosa optic disc  OPTIC DISC OPTIC DISC = BLIND SPOT insensitive to light --Central a. and v. of retina. ---In normal ophthalmoscopic examinations color= PINK --- If optic n. atrophies,color = WHITE  CENTRAL RETINAL ARTERY Courses through optic nerve fibers The first branch of “ophthalmic artery” Branches: – Superior and inferior branches - Each branche divides into temporal & nasal brs. - So 4 aa. supplies each quadrant of retina. No anatomosis  CENTRAL RETINAL ARTERY Branches: Superior temporal retinal a. Inferior temporal retinal a. Superior nasal retinal a. Inferior nasal retinal a.  CENTRAL RETINAL VESSELS ARE THE ONLY VESSELS IN THE BODY WHICH CAN BE INSPECTED DIRECTLY WITH NAKED EYE (Through an ophthalmoscope).  OCULAR REFRACTIVE MEDIA CORNEA AQUEOUS HUMOUR LENS VITREOUS HUMOUR  AQUEOUS HUMOR Fills the anterior and posterior chambers. Secreted by ciliary processes- Functions: -Intraocular pressure -Shape of eyeball -Metabolic avenue for avascular structures- cornea, lens.  VITREOUS HUMOR Occupies vitreous body (chamber/vitreous camera)- posterior to lens. Colorless,structureless,transparent gel(water 99%) BOUNDED - Anteriorly –lens--susp. lig.---ciliary body - Laterally and posteriorly--retina No blood vessels.  LENS Biconvex, transparent body. Has a capsule (capsula lentis) Central points - Anterior pole - Posterior pole-AXIS equator Devoid of vessels