anatomy of The orbit

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Information about anatomy of The orbit
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Published on March 10, 2014

Author: ddert

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The orbitThe orbit

The orbitThe orbit is a pyramidal, bony cavity in the facial skeleton with its base anterior and its apex posterior • The orbits contain and protect the eyeballs and their muscles, nerves, and vessels, together with most of the lacrimal apparatus. • The bones forming the orbit are lined with periorbita (periosteum of the orbit), which forms the fascial sheath of the eyeball

• The periorbita is continuous at the optic canal and superior orbital fissure with the periosteal layer of dura • The periorbital is also continuous over the orbital margins and through the inferior orbital fissure with the periosteum covering the external surface of the skull (pericranium).

The orbit has four walls and an apex • The superior wallThe superior wall (roof) is approximately(roof) is approximately horizontal and is formed mainly by the orbitalhorizontal and is formed mainly by the orbital part of the frontal bone, which separates thepart of the frontal bone, which separates the orbital cavity from the anterior cranial fossa.orbital cavity from the anterior cranial fossa. Near the apex of the orbit, the superior wall isNear the apex of the orbit, the superior wall is formed by the lesser wing of the sphenoidformed by the lesser wing of the sphenoid • The lacrimal gland occupies the fossa for theThe lacrimal gland occupies the fossa for the lacrimal gland (lacrimal fossa) in the orbitallacrimal gland (lacrimal fossa) in the orbital part of the frontal bone.part of the frontal bone.

• The medial wall is formed primarily by the ethemoid bone, along with contributions from the frontal, lacrimal, and sphenoid bones; anteriorly, • the paper-thin medial wall is indented by a lacrimal fossa for the lacrimal sac and the proximal part of the nasolacrimal duct. The medial walls of the two orbits are essentially parallel, separated by the ethmoidal sinuses and the unpper nasal cavity.

• The inferior wall(floorThe inferior wall(floor) is formed mainly by the maxilla and partly by the zygomatic and palatine bones; • the thin floorthe thin floor is partly separated from the lateral wall of the orbit by the inferior orbital fissure. • The lateral wallThe lateral wall is formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid; the lateral wall is thick, especially its posterior part, which separates the orbit from the middle cranial fossa. The lateral walls of the two orbits are nearly perpendicular to each other.

• The,apex of the orbit is at the optic canal, in the lesser wing of the sphenoid just medial to the superior orbital fissure.

Orbital Contents The contents of the orbit are :- • the eyeballthe eyeball • optic nerveoptic nerve • ocular musclesocular muscles • fasciafascia • nervesnerves • vesselsvessels • fatfat • lacrimal glandlacrimal gland • and conjunctival sacand conjunctival sac.

Muscles of the Orbit • Levator palpebrae superioris • Four recti (superior, inferior, medial, and lateral) • Two oblique (superior and inferior).

Levator Palpebrae Superioris • This thin, flat elevator muscle of the superior eyelid broadens into a wide aponeurosis as it approaches its distal attachment to the tarsal plate. This muscle is the opponent of the orbicularis oculi, the sphincter of the palpebral fissure.

Levator Palpebrae Superioris •Tarsal gland •Palpebral surface •Posterior margin •Anterior margin

Recti and Oblique Muscles • The four recti arise from a fibrous cuff, the common tendinous ring, that surrounds the optic canal and part of the superior orbital fissure. • The lateral and medial recti lie in the same horizontal plane, and the superior and inferior recti lie in the same vertical plane. All four recti mus­cles attach to the sclera on the anterior half of the eyebal

• All four recti muscles attach to the sclera on the anterior half of the eyeball.

• • Medial and lateral recti rotate the pupil medially and laterally, respectively • • Superior rectus rotates the pupil superiorly (elevation) • • Inferior rectus rotates the pupil inferiorly (depression). • The inferior oblique directs the pupil laterally and superiorly; therefore, when it works synergistically with the superior rectus, superior movement of the eyeball occurs. Similarly, the superior oblique directs the pupil inferiorly and laterally; therefore, when it works synergistically with the inferior rectus, an inferior movement results.

Tendinous ring

Upper part of the tendinous ring • Lacrimal nerve • Frontal nerve • Trochlear nerve • Superior ophthalmic vein

Middle part of the tendinous ring • Oculomotore nerve with it’s both divisions • Abducent nerve • Nasociliary nerve Lower part transmits only the inferior ophthalmic vein All recti muscles orginated from the ring

Orbital Contents • The contents of the orbit are the eyeball, optic nerve, ocular muscles, fascia, nerves, vessels, fat, lacrimal gland, and conjunctival sac.

1-Orbicularis oculi 2

Nerves of the Orbit • Optic Nerve • The optic nerve enters the orbit from the middle cranial fossa by passing through the optic canal • It is accompanied by the ophthalmic artery, which lies on its lower lateral side. • The nerve is surrounded by sheaths of pia mater, arachnoid mater, and dura mater ().

Nerves of the Orbit • It runs forward and laterally within the cone of the recti muscles and pierces the sclera at a point medial to the posterior pole of the eyeball. • Here, the meninges fuse with the sclera so that the subarachnoid space with its contained cerebrospinal fluid extends forward from the middle cranial fossa, around the optic nerve, and through the optic canal, as far as the eyeball. • A rise in pressure of the cerebrospinal fluid within the cranial cavity therefore is transmitted to the back of the eyeball. •

Nerves of the Orbit • Lacrimal Nerve • The lacrimal nerve arises from the ophthalmic division of the trigeminal nerve. • It enters the orbit through the upper part of the superior orbital fissure ( • ) and passes forward along the upper border of the lateral rectus muscle • . It is joined by a branch of the zygomaticotemporal nerve, which later leaves it to enter the lacrimal gland (parasympathetic secretomotor fibers). • The lacrimal nerve ends by supplying the skin of the lateral part of the upper lid.

Frontal Nerve • The frontal nerve arises from the ophthalmic division of the trigeminal nerve. • It enters the orbit through the upper part of the superior orbital fissure • passes forward on the upper surface of the levator palpebrae superioris beneath the roof of the orbit • It divides into the supratrochlear and supraorbital nerves that wind around the upper margin of the orbital cavity to supply the skin of the forehead; • the supraorbital nerve also supplies the mucous membrane of the frontal air sinus.

Trochlear Nerve • The trochlear nerve enters the orbit through the upper part of the superior orbital fissure • It runs forward and supplies the superior oblique muscle

Oculomotor Nerve • The superior ramus of the oculomotor nerve enters the orbit through the lower part of the superior orbital fissure • . It supplies the superior rectus muscle, then pierces it, and supplies the levator palpebrae superioris muscle ( • The inferior ramus of the oculomotor nerve enters the orbit in a similar manner and supplies the inferior rectus, the medial rectus, and the inferior oblique muscles. • The nerve to the inferior oblique gives off a branch that passes to the ciliary ganglion and carries parasympathetic fibers to the sphincter pupillae and the ciliary muscle

Nasociliary Nerve • The nasociliary nerve arises from the ophthalmic division of the trigeminal nerve. • It enters the orbit through the lower part of the superior orbital fissure ( • . It crosses above the optic nerve, runs forward along the upper margin of the medial rectus muscle, and ends by dividing into the anterior ethmoidal and infratrochlear nerves

Branches of the Nasociliary Nerve • The communicating branch to the ciliary ganglion is a sensory nerve. The sensory fibers from the eyeball pass to the ciliary ganglion via the short ciliary nerves, pass through the ganglion without interruption, and then join the nasociliary nerve by means of the communicating branch. • The long ciliary nerves, two or three in number, arise from the nasociliary nerve as it crosses the optic nerve (They contain sympathetic fibers for the dilator pupillae muscle. The nerves pass forward with the short ciliary nerves and pierce the sclera of the eyeball. • They continue forward between the sclera and the choroid to reach the iris.

Branches of the Nasociliary Nerve • The posterior ethmoidal nerve supplies the ethmoidal and sphenoidal air sinuses (.

Branches of the Nasociliary Nerve • The infratrochlear nerve passes forward below the pulley of the superior oblique muscle and supplies the skin of the medial part of the upper eyelid and the adjacent part of the nose • The anterior ethmoidal nerve passes through the anterior ethmoidal foramen and enters the anterior cranial fossa on the upper surface of the cribriform plate of the ethmoid ( • It enters the nasal cavity through a slit like opening alongside the crista galli. After supplying an area of mucous membrane, it appears on the face as the external nasal branch at the lower border of the nasal bone, and supplies the skin of the nose down as far as the tip

Abducent Nerve • The abducent nerve enters the orbit through the lower part of the superior orbital fissure ( • . It supplies the lateral rectus muscle.

Ciliary Ganglion • The ciliary ganglion is a parasympathetic ganglion about the size of a pinhead • and situated in the posterior part of the orbit. • It receives its preganglionic parasympathetic fibers from the oculomotor nerve via the nerve to the inferior oblique. • The postganglionic fibers leave the ganglion in the short ciliary nerves, which enter the back of the eyeball and supply the sphincter pupillae and the ciliary muscle. • A number of sympathetic fibers pass from the internal carotid plexus into the orbit and run through the ganglion without interruption

Blood Vessels and Lymph Vessels of the Orbit • Ophthalmic Artery • The ophthalmic artery is a branch of the internal carotid artery after that vessel emerges from the cavernous sinus • It enters the orbit through the optic canal with the optic nerve • . It runs forward and crosses the optic nerve to reach the medial wall of the orbit. • It gives off numerous branches, which accompany the nerves in the orbital cavity. • Branches of the Ophthalmic Artery • The central artery of the retina is a small branch that pierces the meningeal sheaths of the optic nerve to gain entrance to the nerve ( • It runs in the substance of the optic nerve and enters the eyeball at the center of the optic disc. Here, • it divides into branches, which may be studied in a patient through an ophthalmoscope. The branches are end arteries.

Blood Vessels and Lymph Vessels of the Orbit •The muscular branches •The ciliary arteries can be divided into anterior and posterior groups. The former group enters the eyeball near the corneoscleral junction; the latter group enters near the optic nerve. •The lacrimal artery to the lacrimal gland •The supratrochlear and supraorbital arteries are distributed to the skin of the forehead (see page 729).

Ophthalmic Veins • The superior ophthalmic vein communicates in front with the facial vein • The inferior ophthalmic vein communicates through the inferior orbital fissure with the pterygoid venous plexus. Both veins pass backward through the superior orbital fissure and drain into the cavernous sinus. • Lymph Vessels • No lymph vessels or nodes are present in the orbital cavity

Intrinsic Muscles • The involuntary intrinsic muscles are the ciliary muscle and the constrictor, and the dilator pupillae of the iris take no part in the movement of the eyeball and are discussed later.

Intrinsic Muscles Fascial Sheath of the Eyeball • The fascial sheath surrounds the eyeball from the optic nerve to the corneoscleral junction ( • It separates the eyeball from the orbital fat and provides it with a socket for free movement. • It is perforated by the tendons of the orbital muscles and is reflected onto each of them as a tubular sheath. • The sheaths for the tendons of the medial and lateral recti are attached to the medial and lateral walls of the orbit by triangular ligaments called the medial and lateral check ligaments. • The lower part of the fascial sheath, which passes beneath the eyeball and connects the check ligaments, is thickened and serves to suspend the eyeball; it is called the suspensory ligament of the eye . By this means the eye is suspended from the medial and lateral walls of the orbit, as if in a hammock.

Structure of the Eye • The eyeball ( • is embedded in orbital fat but is separated from it by the fascial sheath of the eyeball.

The eyeball • consists of three coats, which, from without inward, • the fibrous coat, • the vascular pigmented coat, • the nervous coat.

The eyeball has three layers • The outer fibrous layer — the sclera and cornea • The middle vascular (pigmented) layer — the choroid, ciliary body, and iris • The inner layer — the retina, consisting of optic and nonvisual parts.

cornea lence

Coats of the Eyeball • Fibrous Coat • The fibrous coat is made up of a posterior opaque part, the sclera, and an anterior transparent part, the cornea • The Sclera • The opaque sclera is composed of dense fibrous tissue and is white. Posteriorly, it is pierced by the optic nerve and is fused with the dural sheath of that nerve • . The lamina cribrosa is the area of the sclera that is pierced by the nerve fibers of the optic nerve.

Coats of the Eyeball • The sclera is also pierced by the ciliary arteries and nerves and their associated veins, the venae vorticosae. • The sclera is directly continuous in front with the cornea at the corneoscleral junction, or limbus. • The Cornea • The transparent cornea is largely responsible for the refraction of the light entering the eye ( • It is in contact posteriorly with the aqueous humor.

Vascular Pigmented Coat • The vascular pigmented coat consists, from behind forward, of • the choroid, • the ciliary body, and • the iris.

Vascular Pigmented Coat • The Choroid • The choroid is composed of an outer pigmented layer and an inner, highly vascular layer. • The Ciliary Body • The ciliary body is continuous posteriorly with the choroid, and anteriorly it lies behind the peripheral margin of the iris • It is composed of the • ciliary ring, • the ciliary processes, and • the ciliary muscle.

Vascular Pigmented Coat • The ciliary ring is the posterior part of the body, and its surface has shallow grooves, the ciliary striae. • The ciliary processes are radially arranged folds, or ridges, to the posterior surfaces of which are connected the suspensory ligaments of the lens. • The ciliary muscle . is composed of meridianal and circular fibers of smooth muscle. The meridianal fibers run backward from the region of the corneoscleral junction to the ciliary processes. • The circular fibers are fewer in number and lie internal to the meridianal fibers.

Vascular Pigmented Coat • Nerve supply: • The ciliary muscle is supplied by the parasympathetic fibers from the oculomotor nerve. After synapsing in the ciliary ganglion, the postganglionic fibers pass forward to the eyeball in the short ciliary nerves. • Action: Contraction of the ciliary muscle, especially the meridianal fibers, 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.

Outer Fibrous Layer of the Eyeball • The sclera is the opaque part of the fibrous coat of the eyeball covering the posterior 5/6 of the eyeball. • The anterior part of the sclera is visible through the transparent bulbar conjunctiva as "the white of the eye." • The cornea is the transparent part of the fibrous coat covering the anterior one-sixth of the eyeball.

Nervous Coat: The Retina • The retina consists of an outer pigmented layer and an inner nervous layer • . Its outer surface is in contact with the choroid, and its inner surface is in contact with the vitreous body • The posterior three fourths of the retina is the receptor organ. • Its anterior edge forms a wavy ring, the ora serrata, and the nervous tissues end here. • The anterior part of the retina is nonreceptive and consists merely of pigment cells, with a deeper layer of columnar epithelium. This anterior part of the retina covers the ciliary processes and the back of the iris.

Nervous Coat: The Retina • At the center of the posterior part of the retina is an oval, yellowish area, the macula lutea, which is the area of the retina for the most distinct vision. It has a central depression, the fovea centralis ( • The optic nerve leaves the retina about 3 mm to the medial side of the macula lutea by the optic disc. • The optic disc is slightly depressed at its center, where it is pierced by the central artery of the retina. • At the optic disc is a complete absence of rods and cones so that it is insensitive to light and is referred to as the blind spot. • ‌ On ophthalmoscopic examination, the optic disc is seen to be pale pink in color, much paler than the surrounding retina.

Nervous Coat: The Retina Contents of the Eyeball • The contents of the eyeball consist of the • refractive media, • the aqueous humor, • the vitreous body, and • the lens. • Aqueous Humor

Nervous Coat: The Retina Contents of the Eyeball • The aqueous humor is a clear fluid that fills the anterior and posterior chambers of the eyeball • . It is believed to be a secretion from the ciliary processes, from which it enters the posterior chamber. It then flows into the anterior chamber through the pupil and is drained away through the spaces at the iridocorneal angle into the canal of Schlemm.

Nervous Coat: The Retina Contents of the Eyeball • Obstruction to the draining of the aqueous humor results in a rise in intraocular pressure called glaucoma • . This can produce degenerative changes in the retina, with consequent blindness. • The function of the aqueous humor is to support the wall of the eyeball by exerting internal pressure and thus maintaining its optical shape. It also nourishes the cornea and the lens and removes the products of metabolism; these functions are important because the cornea and the lens do not possess a blood supply.

Vitreous Body • The vitreous body fills the eyeball behind the lens ( • ) and is a transparent gel. • The hyaloid canal is 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. • The function of the vitreous body is to contribute slightly to the magnifying power of the eye. It supports the posterior surface of the lens and assists in holding the neural part of the retina against the pigmented part of the retina.

Vitreous Body The Lens • The lens is a transparent, biconvex structure enclosed in a transparent capsule. • It is situated behind the iris and in front of the vitreous body and is encircled by the ciliary processes.

Vitreous Body The Lens • The lens consists of an elastic capsule, which envelops the structure; a cuboidal epithelium, which is confined to the anterior surface of the lens; and lens fibers, which are formed from the cuboidal epithelium at the equator of the lens. • The lens fibers make up the bulk of the lens.

Vitreous Body The Lens • The elastic lens capsule is under tension, causing the lens constantly to endeavor to assume a globular rather than a disc shape. • The equatorial region, or circumference, of the lens is attached to the ciliary processes of the ciliary body by the suspensory ligament. • The pull of the radiating fibers of the suspensory ligament tends to keep the elastic lens flattened so that the eye can be focused on distant objects.

•The end

Middle Vascular Layer of the Eyeball • The chroid a dark brown membrane between the sclera and retina — forms the largest part of the vascular layer of the • Eyeball and lines most of the sclera. • It terminates anteriorly in the ciliary body. • The choroid attaches firmly to the pigment layer of the retina, but it can easily be stripped from the sclera.

The ciliary body which is muscular as well as vascular — connects the choroid with the circumference of the iris • . Folds on its internal surface — the ciliary processes • secrete aqueous humor, which fills the anterior and posterior chambers

• The anterior chamber of the eye is the space between the cornea anteriorly and the iris/pupil posteriorly, • The posterior chamber of the eye is between the iris/pupil anteriorly and the lens and ciliary body posteriorly

• The iris which literally lies on the anterior surface of the anterior surface of the lens, is a thin, contractile diaphragm with a central aperture the pupil for transmitting light. When a person is awake, the size of the pupil varies continually to regulate the amount of light entering the eye. • Two muscles control the size of the pupil: the sphincter pupillae closes the pupil and the dilator pupillae opens it.

Inner Layer of the Eyeball (Retina( • Grossly, the retina consists of three parts: • Optic part • Ciliary part • Iridial part.

The optic part of the retina • which receives the visual light rays. • has two layers: a neural layer and pegmented cell layer. • The neural layer is the light-receptive part. • The pigmented layer consists of a single layer of cells that reinforces the light-absorbing property of the choroid in reducing the scattering of light in the eye. • The ciliary and iridial parts of the retina are anterior continuations of the pigmented layer and a layer of supporting cells over the ciliary body and the posterior surface of the iris, respectively.

• In the fundus (posterior part) of the eye is a circular depressed area—the optic disc (optic papilla)—where the optic nerve enters the eyeball. Because it contains nerve fibers and no photoreceptors, the optic disc is insensitive to light. Just lateral to this "blind spot" of the retina is the macula lutea (L. yellow spot).

• The yellow color of the macula is apparent only when the retina is examined with red-free light. The macula lutea— a small oval area of the retina with special photoreceptor cones—is specialized for acuity of vision; it is not normally observed with an ophthalmoscope,( a device for viewing the interior of the eyeball through the pupil). At the center of the macula lutea is a depression—the fovea centralis (L. central pit)—the area of most acute vision. The fovea is ap-proximately 1.5 mm in diameter; its center—the foveola— does not have the capillary network visible elsewhere deep to the retina.

• The functional optic part of the retina terminates anteriorly along the ora serrata (L. serrated edge), an irregular border slightly posterior to the ciliary body. The ora serrata marks the anterior termination of the part of the retina light-receptive

• the retina is supplied by the central artery of the retina, *a branch of the ophthalmic artery. The cones and rods of the outer neural layer receive nutrients from the choriocapillaris, • A corresponding system of retinal veins units to form the central vein of the retina.

Refractive Media of the Eye • On their way to the retina, light waves pass through the re­fractive media of the eye: cornea, aqueous humor, lens, and vitreous humor, • The cornea is the circular area of the anterior part of the outer fibrous layer of the eyeball; it is largely responsible for refraction of the light that enters the eye. It is transparent, avascular, and sensitive to touch. The cornea is supplied by the ophthalmic nerve and is nourished by aqueous humor, tears, and oxygen absorbed from the air

• The aqueous humor in the anterior and posterior chambers of the eye is produced by the ciliary processes. This clear watery solution provides nutrients for the avascular cornea and lens. After passing through the pupil from the posterior chamber into the anterior chamber, the aqueous humor drains into the scleral venous sinus (L. sinus venosus sclerae, canal of Schlemm) at the iridocorneal angle.

• The lens, posterior to the iris and anterior to the vitreous humor of the vitreous body, is a transparent biconvex structure enclosed in a capsule. The lens capsule is anchored by the suspensory ligament of the lens to the ciliary body and encir-cled by the ciliary processes. The convexity of the lens, particularly its anterior surface, constantly varies to focus near or distant objects on the retina. The ciliary muscle in the ciliary body changes the shape of the lens; in this way the isolated unattached lens assumes a nearly spherical shape.

• Stretched within the circle of the relaxed ciliary body, the at­tachments around its periphery pull the lens relatively flat so that its refraction enables far vision. When parasympathetic stimulation causes the smooth muscle of the circular ciliary body to contract, the circle—like a sphincter—becomes smaller in size and the tension on the lens is reduced, allowing the lens to round up. The increased convexity makes its refraction suitable for near vision. In the absence of parasympathetic stimulation, the ciliary muscles relax again and the lens is pulled into its flatter, far vision shape

• The vitreous humor is a watery fluid enclosed in the meshes of the vitreous body, a transparent jellylike substance in the posterior four­fifths of the eyeball posterior to the lens (postremal or vitreous chamber, or posterior segment). In ad­ dition to transmitting light, the vitreous humor holds the retina in place and supports the lens.

Innervation of the Orbit • In addition to the optic nerve, the nerves of the orbit include those that enter through the superior orbital fissure and supply the ocular muscles: oculomotor III, trochlear, IV; and abducent, VI • • CN III supplies the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique. • • CN IV supplies the superior oblique. • • CN VI supplies the lateral rectus.

Several branches of the ophthalmic nerve (CN Vi) pass through the superior orbital fissure and supply structures in the orbit. • The lacrimal nerve arises in the lateral wall of the cavernous sinus and passes to the lacrimal gland, giving branches to the conjunctiva and skin of the superior eyelid and providing secretomotor fibers conveyed to it from the zygomatic nerve (CN V2

• The frontal nerve divides into the supraorbital nerve and supratrochlear nerve, which supply the upper eyelid, forehead, and scalp. • The nasociliary nerve, the sensory nerve to the eye, supplies several branches to the orbit­

• The infratrochlear nerve, a terminal branch of the nasociliary nerve, supplies the eyelids, conjunctiva, skin of the nose, and lacrimal sac • The ethmoidal nerves, also branches of the nasociliary nerve, supply the mucous membrane of the sphenoidal and ethmoidal sinuses and the nasal cavities, and the dura of the anterior cranial fossa.

• The short ciliary nerves, branches of the ciliary ganglion , carry parasympathetic and sympathetic fibers to the ciliary body and iris. • . The ciliary ganglion is a small group of nerve cell bodies between the optic nerve and lateral rectus toward the posterior limit of the orbit. The short ciliary nerves consist of postsynaptic parasympathetic fibers origi­nating in the ciliary ganglion, afferent fibers from the nasocil­iary nerve that pass through the ganglion, and postsynaptic sympathetic fibers that also pass through it. The long ciliary nerves, branches of the nasociliary nerve (CN Vi), transmit postsynaptic sympathetic fibers to the dilator pupillae and af­ferent fibers from the iris and cornea.

Vasculature of the Orbit Arteries of the Orbit • The blood supply of the orbit is mainly from the ophthalmic artery; • the infraorbital artery also contributes blood to this region • The central artery of the retina, a branch of the ophthalmic artery inferior to the optic nerve, runs within the dural sheath of the optic nerve until it approaches the eyeball. • The central artery pierces the optic nerve and runs within it to emerge at the optic disc. • Branches of the central artery spread over the internal surface of the retina. • The terminal branches of the central artery are end arteries that provide the only blood supply to the retina. • The retina is also supplied by the capillary layer of the choroid the choriocapillary layer (lamina). Of the eight or so posterior ciliary arteries—also branches of the ophthalmic artery—six short posterior ciliary arteries directly supply the choroid, which nourishes the outer nonvascuiar layer of the retina. Two long posterior ciliary arteries, one on each side of the eyeball, pass between the sclera and choroid to anastomose with the anterior ciliary arteries—continuations of the muscular branches of the ophthalmic artery— supplying the ciliary plexus.

Veins of the Orbit • Venous drainage of the orbit is through the superior and inferior ophthalmic veins that pass through the superior orbital fissure and enter the cavernous sinus. • The central vein of the retina. usually enters the cavernous sinous directly, but it may join one of the ophthalmic veins. • The vortex or vorticose veins from the vascular layer drain into lie inferior ophthalmic vein. • The scleral venous sinus is a vascular structure encircling the anterior chamber of the eye through which the aqueous humor is returned to the blood circulation.

Lacrimal Apparatus • The lacrimal apparatus consists of: • • Lacrimal glands, which secrete lacrimal fluid • • Lacrimal ducts, which convey lacrimal fluid from the lacrimal glands to the conjunctiva! sac • • Lacrimal canaliculi (L. small canals), each commencing at a lacrimal punctum (opening) on the lacrimal papilla near the medial angle of the eye, which conveys the lacrimal fluid from the lacrimal lake—a triangular space at the me­dial angle of the eye where the tears collect—in the lacrimal sac, the dilated superior part of the nasolacrimal duct

Lacrimal Apparatus

Temporal Region • The temporal region includes the temporal and infratemporal fossae—superior and inferior to the zygomatic arch, respectively

Temporal Fossa • The temporal fossa, in which the temporal muscle is located, is bounded: • Posteriorly and superiorly by the temporal lines. • Anteriorly by the frontal and zygomatic bones • Laterally by the zygomatic arch • Inferiorly by the infratemporal crest

The floor of the temporal fossa • formed by parts of the four bones that form the pterion: frontal, parietal, temporal, and greater wing of the sphenoid. • The fan­shaped temporal mus­cle arises from the floor (i.e., the temporal fossa extending to the inferior temporal line) and the overlying temporal fascia. • which comprises the roof of the temporal fossa

This tough fascia covers the temporal muscle, extending to • Superior temporal line • Inferiorly, the fascia splits into two layers that attached to the superior margine of the zygomatic arch. • It tethers the zygomatic arch superiorly. • When the masseter muscle attached to the inferior border of the arch contracts, exerting a strong downward pull the fascia provides resistance.

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