The Orbit & Eye

Head & Neck Unit – Lecture 7األعسم. جليل حيدر د

The OrbitThe Orbits: are a pair of pyramidal cavities with its base in front and its apex behind.

Boundaries:•The orbital margin is formed above by the frontal bone, the lateral margin is formed by the processes of the frontal and zygomatic bones, the inferior margin is formed by the zygomatic bone and the maxilla, and the medial margin is formed by the processes of the maxilla and the frontal bone. •Roof: orbital plate of the frontal bone.•Floor: orbital plate of the maxilla. •Lateral wall: zygomatic bone & greater wing of sphenoid. •Medial wall: frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid & body of the sphenoid.

The OrbitOpenings into the Orbital Cavity:

1.Orbital opening: About 1/6 of the eyeball is exposed outside the orbital walls.2.Supraorbital notch (Foramen): is situated on superior orbital margin. It transmits supraorbital nerve & vessels. 3.Infraorbital groove and canal: Situated on floor of orbit; they transmit infraorbital nerve & vessels. 4.Nasolacrimal canal: Located on medial wall of the orbit. It transmits the nasolacrimal duct.5.Inferior orbital fissure: Located posteriorly between the maxilla and the greater wing of the sphenoid. It transmits the maxillary nerve and its zygomatic branch, the inferior ophthalmic vein, and sympathetic nerves. 6.Superior orbital fissure: Located posteriorly between the greater and lesser wings of the sphenoid. It transmits lacrimal nerve, frontal nerve, trochlear nerve, oculomotor nerve, abducent nerve, nasociliary nerve & superior ophthalmic vein. 7.Optic canal: Located posteriorly in the lesser wing of the sphenoid. It transmits optic nerve & ophthalmic artery.

The EyelidThe eyelids: are two thin, movable folds that protect the eye from injury and excessive light by their closure. The palpebral fissure is elliptical opening between the eyelids. The conjunctiva is a thin mucous membrane that lines the eyelids and is reflected at the superior and inferior fornices onto the anterior surface of the eyeball.Conjunctival sac: is a potential space formed by conjuctiva and is open at the palpebral fissure. The upper lateral part of the superior fornix is pierced by the ducts of the lacrimal gland.Glands of Zeis: are sebaceous glands of the eyelid & open directly into the eyelash follicles. The ciliary glands (glands of Moll) are modified sweat glands that open separately between adjacent lashes. The tarsal glands: are long, modified sebaceous glands that pour their oily secretion onto the margin of the lid.Lacus lacrimalis: is a small space separate the rounded medial angle from the eyeball byCaruncula lacrimalis: is a small, reddish yellow elevation in the center of lacus lacrimalis.Plica Semilunaris: is a reddish semilunar fold that lies on the lateral side of the caruncle. Papilla Lacrimalis: is a small elevation near medial angle of the eye.Punctum Lacrimale: is a small hole on the summit of the papilla Lacrimalis which leads into the canaliculus lacrimalis.

The EyelidThe orbital septum: is a fibrous sheet attached to periosteum at the orbital margins & forming the framework of the eyelid. The orbital septum is thickened at the margins of the lids to form the superior and inferior tarsal plates. Lateral palpebral ligament: is a band attaching the lateral ends of the tarsal plates to a bony tubercle just within the orbital margin. Medial palpebral ligament: is band attaching the medial ends of the tarsal plates to the crest of the lacrimal bone. The superficial surface of the tarsal plates and the orbital septum are covered by the palpebral fibers of Orbicularis Oculi Muscle. The aponeurosis of insertion of the levator palpebrae superioris muscle pierces the orbital septum to reach the anterior surface of the superior tarsal plate and the skin. Movements of the Eyelids: •They are closed by contraction of the orbicularis oculi and the relaxation of the levator palpebrae superioris muscles. •The eye is opened by the levator palpebrae superioris raising the upper eyelid.

Lacrimal Apparatus Lacrimal Gland: •The lacrimal gland consists of a large orbital part and a small palpebral part, which are continuous with each other around the lateral edge of the aponeurosis of the levator palpebrae superioris. •Situated above the eyeball in the anterior and upper part of the orbit posterior to the orbital septum. The gland opens into the lateral part of the superior fornix of the conjunctiva by 12 ducts.

Lacrimal Apparatus Lacrimal Ducts:•Tears circulate across the cornea and accumulate in the lacus lacrimalis. From here, the tears enter the canaliculi lacrimales through the puncta lacrimalis. •The canaliculi lacrimales pass medially and open into the lacrimal sac, which lies in the lacrimal groove behind the medial palpebral ligament and is the upper blind end of the nasolacrimal duct. •The nasolacrimal duct is about 1.3 cm long and emerges from the lower end of the lacrimal sac. The duct descends downward, backward, and laterally in a bony canal and opens into the inferior meatus of the nose. The opening is guarded by a fold of mucous membrane known as the lacrimal fold. This prevents air from being forced up the duct into the lacrimal sac on blowing the nose.

Lacrimal Gland - Innervation

• The parasympathetic secretomotor nerve supply is from facial nerve. The preganglionic fibers are carried by great petrosal nerve & nerve of pterygoid canal to reach pterygopalatine ganglion (sphenopalatine ganglion). The postganglionic fibers leave the ganglion and join the maxillary nerve where they pass into its zygomatic branch and the zygomaticotemporal nerve. Then, they reach the lacrimal gland within the lacrimal nerve. • The sympathetic postganglionic nerve supply is from the internal carotid plexus and

travels in the deep petrosal nerve, nerve of pterygoid canal, maxillary nerve, zygomatic nerve, zygomaticotemporal nerve, and finally lacrimal nerve.

Nerves of the OrbitA. Nerve passing through optic Canal:Optic Nerve: It is surrounded by sheaths of pia mater, arachnoid mater, and dura mater. A rise in pressure of CSF within cranial cavity; therefore is transmitted to the back of the eyeball.

B. Nerves passing through upper part of superior orbital fissure:

1-Lacrimal Nerve: arises from ophthalmic division of trigeminal nerve & joined by a branch of zygomatico-temporal nerve, which later leaves it to enter the lacrimal gland (parasympathetic secretomotor fibers). It also supplies the skin of the lateral part of the upper lid.

2-Frontal Nerve: arises from the ophthalmic division of trigeminal nerve. It divides into supratrochlear and supraorbital nerves. They supply the upper eyelid, skin of forehead & also mucous membrane of frontal air sinus.

3-Trochlear Nerve: supplies superior oblique muscle

Nerves of the OrbitC. Nerves passing through lower part of superior orbital fissure:1- Oculomotor Nerve: supplies superior rectus, medial rectus, inferior rectus, inferior oblique and levator palpebrae superioris muscles. It gives off a branch the ciliary ganglion (Parasympathetic fibers to the sphincter pupillae and the ciliary muscle). 2- Nasociliary Nerve: arises from ophthalmic division of trigeminal nerve. It divides into Anterior Ethmoidal and infratrochlear nerves. 3- Abducent Nerve: supplies only lateral rectus muscle.

Ciliary Ganglion (Parasympathetic):•It is a parasympathetic ganglion situated in the posterior part of the orbit. It receives its preganglionic parasympathetic fibers from the oculomotor nerve. The postganglionic fibers are carried by short ciliary nerves to supply the sphincter pupillae and the ciliary muscle. •Sympathetic fibers pass from internal carotid plexus into orbit & run through this ganglion without interruption.

Blood Supply of the Orbit1.Ophthalmic Artery: It is a branch of the internal carotid

artery and enters the orbit through the optic canal. It runs forward and crosses the optic nerve to reach the medial wall of the orbit. Branches of the Ophthalmic Artery

2.Central artery of the retina: is a small branch that enters the meningeal sheaths of optic nerve to run inside the optic nerve and enters the eyeball at the center of the optic disc.

3.Muscular branches to the muscles4.Ciliary arteries: some enter the eyeball near the

corneoscleral junction; others enter near the optic nerve. 5.Lacrimal artery to the lacrimal gland 6.Supratrochlear and supraorbital arteries. Ophthalmic Veins:There are superior & inferior ophthalmic veins that

communicate with facial vein and pterygoid venous plexus, respectively. Both veins pass backward through the superior orbital fissure and drain into the cavernous sinus.

The EyeballThe eyeball is embedded in orbital fat but separated from it by fascial sheath of the eyeball. Fascial Sheath of Eyeball: 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 Medial & Lateral check ligaments. Suspensory ligament of the eye: is thickening of the lower part of the fascial sheath, which passes beneath the eyeball and connects the check ligaments to suspend the eyeball.

Coats of the Eyeball – Fibrous layer1- Fibrous Coat: composed of sclera & Cornea •The Sclera: is posterior opaque part, white in colour & composed of dense fibrous tissue. Posteriorly, it is pierced by the optic nerve and is fused with its dural sheath. The lamina cribrosa is the area of the sclera that is pierced by the nerve fibers of the optic nerve. The sclera is also pierced by the ciliary arteries and ciliary nerves and their associated veins (venae vorticosae). The sclera is directly continuous in front with cornea at the corneoscleral junction (Limbus).•The Cornea: is anterior transparent part that is responsible for refraction of light entering the eye. It is in contact posteriorly with aqueous humor. The cornea is avascular and nourished by diffusion from aqueous humor and innervated by ciliary nerves.

Coats of the Eyeball – Pigmented Layer2. Vascular Pigmented Coat: consist of: A. The Choroid: (outer pigmented layer & inner vascular layer).

B. The Ciliary Body: composed of ciliary ring, ciliary processes & ciliary muscle. •Nerve supply: ciliary muscle by preganglionic parasympathetic fibers from oculomotor nerve & postganglionic fibers by short ciliary nerves.•Action of ciliary muscle: change refractive power of lens by changing its shape through suspensory fibers of lens.

C. The Iris and Pupil: is a thin, contractile, pigmented diaphragm with a central aperture (pupil). It divides the space between lens & cornea into anterior & posterior chambers. Iris muscle fibres are involuntary & consist of circular (Sphincter pupillae) and radiating fibers (Dilator pupillae ). •Nerve supply: Sphincter pupillae by parasympathetic oculomotor fibrers (Short ciliary nerves). Dilator pupillae by sympathetic fibers of long ciliary nerves. •Action: Sphincter pupillae constricts pupil in bright light & for accommodation while dilator pupillae dilates pupil in dim light & in fright.

Coats of the Eyeball – Nervous Layer3. Nervous Coat (Retina): consists of an outer pigmented layer and an inner nervous layer. The receptor organ is posterior 3/4 of retina while anterior non-receptive part forms a wavy ring Ora Serrata, where nervous tissues end. This anterior part of the retina covers the ciliary processes and back of the iris. Macula Lutea: is an oval, yellowish area at the center of the posterior part of the retina, which is the area of most distinct vision. It has a central depression fovea centralis.Optic disc: is the optic nerve exit and is completely insensitive to light (the blind spot). It is about 3 mm medial to macula lutea. The optic disc is pierced by the central artery of the retina.

Contents of the EyeballThe eyeball contains three refractive media: Aqueous humor, Vitreous body & lens. •Aqueous Humor: It is a clear fluid filling anterior and posterior chambers of the eyeball. It is secreted from the ciliary processes to enter the posterior chamber & flows into the anterior chamber through the pupil and then is drained away through the spaces at the iridocorneal angle into Canal of Schlemm. Obstruction to this drainage results in a rise in intraocular pressure called (Glaucoma).•Function of Aqueous Humor is to maintain optical shape of the eyeball and to nourish the cornea and the lens and removes the products of metabolism.•Vitreous Body: it is a transparent gel filling the eyeball behind the lens. The hyaloid canal is a rudimentary narrow channel running through vitreous body from optic disc to posterior surface of lens (filled by hyaloid artery in fetus).

•Function of Vitreous Body is to supports posterior surface of lens, assists in holding the retina against the pigmented part of the retina & contribute slightly to the magnifying power of the eye.The Lens: is a transparent, biconvex structure enclosed in a transparent elastic capsule. It is encircled by and attached to the ciliary processes by suspensory ligament of the lens.

Extrinsic Muscles of the Eye • They are 6 skeletal striated voluntary

muscles• The are all supplied by oculomotor nerve

except superior oblique muscle by trochlear nerve and lateral rectus by abducent nerve.• They are responsible for movement of

the eyeball in different directions and paralysis of any one may cause squint of the eye.

1- Superior Rectus2- Inferior Rectus3- Medial Rectus4- Lateral Rectus5- Superior Oblique 6- Inferior Oblique

Actions of the Extra-ocular muscles

End of the Lecture

GOOD LUCK