Eye &Visual Pathway

Dr. NimirDr. Safaa

OjectivesDescribe the location of the orbit.Make a list of structures making the orbit

starting from orbital margin.Define each component. Describe openings into orbital cavity.Describe muscles of the orbit, their cone

arrangement, origin, insertion, nerve supply and their function.

Describe the visual pathwayDiscuss the central connections of the cranial

nerves (III,IV,VI)

The Orbital RegionThe orbits are a pair of bony cavities

It contains: The eyeballs &their associated muscles

Nerves, vessels, and fat

Most of the lacrimal apparatus.

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The OrbitDescriptionIt is a pyramidal cavity

with its base in front and its apex behind.

The orbital margin is formed: Superiorly: Frontal bone

Laterally: Processes of the frontal and zygomatic bones

Inferiorly: zygomatic bone and the maxilla,

Medially :the processes of the maxilla and the frontal bone.

The orbital walls :Roof: Formed by the

orbital plate of the frontal bone

Lateral wall: Formed by the zygomatic bone and the greater wing of the sphenoid

Floor: Formed by the orbital plate of the maxilla

Medial wall: Formed from before backward by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid

Eyelids: The orbital opening is guarded by eyelidsUpper & lower eyelid

meet each other at medial and lateral angles.

The palpebral fissure is elliptical opening between eyelids.

Superficial surface of eyelids is covered by skin, and deep surface is covered by a mucous membrane, called the conjunctiva.

Eyelids are formed by orbital septum (fibrous sheet),which is attached to periosteum at orbital margins.

Orbital septum is thickened at margins of lids to form superior and inferior tarsal plates.

Lateral & medial ends of the plates are attached by lateral palpebral ligament & medial palpebral ligaments to orbital bones.

Tarsal glands are long, modified sebaceous glands that secrete oily sustance onto margin of eyelid.

They are embedded in tarsal plates .

Eyelashes are short, curved hairs on free edges of eyelids at mucocutaneous junction.

The conjunctiva is a thin mucous membrane that lines eyelids and is reflected onto anterior surface of eyeball. Its epithelium is continuous with that of cornea.

Sebaceous glands (glands of Zeis) open directly into eyelash follicles.

The ciliary glands (glands of Moll) are modified sweat glands that open separately between adjacent lashes.

Lacrimal Gland:It consists of a large

orbital part and a small palpebral part & situated in superolateral region of the orbit.

It has about 12 ducts which empty tears into lateral part of superior fornix of the conjunctiva.

Tears enter lacrimal canaliculi which open into lacrimal sac then to nasolacrimal duct.

Nasolacrimal duct is about 0.5 in. (1.3 cm) long.

It descends in a bony canal and opens into inferior meatus of the nose.

Openings into orbital cavity:

Superior orbital fissure: It communicates with

middle cranial fossa.It transmits, lacrimal

nerve, frontal nerve, trochlear nerve, abducent nerve, nasociliary nerve, and superior ophthalmic vein.

Inferior orbital fissure communicates with pterygopalatine fossa.

It transmits maxillary nerve and its zygomatic branch, inferior ophthalmic vein, and sympathetic nerves.

Optic canal: It communicates with

middle cranial fossa.It transmits optic nerve

and ophthalmic artery.Supraorbital notch

(Foramen) for supraorbital nerve and blood vessels.

Infraorbital groove and canal for infraorbital nerve and blood vessels.

Nasolacrimal canal communicates with inferior meatus of nose & transmits the nasolacrimal duct.

Blood VesselsOphthalmic Artery:The ophthalmic

artery is a branch of the internal carotid artery.

Branches:The central artery of

the retina.The muscular

branchesThe ciliary arteries The lacrimal artery The supratrochlear

and supraorbital arteries

Ophthalmic Veins:The superior

ophthalmic vein communicates with the facial vein .

The inferior ophthalmic vein communicates through the inferior orbital fissure with the pterygoid venous plexus.

Both veins through the superior orbital fissure and drain into the cavernous sinus.

There are six voluntary muscles:

Levator palpebrae superioris

Superior rectus Inferior rectusMedial rectus Lateral rectus Superior oblique Inferior oblique.

Muscle Origin Insertion Innervation Function

Levator palpebrae superioris

Lesser wing of sphenoid anterior to optic canal

Anterior surface of tarsal plate; a few fibers to skin and superior conjunctival fornix

Oculomotor nerve [III]- superior branch

Elevation of upper eyelid

Superior rectus Superior part of common tendinous ring

Anterior half of eyeball superiorly

Oculomotor nerve [III]- superior branch

Elevation, adduction, medial rotation of eyeball

Inferior rectus Inferior part of common tendinous ring

Anterior half of eyeball inferiorly

Oculomotor nerve [III]- inferior branch

Depression, adduction, lateral rotation of eyeball

Medial rectus Medial part of common tendinous ring

Anterior half of eyeball medially

Oculomotor nerve [III]- inferior branch

Adduction of eyeball

Lateral rectus Lateral part of common tendinous ring

Anterior half of eyeball laterally

Abducent nerve [VI] Abduction of eyeball

Superior oblique Body of sphenoid, superior and medial to optic canal

Outer posterior quadrant of eyeball

Trochlear nerve [IV] Depression, abduction, medial rotation of eyeball

Inferior oblique Medial floor of orbit posterior to rim; maxilla lateral to nasolacrimal groove

Outer posterior quadrant of eyeball

Oculomotor nerve [III]- inferior branch

Elevation, abduction, lateral rotation of eyeball

Contents of the Eyeball:

Aqueous humor which secreted from ciliary processes, enters posterior chamber then flows into anterior chamber through the pupil and is drained away into canal of Schlemm.

Vitreous body fills the eyeball behind the lens and it supports lens and retina.

Lens is a transparent, biconvex structure which is situated behind iris and in front of vitreous body.

The eyeball consists of three coats:

1-Fibrous coat consists of:

Sclera(‘White of the eye'posterior opaque part).

Cornea(anterior transparent part).

2- Vascular coat consists of:

Choroid.Ciliary body. Iris.

3-Nervous coat(Retina). It has macula lutea(area of most distinct vision) & optic disc without rods and cones (blind spot).

It consists of: Outer pigmented

layer. Inner nervous

layer(retina proper) which consists of many layers but most important are:

Rods & cones Bipolar cells Axons of ganglion

cells

Optic Nerve (Cranial Nerve II):

Fibers of optic nerve are axons of neurons in ganglionic layer of the retina.

They form optic nerve which leaves orbital cavity through optic canal and unites with optic nerve of opposite side to form optic chiasma.

In optic chiasma, nasal (medial) fibers of retina, including the nasal half of macula, cross midline and enter optic tract of opposite side, while temporal (lateral) fibers, including temporal half of macula, pass in same side.

Optic tract passes around cerebral peduncle. Most of its fibers synapse in lateral geniculate body of thalamus.

Few fibers pass to pretectal nucleus and superior colliculus of midbrain for light reflexes.

Axons of geniculate body neurons form optic radiation which terminates in the visual cortex (area 17).