Anatomy of Eye and Orbit pdf - D. Muataz

Anatomy of Orbit and Eye

Dr. Muataz Hasan

Orbit

Orbital Region

The orbits are a pair of bony cavities that contain the eyeballs; their associated muscles,

nerves, vessels, and fat; and most of the lacrimal apparatus.

Eyelids

The eyelids protect the eye from injury and excessive light by their closure. The upper eyelid

is larger and more mobile than the lower, and they meet each other at the medial and lateral

angles.



The superficial surface of the eyelids is covered by skin, and the deep surface is

covered by a mucous membrane, called the conjunctiva. The eyelashes are short,

curved hairs on the free edges of the eyelids. They are arranged in double or triple

rows at the mucocutaneous junction.



The sebaceous glands (glands of Zeis) 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; their openings lie behind the

eyelashes.



The more rounded medial angle is separated from the eyeball by a small space, the

lacus lacrimalis, in the center of which is a small, reddish yellow elevation, the

caruncula lacrimalis . A reddish semilunar fold, called the plica semilunaris, lies on

the lateral side of the caruncle.



Near the medial angle of the eye a small elevation, the papilla lacrimalis, is present.

On the summit of the papilla is a small hole, the punctum lacrimale, which leads into

the canaliculus lacrimalis. The papilla lacrimalis projects into the lacus, and the

punctum and canaliculus carry tears down into the nose.

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.

The framework of the eyelids is formed by a fibrous sheet, the orbital septum. This is

attached to the periosteum at the orbital margins. The orbital septum is thickened at the

margins of the lids to form the superior and inferior tarsal plates. The lateral ends of the

plates are attached by a band, the lateral palpebral ligament, to lacrimal bone a bony

tubercle just within the orbital margin. The medial ends of the plates are attached by a band,

the medial palpebral ligament, to the crest of the lacrimal bone.

Movements of the Eyelids

The position of the eyelids at rest depends on the tone of the orbicularis oculi and the levator

palpebrae superioris muscles and the position of the eyeball. The eyelids are closed by the

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 lid. On

looking upward, the levator palpebrae superioris contracts, and the upper lid moves with the

eyeball. On looking downward, both lids move, the upper lid continues to cover the upper

part of the cornea, and the lower lid is pulled downward slightly by the conjunctiva, which is

attached to the sclera and the lower lid.

Muscles of the Eyeball and Eyelids

Muscle

Origin

Insertion

Nerve Supply

Action

Extrinsic Muscles of Eyeball (Striated Skeletal Muscle)



Superior

rectus

Tendinous

ring on

posterior

wall of

orbital

cavity

Superior

surface of

eyeball just

posterior to

corneoscleral

junction

Oculomotor

nerve (third

cranial nerve)

Raises cornea

upward and

medially



Inferior

rectus

Tendinous

ring on

posterior

wall of the

orbit

Inferior surface

of eyeball just

posterior to

corneoscleral

junction

Oculomotor

nerve (third

cranial nerve)

Depresses cornea

downward and

medially



Medial

rectus

Tendinous

ring on

posterior

wall of the

orbit

Medial surface

of eyeball just

posterior to

corneoscleral

junction

Oculomotor

nerve (third

cranial nerve)

Rotates eyeball so

that cornea looks

medially



Lateral

rectus

Tendinous

ring on

posterior

wall of the

orbit

Lateral surface

of eyeball just

posterior to

corneoscleral

junction

Abducent nerve

(sixth cranial

nerve)

Rotates eyeball so

that cornea looks

laterally



Superior

oblique

Posterior

wall of

orbital

cavity

Passes through

pulley and is

attached to

superior surface

of eyeball

beneath superior

rectus

Trochlear nerve

(fourth cranial

nerve)

Rotates eyeball so

that cornea looks

downward and

laterally



Inferior

oblique

Floor of

orbital

cavity

Lateral surface

of eyeball deep

to lateral rectus

Oculomotor

nerve (third

cranial nerve)

Rotates eyeball so

that cornea looks

upward and

laterally

Intrinsic Muscles of Eyeball (Smooth Muscle)



Sphincter

pupillae of

iris

Parasympathetic

via oculomotor

nerve

Constricts pupil



Dilator

pupillae of

iris

Sympathetic

Dilates pupil



Ciliary

muscle

Parasympathetic

via oculomotor

nerve

Controls shape of

lens; in

accommodation,

makes lens more

globular

Muscles of Eyelids



Levator

palpebrae

superioris

Back of

orbital

cavity

Anterior surface

and upper margin

of superior tarsal

plate

Striated muscle

oculomotor nerve,

smooth muscle

sympathetic

Raises upper lid

Lacrimal Apparatus

Lacrimal Gland

The lacrimal gland consists of a large orbital part and a small palpebral part, It is 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 Ducts

The 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.

Bony Orbit

The orbit is a pyramidal cavity with its base in front and its apex behind. 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.

The orbital walls are:



The Roof: it is made of two bones; the lesser wing of sphenoid and the orbital plate of
the frontal bone, located subjacent to the anterior cranial fossa.



The Lateral Wall: it is made of two bones; the greater wing of the sphenoid and
zygomatic bone.



The Floor: it is made of three bones; the zygomatic, maxillary (both form the anterior
2/3) and palatine (forms posterior 1/3) bones.



The Medial Wall: It is made of four bones; the maxilla (frontal process), lacrimal,
ethmoid and the body of sphenoid.

Openings Into the Orbital Cavity



Orbital opening: Lies anteriorly. About one-sixth of the eye is exposed; the remainder

is protected by the walls of the orbit.



Supraorbital notch (Foramen): The supraorbital notch is situated on the superior

orbital margin. It transmits the supraorbital nerve and blood vessels.



Infraorbital groove and canal: Situated on the floor of the orbit in the orbital plate of

the maxilla; they transmit the infraorbital nerve (a continuation of the maxillary nerve)

and blood vessels.



Nasolacrimal canal: Located anteriorly on the medial wall; it communicates with the

inferior meatus of the nose. It transmits the nasolacrimal duct.



Inferior orbital fissure: Located posteriorly between the maxilla and the greater wing

of the sphenoid; it communicates with the pterygopalatine fossa. It transmits the

maxillary nerve and its zygomatic branch, the inferior ophthalmic vein, and

sympathetic nerves.



Superior orbital fissure: Located posteriorly between the greater and lesser wings of

the sphenoid; it communicates with the middle cranial fossa. It transmits the lacrimal

nerve, the frontal nerve, the trochlear nerve, the oculomotor nerve (upper and lower

divisions), the abducent nerve, the nasociliary nerve, and the superior ophthalmic vein.



Optic canal: Located posteriorly in the lesser wing of the sphenoid; it communicates

with the middle cranial fossa. It transmits the optic nerve and the ophthalmic artery.

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. The nerve is surrounded by sheaths of pia

mater, arachnoid mater, and dura mater. 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.



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



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 and 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 long ciliary nerves, two or three in number, arise from the nasociliary nerve as it

crosses the optic nerve.



The posterior ethmoidal nerve supplies the ethmoidal and sphenoidal air sinuses.



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.



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:

It is a branch from the internal carotid artery as it emerges from the cavernous sinus.

It passes forward and enters the orbit through the optic canal below the optic nerve. In the

orbit, at first it lies below the optic nerve then pierces the arachnoid and the dural sheaths and

winding round the lateral side of the optic nerve, then it crosses above the nerve with the

nasociliary nerve to reach the medial side of the orbit.

It runs forwards along the medial wall of the orbit between the medial rectus and the superior

oblique, and terminates near the medial angle of the eye by dividing into the supratroclear

artery and the dorsal nasal artery.

Branches:

1. Branches to the eyeball

o central artery of the retina.

o posterior ciliary branches [2 long and 7 short].

2. Branches to the orbital muscles: muscular branches

3. Branch along the lateral wall of the orbit: lacrimal artery to the lacrimal gland

4. Branches along the medial wall of the orbit:

o Posterior ethmoidal artery.

o Anterior ethmoidal artery.

o Supraorbital artery.

o Supratrochlear artery .

o Dorsal nasal artery.

o Medial palpebral artery.

Ophthalmic Veins

1. Superior ophthalmic vein: it begins in the anterior part of the orbit close to the

ophthalmic artery, and then it runs with this artery. It communicates with supra-orbital

tributaries of the facial vein.

2. Inferior ophthalmic vein: is smaller than superior ophthalmic vein and lies below the

optic nerve. It communicates with pterygoid venous plexus by small vein through the

inferior orbital fissure.

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

Lymph Vessels

No lymph vessels or nodes are present in the orbital cavity.

Orbital fascia:

It is the periosteum of the bones that form the walls of the orbit. It is loosely attached to the

bones and is continuous with the periosteum covering the outer surface of the bones through

the foramina and the fissures. It encloses all the contents of the orbit except the zygomatic

nerve and the infra-orbital nerve and vessels.

Bulbar fascia [fascial sheath of the eyeball]:

It forms a thin membranous socket around the eyeball [but is deficient in front over the

cornea]. It is separated from the eyeball by soft, semifluid tissue which allows the eyeball to

slide freely in the sheath. The free anterior margin fuses with the conjunctiva close to the

margin of the cornea, while the posterior margin fuses with the dural sheath of the optic

nerve.

This fascia separates the eyeball from the orbital fat and form a tubular sheaths covering

each orbital muscle. Each of the extraocular muscles pierces the fascial sheath at the equator

of the eyeball and receives covering sleeve with it. These sleeves prevent the muscles

compressing the eyeball when it contracts.

The facial sheath is connected to the orbital walls by:

1. Lateral and medial check ligaments: these are strong bands pass from the sheaths around

the lateral and medial rectus to the medial and lateral walls.

2. The suspensory ligament: it is a sling stretched across the anterior part of the orbit

between the lateral and medial check ligaments.

The Eye

Structure of the Eye

consists of three coats, the fibrous coat, the vascular pigmented coat, and the nervous coat.

 Fibrous Coat

The fibrous coat is made up of a posterior opaque part, the sclera, and an anterior transparent

part, the cornea



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 sclera is directly

continuous in front with the cornea at the corneoscleral junction, or limbus.



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.

Blood Supply

The cornea is avascular and devoid of lymphatic drainage. It is nourished by diffusion from

the aqueous humor and from the capillaries at its edge.

Nerve Supply

Long ciliary nerves from the ophthalmic division of the trigeminal nerve

Function of the Cornea

The cornea is the most important refractive medium of the eye. This refractive power occurs

on the anterior surface of the cornea.

 Vascular Pigmented Coat

The vascular pigmented coat consists, from behind forward, the choroid, the ciliary body,

and the iris.



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.

 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, 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.



The Iris and Pupil

The iris is a thin, contractile, pigmented diaphragm with a central aperture, the pupil. It is

suspended in the aqueous humor between the cornea and the lens. It divides the space

between the lens and the cornea into an anterior and a posterior chamber.

The muscle fibers of the iris are involuntary and consist of circular and radiating fibers. The

circular fibers form the sphincter pupillae and are arranged around the margin of the pupil.

The radial fibers form the dilator pupillae and consist of a thin sheet of radial fibers that lie

close to the posterior surface.

Nerve supply:

 The sphincter pupillae is supplied by parasympathetic fibers from the oculomotor

nerve.

 dilator pupillae is supplied by sympathetic fibers, which pass forward to the

eyeball in the long ciliary nerves.

Action:

 The sphincter pupillae constricts the pupil in the presence of bright light and during

accommodation.

 The dilator pupillae dilates the pupil in the presence of light of low intensity or in

the presence of excessive sympathetic activity.

 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. Its

anterior edge forms a wavy ring called the ora serrata.

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.

Aqueous Humor

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.

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 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.

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.