orbit & lacrimal apparatus · 2020. 12. 1. · thus, a lesion of each cranial nerve has its own...

THE ORBITKhaleel Alyahya, PhD, MEd

www.khaleelalyahya.net

Resources

Atlas of Human Anatomy

By Frank Netter

Gray’s Anatomy

By Richard Drake, Wayne Vogl

& Adam Mitchell

Essential of Human

Anatomy & Physiology

By Elaine Marieb and Suzanne

Keller

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Khaleel Alyahya, PhD, MEd

Introduction

The bony orbits (Sometimes called eye sockets) are

bilateral and symmetrical cavities in the head.

They enclose the eyeball and its associated structures.

The orbit can be thought of as a pyramidal structure, with

the apex pointing posteriorly and the base situated

anteriorly.

The boundaries of the orbit are formed by six bones.

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Borders & Relations

Roof (superior wall): Formed by the frontal bone and thelesser wing of the sphenoid. The frontal bone separates theorbit from the anterior cranial fossa.

Floor (inferior wall): Formed by the maxilla, palatine andzygomatic bones. The maxilla separates the orbit from theunderlying maxillary sinus.

Medial wall: Formed by the ethmoid, maxilla, lacrimaland sphenoid bones. The ethmoid bone separates the orbitfrom the ethmoid sinus.

Lateral wall: Formed by the zygomatic bone and greaterwing of the sphenoid.

Apex: Located at the opening to the optic canal, the opticforamen.

Base: Opens out into the face and is bounded by theeyelids. It is also known as the o

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Content

Eyeball and related structures.

Extraocular muscles: These muscles are separate from theeye. They are responsible for the movement of the eyeball andsuperior eyelid.

Eyelids: These cover the orbits anteriorly.

Nerve: Several cranial nerves supply the eye and its structures.Thoseare optic, oculomotor, trochlear, trigeminal and abducens nerves.

Blood vessels: The eye receives blood primarily from theophthalmic artery. Venous drainage is via the superior andinferior ophthalmic veins.

Orbital fat: it fill any space within the orbit that is not occupied.This tissue cushions the eye and stabilizes the extraocularmuscles.

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Openings

There are three main pathways by whichstructures can enter and leave the orbit:

• Optic canal transmits the optic nerve and ophthalmic artery.

• Superior orbital fissure transmits the lacrimal,frontal, trochlear (CN IV), oculomotor (CN III), nasociliaryand abducens (CN VI) nerves. It also carries the superiorophthalmic vein.

• Inferior orbital fissure transmits the maxillary nerve (abranch of CN V), the inferior ophthalmic vein, andsympathetic nerves.

There are other minor openings into the orbitalcavity.

• Nasolacrimal canal which drains tears from the eye to thenasal cavity, is located on the medial wall of the orbit.

• Other small openings include the supraorbitalforamen and infraorbital canal which carry smallneurovascular structures.

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Bony orbit fractures

It is a fracture of the bones forming the outer rim of the bonyorbit.

It usually occurs at the sutures joining the three bones of theorbital rim – the maxilla, zygomatic and frontal.

Any fracture of the orbit will result in infraorbital pressure,raising the pressure in the orbit,causing exophthalmos (protrusion of the eye).

There may also be involvement of surrounding structures.

Example: hemorrhage into one of the neighboring sinuses.

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Eyelids

The eyelids are thin, mobile folds that cover the eyeballanteriorly.

They offer protection from excessive light or injury andmaintain lubrication by distributing tears over the surfaceof the eyeball.

The eyelids are split into upper and lower portions, whichmeet at the medial and lateral canthi of the eye.

The opening between the two eyelids is calledthe palpebral opening.

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Eyelids layers

The skin and subcutaneous tissue form the mostsuperficial layer of the eyelid.

The layer of skin is among the thinnest in the humanbody.

In the subcutaneous layer, there is loose connectivetissue but no subcutaneous fat.

The eyelashes are attached here with theiraccompanying modified sweat glands.

The eyelid consists of five main layers (superficial todeep):

• Skin and subcutaneous tissue

• Orbicularis oculi

• Tarsal plates

• Levator apparatus

• Conjunctiva

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Blood vessels

The eyelid has a rich arterial supply from numerousvessels:

• Ophthalmic artery: lacrimal, medial palpebral, supraorbital andsupratrochlear arteries.

• Facial artery: angular branch.

• Superficial temporal artery: transverse facial artery branch.

Venous drainage is provided by a rich network aroundthe eyelid:

• Medially, medial palpebral vein into the angular and ophthalmicveins.

• Laterally, blood drains into the superficial temporal vein fromthe lateral palpebral vein.

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Innervation

Sensory innervation to the eyelids is supplied bybranches of the trigeminal nerve:

• Ophthalmic nerve (V1): supraorbital, supratrochlear,infratrochlear and lacrimal branches.

• Maxillary nerve (V2): infraorbital branch.

The motor innervation to the muscles of the eyelid is via:

facial nerve (orbicularis oculi)

oculomotor nerve (levator palpebrae superioris)

sympathetic fibers (superior tarsal muscle)

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MUSCLES OF ORBIT

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Muscles of orbit

The extraocular muscles are located within the orbit but areextrinsic and separate from the eyeball itself.

They act to control the movements of the eyeball andthe superior eyelid.

There are seven extraocular muscles:

• levator palpebrae superioris

• superior rectus

• inferior rectus

• medial rectus

• lateral rectus

• inferior oblique

• superior oblique

Functionally, they can be divided into two groups:

• responsible for eye movement: Recti and oblique muscles.

• responsible for superior eyelid: levator palpebrae superioris13


Levator palpebrae superioris

The only muscle involved in raising the superior eyelid.

It has a small portion contains a collection of smooth musclefibers called superior tarsal muscle.

It originates on the lesser wing of the sphenoid bone just abovethe optic foramen.

It broadens and decreases in thickness (becomes thinner) andthen becomes the levator aponeurosis.

This portion inserts on the skin of the upper eyelid, as well asthe superior tarsal plate.

Action: It elevates and retracts the upper eyelid.

Innervation: Oculomotor nerve.

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Recti muscles

There are four recti muscles:

• superior rectus

• inferior rectus

• medial rectus

• lateral rectus

These muscles originate from the common tendinous ring of fibroustissue, which surrounds the optic canal at the back of the orbit.

From their origin, the muscles pass anteriorly to attach to the scleraof the eyeball.

The name recti is derived from the latin for ‘straight’ – thisrepresents the fact that the recti muscles have a direct path fromorigin to attachment.

This in contrast with oblique eye muscles which have an angularapproach to the eyeball.

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Superior rectus

Attachments: Originates from the superior part of the common

tendinous ring and attaches to the superior and anterior aspect

of the sclera.

Actions: Main movement is elevation. Also contributes to

adduction and medial rotation of the eyeball.


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Inferior rectus

Attachments: Originates from the inferior part of the common

tendinous ring and attaches to the inferior and anterior aspect of

the sclera.

Actions: Main movement is depression. Also contributes to

adduction and lateral rotation of the eyeball.


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Medial rectus

Attachments: Originates from the medial part of the common

tendinous ring and attaches to the anterio-medial aspect of the

sclera.

Actions: Adducts the eyeball.


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Lateral rectus

Attachments: Originates from the lateral part of the common

tendinous ring and attaches to the anterio-lateral aspect of the

sclera.

Actions: Abducts the eyeball.

Innervation: Abducens nerve.

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Oblique muscles

There are two oblique muscles:

• superior oblique.

• inferior oblique.

Unlike the recti group of muscles, oblique muscles do notoriginate from the common tendinous ring.

From their origin, the oblique muscles take an angular approachto the eyeball (in contrast to the straight approach of the rectimuscles).

They attach to the posterior surface of the sclera.

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Superior oblique

Attachments: Originates from the body of the sphenoid bone.Its tendon passes through a trochlear, and then attaches to thesclera of the eye, posterior to the superior rectus.

Actions: Depresses, abducts and medially rotates the eyeball.

Innervation: Trochlear nerve

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Inferior oblique

Attachments: Originates from the anterior aspect of the orbitalfloor. Attaches to the sclera of the eye, posterior to the lateralrectus.

Actions: Elevates, abducts and laterally rotates the eyeball.

Innervation: Oculomotor nerve

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Cranial nerves palsies

The extraocular muscles are innervated by three cranialnerves.

Damage to one of the cranial nerves will causeparalysis of its respective muscles.

This will alter the resting gaze of the affected eye.

Thus, a lesion of each cranial nerve has its owncharacteristic appearance:

• Oculomotor nerve: A lesion of this nerve affects most of theextraocular muscles. The affected eye is displaced laterallyby the lateral rectus and inferiorly by the superior oblique.The eye adopts a position known as down and out.

• Trochlear nerve: A lesion of this nerve will paralyze thesuperior oblique muscle. There is no obvious affect of theresting orientation of the eyeball. However, the patient willcomplain of diplopia (double vision) and may develop a headtilt away from the site of the lesion.

• Abducens nerve: A lesion of this nerve will paralyze thelateral rectus muscle. The affected eye will be adducted bythe resting tone of the medial rectus. 23


Intrinsic muscles

Iris Sphincter (Sphincter Pupillae)

• Nerve supply: Parasympathetic fibers from oculomotor nerve, vianerve to inferior oblique after relay in ciliary ganglion, postganglionicfibers pass to eyeball via short ciliary nerves.

• Action: constricts the pupil in bright light and in accommodation.

Dilator Pupillae

• Nerve supply: Sympathetic fibers via long ciliary nerves.

• Action: dilates the pupil in dim light and in excessive sympathetic

activity as in fright.

Ciliary muscle

• Smooth muscle in the ciliary body.

• Nerve supply: Parasympathetic from oculomotor.

• Action: accommodation by making the lens more convex.

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Blood supply of orbit

The main arterial supply to the lacrimal gland is fromthe lacrimal artery, which is derived from the ophthalmicartery – a branch of the internal carotid.

Venous drainage is via the superior ophthalmic vein, andultimately empties into the cavernous sinus.

Lymphatic drainage is to the superficial parotid lymphnodes. They empty into the superior deep cervical nodes.

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Ophthalmic artery

It is a branch of internal carotid artery.

It passes through optic canal, below optic nerve & withinthe common tendinous ring.

It lies below then lateral then superior to optic nerve.

It runs close to medial wall of orbit close to its roof,where it divides into supratrochlear & dorsal nasalarteries.

Branches:

• Central artery of retina

• Lacrimal artery.

• long post ciliary artery

• Short post ciliary artery

• Post ethmoidal artery

• Ant ethmoidal artery

• Supraorbital artery

• Medial palpebral artery

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Ophthalmic Vein

It has two branches:

• Superior Ophthalmic Vein

• Inferior Ophthalmic Vein

They pass through the superior orbital fissure to end inthe cavernous sinus.

They communicate with veins of the face & pterygoidplexus of veins through Inferior orbital fissure.

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Innervation of orbit

Sensory Nerves

• Optic nerve

• Branches from ophthalmic division of trigeminal nerve

Motor Nerves

• Occulomotor nerve

• Trochlear nerve

• Abducent nerve

Please note that the maxillary nerve passes through theinferior orbital fissure, enters into the groove in floor ofthe orbit.

Then continues as infraorbital nerve.

Exits through infraorbital foramen and supplies the skinof the face.

It does not supply any of the orbital contents though.

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Optic nerve

It located in the back of the eye.

It is the 2nd cranial nerve.

It carries the transmission of special sensory informationfrom the retina of the eye to the primary visual cortex ofthe brain.

It arises from retina and pierces the posterior surface ofthe sclera.

It passes through the optic canal.

It accompanied by the ophthalmic artery that lies belowit.

It surrounded by meninges and subarachnoid spacecontaining CSF.

It runs forward & laterally within the cone of the rectimuscles

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Ophthalmic nerve

It is the smallest of the three divisions of the trigeminalnerve.

It runs in the lateral wall of the cavernous sinus anddivides into:

• Lacrimal nerve

• Frontal nerve

• Nasociliary nerve

It enters the orbit through the superior orbital fissure.

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Lacrimal nerve

One of the terminal branches of Ophthalmic nerve.

It enters orbit through the superior orbital fissureoutside the tendinous ring.

It passes above lateral rectus to enter lacrimal gland.

It provides sensory fibers to:

• Lacrimal gland

• Skin of the lateral part of the upper eyelid

Please note that the zygomatic nerve of the maxillary isconnected to the lacrimal nerve to carry autonomic fibers(sympathetic and parasympathetic) fibers to the lacrimalgland.

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Frontal nerve


It enters the orbit through the superior orbital fissure,outside the tendinous ring.

It runs over the levator palpebrae superioris.

It divides into:

• Supratrochlear Nerve: supplies skin of forehead &scalp.

• Supraorbital Nerve: supplies skin of forehead & scalp.

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Nasociliary nerve


It enters the orbit through the superior orbital fissure,within the tendinous ring.

It crosses above the optic nerve with the ophthalmicartery, to reach the medial wall of the orbit.

It runs along the upper margin of the medial rectus, andends by dividing into:

• anterior ethmoidal nerve

• infratrochlear nerve

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Oculomotor nerve

It divides into superior and inferior divisions beforeentering the orbit.

Both enter the orbit through the superior orbital fissurewithin the tendinous ring.

Superior division supplies:

• Superior rectus

• Levator Palpebrae superioris

Inferior division supplies:

• Inferior rectus

• Inferior oblique

• Medial rectus

Please note that the nerve to inferior oblique gives offpreganglionic fibers to ciliary ganglion and carriesparasympathetic fibers to the sphincter pupillae &ciliary muscles, via short ciliary nerves.

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Trochlear nerve

It enters orbit through the superior orbital fissure outsidethe tendinous ring.

It supplies superior oblique muscle.

Lesion of this nerve results in diplopia on looking down,and inability to look infero-laterally.

Thus, the eye deviates; upward and slightly inward.

The effected person will have difficulty in walkingdownstairs.

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Abducent nerve

It enters orbit through the superior orbital fissure withinthe tendinous ring.

It runs forward on the deeper surface of the lateral rectusmuscle to supplies it.

Lesion of this nerve leads to diplopia & medial squint.

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Ciliary ganglion

A parasympathetic ganglion.

Located in the upper part of the orbit, lateral to the opticnerve.

Afferent (preganglionic) fibers: Carried by theocculomotor nerve, reach the ganglion via the nerve tothe inferior oblique.

Efferent (postganglionic) fibers: Carried by the shortciliary nerves to supply the constrictor pupillae and ciliarymuscle.

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Summary 38


Questions?

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orbit & lacrimal apparatus · 2020. 12. 1. · thus, a lesion of each cranial nerve has its own...

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