ORBIT

Sanket Parajuli

Embryology Orbit

• Orbital bones From mesenchyme that encircles optic vesicle.• Medial wall from frontonasal process• Lateral + inferior wall from maxillary

process• Superior wall mesenchymal capsule of

forebrain• Optic axis initially directed laterally

toward side of head• Later directed anteriorly

• Eyeball: adult size until 3yrs • Orbit undergoes alteration until

puberty

The bones differentiate in 3rd month of IUL

Ophthalmic artery and it’s Branches:1.Central artery of the Retina2.Lacrimal artery3.Muscular branches4.Ciliary arteries5.Supraorbital ateries6.Posterior ethmoidal arteries7.Anterior ethmoidal arteries8.Meningeal arteries9.Medial palpebral arteries10.Supratrochlear arteries11.Dorsal nasal arteries12.Recurrent artery

External carotid artery 1. Facial artery: arises at angle of mandible…gives

angular artery which supplies lacrimal sac, medial part of lower lid

2. Superficial temporal artery:3 branchesa) Anterior temporal: skin and muscles of foreheadb) Zygomatic artery: orbicularis oculic) Transverse facial artery: skin of cheek

3. Maxillary artery: passes through infratemporal fossa...passes along pterygopalatine fossa…enters orbit through inferior orbital fissure as inferior orbital artery ….runs in infraorbital canal(here supplies IR and IO) …exits via infraorbital foramen…supplies lower lid and lacrimal sac

VEINS OF ORBIT• Tortuous and freely anastomose with one another• Have no valves• Orbit drained by superior and inferior ophthalmic veins which

in turn drain into cavernous sinus

Superior ophthalmic vein• medial part of upper eyelid • union of a branch of the supraorbital vein

and a branch of facial vein• passes posteriorly in orbital fat• Communicates with central vein of retina

and near the apex of orbit (it commonly receives inf oph vein)• Also recieves 2 vorticose veins from upper

part of eyball• It leaves orbit through upper part of sup

orbital fissure to join cavernous sinus

Inferior ophthalmic vein• Arises from venous plexus on the

anterior part on the floor of the orbital cavity• It communicates with pterygoid venous

plexus through the inferior orbital fissure• Passes posteriorly in orbital fat • receives muscular branches and 2

inferior vorticose veins from lower part of eyeball• Drains into cav sinus or empty into

pterygoid venous plexus

LYMPHATIC DRAINAGE

• No lymphatic vessels occur in the globe proper• lymphatics are found in the conjunctiva and

the eyelids.• medial aspects of the lids and the medial

canthal structures (including the lacrimal sac) ……submandibular lymph nodes• lateral eyelids and the lacrimal gland empty

into the parotid lymph nodes in the preauricular area

ORBIT

• Orbital cavity: Pear-shaped/Quadrilateral pyramid• Medial wall: runs AP parallel to sagittal plane• Lateral wall: Diverged @ 45 deg • Base, directed forwards, laterally and slightly

downwards• Apex is between the optic foramen and medial end

of the superior orbital fissure

Orbital margins • Quadrilateral shape with round corners• Adult: width > heightSupraorbital margin: frontal bone(sharp lat 2/3 round med 1/3) @ junction is supraorbital notchSupraciliary canal appears in about 50% of skulls It has a small opening near the supraorbital notch, and transmits a nutrient artery and a branch of the supraorbital nerve to the frontal air sinusInfraorbital margin: sharp, Zygomatic bone (laterally) &Maxilla (medially)Lateral margin: strongest, frontal process of zygomatic bone below and zygomatic process of frontal bone aboveMedial margin : above by maxillary process of frontal bone and below by lacrimal crest of frontal process of maxilla

• Each side measures about 40 mm, but usually the width is greater than the height• orbital index

• Three classes of orbit are recognized (1) Megaseme (large): the index is 89 or more(Mongolian races)(2) Mesoseme (intermediate):index between 89 and 83(Caucasians)(3) Microseme (small): index 83 or less (negroid)

THE ROOF OR VAULT OF THE ORBIT• The roof of the orbit is triangular • Formed by the triangular orbital plate

of the frontal bone, and behind by the lesser wing of the sphenoid .

• It is markedly concave anteriorly and flatter posteriorly

The fossa for the lacrimal gland

• The fossa for the lacrimal gland lies behind the zygomatic process of the frontal bone

• contains the lacrimal gland & some orbital fat, principally at its posterior part (accessory fossa of Rochon-Duvigneaud).

• It is bounded below by the zygomaticofrontal suture, at the junction of roof and lateral wall of the orbit

The fovea/Trochlear fossa• small depression about 4 mm from the orbital

margin• 10% of cases… the ligaments which attach

the U-shaped cartilage of the pulley to it are ossified….a spicule of bone (the spina trochlearis).

The frontosphenoidal suture

• between the orbital plate of the frontal bone and the lesser wing of the sphenoid

Structure & Applied

• Roof of the orbit is thin, translucent and fragile except where formed by the lesser wing of the sphenoid, which is 3 mm thick.

• Penetrating wounds through the lids, inflicted by pointed objects, are sometimes complicated by orbital fracture and injury to the frontal lobe of the cerebrum.

• Its not perforated by any major nerves or bvs thus can be easily nibbled away in transfrontal orbitotomy

Relations

• Frontal nerve • Supraorbital artery only

in the anterior half.• LPS and SR• Trochlear nerve lies

medially• lacrimal gland adjoins

the lacrimal fossa • SO

THE MEDIAL WALL OF THE ORBIT

• the only wall which is not obviously triangular: (flat or slightly convex)• Lies parallel to the sagittal plane, and consists, from

the front backwards, of four bones united by vertical sutures :

1. the frontal process of the maxilla2. the lacrimal bone3. the orbital plate of the ethmoid4. a small part of the body of the sphenoidOf these, the orbital plate of the ethmoid is the largest. It usually shows a mosaic of light and dark areas . The dark areas correspond to the ethmoidal sinuses

Structure & Applied• Medial wall is the thinnest orbital wall • It is translucent, so that the ethmoidal sinuses are

visible as a mosaic pattern upon the wall. • The orbital plate of the ethmoid (lamina

papyracea) is as thin as paper. Infection of the ethmoidal sinuses can easily extend into the orbit and the most common cause of orbital cellulitis.

• However, the orbital plate of ethmoid rarely shows senile absorption, whereas the thicker lacrimal bone, especially in the lacrimal fossa, is often absorbed.

• During surgery hemorrhage most troublesome due to injury of ethmoidal vessels

Relations

o the lateral nasal wall, oethmoidal sinuses, and osphenoidal air sinus. ooptic foramen is located at the posterior end of the medial wall oSO is in the angle between roof and medial wall oMRo termination of the ophthalmic artery o lacrimal sac

THE FLOOR OF THE ORBIT• is triangular. • is formed by three bones:1. the orbital plate of the maxilla;2. the orbital surface of the zygomatic bone; 3. the orbital process of the palatine bone. The maxillary area is the largestInfraorbital sulcus: runs forwards from the inferior orbital (sphenomaxillary) fissure. …near the floor's mid point the sulcus becomes a canal……infraorbital canal descends in the orbital floor to open….. at the infraorbital foramen about 4 mm below the orbital margin. It transmits the infraorbital vessels and nerve

Relations and structure

• Below most of the floor of the orbit is the maxillary sinus• Bone is only 0.5-1 mm thick here, tumours of the sinus can easily invade

the orbit• Commonly involved in blow out fractures

THE LATERAL WALL OF THE ORBIT

• triangular; its base is anterior. • It makes an angle of 45° with the midline• The lateral wall is formed by two bones:1. posteriorly by the orbital surface of the

greater wing of the sphenoid; 2. anteriorly by the orbital surface of the

zygomatic bone.

The sphenoidal area is separated from roof and floor by the superior and inferior orbital fissures. The zygomatic area merges with the floor, and joins the roof at the frontozygomatic suture

The spina musculi recti lateralis

• small bony projection, on the inferior margin of the superior orbital fissure at the junction of its wide and narrow portions,• produced mainly by a groove for the superior ophthalmic vein• A part of the lateral rectus muscle is attached to it

The lateral orbital tubercle(of whitnall)

This is a small elevation on the orbital surface of the zygomatic bone behind the lateral orbital margin and about 11 mm below the frontozygomatic suture.

It gives attachment to:• the check ligament of the lateral rectus muscle;• the suspensory ligament of the eyeball;• the aponeurosis of the levator palpebrae superioris

Structure & Applied

• Being much exposed to stress, the lateral wall is the thickest orbital wall, especially at the orbital margin ..needs to be sawed open during lateral orbitotomy

• Zygomatico-sphenoid suture important landmark in creating flap in kronlein’s operation

Relations• The lateral wall separates the orbit

anteriorly from the temporal fossa and muscle, posteriorly from the middle cranial fossa and temporal lobe of the cerebrum• LR.. in contact with the whole of this

wall• lacrimal nerve and artery• Inferior pole of the lacrimal gland

THE SUPERIOR ORBITAL (SPHENOIDAL) FISSURE

• lies between the roof and the lateral wall, separating the lesser and greater wings of the sphenoid,• Wider at the medial end below the optic foramen, • usually it shows a narrow lateral and a wider medial part,

at the junction of which is the spine for the lateral rectus • The fissure is about 22 mm long, and is the largest

communication between the orbit and middle cranial fossa• The medial end is separated from the optic foramen by

the posterior root of the lesser wing of the sphenoid, on which is the infra optic tubercle

Contents: • Above the annulus are the 1. trochlear, 2. frontal, and

3. lacrimal nerves, 4. superior ophthalmic vein, and the recurrent lacrimal artery.

• Within the annulus or between the two heads of the lateral rectus are the

1. superior division of the oculomotor nerve, 2. nasociliary and sympathetic roots of the ciliary ganglion, 3. inferior division of the oculomotor, 4. abducent nerve and

• sometimes the ophthalmic vein or veins - Only the inferior ophthalmic vein is, occasionally, below the annulus.

SUPERIOR ORBITAL SYNDROME(Rochon-Duvigneaud syndrome)

Fracture at superior orbital fissure

Involvement of cranial nerves

Diplopia, Ophthalmoplegia, Exophthalmos, Ptosis

THE INFERIOR ORBITAL (SPHENOMAXILLARY) FISSURE• lies between the lateral wall and the floor of the

orbit • joins the orbit to the pterygopalatine and

infratemporal fossa • It commences inferolateral to the optic

foramen, at the medial end of the superior orbital fissure, and• runs anterolaterally for 20 mm to end about 2

cm from the inferior orbital margin • It transmits the infraorbital and zygomatic

nerves, orbital periosteal branches from the pterygopalatine ganglion, and a branch from the inferior ophthalmic vein to the pterygoid plexus

THE ETHMOIDAL FORAMINA

• between the roof and medial wall of the orbit

THE ANTERIOR ETHMOIDAL CANAL• opens in the anterior cranial fossa at the side of

the cribriform plate, and transmits the anterior ethmoidal nerve and artery.

THE POSTERIOR ETHMOIDAL CANAL• This canal transmits the posterior ethmoidal

nerve and artery.

THE OPTIC FORAMEN/ optic canal

• connects the MCF to the apex of the orbit• formed by the two roots of the lesser wing of the

sphenoid.• directed anterolaterally+downwards@36° with midline• Projected backwards the two optic axes meet on the

dorsum sellae at about 90°. • The distance between the intracranial openings is 25

mm; between the orbital openings 30 mm. • Anteriorly the roof of each canal extends more than its

floor, while posteriorly the floor projects beyond the roof, this gap being filled in by dura mater with a posterior edge (the falciform fold)

• The canal transmits the1. optic nerve and its meningeal coverings 2. the ophthalmic artery, located at first below, then lateral to the nerve and

embedded in its dural sheath and 3. branches from the periarterial sympathetic plexus

Average measurements of the optic canal• The orbital opening is 6-6.5 mm vertically and 4.5-5 mm horizontally. • The roof of the canal reaches farther forwards than the floor anteriorly, while

posteriorly, the floor projects beyond the roof• Length ≈ 4-10 mm

Zygomaticofacial & zygomaticotemporal foramina

Zygomaticofacial foramen• Small foramina on lateral wall of orbit• Transmits zygomaticofacial nerve

zygomaticotemporal foramina• transmits zygomaticotemporal nerve

Contents of orbit• Eyeball-1/5th of the orbital volume• Muscles• Nerves: 2nd 3rd 4th 6th CN and branches of ophthalmic div of 5th (lacrimal frontal and nasociliary) and br of maxillary div of 5th (infraorbital and zygomatic)• Vessles• Orbital fat • Lacrimal gland and sac

• CILIARY GANGLION

…..Peripheral parasympathetic ganglion…...Lies between Optic nerve and Lateral Rectus muscle…….≈1cm anterior to the optic foramen

3 posterior roots- Sensory rootArises frm Nasociliary Nerve- Motor root/psm root…contains preganglionic fibers from EWN…postganglionic fibers arising from ganglion pass through short ciliary nerves to supply Sphincter pupillae nd ciliary muscle- Sympathetic root..contains postganglionic fibers arising frm superior cervical ganglion…pass out of ganglion in short ciliary nerves to supply bvs + dilator pupillae

AGE AND SEX CHANGES

• orbital margin is sharp and well ossified at birth• Infantile orbits diverge more than the adult i.e.

their axes, from the middle of the orbital opening to the optic foramen, make an angle of 115°, and, if projected backwards, meet at the nasal septum. In the adult these axes make an angle of 40-45°, and meet at the upper part of the clivus of the sphenoid. • The orbital index is high in children, the vertical

diameter being almost the same as the horizontal, but in adults the latter increases • In children the interorbital distance is small and

can appear as squint

SENILE CHANGES

• Senile changes are largely due to absorption of bone.• Thus, in elderly skulls holes sometimes occur in the roof of the orbit, the

periorbita being in direct contact with dura mater• The medial wall, although normally thin, rarely shows absorption in its

ethmoidal area, but its lacrimal part usually does • The lateral wall often displays absorption or marked thinning• In the floor, senile changes rarely produce holes• The orbital fissures, especially the inferior, are widened by absorption

of their margins.

• There is a great difference between the measurements given by different authorities. The following are average:

Sex differences• Up to puberty sexual differences between the orbits are slight. • Thereafter the male develops 2ndary sexual characters, especially in the

mandible and frontal region. The female skull remains more infantile in form. • Female orbits: Remain rounder Glabella and superciliary ridges are less markedzygomatic process of the frontal bone is more slender and pointed Female orbit is more elongated and relatively larger than the male • In contrast, greater development of the frontal sinuses in the male produces

distinct superciliary ridges, and hence a less vertical forehead and less pronounced frontal eminences.

THE PERIORBITA

• The periorbita or orbital periosteum invests every surface of the bones of the orbit, to which it is in general loosely adherent• At various points, however, it is firmly

fixed: a) at the orbital margin, where it is

thickened to form the arcus marginale and continuous with the periosteum of the bones of face;

b) at the sutures, where it is continuous with sutural 'ligaments';

c) at fissures and foramina;d) at the lacrimal fossa. At superior orbital fissure, the optic foramen, and anterior ethmoidal canal the periorbita is continuous with the dura mater

In the superior orbital fissure the periorbita is dense but allows various structures to pass through.In the optic foramen periorbita splits, a) continuous with the dural sheath of ON , and also b) providing attachment for muscles (contribute to formation of annulus of

zinn)Fine processes also pass from the periorbita, to divide fat into lobules and to form coverings for vessels and nerves. In the inferior orbital fissure the periorbita blends with periosteum in the infratemporal and pterygopalatine fossaeAt lacrimal crest encloses the lacrimal fossa, separated from the sac by loose areolar tissue. Its then continuous with lining of NL canal to merge with periosteum in the inferior meatus

Orbital Septum

• At the orbital margins the periorbita is continuous with a connective tissue sheet known as the orbital septum/septum orbitale

• This dense connective tissue sheet is circular and runs from the entire rim of the orbit to the tarsal plates which are embedded in the eyelids.

• Laterally, lies in front of the LPL and the check ligament for the LR

• Superiorly, passes in front of the trochlea and bridges the supraorbital and supratrochlear notches.

• Medially, lies in front of the check ligament for the MR & behind MPL

Tenon’s Capsule/ (bulbar fascia)

• sheet of dense connective tissue that encases the globe• lies between the conjunctiva and the episclera and

merges with them anteriorly in the limbal area.• It’s pierced by the ON , the vortex veins, the ciliary

vessels and nerves, and the EOMs. • Posteriorly, Tenon’s capsule merges with the dural

sheath of the optic nerve.

• acts as a barrier to prevent the spread of orbital infections into the globe.

Suspensory Ligament (of Lockwood)

Hammock-like sheet of dense connective tissue Runs from its attachment on the lacrimal bone (medially) to the zygomatic bone(laterally)• Formed by:Tenon’s capsulesheaths of the two inferior EOMsinferior eyelid aponeurosis

• Helps to support the globe, particularly in the absence of the bones of the orbital floor.

THE ORBITAL MUSCLE OF MULLER (MUSCULUS ORBITALIS)

• Associated with the periorbita, near the inferior orbital fissure• Aggregation of non-striated muscle fibres…not only spans the fissure but also

extends back, deep to the annular tendon as far as the cavernous sinus.

• Anteriorly it fades away in the periorbita.

• Nerve supply The orbital muscle of Muller is supplied by a branch from the pterygopalatine ganglion (sympathetic)

Orbital Septal System

• A complex web of interconnecting connective tissue septa organize the orbital space surrounding the globe into radial compartments.

• Collagenous strands connect the periorbita to Tenon’s capsule and intermuscular membranes.

• This connective tissue system of “slings” anchors and supports the extraocular muscles and blood vessels attaching them to adjacent orbital walls.

Orbital Fat

• The spaces not occupied by ocular structures, connective tissue, nerves, or vessels become filled with adipose tissue.

• Usually, four adipose tissue compartments are located within the muscle cone surrounding the optic nerve and separate it from the extraocular muscles.

INJURY TO THE FACE AND ORBIT

• Blunt injury to the skull may cause fractures at points of weakness.• 'Blow-out' fracture of the ethmoidal or maxillary sinus results from closed

injury to the orbit and fracture of the medial orbital wall (lamina papyracea of the ethmoid), or floor of the orbit (medial to the infraorbital canal) respectively.

• Blow out # floor of orbit• Patient presents with

• Diplopia• Restricted movements• Paresthesia• Enophthalmos

• Le Fort described anatomical lines of weakness in the facial skeleton which render it susceptible to fracture, on frontal impact. • Le Fort type II fracturei. runs across the nasal bonesii. the frontal process of the maxillaiii. nasolacrimal canaliv. floor of the orbit

• Le Fort type III fracture • upper part of the nasal bones• medial wall of the orbit and• extends back to the inferior orbital fissure

Surgical approaches to orbit

• Superior approaches: supraorbital notch is an important landmark coz. It marks exit of supraorbital nerve and artery

• Attachment of trochlea for SO is preserved

• Inferior approaches involve less important anatomic structures and fewer blood vessles are encountered

Surgical spaces in the orbit

Subperiosteal spaceBetween orbit bones and periorbitaLimited anteriorly by strong adhesions of periorbita to orbital rimCommonly seen in this space are:1. Dermoid cyst2. Epidermoid cyst3. Mucocele4. Subperiosteal abscess5. hematoma

Peripheral orbital space(Extraconal) Limited peripherally by periorbita….internally by 4 EOM…anteriorly by septum orbitale• Contents:Peripheral orbital fatSOIOLPSSup nd inf ophthalmic veinsLacrimal gland

Malignant lymphoma & capillary hemangioma commonly arise in this space

Central space/Intraconal• Aka muscular cone or retrobulbar space• Bounded anteriorly by tenon’s capsule lining back of the eye

and peripherally by rectus muscles and their intermuscular septa anteriorly

• Posteriorly the space is continuous with peripheral orbital space• Contents:a) ONb) 3rd CNc) 6th CNd) Ciliary ganglione) Ophthalmic arteryf) Sup ophthalmic vein

Cavernous hemangioma, solitary neurofibroma, ON gliomas occur commonly here

Sub-Tenon’s /Episcleral space

• Potential space between sclera and Tenons capsule• If pus collected: drained by incision of tenons capsule through

conjunctiva

Subarachnoid surgical space

• Between ON & nerve sheath

END