THE ORBITAL CAVITY

- quadrilateral pyramid - apex is directed posterioly , medially , slightly upward

DIMENSIONS - volume of orbit = 30 cc in adults

* RIMhorizontally = 40mmvertically = 35 mm

DEPTH * medially = 42 mm* laterally = 50 mm

- 45 degree between lateral and sagital plane - 23 degree between visual and orbital axis

ORBITAL MARGINeORn lateral wall * supraorbital margin = frontal bone* infraorbital margin = laterally ----> zygomatic bone medially ----> maxilla * lateral margin = frontal process of zygomatic bone zygomatic process of frontal bone * medial margin = above = maxillary process of frontal bone below = frontal process of maxilla CLINICAL

1. infeiror orbital margin- at junctin of lateral 2/3rd and meidal 1/3 small depression origin of infeiror oblique- prone to fracture --> disruption of IO --> diplopia

2. lateral orbital margin- narrowest and weakest part is the frontozygomatic suture ---> prone for separation following blunt trauma

3. lateral orbital margin- lateral orbital rim is recessed on its deep aspect = 0.75 cm above the rim margin to accomodate the lacrimal gland ---> prone to fracture

ROOF - separates it from ant cranial fossa and frontal sinus

BONES - orbital plate of frontal bone- lesser wing of sphenoid

LANDMARKS1. FOSSA FOR THE LACRIMAL GLAND-

LOCATION:behind the zygomatic process of the frontal bone

CONTENTS:lacrimal glandsome orbital fat (accessory fossa of Rochon-Duvigneaud)

2. TROCHLEAR FOSSA (FOVEA)LOCATION:4 mm from the orbital marginCONTENTS:insertion of tendinous pulley of Superior Oblique

SURFACE ANATOMY:Palpable just within the supero-medial angle

3. SUPRAORBITAL NOTCH:LOCATION:15 mm lateral to the superomedial angle

TRANSMITS:Supraorbital nerveSupraorbital vessels

SURFACE ANATOMY: At the junction of lateral 2/3rd and medial 1/3rdAbout two finger breadth from the medial plane

4. OPTIC FORAMEN:- leads from middle cranial fossa to apex of orbit- 8 12 mm LOCATION:Lies medial to superior orbital fissureat the apexPresent in the lesser wing of sphenoid

TRANSMITS:Optic nerve with its meningesOphthalmic artery

CLINICAL - optic nerve glioma or meningioma may lead to unilateral enlargement of optic canal

5. cribra orbitalia- apertures on medial side of ant portion of lacrimal fossa- for veins from diploe to the orbit- best marked in fetus and infant

6. frontosphenoidal suture- between frontal and lesser wing of sphenoid- usually obliterated in adults

CLINICAL ** orbital roof anomaly / fractureCSF pulsation ------> pulsatile exophthalmos

** Laterally- greater wing of sphenoidAnteriorly- superior orbital margin ---->

So, fractures tend to pass towards medial side --->

At junction of the roof and medial wall, the suture line lies in proximity to cribriform plate of ethmoid --->rupture of dura mater --->

CSF escapes into orbit/nose/both

** Since the roof is perforated neither by major nerves nor by blood vessels, so it can be easily nibbled away in transfrontal orbitotomy.

FLOOR - Shortest orbital wall- Roughly triangular

BONES Orbital plate of maxilla (major)Orbital surface of Zygomatic bone (anterolateral)Orbital plate of Palatine bone

Bordered laterally by inferior orbital fissure and medially by maxilloethmoidal suture

Overlies maxillary sinus

LANDMARKS1. INFERIOR ORBITAL NOTCH 4 mm inferior to the inferior orbital marginTransmitsInfraorbital nerveInfraorbital vessels

CLINICAL SIGNIFICANCE

**BLOW OUT FRACTURES:- Fractures of the orbital floor- Infraorbital nerves and vessels are almost invariably involved

LATERAL WALL Formed by-1. Zygomatic bone2. Greater wing of sphenoid

- Thickest orbital wall

Separates orbit from-Middle cranial fossa Temporal fossa

- At an angle of about 90 with each other

LANDMARKS1.LATERAL ORBITAL TUBERCLE OF WHITNALL:

4-5 mm behind the lateral orbital rim11 mm inferior to the frontozygomatic suture line* Gives attachment to:

- Check ligament of lateral rectus- Lockwoods ligament- Lateral canthal tendon- The aponeurosis of the levator palpebrae superioris- Orbital septum- Lacrimal fascia

2. zygomatic groove- from ant end of inferior orbital fissure to a foramen in zygomatic bone

contents- zygomatic nerve , vessels

CLINICAL ** in resection of maxilla , the whitnall's tubercle is spared , otherwise ---> damage to lockwood's ligament ---> infeiror dystopia of eyeball ---> diplopia

**Lateral wall protects only the posterior half of the eyeball, hence palpation of retrobulbar tumours is easier.

** Frontal process of zygoma & zygomatic process of frontal bone protect the globe from lateral trauma- known as facial buttress area.

** Just behind the facial buttress area, is the zygomaticosphenoid suture, which is the preferred site for lateral orbitotomy.

MEDIAL WALL - Thinnest orbital wallBONES 1. Frontal process of Maxilla2. Lacrimal bone3. Orbital plate of Ethmoid4. Body of the sphenoidLANDMARKS1. LACRIMAL FOSSA:

Formed by:frontal process of maxillalacrimal bone

Boundaries:Anterior- anterior lacrimal crestPosterior- posterior lacrimal crest

Dimensions-Length 14 mmDepth 5 mmContinuous below with bony nasolacrimal canal

Content-Lacrimal sac

ANTERIOR LACRIMAL CREST*-

upward continuation of the inferior orbital marginIll defined above but well marked belowSurface anatomy-Palpable along the medial orbital margin (anteriorly)

POSTERIOR LACRIMAL CREST*-

downward extension of the superior orbital marginSurface anatomy-Palpable along the medial orbital margin, posterior to the lacrimal fossa

*significant landmarks in lacrimal sac surgeryFRONTO ETHMOIDAL SUTURE LINE- Marks the approximate level of ethmoidal sinus roof- Breach of this suture may open the frontal sinus, or the cranial cavity- Anterior and posterior ethmoidal foramina are present in the suture line

Anterior ethmoidal foramen- 20-25 mm posterior from the anterior lacrimal crest- Opens in the anterior cranial fossa at the side of the cribriform plate of ethmoid

Transmits- anterior ethmoidal nerve & vessels

Posterior ethmoidal foramen- 32-35 mm posterior from anterior lacrimal crest7 mm anterior to the anterior rim of optic canal

Transmits posterior ethmoidal nerve & vessels

Webers suture- Lies anterior to lacrimal fossa- Also known as sutura longitudinalis imperfecta- Runs parallel to anterior lacrimal crest- Branches of infraorbital artery pass through this groove to supply the nasal mucosa- Bleeding may occur from these vessels during DCR surgeries

MEDIAL WALL CLINICAL ** orbital cellulitisthin wall ---> prone for damage and sinusitis infection spread across ----> orbital cellulitis

** medial wall is extremely fragile ( presence of ethmoidal air cells and nasal cavity )

** accidental lateral displacement of medial wall --> traumatic hypertelorism

*medial wall provides alternate access route to the orbit through the sinus

** tumors of nasal cavity can breach the lamina papyracea to involve the orbit

** lacrimal bone can be easily penetrated during endoscopic DCR

SURGICAL SPACES IN ORBIT 1. sub periosteal space- Between orbital bones and the periorbita- Limited anteriorly by strong adhesions of periorbita to the orbital rim

2. peripheral spaceBounded:- peripherally by periorbita- internally by the four recti with their intermuscular septa- anteriorly by the septum orbitale- Posteriorly, it merges with the central space

CONTENTS:

Peripheral orbital fat* MusclesSuperior obliqueInferior obliqueLevator palpebrae superioris* NervesLacrimalFrontalTrochlearAnterior ethmoidalPosterior ethmoidal* VeinsSuperior ophthalmicInferior ophthalmic* Lacrimal gland* Lacrimal sac

3. central space- Also known as muscular cone or retrobulbar space

Bounded:- Anteriorly by Tenons capsule- Peripherally by four recti with their intermuscular septa- In the posterior part, continuous with the peripheral orbital space

CONTENTS:

* Central orbital fat* NervesOptic nerve (with its meninges)OculomotorSuperior and inferior divisionsAbducentNasociliaryCiliary ganglion* VesselsOphthalmic arterySuperior ophthalmic vein

4. tenon's spaceBetween the sclera and the Tenons capsule

*Pus collected in this space is drained by incision of Tenons capsule through the conjunctiva*Site for drug instillation

ORBITAL CAVITY RELATIONS

* Superiorly Anterior cranial fossa* Medially - Nasal cavity & Ethmoidal air sinuses* Inferiorly - Maxillary sinus* Laterally - Middle cranial fossa & Temporal fossa

SUPERIOR ORBITAL FISSURE

- Also known as Sphenoidal fissure- Lateral to the optic foramen at the orbital apex- comma-shaped gap between the roof and the lateral wall- Bounded by- Lesser and greater wings of the sphenoid- 22 mm long- Largest communication between the orbit and the middle cranial fossa- Its tip lies 30-40 mm from the frontozygomatic suture- Lateral superior part of the fissure is narrower than the medial inferior part.- At the junction of the two lies spina recti lateralis

LANDMARK ** Annulus of Zinn- Spans both superior orbital fissure & the optic canal- Gives origin to the four recti muscle

CLINICAL ** inflammation of the superior orbital fissure and apex may result in a multitude of isgns including ophthalmoplegia and venous outflow obstruction ---> TOLOSA HUNT SYNDROME

** fracture at superior orbital fissure --> involvement of cranial nerves --> diplopia , opthalmoplegia , exophthalmos , ptosis SUPERIOR ORBITAL SYNDROME ( rochon duvingneaud syndrome )

** Manner of involvement of nerves may be helpful in predicting the site and extent of the lesion.

Divisions of IIIrd nerve VIth nerve--->Annulus of Zinn (Purely intraconal lesion)IIIrd, IVth and VIth nerve---> Entire length of the fissure involved

INFERIOR ORBITAL FISSURE

- Also known as sphenomaxillary fissure- Between floor and the lateral wall

Bounded by- Medially- Maxilla and orbital process of palatineLaterally- Greater wing of the sphenoidAnterior aspect- closed by Zygomatic bone

Transmits-- Venous drainage from the inferior part of the orbit to the pterygoid plexus- neural branches from the pterygopalatine ganglion- the zygomatic nerve- the infraorbital nerve

- Closed in the living by the periorbita & the Mullers muscle- Serves as the posterior limit of surgical subperiosteal dissection along the orbital floor

CONTENTS OF ORBIT 1. eyeball2. muscles- 4 recti- 2 oblique- LPS- muller's muscle3. nerves - Sensory- branches of Vth Nerve- Motor- IIIrd, IVth & VIth Nerve- Autonomic- Nerves to the Lacrimal gland- Ciliary ganglion4. vessels* arteriesInternal carotid system- branches of ophthalmic arteryExternal carotid system- a branch of internal maxillary artery* Veins-Superior ophthalmic veinInferior ophthalmic vein* Lymphatics-none5. lacrimal gland6. lacrimal sac7. orbital fat , reticular tissue and orbital fascia 8. ciliary ganglion