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Orbit

The document discusses the anatomy of the orbit, including its embryology, dimensions, boundaries, and clinical significance. It can be summarized as follows: The orbit is a pyramid-shaped space bounded by seven bones and containing the eye. It develops from the frontal process, maxillary process, and lateral nasal process in embryology. The thin medial wall and floor are most prone to fractures. Landmarks like the lacrimal fossa and infraorbital foramen have clinical importance. Fractures of the orbit can damage surrounding structures and cause diplopia or sensory changes.

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 EMBRYOLOGY  ANATOMY  APPLIED ASPECTS - OPTOM FASLU MUHAMMED
INTRODUCTION  Orbit is the anatomical space bounded:  Superiorly – Anterior cranial fossa  Medially - Nasal cavity & Ethmoidal air sinuses  Inferiorly - Maxillary sinus  Laterally - Middle cranial fossa & Temporal fossa
EMBRYOLOGY  Orbital walls- derived from cranial neural crest cells which expand to form:  Frontonasal process  Maxillary process  Lateral nasal process + Maxillary process = medial, inferior and lateral orbital walls  Capsule of forebrain forms orbital roof
 Early in the human development eyes point almost in the opposite direction.  As the facial growth occurs, the angle between the optic stalks decreases and is ~68˚ in an adult. EMBRYOLOG Y
OSSIFICATION Enchondral Membranous EMBRYOLOG
 Frontal, Zygomatic, Maxillary and Palatine bones- Intramembranous origin  First bone- Maxillary (at 6 wks of intrauterine life) - develops from elements in the region of the canine tooth - secondary ossification centres in the orbitonasal and premaxillary regions  Other bones develop at around 7 wks of intrauterine life EMBRYOLOG
 Sphenoid bone- both enchondral and intramembranous origins Lesser wing of the sphenoid- 7 wks (Enchondral) Greater wing of the sphenoid- 10 wks (Intramembranous) Both wings join- 16 wks  Ossification is complete at birth (except orbital apex) EMBRYOLOG
CLINICAL SIGNIFICANCE DERMOID CYSTS:  Most common orbital cystic lesions  Origin: ◦ Pouches of ectoderm trapped into bony sutures ◦ Most common site frontozygomatic suture
CEPHALOCOELES:  Reflect orbital entrapment of neuroectoderm  Most commonly- ◦ At the junction of frontal & ethmoid  Pathology: ◦ Herniation of brain parenchyma into the orbit EMBRYOLOG
FIBROUS DYSPLASIA:  Benign, developmental fibro-osseous lesion  Origin: ◦ Arrest in maturation at woven bone stage  Pathology: ◦ Bone replaced by fibrous tissue EMBRYOLOG
DIMENSIONS  Quadrilateral pyramid  Base - forwards, laterally, downwards  Apex - optic foramen  Volume of orbital cavity ≈ 30 cc in adults
 Rim: - Horizontally ≈ 40 mm - Vertically ≈ 35 mm  Interorbital width  ≈ 25 mm  Extraorbital width  ≈ 100 mm  Depth ◦ Medially ≈ 42 mm ◦ Laterally ≈ 50 mm DIMENSIONS
COMPOSED OF:  7 Bones:  Ethmoid  Frontal  Lacrimal  Maxillary  Palatine  Sphenoid  Zygomatic Right orbit FSlMLESbMZPZSz 2432
BOUNDARIES
4 WALLS ROOF FLOOR MEDIAL WALL LATERAL WALL BOUNDARIES
ROOF  Underlies Frontal sinus and Anterior cranial fossa  Formed by- ◦ 1. Frontal bone (Orbital plate) ◦ 2. Lesser wing of Sphenoid  Triangular  Faces downwards, and slightly forwards Left orbit
 Concave anteriorly, almost flat posteriorly  The anterior concavity is greatest about 1.5 cm from the orbital margin & corresponds to the equator of the globe.  Thin, transluscent and fragile (except the lesser wing of the sphenoid) ROOF
LANDMARKS • 1. FOSSA FOR THE LACRIMAL GLAND-  LOCATION: behind the zygomatic process of the frontal bone  CONTENTS: lacrimal gland some orbital fat ROOF
2. TROCHLEAR FOSSA (FOVEA)  LOCATION: 4 mm from the orbital margin  CONTENTS: insertion of tendinous pulley of Superior Oblique o sometimes (≈10%) surmounted by a spicule of bone (Spina trochlearis) o Extremely rarely trochlea completely ossified cracks easily  SURFACE ANATOMY: Palpable just within the supero-medial angle ROOF
3. SUPRAORBITAL NOTCH:  LOCATION: ≈15 mm lateral to the superomedial angle  TRANSMITS: - Supraorbital nerve - Supraorbital vessels  SURFACE ANATOMY: - At the junction of lateral 2/3rd and medial 1/3rd - About two finger breadth ROOF Right orbit
4. OPTIC FORAMEN: LOCATION: - Lies medial to superior orbital fissure - at the apex - Present in the lesser wing of sphenoid TRANSMITS: - Optic nerve with its meninges - Ophthalmic artery ROOF Left orbit
 Cribra orbitalia: - apertures apparent on the medial side of anterior portion of the lacrimal fossa - for veins from diploë to the orbit - Best marked in the fetus and infant  Frontosphenoidal suture: - between frontal and the lesser wing of the sphenoid - usually obliterated in the adults ROOF
CLINICAL SIGNIFICANCE Thin and fragile Easily fractured by direct violence (penetrating orbital injuries) Frontal lobe injury ROOF
 Reinforced - Laterally- greater wing of sphenoid - Anteriorly- 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 ROOF
 Since the roof is perforated neither by major nerves nor by blood vessels, so it can be easily nibbled away in transfrontal orbitotomy. ROOF
MEDIAL WALL  Thinnest orbital wall  Formed(Antero-posteriorly)  1. Frontal process of Maxilla  2. Lacrimal bone  3. Orbital plate of Ethmoid  4. Body of the sphenoid  Almost parallel to each other Left orbit
LANDMARKS  LACRIMAL FOSSA: - Formed by: - frontal process of maxilla - lacrimal bone - Boundaries: - Anterior- anterior lacrimal crest - Posterior- posterior lacrimal crest Right orbit
- Dimensions- - Length≈ 14 mm - Depth≈ 5 mm - Continuous below with bony nasolacrimal canal - Content- - Lacrimal sac MEDIAL WALL
 ANTERIOR LACRIMAL CREST*- - upward continuation of the inferior orbital margin - Ill defined above but well marked below - Surface anatomy- - Palpable along the medial orbital margin (anteriorly)  POSTERIOR LACRIMAL CREST*- - downward extension of the superior orbital margin - Surface anatomy- - Palpable along the medial orbital margin, posterior to the lacrimal fossa *significant landmarks in lacrimal sac surgery MEDIAL WALL
 FRONTO 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 MEDIAL WALL
 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 MEDIAL WAL
 Posterior ethmoidal foramen - 32-35 mm posterior from anterior lacrimal crest - 7 mm anterior to the anterior rim of optic canal - Transmits - posterior ethmoidal nerve & vessels MEDIAL WALL Left orbit
Weber’s 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 WAL
CLINICAL SIGNIFICANCE  Anteriorly located suture indicates predominance of lacrimal bone  Posteriorly located suture indicates the predominance of maxillary bone* *If maxillary component is predominant, it becomes difficult to perform osteotomy to reach the sac during DCR, because the maxillary bone is very thick. MEDIAL WALL
 Medial wall 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 MEDIAL WALL
 Ethmoid - Thinnest bone of the orbit - Vascular connections with ethmoid sinus through foramina - Inflammation in the ethmoid sinus spreads readily to the orbit  Tumours of the nasal cavity can breach the lamina papyracea to involve the orbit  Lacrimal bone can be easily penetrated during endoscopic DCR  During surgery, hemorrhage is most troublesome due to injury to ethmoidal vessels. MEDIAL WAL
FLOOR • Shortest orbital wall • Roughly triangular • Formed by- • Orbital plate of maxilla (major) • Orbital surface of Zygomatic bone (anterolateral) • Orbital plate of Palatine bone Right orbit
 Bordered laterally by inferior orbital fissure and medially by maxilloethmoidal suture  Overlies maxillary sinus FLOOR
LANDMARKS Infraorbital groove Infraorbital canal Infraorbital foramen  ≈4 mm inferior to the inferior orbital margin  Transmits - Infraorbital nerve - Infraorbital vessels FLOOR
CLINICAL SIGNIFICANCE  BLOW OUT FRACTURES: ◦ Fractures of the orbital floor ◦ Infraorbital nerves and vessels are almost invariably involved ◦ Patient presents with  Diplopia  Restricted movements(upgaze)  Paresthesia FLOOR
LATERAL WALL  Formed by- ◦ 1. Zygomatic bone ◦ 2. Greater wing of sphenoid  Thickest orbital wall  Separates orbit from- ◦ Middle cranial fossa ◦ Temporal fossa  At an angle of about 90° with each other Right orbit
LANDMARKS  LATERAL ORBITAL TUBERCLE OF WHITNALL: - 4-5 mm behind the lateral orbital rim - 11 mm inferior to the frontozygomatic suture line LATERAL WALL Right orbit
- Gives attachment to: - Check ligament of lateral rectus - Lockwood’s ligament - Lateral canthal tendon - The aponeurosis of the levator palpebrae superioris - Orbital septum - Lacrimal fascia LATERAL WALL
CLINICAL SIGNIFICANCE  In resection of maxilla, the Whitnall’s tubercle is spared, otherwise Damage to Lockwood’s ligament Inferior dystopia of eye ball Diplopia LATERAL WALL
 SPINA RECTI LATERALIS: - at the junction of wide & narrow portions of the superior orbital fissure - Produced by a groove lodging superior ophthalmic vein - Gives origin to a part of Lateral Rectus LATERAL WAL
 ZYGOMATIC GROOVE: - EXTENT: - From the anterior end of the inferior orbital fissure to a foramen in the zygomatic bone - CONTENTS: - Zygomatic nerve - Zygomatic vessels LATERAL WAL
CLINICAL SIGNIFICANCE  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. LATERAL WAL
Anteriorly, superior margin of inferior Orbital fissure joins suture between zygomatic and greater wing of sphenoid (line of relative weakness) extends to frontozygomatic suture Frequently involved in zygomatic bone fracture LATERAL WAL
ORBITAL MARGINS
SUPERIOR ORBITAL MARGIN - formed by- Frontal bone - concave downwards, convex forwards - sharp in lateral 2/3rd ,rounded in medial 1/3rd - at the junction- supraorbital notch (sometimes foramen)* - *Site for nerve block.
 Sometimes- o Arnold’s notch/foramen Present medial to supraorbital notch Transmits medial branches of supraorbital nerve & vessels o Supraciliary canal Near the supraorbital notch Transmits nutrient artery a branch of supraorbital nerve to frontal air sinus SUPERIOR ORBITAL MARGIN
 SURFACE ANATOMY: - Well marked prominence - More prominent laterally than medially - Eyebrow corresponds to the margin only in a part - Head- under the margin - Body- along the margin - Tail- above the margin SUPERIOR ORBITAL MARGIN
LATERAL ORBITAL MARGIN: - formed by - zygomatic process of frontal - the zygomatic bone - strongest portion of margin
CLINICAL SIGNIFICANCE  Lateral orbital rim is recessed on its deep aspect ≈ 0.75 cm above the rim margin to accommodate the lacrimal gland Prone to fracture LATERAL ORBITAL MARGIN
 Narrowest and weakest part- frontozygomatic suture Prone for separation following blunt trauma LATERAL ORBITAL MAR
INFERIOR ORBITAL MARGIN:  Formed by- - Zygomatic - Maxilla - suture between the two is sometimes marked by a tubercle- felt 4-5 mm above the infraorbital foramen  SURFACE ANATOMY: - Palpable as a sharp ridge, beyond which the finger can pass into the orbit
CLINICAL SIGNIFICANCE  At the junction of lateral 2/3rd & medial 1/3rd just within the rim- small depression- origin of Inferior oblique Prone to fracture Disruption of Inferior oblique Diplopia  Penetrating injuries may severe lacrimal passages INFERIOR ORBITAL MAR
MEDIAL ORBITAL MARGIN: - Formed by - Frontal process of maxilla (anterior lacrimal crest) - Lacrimal bone (posterior lacrimal crest)
 Orbital index= (Height/Width)X 100 1. Megaseme- ≥89% (Orbital opening-round) 2. Mesoseme- 82-88% 3. Microseme- ≤83% (Orbital opening-rectangular)
FISSURES AND FORAMINA
OPTIC CANAL  Leads from the middle cranial fossa to the apex of the orbit  Orbital opening- vertically oval  In the middle- circular (≈5mm)  Intracranial- horizontally oval  Length ≈ 8-12 mm - Attained at 4-5 years of age  Boundaries- - Medially- Body of the sphenoid - Laterally- Lesser wing of the sphenoid Right orbit
 Directed- forwards, laterally and downwards  Distance between ◦ Intracranial openings≈ 25mm ◦ Orbital openings≈ 30mm  Transmits- ◦ Optic nerve & its meninges ◦ Ophthalmic artery OPTIC CANAL
 Processus falciformis: The roof of the canal reaches farther forwards than the floor anteriorly, while posteriorly, the floor projects beyond the roof. Fold of dura mater filling the gap in the roof is called Processus falciformis. OPTIC CANA
CLINICAL SIGNIFICANCE  Optic nerve glioma or Meningioma may lead to unilateral enlargement of Optic canal OPTIC CANA Strut view of Optic Canal (Normal) CT-Scan showing lesion in Left optic nerve
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 Left orbit
SUPERIOR ORBITAL FISSURE Right superior orbital fissure
 22 mm long  Largest communication between the orbit and the middle cranial fossa  Its tip lies 30-40 mm from the frontozygomatic suture SUPERIOR ORBITAL FISSURE
 Lateral superior part of the fissure is narrower than the medial inferior part. - At the junction of the two lies spina recti lateralis SUPERIOR ORBITAL FISSURE
LANDMARK  Annulus of Zinn - Spans both superior orbital fissure & the optic canal - Gives origin to the four recti muscles SUPERIOR ORBITAL FISSURE
CLINICAL SIGNIFANCE  Inflammation of the superior orbital fissure and apex may result in a multitude of signs including ophthalmoplegia and venous outflow obstruction TOLOSA HUNT SYNDROME SUPERIOR ORBITAL FISSURE
SUPERIOR ORBITAL SYNDROME (Rochon-Duvigneaud syndrome) Fracture at superior orbital fissure Involvement of cranial nerves Diplopia, Ophthalmoplegia, Exophthalmos, Ptosis, SUPERIOR ORBITAL FISSURE
 Manner of involvement of nerves may be helpful in predicting the site and extent of the lesion. Divisions of III’rd nerve ± VI’th nerve Annulus of Zinn (Purely intraconal lesion) III’rd, IV’th and VI’th nerve Entire length of the fissure involved SUPERIOR ORBITAL FISSURE
INFERIOR ORBITAL FISSURE  Also known as sphenomaxillary fissure  Between floor and the lateral wall  Bounded by- oMedially- Maxilla and orbital process of palatine oLaterally- Greater wing of the sphenoid oAnterior aspect- closed by Zygomatic bone Left orbit
 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 Muller’s muscle  Serves as the posterior limit of surgical subperiosteal dissection along the orbital floor INFERIOR ORBITAL FISSURE
CONNECTIVE TISSUE SYSTEM  Periorbita  Orbital septal system  Tenon’s capsule
PERIORBITA (Orbital periosteum)  Loosely adherent to the bones  Sensory innervation by branches of V’th nerve  Fixed firmly at - Orbital margins (Arcus marginale) - Suture lines - Various fissures & foramina - Lacrimal fossa
CLINICAL SIGNIFICANCE  Surgery in the orbital roof in the areas of fissures and suture lines may be complicated by cerebrospinal fluid leakage . PERIORBITA
ORBITAL SEPTAL SYSTEM  Includes the connective tissue septa which are suspended from the periorbita to form a complex radial and circumferential interconnecting slings.  These septa surround Extraocular muscles, Optic nerve, neuro-vascular elements and the fat lobules.
TENON’S CAPSULE  Also known as Fascia bulbi or bulbar sheath.  Dense, elastic and vascular connective tissue that surrounds the globe (except over the cornea).  Begins anteriorly at the perilimbal sclera, extends around the globe to the optic nerve, and fuses with the dural sheath and the sclera.  Separated from the sclera by periscleral lymph space, which is in continuation with subdural and subarachnoid spaces.
CONTENTS OF THE ORBIT  Eye ball  Muscles ◦ 4 Recti ◦ 2 obliques ◦ Levator palpebrae superioris ◦ Muller’s muscle (Musculus orbitalis)  Nerves ◦ Sensory- branches of V’th Nerve ◦ Motor- III’rd, IV’th & VI’th Nerve ◦ Autonomic- Nerves to the Lacrimal gland ◦ Ciliary ganglion Left orbit
 Vessels ◦ Arteries-  Internal carotid system- branches of ophthalmic artery  External carotid system- a branch of internal maxillary artery ◦ Veins-  Superior ophthalmic vein  Inferior ophthalmic vein ◦ Lymphatics-  none  Lacrimal gland  Lacrimal sac  Orbital fat, reticular tissue & orbital fascia CONTENTS OF THE ORBIT
Arterial supply
Venous drainage
 CILIARY GANGLION - Peripheral parasympathetic ganglion - Lies between Optic nerve and Lateral Rectus muscle - ≈1cm anterior to the optic foramen - 3 posterior roots - Sensory root - Nasociliary Nerve - Motor root - Nerve to inferior oblique - Sympathetic root - Branches from internal NERVES
SURGICAL SPACES  SUBPERIOSTEAL SPACE: ◦ Between orbital bones and the periorbita ◦ Limited anteriorly by strong adhesions of periorbita to the orbital rim
 PERIPHERAL ORBITAL SPACE (ORBITAL SPACE) - Bounded: - peripherally by periorbita - internally by the four recti with their intermuscular septa - anteriorly by the septum orbitale - Posteriorly, it merges with the central space SURGICAL SPACES
 CONTENTS:  Peripheral orbital fat  Muscles ◦ Superior oblique ◦ Inferior oblique ◦ Levator palpebrae superioris  Nerves ◦ Lacrimal ◦ Frontal ◦ Trochlear ◦ Anterior ethmoidal ◦ Posterior ethmoidal  Veins ◦ Superior ophthalmic ◦ Inferior ophthalmic  Lacrimal gland  Lacrimal sac SURGICAL SPACES
 CENTRAL SPACE - Also known as muscular cone or retrobulbar space - Bounded: - Anteriorly by Tenon’s capsule - Peripherally by four recti with their intermuscular septa - In the posterior part, continuous with the peripheral orbital space SURGICAL SPACES
 CONTENTS:  Central orbital fat  Nerves ◦ Optic nerve (with its meninges) ◦ Oculomotor  Superior and inferior divisions ◦ Abducent ◦ Nasociliary ◦ Ciliary ganglion  Vessels ◦ Ophthalmic artery ◦ Superior ophthalmic vein SURGICAL SPACES
 SUBTENON’S SPACE* - Between the sclera and the Tenon’s capsule - *Pus collected in this space is drained by incision of Tenon’s capsule through the conjunctiva - *Site for drug instillation SURGICAL SPACES
AGE RELATED VARIATIONS  Infantile orbits are more divergent (≈115°) than those of adults (≈40-45°)  Orbital axes - Lie in horizontal plane in infants - slope downwards (≈15-20°) in adults
 Orbital fissures are relatively larger in childhood than in adults (owing to the narrowness of the greater wing of sphenoid)  Orbital index- higher in children than in adults (transverse diameter increases relatively more in the later life)  Interorbital distance is smaller in children- may give false impression of squint AGE RELATED VARIATIONS
 Roof much larger than floor in infancy  Optic canal has no length at birth- a foramen - at 1 year of age≈ 4 mm  Periorbita much thicker and stronger at birth than in adults AGE RELATED VARIATIONS
 SENILE CHANGES-  Holes, particularly in the roof due to absorption of the bony wall  Orbital fissures become wider AGE RELATED VARIATIONS
GENDER RELATED VARIATIONS MALES • Glabella & supraciliary ridges more marked FEMALES • Larger • More elongated • Rounder • Upper margins sharper • Frontal eminences more marked
TAKE HOME MESSAGE…………………...  Knowledge of orbital anatomy and its variations helps to determine the pathology as well as the site, direction and extent of the incision during elective exploration of the orbit.  It is also must for understanding the clinical course and planning the management in cases of accidental incisions/explorations.