EMBRYOLOGY ANATOMY APPLIED ASPECTS- Ajay Kumar Singh- Bhumika Sharma• Department of Ophthalmology• King George‘s Medical University, Lucknow (INDIA)
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
EMBRYOLOG Y 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 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)
CLINICAL SIGNIFICANCEDERMOID CYSTS: Most common orbital cystic lesions Origin: ◦ Pouches of ectoderm trapped into bony sutures ◦ Most common site frontozygomatic suture
EMBRYOLOGCEPHALOCOELES: Reflect orbital entrapment of neuroectoderm Most commonly- ◦ At the junction of frontal & ethmoid Pathology: ◦ Herniation of brain parenchyma into the orbit
EMBRYOLOGFIBROUS DYSPLASIA: Benign, developmental fibro-osseous lesion Origin: ◦ Arrest in maturation at woven bone stage Pathology: ◦ Bone replaced by fibrous tissue
DIMENSIONS Quadrilateral pyramid Base - forwards, laterally, downwards Apex - optic foramen Volume of orbital cavity ≈ 30 cc in adults
ROOF Underlies Frontal sinus and Anterior cranial fossa Formed by- ◦ 1. Frontal bone (Orbital plate) ◦ 2. Lesser wing of Sphenoid Triangular Faces downwards, and Left orbit slightly forwards
ROOF 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)
ROOFLANDMARKS• 1. FOSSA FOR THE LACRIMAL GLAND- LOCATION: behind the zygomatic process of the frontal bone CONTENTS: lacrimal gland some orbital fat (accessory fossa of Rochon- Duvigneaud)
ROOF2. TROCHLEAR FOSSA (FOVEA) LOCATION: 4 mm from the orbital margin CONTENTS: insertion of tendinous pulley of Superior Obliqueo 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: Right orbit - At the junction of lateral 2/3rd and medial 1/3rd - About two finger breadth
ROOF4. 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 Left orbit - Ophthalmic artery
ROOF 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
ROOFCLINICAL 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 sideAt 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.
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 Right orbit - Posterior- posterior lacrimal crest
MEDIAL WALL- 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 WAL 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 WALL Posterior ethmoidal foramen - 32-35 mm posterior from anterior lacrimal crest - 7 mm anterior to the anterior rim of optic canal - Transmits Left orbit - posterior ethmoidal nerve & vessels
MEDIAL WALWeber’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 WALLCLINICAL 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 WAL 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.
FLOOR• Shortest orbital wall• Roughly triangular• Formed by- • Orbital plate of maxilla (major) • Orbital surface of Zygomatic bone (anterolateral) • Orbital plate of Palatine Right orbit bone
FLOOR Bordered laterally by inferior orbital fissure and medially by maxilloethmoidal suture Overlies maxillary sinus
FLOORLANDMARKS Infraorbital Infraorbital Infraorbital groove canal foramen ≈4 mm inferior to the inferior orbital margin Transmits - Infraorbital nerve - Infraorbital vessels
FLOORCLINICAL 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
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° Right orbit with each other
LATERAL WALLLANDMARKS LATERAL ORBITAL TUBERCLE OF WHITNALL: - 4-5 mm behind the lateral orbital rim - 11 mm inferior to the frontozygomatic suture line Right orbit
LATERAL WALL- 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 WAL 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 WALCLINICAL 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 WALAnteriorly, superior margin of inferiorOrbital fissure joins suture betweenzygomatic and greater wing of sphenoid(line of relative weakness) extends to frontozygomatic suture Frequently involved in zygomatic bone fracture
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.
SUPERIOR ORBITAL MARGIN Sometimes-o Arnold’s notch/foramen Present medial to supraorbital notch Transmits medial branches of supraorbital nerve & vesselso 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
LATERAL ORBITAL MARGIN: - formed by - zygomatic process of frontal - the zygomatic bone - strongest portion of margin
LATERAL ORBITAL MARGINCLINICAL 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 MAR Narrowest and weakest part- frontozygomatic suture Prone for separation following blunt trauma
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
INFERIOR ORBITAL MARCLINICAL 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
MEDIAL ORBITAL MARGIN:- Formed by - Frontal process of maxilla (anterior lacrimal crest) - Lacrimal bone (posterior lacrimal crest)
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 Right orbit - Laterally- Lesser wing of the sphenoid
OPTIC CANAL Directed- forwards, laterally and downwards Distance between ◦ Intracranial openings≈ 25mm ◦ Orbital openings≈ 30mm Transmits- ◦ Optic nerve & its meninges ◦ Ophthalmic artery
OPTIC CANA 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 CANACLINICAL SIGNIFICANCE Optic nerve glioma or Meningioma may lead to unilateral enlargement of Optic canal CT-Scan showing lesion in Left Strut view of Optic optic nerve Canal (Normal)
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 Left orbit Bounded by- Lesser and greater wings of the sphenoid
SUPERIOR ORBITAL FISSURERight superior orbital fissure
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 FISSURELANDMARK Annulus of Zinn - Spans both superior orbital fissure & the optic canal - Gives origin to the four recti muscles
SUPERIOR ORBITAL FISSURECLINICAL 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 FISSUREFracture at superior orbital fissure Involvement of cranial nerves Diplopia, Ophthalmoplegia, Exophthalmos, Ptosis, SUPERIOR ORBITAL SYNDROME (Rochon-Duvigneaud syndrome)
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
INFERIOR ORBITAL FISSURE Also known as sphenomaxillary fissure Between floor and the lateral wall Bounded by- o Medially- Maxilla and orbital process of palatine o Laterally- Greater wing of the sphenoid o Anterior aspect- closed by Zygomatic bone Left orbit
INFERIOR ORBITAL FISSURE 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
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
PERIORBITACLINICAL SIGNIFICANCE Surgery in the orbital roof in the areas of fissures and suture lines may be complicated by cerebrospinal fluid leakage .
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) Left orbit Nerves ◦ Sensory- branches of V’th Nerve ◦ Motor- III’rd, IV’th & VI’th Nerve ◦ Autonomic- Nerves to the Lacrimal gland ◦ Ciliary ganglion
CONTENTS OF THE 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
NERVES 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
SURGICAL SPACES SUBPERIOSTEAL SPACE: ◦ Between orbital bones and the periorbita ◦ Limited anteriorly by strong adhesions of periorbita to the orbital rim
SURGICAL SPACES 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 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 CONTENTS: SPACES 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 SUBTENON’S SPACE* SPACES- 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
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
AGE RELATED VARIATIONS 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
GENDER RELATED VARIATIONS MALES FEMALES• Glabella & • Larger supraciliary ridges • More elongated more marked • Rounder • Upper margins sharper • Frontal eminences more marked
TAKE HOMEMESSAGE…………………... 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.