1. EMBRYOLOGY ANATOMY APPLIED ASPECTS- Ajay Kumar Singh- Bhumika Sharma Department ofOphthalmology King Georges MedicalUniversity, Lucknow(INDIA)

2. 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 3. EMBRYOLOGY Orbital walls- derived from cranial neural crestcells 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 4. EMBRYOLOG Y Early in the humandevelopment eyes pointalmost in the oppositedirection. As the facial growth occurs,the angle between the opticstalks decreases and is ~68in an adult. 5. EMBRYOLOG OSSIFICATIONEnchondral Membranous 6. 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 andpremaxillary regions Other bones develop at around 7 wks of intrauterinelife 7. EMBRYOLOG Sphenoid bone- both enchondral andintramembranous originsLesser 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) 8. CLINICAL SIGNIFICANCEDERMOID CYSTS: Most common orbitalcystic lesions Origin: Pouches of ectodermtrapped into bonysutures Most common sitefrontozygomatic suture 9. EMBRYOLOGCEPHALOCOELES: Reflect orbitalentrapment ofneuroectoderm Most commonly- At the junction of frontal& ethmoid Pathology: Herniation of brainparenchyma into theorbit 10. EMBRYOLOGFIBROUS DYSPLASIA: Benign, developmentalfibro-osseous lesion Origin: Arrest in maturation atwoven bone stage Pathology: Bone replaced byfibrous tissue 11. DIMENSIONS Quadrilateral pyramid Base - forwards, laterally, downwards Apex - optic foramen Volume of orbital cavity 30 cc in adults 12. DIMENSIONS Rim:- Horizontally 40 mm- Vertically 35 mm Interorbital width 25 mm Extraorbital width 100 mm Depth Medially 42 mm Laterally 50 mm 13. COMPOSED OF: 7 Bones: Ethmoid Frontal Lacrimal Maxillary Palatine Sphenoid ZygomaticRight orbit 14. BOUNDARIES 15. BOUNDARIES4 WALLSROOF MEDIAL LATERAL FLOORWALL WALL 16. ROOF Underlies Frontal sinus andAnterior cranial fossa Formed by- 1. Frontal bone (Orbitalplate) 2. Lesser wing of Sphenoid Triangular Faces downwards, and Left orbitslightly forwards 17. ROOF Concave anteriorly, almost flat posteriorly The anterior concavity is greatest about 1.5 cm fromthe orbital margin & corresponds to the equator ofthe globe. Thin, transluscent and fragile (except the lesserwing of the sphenoid) 18. 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) 19. 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 ossifiedcracks easily SURFACE ANATOMY:Palpable just within the supero-medial angle 20. ROOF 3. SUPRAORBITALNOTCH: LOCATION:15 mm lateral to thesuperomedial 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 21. 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 meningesLeft orbit - Ophthalmic artery 22. ROOF Cribra orbitalia:- apertures apparent on the medial side of anteriorportion of the lacrimal fossa- for veins from diplo 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 23. ROOFCLINICAL SIGNIFICANCE Thin and fragileEasily fractured by directviolence (penetrating orbitalinjuries) Frontal lobe injury 24. ROOF Reinforced- Laterally- greater wing of sphenoid- Anteriorly- superior orbital marginSo, fractures tend to pass towards medial sideAt junction of the roof and medial wall, the suture line liesin proximity to cribriform plate of ethmoidrupture of dura mater CSF escapes into orbit/nose/both 25. ROOF Since the roof is perforated neither by majornerves nor by blood vessels, so it can be easilynibbled away in transfrontal orbitotomy. 26. MEDIAL WALL Thinnest orbital wall Formed(Antero-posteriorly) 1. Frontal process ofMaxilla 2. Lacrimal bone 3. Orbital plate of Ethmoid 4. Body of the sphenoid Almost parallel to each other Left orbit 27. LANDMARKS LACRIMAL FOSSA:- Formed by:- frontal process ofmaxilla- lacrimal bone- Boundaries:- Anterior- anteriorlacrimal crestRight orbit - Posterior- posteriorlacrimal crest 28. MEDIALWALL- Dimensions-- Length 14 mm- Depth 5 mm- Continuous below with bony nasolacrimal canal- Content-- Lacrimal sac 29. 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 tothe lacrimal fossa*significant landmarks in lacrimal sac surgery 30. MEDIAL WALL FRONTO ETHMOIDAL SUTURE LINE- Marks the approximate level of ethmoidal sinusroof- Breach of this suture may open the frontal sinus,or the cranial cavity- Anterior and posterior ethmoidal foramina arepresent in the suture line 31. MEDIAL WAL Anterior ethmoidal foramen- 20-25 mm posterior from the anterior lacrimal crest- Opens in the anterior cranial fossa at the side of thecribriform plate of ethmoid- Transmits-- anterior ethmoidal nerve & vessels 32. MEDIALWALL Posterior ethmoidalforamen- 32-35 mm posterior fromanterior lacrimal crest- 7 mm anterior to theanterior rim of opticcanal- TransmitsLeft orbit- posterior ethmoidalnerve & vessels 33. MEDIAL WALWebers suture Lies anterior to lacrimal fossa Also known as sutura longitudinalis imperfecta Runs parallel to anterior lacrimal crest Branches of infraorbital artery pass through thisgroove to supply the nasal mucosa Bleeding may occur from these vessels duringDCR surgeries 34. MEDIAL WALLCLINICAL SIGNIFICANCE Anteriorly located suture indicates predominanceof lacrimal bone Posteriorly located suture indicates thepredominance of maxillary bone* *If maxillary component is predominant, itbecomes difficult to perform osteotomy to reachthe sac during DCR, because the maxillary boneis very thick. 35. MEDIAL WALL Medial wall extremely fragile (presence ofethmoidal air cells and nasal cavity) Accidental lateral displacement of medial wall-traumatic hypertelorism Medial wall provides alternate access route tothe orbit through the sinus 36. MEDIAL WAL Ethmoid- Thinnest bone of the orbit- Vascular connections with ethmoid sinus through foramina- Inflammation in the ethmoid sinus spreads readily to theorbit Tumours of the nasal cavity can breach the laminapapyracea to involve the orbit Lacrimal bone can be easily penetrated duringendoscopic DCR During surgery, hemorrhage is most troublesome due toinjury to ethmoidal vessels. 37. FLOOR Shortest orbital wall Roughly triangular Formed by- Orbital plate of maxilla(major) Orbital surface ofZygomatic bone(anterolateral) Orbital plate of Palatine Right orbitbone 38. FLOOR Bordered laterally by inferior orbital fissure andmedially by maxilloethmoidal suture Overlies maxillary sinus 39. FLOORLANDMARKS InfraorbitalInfraorbitalInfraorbital groove canal foramen 4 mm inferior to the inferior orbital margin Transmits- Infraorbital nerve- Infraorbital vessels 40. FLOORCLINICAL SIGNIFICANCE BLOW OUT FRACTURES: Fractures of the orbital floor Infraorbital nerves andvessels are almost invariablyinvolved Patient presents with Diplopia Restricted movements(upgaze) Paresthesia 41. LATERAL WALL Formed by- 1. Zygomatic bone 2. Greater wing ofsphenoid Thickest orbital wall Separates orbit from- Middle cranial fossa Temporal fossa At an angle of about 90 Right orbitwith each other 42. LATERALWALLLANDMARKS LATERAL ORBITALTUBERCLE OFWHITNALL:- 4-5 mm behind thelateral orbital rim- 11 mm inferior to thefrontozygomaticsuture lineRight orbit 43. LATERALWALL- Gives attachment to: - Check ligament of lateral rectus - Lockwoods ligament - Lateral canthal tendon - The aponeurosis of the levator palpebrae superioris - Orbital septum - Lacrimal fascia 44. LATERAL WALLCLINICAL SIGNIFICANCE In resection of maxilla, the Whitnalls tubercle isspared, otherwise Damage to Lockwoods ligamentInferior dystopia of eye ball Diplopia 45. LATERAL WAL SPINA RECTI LATERALIS:- at the junction of wide & narrow portions of thesuperior orbital fissure- Produced by a groove lodging superior ophthalmicvein- Gives origin to a part of Lateral Rectus 46. LATERAL WAL ZYGOMATIC GROOVE:- EXTENT:- From the anterior end of the inferior orbital fissure to aforamen in the zygomatic bone- CONTENTS:- Zygomatic nerve- Zygomatic vessels 47. LATERAL WALCLINICAL SIGNIFICANCE Lateral wall protects only the posterior half of theeyeball, hence palpation of retrobulbar tumours iseasier. Frontal process of zygoma & zygomatic process offrontal bone protect the globe from lateral trauma-known as facial buttress area. Just behind the facial buttress area, is thezygomaticosphenoid suture, which is the preferredsite for lateral orbitotomy. 48. 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 49. ORBITAL MARGINS 50. 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. 51. SUPERIOR ORBITAL MARGIN Sometimes-o Arnolds notch/foramenPresent medial to supraorbital notchTransmits medial branches of supraorbital nerve & vesselso Supraciliary canalNear the supraorbital notchTransmits nutrient artery a branch of supraorbital nerve to frontal air sinus 52. SUPERIOR ORBITALMARGIN 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 53. LATERAL ORBITAL MARGIN: - formed by- zygomatic process of frontal- the zygomatic bone - strongest portion of margin 54. LATERAL ORBITAL MARGINCLINICAL SIGNIFICANCE Lateral orbital rim is recessed on its deep aspect 0.75 cm above the rim margin to accommodate thelacrimal gland Prone to fracture 55. LATERAL ORBITAL MAR Narrowest and weakest part- frontozygomatic sutureProne for separation following blunt trauma 56. INFERIOR ORBITAL MARGIN: Formed by-- Zygomatic- Maxilla- suture between the two is sometimes marked by atubercle- felt 4-5 mm above the infraorbital foramen SURFACE ANATOMY:- Palpable as a sharp ridge, beyond which the finger canpass into the orbit 57. INFERIOR ORBITAL MARCLINICAL SIGNIFICANCE At the junction of lateral 2/3rd & medial 1/3rd just withinthe rim- small depression- origin of Inferior obliqueProne to fractureDisruption of Inferior oblique Diplopia Penetrating injuries may severe lacrimal passages 58. MEDIAL ORBITAL MARGIN:- Formed by- Frontal process of maxilla (anterior lacrimal crest)- Lacrimal bone (posterior lacrimal crest) 59. Orbital index= (Height/Width)X 1001. Megaseme- 89% (Orbital opening-round)2. Mesoseme- 82-88%3. Microseme- 83% (Orbital opening-rectangular) 60. FISSURESANDFORAMINA 61. OPTIC CANAL Leads from the middle cranial fossa to the apex ofthe 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 62. OPTICCANAL Directed- forwards, laterally and downwards Distance between Intracranial openings 25mm Orbital openings 30mm Transmits- Optic nerve & its meninges Ophthalmic artery 63. OPTIC CANA Processus falciformis: The roof of the canalreaches farther forwards than the flooranteriorly, while posteriorly, the floor projectsbeyond the roof. Fold of dura mater filling thegap in the roof is called Processus falciformis. 64. OPTIC CANACLINICAL SIGNIFICANCE Optic nerve glioma or Meningioma may lead tounilateral enlargement of Optic canal CT-Scan showing lesion in Left Strut view of Optic optic nerveCanal(Normal) 65. SUPERIOR ORBITAL FISSURE Also known as Sphenoidalfissure Lateral to the optic foramen at the orbital apex comma-shaped gap between theroof and the lateral wall Left orbit Bounded by- Lesser and greaterwings of the sphenoid 66. SUPERIOR ORBITAL FISSURERight superior orbital fissure 67. SUPERIOR ORBITAL FISSURE 22 mm long Largest communication between the orbit andthe middle cranial fossa Its tip lies 30-40 mm from the frontozygomaticsuture 68. SUPERIOR ORBITALFISSURE Lateral superior part of the fissure is narrowerthan the medial inferior part.- At the junction of the two lies spina rectilateralis 69. SUPERIOR ORBITAL FISSURELANDMARK Annulus of Zinn - Spans both superior orbital fissure & the optic canal - Gives origin to the four recti muscles 70. SUPERIOR ORBITAL FISSURECLINICAL SIGNIFANCE Inflammation of the superior orbital fissure andapex may result in a multitude of signsincluding ophthalmoplegia and venous outflowobstruction TOLOSA HUNT SYNDROME 71. SUPERIOR ORBITAL FISSUREFracture at superior orbital fissure Involvement of cranial nervesDiplopia, Ophthalmoplegia,Exophthalmos, Ptosis, SUPERIOR ORBITAL SYNDROME (Rochon-Duvigneaud syndrome) 72. SUPERIOR ORBITALFISSURE Manner of involvement of nerves may be helpful inpredicting the site and extent of the lesion.Divisions of IIIrd nerve VIth nerveAnnulus of Zinn (Purely intraconal lesion) IIIrd, IVth and VIth nerve Entire length of the fissure involved 73. INFERIOR ORBITAL FISSURE Also known as sphenomaxillaryfissure Between floor and the lateral wall Bounded by-o Medially- Maxilla and orbitalprocess of palatineo Laterally- Greater wing of thesphenoido Anterior aspect- closed byZygomatic bone Left orbit 74. INFERIOR ORBITAL FISSURE Transmits-- Venous drainage from the inferior part of theorbit to the pterygoid plexus- neural branches from the pterygopalatineganglion- the zygomatic nerve- the infraorbital nerve Closed in the living by the periorbita & theMullers muscle Serves as the posterior limit of surgicalsubperiosteal dissection along the orbital floor 75. CONNECTIVE TISSUE SYSTEM Periorbita Orbital septal system Tenons capsule 76. PERIORBITA (Orbital periosteum) Loosely adherent to the bones Sensory innervation by branches of Vth nerve Fixed firmly at- Orbital margins (Arcus marginale)- Suture lines- Various fissures & foramina- Lacrimal fossa 77. PERIORBITACLINICAL SIGNIFICANCE Surgery in the orbital roof in the areas offissures and suture lines may be complicatedby cerebrospinal fluid leakage . 78. ORBITAL SEPTAL SYSTEM Includes the connective tissue septa which aresuspended from the periorbita to form acomplex radial and circumferentialinterconnecting slings. These septa surround Extraocular muscles,Optic nerve, neuro-vascular elements and thefat lobules. 79. TENONS CAPSULE Also known as Fascia bulbi or bulbar sheath. Dense, elastic and vascular connective tissue thatsurrounds the globe (except over the cornea). Begins anteriorly at the perilimbal sclera, extends aroundthe globe to the optic nerve, and fuses with the duralsheath and the sclera. Separated from the sclera by periscleral lymph space,which is in continuation with subdural and subarachnoidspaces. 80. CONTENTS OF THE ORBIT Eye ball Muscles 4 Recti 2 obliques Levator palpebrae superioris Mullers muscle (Musculus orbitalis) Left orbit Nerves Sensory- branches of Vth Nerve Motor- IIIrd, IVth & VIth Nerve Autonomic- Nerves to the Lacrimal gland Ciliary ganglion 81. CONTENTS OF THEORBIT Vessels Arteries- Internal carotid system- branches of ophthalmic artery External carotid system- a branch of internal maxillaryartery Veins- Superior ophthalmic vein Inferior ophthalmic vein Lymphatics- none Lacrimal gland Lacrimal sac Orbital fat, reticular tissue & orbital fascia 82. NERVES CILIARY GANGLION- Peripheral parasympatheticganglion- Lies between Optic nerve andLateral Rectus muscle- 1cm anterior to the opticforamen- 3 posterior roots- Sensory root- Nasociliary Nerve- Motor root- Nerve to inferior oblique- Sympathetic root- Branches from internal 83. SURGICAL SPACES SUBPERIOSTEAL SPACE: Between orbital bones and the periorbita Limited anteriorly by strong adhesions of periorbita tothe orbital rim 84. SURGICALSPACES PERIPHERAL ORBITAL SPACE (ORBITAL SPACE)- Bounded:- peripherally by periorbita- internally by the four recti with their intermuscularsepta- anteriorly by the septum orbitale- Posteriorly, it merges with the central space 85. SURGICAL CONTENTS:SPACES 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 86. SURGICALSPACES 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 orbitalspace 87. 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 88. SURGICAL SUBTENONS SPACE* SPACES- Between the sclera and the Tenons capsule- *Pus collected in this space is drained by incision ofTenons capsule through the conjunctiva- *Site for drug instillation 89. AGE RELATED VARIATIONS Infantile orbits are more divergent (115) thanthose of adults (40-45) Orbital axes- Lie in horizontal plane in infants- slope downwards (15-20) in adults 90. AGE RELATED VARIATIONS Orbital fissures are relatively larger in childhood thanin adults (owing to the narrowness of the greaterwing of sphenoid) Orbital index- higher in children than in adults (transverse diameter increases relatively more inthe later life) Interorbital distance is smaller in children- may givefalse impression of squint 91. 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 inadults 92. AGE RELATED VARIATIONS SENILE CHANGES- Holes, particularly in the roof due to absorption ofthe bony wall Orbital fissures become wider 93. GENDER RELATED VARIATIONSMALESFEMALES Glabella & Largersupraciliary ridges More elongatedmore marked Rounder Upper marginssharper Frontal eminencesmore marked 94. TAKE HOMEMESSAGE... Knowledge of orbital anatomy and its variationshelps to determine the pathology as well as thesite, direction and extent of the incision duringelective exploration of the orbit. It is also must for understanding the clinicalcourse and planning the management in casesof accidental incisions/explorations.