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Anatomy of orbit by Dr.Prakash Bam
- 1. Dr Prakash Bam 1st Year Resident TIO, 2021
- 2. Orbit wall – derived from neural crest cells The maxillary wave of neural crest cells curve around the developing eye from below , while a front nasal wave migrates over the prosencephalon and approaches the optic stalk from above Embryology and Development
- 3. Orbit is essentially a socket for the eyeball, containing the muscles, nerves and vessels . It resembles a quadrilateral pyramid whose base is directed forward, laterally and slightly downwards It is not a true quadrilateral pyramid, since the floor ( shortest orbit wall ) fails to reach the apex. Also, because the orbit is developed around the eye and is bulged out by the lacrimal gland, it tends towards spheroidal form. Bony Orbit
- 4. Shape and Dimensions of Orbit Whitnall compared the orbit to a Pear, the anterior orbital aperture compared to the base of the pear and optic canal to its stalk
- 5. Shape and Dimensions of Orbit Base of Orbit : Width 40mm Height 35mm Intra orbital width : 25mm Extra orbital width : 100mm Depth : Medially 42mm Laterally 50mm Volume: 30ml Ratio of Orbit volume to Globe: 4.5:1
- 7. Shape and Dimensions of Orbit Relationship between height and width of the orbit : Orbital Index shows the racial variation
- 8. Changes in the Orbital Opening with age
- 9. Bony Orbit & Ossification Frontal Ethmoid Maxillary Lacrimal Zygomatic Palatine Sphenoid Membranous Ossification ( Plus greater horn of Sphenoid) Endochondral Ossification ( Only the lessor horn)
- 11. Walls of the orbit Medial Wall Lateral Wall Roof of Orbit Floor / Inferior Wall of Orbit
- 12. Walls of the orbit Medial wall Frontal process of Maxilla Lacrimal Bone Orbital plate of Ethmoid Body of the Sphenoid
- 13. APPLIED ASPECTS Medial Orbital wall is the thinnest wall of the orbit ( 0.2-0.4mm) Ethmoiditis – m/c cause of orbital cellulitis in children Easily fractured during injuries and during orbitotomy Hemorrhage is most troublesome due to injury to ethmoidal vessel
- 14. Walls of the orbit Inferior wall Medially : Maxillary Bone Laterally : Zygomatic bone Posteriorly : Palatine bone
- 15. APPLIED ASPECTS Orbital floor being quite thin ( thinnest just medial to infra orbital canal ) , commonly involved in ‘blow – out fracture’ Invaded by the tumors of the maxillary antrum Tear drop Sign Tumors of the maxillary antrum
- 16. Walls of the orbit Lateral Wall Anteriorly – Zygomatic Bone Posteriorly – Greater wing of Sphenoid
- 17. The lateral orbital tubercle of Whitnall: Located on the lateral Orbital wall just inferior (1 cm) to the frontozygomatic suture Provides attachment to o Lateral canthal tendon o Lateral horn of the levator aponeurosis o The check ligament of the lateral rectus o The lockwood ligament ( the suspensory ligament of the globe) o The whitnall ligament
- 18. APPLIED ASPECTS Lateral wall protects only the posterior half of the eye ball, palpation of retro bulbar tumors is easier from the lateral side than the nasal side
- 19. Walls of the orbit Roof of the Orbit Frontal bone ( Orbital plate) Lesser wing of Sphenoid
- 20. APPLIED ASPECTS The superior wall is rather thin and the periorbita easily peels away from its under surface , therefore a sharp object introduced into the orbit through the upper lid penetrates the roof and may damage the frontal lobe. Because the roof is perforated neither by major vessels or nerves, it can be easily nibbled away in transfrontal orbitotomy.
- 21. Orbital Foramina, Canals and Fissures Optic Canal: Optic foramen passes through the lesser wing of the sphenoid It connects orbit to middle cranial fossa Transmits : optic nerve & Ophthalmic artery Length 8-10 mm Anterior Ethmoidal foramen: Is located at the frontoethmoidal suture and transmits the anterior ethmoidal vessels and nerves Posterior Ethmoidal Foramen: lies at the junction of the roof and the medial wall of the orbit and transmit the posterior ethmoidal vessels
- 22. Orbital Foramina, Canals and Fissures Superior Orbital Fissure: Between greater and lesser wing of sphenoid 22 mm long Divided into upper, middle and lower parts by common tendinous ring ( annulus of zinn ) Upper part: 1. Lacrimal Nerve of V1 2. Frontal nerve of V1 3. CN IV 4. Sup. Ophthalmic Vein Middle part: 1. Nasociliary branch of V1 2. Sup and Inf division of CNIII 3. CNVI Lower part: 1. Inf ophthalmic Vein
- 24. Orbital Foramina, Canals and Fissures Inferior Orbital Fissure: Lies just below the superior orbital fissure Transmits Infraorbital and Zygomatic branches of Maxillary Nerve ( CN V2)
- 25. Surgical Spaces in the Orbit 5 surgical Spaces : Subperiorbital ( sub periosteal) surgical space) : is the potential space between the bone and the periorbita Extraconal ( Peripheral) surgical space: lies between the periorbita and the muscle cone with its fascia Intra conal ( central ) surgical space : Space between tenon capsule and rectus muscle along with their intermuscular septa Sub – tenon surgical space: Between the sclera and tenon capsule Subarachnoid Surgical space : lies between the optic nerve and the nerve sheath
- 27. Clinical Significances of Surgical Spaces Sub periosteal space: Tumors commonly seen : dermoid cyst, epidermiod cyst, mucocele, subperiosteal abscess, myeloma, hematoma and fibrous dysplasia . As the tumor grow the periorbita becomes thicker and tougher forming as effective barrier against the tumor spread. Tumors present here produce eccentric proptosis.
- 28. Peripheral orbital space : Tumors present in this space produce eccentric proptosis and can usually be palpated. Common tumors found in this space are malignant lymphoma, capillary haemangioma of childhood, pseudo . Clinical Significances of Surgical Spaces
- 29. Central space: Tumors present in this space produce axial proptosis . Common tumors are cavernous hemangioma of adult, solitary neurofibroma, nodular orbital meningiomas and optic nerve gliomas. Sub- Tenon Space : Collection of fluid in this space causes axial proptosis within the muscle cone. Clinical Significances of Surgical Spaces
- 30. Periorbita Periorbita refers to the periosteum lining the orbital surface of the bones . It is loosely adherent to the bone, however it is firmly attached at the orbital margins, superior and inferior orbital fissures, the optic canal, the lacrimal fossa and at the sutures. In the optic canal, the dural sheath of the optic nerve is closely adherent to periorbita. thickened at apex to form the common tendinous ring At the posterior lacrimal crest, the periorbita splits , which reunites at the anterior lacrimal crest, these two layers enclose the lacrimal sac.
- 31. Loose attachment of periorbita to the bones permits the accumulation of blood and pus In the exenteration, periorbita can be easily separated except at the sites of firm attachment Fused with duramater at the margins of optic canal and superior orbital fissure - trauma or surgery in these areas may be complicated by CSF leakage APPLIED ASPECTS
- 32. Orbital Fascia Orbital fascia is thin connective tissue membrane lining the various intraorbital structure . For descriptive convenience its divided into: Fascia bulbi Fascial sheath of extraocular muscles Fascial expansion of extraocular muscles Intermuscular septa/membrane
- 33. Fascia Bulbi ( Tenon’s Capsule) Fascia Bulbi is dense elastic and vascular tissue that envelops the globe from the limbus to the optic disc. Inner surface is in close contact with sclera while outer surface is in close contact with orbital fat posteriorly and with subconjunctival tissue anteriorly Tenon’s capsule is separated from sclera by episcleral space ( Sub-Tenon’s space) Lower part of fascia bulbi is thickened to take part in formation of sling / hammock aka Suspensory ligament of lockwood)
- 34. APPLIED ASPECTS During enucleation of the eyeball the fascial sheath should be preserved to serve as socket for prosthesis. Functions as extraocular muscles pulley. Provides socket which separates the globe from the surrounding fat and allows free movement. Sub tenon space ( Episcleral space) is used in anaesthetizing the globe.
- 35. Suspensory Ligament of Lockwood It is a thickened sling or hammock of fascial sheath extending from the posterior lacrimal crest to the lateral orbital tubercle, on which the eye ball rest. Formed from the fusion of muscular sheath of the Medial rectus Lateral rectus Inferior rectus Inferior oblique Thickened inferior part of Tenon’s capsule
- 36. Superior Transverse Ligament of the Whitnall It is the thickened band of orbital fascia which extends from the trochlear pulley to the lacrimal gland and its fossa. Main suspensory ligament of the upper eyelid Check ligament of the levator muscle and also indicates a definite landmark during the procedure of external levator resection
- 37. Orbital Septa Is thin membrane formed by multilayered fibrous tissue Attached centrally to tarsal plates and peripherally to periosteum of orbital margin called arcus marginale Covered anteriorly by preseptal orbicularis oculi muscle. Acts as the physical barrier against pathogens.
- 38. Extra Ocular Muscles Muscles Origin Insertion Innervation Functions Superior Rectus Common tendinous ring Anterior and superior surface CN III 10 Elevation 20 Intorsion 30 Adduction Lateral Rectus Common tendinous ring Anterior and lateral surface CN VI Abduction Inferior Rectus Common tendinous ring Anterior and Inferior Surface CN III 10 Depression 20 Extorsion 30 Adduction Medial Rectus Common tendinous ring Anterior and medial surface CN III Adduction
- 39. Muscles Origin Insertion Innervati on Functions Superior Oblique Sphenoid, medial of optic foramen Posterior tempero superior quadrant CN IV 10 Intorsion 20 Depression 30 Abduction Inferior Oblique maxilla, lateral to nasolacrimal duct Posterior tempero inferior quadrant CN III 10 Extorsion 20 Elevation 30 Abduction Levator Palpebrae Superioris above common tendinous ring Superior Tarsal plate CN III Lid elevation
- 41. Spiral of Tillaux Clinical Significance Important landmark during Strabismus surgery Sclera is thinnest (0.3mm) at the insertion of rectus muscle- common site of perforation during severe blunt trauma to the globe
- 42. Links and References : Wolff’s anatomy of eye and orbit,8th edition Clinical Anatomy 9th edition, Richard S. Snell, MD,PhD Kanski’s clinical ophthalmology, 9th edition Oxford handbook of ophthalmology, 4th edition Aetiopathogenesis and management of Eccentric Proptosis by Dr. H.N. Shivakumar, MBBS,DOMS www.medscape.com www.eoptha.com www.aao.org www.pubmed.com
Editor's Notes
- Thus . The floor and the lateral walls of the orbit are contributed by maxillary process whereas the lacrimal and ethmoidal bones are contributed by the frontonasal process.
- The nodal points are the two axial points such that a ray directed at the first nodal point will seem to emerge from the second nodal point parallel to its original direction.
- Endochondral ossification- Cartilaginous model of bone is first formed by chondrocytes Membranous ossification – Directly woven bones are formed from sheet of mesenchyma ( without forming cartilage first)
- Lamina papyracea- orbital lamina of ethmoid bone
- Whitnall’s Ligament acts as a suspensory ligament to support the upper eyelid, the lacrimal gland, and the superior orbit [6, 3].[3][6] It also acts as a fulcrum, changing the direction of the levator aponeurosis from anterior-posterior to superior-inferior.[3][4] When Whitnall’s ligament functionally fails, the levator palpebrae muscle becomes prolonged and sunken, causing decreased elevation of the eyelid. Check ligaments The fascial expansion of lateral and medial rectus muscles are strong and are attached to orbital tubercle of zygomatica bone and lacrimal bone respectively.
- In anatomy, a fissure (Latin fissura, plural fissurae) is a groove, natural division, deep furrow, elongated cleft, or tear in various parts of the body. In anatomy, a canal (or canalis in Latin) is a tubular passage or channel which connects different regions of the body. A foramen (pl. foramina) is an opening that allows the passage of structures from one region to another.
- In anatomy, a fissure (Latin fissura, plural fissurae) is a groove, natural division, deep furrow, elongated cleft, or tear in various parts of the body. In anatomy, a canal (or canalis in Latin) is a tubular passage or channel which connects different regions of the body. A foramen (pl. foramina) is an opening that allows the passage of structures from one region to another.
- Apical Space: It’s a surgical space at apex where central and peripheral spaces merge together to form the single space
- Axial proptosis: forward protrusion of the eye ball Eccentric proptosis: both forward and side wards protrusion of eye ball.
- Pseudo Tumor ( aka Idiopathic orbital inflammatory disease): Pseudo tumor is coined for those condition of the orbit which clinically present as tumors but histopathologically proved to be chronic inflammations.
- Exenteration is a surgical procedure involving removal of the entire globe and its surrounding structures including muscles, fat, nerves, and eyelids (extent determined by disease being treated) Enucleation is the surgical procedure that involves removal of the entire globe and its intraocular contents, with preservation of all other periorbital and orbital structures Evisceration is a surgical technique by which all intraocular contents are removed while preserving the remaining scleral shell, extraocular muscle attachments, and surrounding orbital adnexa.
- Fascial expansion of lateral rectus muscle – lateral check ligament – attach to orbital tubercle on the zygomatic bone Fascial expansion of medical rectus muscle – medial check ligament- attach to lacrimal bone
- The trochlea is a cartilaginous structure , situated superior medial aspect of frontal bone , it act as pully to superior oblique muscle
- The trochlea of superior oblique is a pulley-like structure, The tendon of the superior oblique muscle passes through it. Situated on the superior nasal aspect of the frontal bone, structure in the eye
- The 4 rectus muscles do not insert at the same distance from the limbus; the medial rectus inserts closest to the limbus, with the inferior rectus, lateral rectus, and superior rectus muscles progressively inserting farther away, resulting in an imaginary spiral termed the spiral of Tillaux.