Orbit - Lecture Notes PDF

ORBIT DR ATIKA, DR AZIZAH 1  Orbital margin !Thickened rim of bone that helps protect the orbital contents !Made up of frontal, zygomatic and maxilla !Lateral margin is thickest because it is the most exposed and therefore prone to trauma !Medial marg...

ORBIT DR ATIKA, DR AZIZAH 1  Orbital margin !Thickened rim of bone that helps protect the orbital contents !Made up of frontal, zygomatic and maxilla !Lateral margin is thickest because it is the most exposed and therefore prone to trauma !Medial margin is sharp and distinct in its lower half but indistinct superiorly 2  OSTEOLOGY OF THE ORBIT !Roughly the shape of Quadrilateral pyramid !Floor , Roof , Medial wall, Lateral wall !The volume is approximately 30 ml, of which one-fifth is occupied by the eye 3 THE ROOF OF THE ORBIT !Fossa for the lacrimal gland – fossa lies in the anterolateral aspect of the roof behind the zygomatic process of the frontal bone !Trochlear fossa (fovea) This lies in the anteromedial aspect of the roof !Anterior and posterior ethmoidal canals- positioned at the junction of the roof and medial wall above the frontoethmoidal suture. !Relations: Roof is thin and translucent (except at lesser wing of sphenoid) – separates the orbit from anterior cranial fossa and frontal lobes of the brain 4  3/23/16 THE MEDIAL WALL OF THE ORBIT !Oblong in shape, and thin (0.2 – 0.4 mm) !The four bones that comprise this wall are separated by vertical sutures !Lacrimal fossa for the lacrimal sac : bound by anterior and posterior lacrimal crests and is continuous below with the nasolacrimal canal !Relations: thinnest of the walls transparent or semitransparent Ethmoidal air sinuses can easily be seen through this wall in dried skull 5  3/23/16 THE LATERAL WALL OF THE ORBIT !Spina recti lateralis – a small bony spine near apex of the orbit on the greater wing of sphenoid – gives origin to part of the lateral rectus !Zygomatic foramen – transmit zygomatic nerve and vessels to temporal fossa and cheek (zygomaticotemporal nerve and zygomaticofacial nerve) !Lateral orbital tubercle : the origin of the ligament of the lateral rectus, suspensory ligament of the eye and aponeurosis of levator palpebrae superioris !Foramina for small veins that communicate with middle cranial fossa !Relations: Laterally – skin, temporal fossa and middle cranial fossa in an anterior – posterior sequence 6  3/23/16 THE FLOOR OF THE ORBIT !Slopes slightly downwards from medial to the lateral wall. !It is crossed by the infraorbital groove, which runs forward from the inferior orbital fissure. Before it reaches the orbital margin, it becomes infraorbital canal, which opens as the infraorbital foramen. !Relations: Below the floor lies the maxillary sinus, the bone being only 0.5 – 1 mm in thickness 7 ORBITAL FLOOR FRACTURE studyblue.com 8  3/23/16 Superior orbital fissure !‘a gap’, ‘comma-shaped’, wider at its medial end and narrowest at lateral end !Lies between the roof and lateral wall of the orbit !Bounded by lesser and greater wings of sphenoid !Largest communication between orbital and cranial cavities. 10  3/23/16 Mnemonic – “Live Frankly To See Absolutely No Insult” The nerves passing through superior orbital fissure are (from top to bottom) : Lacrimal nerve Frontal nerve Trochlear nerve Superior division of oculomotor nerve Abducens nerve Nasociliary nerve (branch of ophthalmic nerve) Inferior division of oculomotor nerve pgblazer.com 10  3/23/16 Inferior orbital fissure !Between lateral wall and floor of the orbit. !Forms communication between orbit and infratemporal fossa and pterygopalatine fossa. !Its posterior end lies below and lateral to the optic foramen near the superior orbital fissure. !Narrowest in the middle section !Covered by periorbita and a sheet of smooth muscle of unknown function – Muscle of Muller !Transmits infraorbital nerve, zygomatic nerve and branches from pterygopalatine ganglion 11  3/23/16 Optic canal !Bony channel in the sphenoid that passes anteriorly, inferiorly and laterally from the middle cranial fossa to the apex of the orbit !It is formed by the two roots of the lesser wing of the sphenoid. !The two optic canals are 25 mm apart posteriorly and 30 mm anteriorly !Funnel-shaped, narrowest anteriorly where opening into the orbit is oval with sharp upper and lower borders and prolonged roof. !The opening at cranial aspect is oval with prolonged floor. !Transmit optic nerve with its meningeal coverings and ophtalmic artery, which lies below and lateral to the nerve within the dural sheath for part of its course. Sympathetic nerve fibers accompany the artery. 12  3/23/16 Blood vessels of the orbit !Supplied chiefly by ophthalmic artery !Arises from internal carotid artery shortly after it emerges from the roof of cavernous sinus !Commences its course beneath optic nerve, closely bound to the dura while in optic canal then winds around its lateral aspect and finally passes above the nerve 13 EXTRAOCULAR MUSCLES Watch the video at the following link for attachment and action of the extraocular muscles. https://www.youtube.com/watch?v=f_rb6FMVHPk “COMMON TENDINOUS RING” EXTRAOCULAR MUSCLES 2 softwares to install for practical session… Go to https://account.eon-xr.com/Home/IndexV2 >> choose Start for free , or Download the eon XR software from Apple App Store / Google Play Store You are also required to install the complete anatomy software from Google Play Store