Orbit

ORBIT Pyramidal bony cavities on each side of the roof of the nose Sockets for the rotatory movements of eyeballs Protects eyeballs

Shape and Disposition Each orbit resembles 4 sided pyramids Apex: Post.end of the orbit Base: Orbital opening on the face 4 Walls: Roof, Floor,Lat. and medial wall (Two medial wall are parallel and lateral walls make on right angle)

Roof Concave from side to side formed mainly by orbital plate of frontal bone and is completed posteriorly by lesser wing of sphenoidal bone. Relations: Named Features

Lateral walls Thickest & strongest walls of orbit. Relations: Greater wings of sphenoid separates orbit from middle cranial fossa Zygomatic bone separates from temporal fossa. Named features:

Floor It slopes upward and medially to join medial wall formed by the orbital surface of maxilla. Ant.lat post part of orbital surface of Zygomatic bone. At post. Angle orbital plate of palantine. Relations: It separates orbit from maxillary sinus

Medial wall It is very thin. From back the frontal process of maxilla,lacrimal bone, orbital plate of ethmoid, body of sphenoid are seen. Relations: Named features:

CONTENTS OF THE ORBIT -

Pyramidal cavities. Socket for voluntary movement of eyeballs Contents of orbits are - Eye balls - Fascia: Orbital and Bulbar - Muscles: Extraocular - Vessels: Opthalmic artery,Sup. Inf. Opthamlic veins L/N - Nerves: II,III,IV & VI Cranial nerves, branches of opthalmic nerve and sympathetic nerves - Lacrimal glands - Orbital fats

ORBITAL AND BULBAR FASCIA Orbital Fascia or Periorbita - Perisoteum of the bony orbit - Posteriorly cont. with dura & sheath of the optic nerve - Anteriorly Cont. with periosteum of orbital marg.

Fascia Sheath or Bulbar Fascia Tenon’s Capsule also known as Bulbar Fascia: Separated by the episcleral space. Eye ball can freely move here. Facial sheath is pierced by the tendons of various Extraocular muscles and ciliary nerves and vessels. Gives no. of expansions: : covers each muscles : 2 triangular expansions Medial check ligament Lateral check ligament

Lower part of Tenon’s capsule is thickened and named suspensory ligament of eye or suspensor ligament of Lockwood. It is expanded in the center like Hammock.

Extraocular muscles Voluntary muscles: 1) 4 recti muscles: sup.rectus, inf. Rectus medial rectus, lateral rectus 2) 2 oblique muscles: sup. oblique, inf. oblique 3) Levator palpabrae: elavates upper lids Involuntary muscles 1) Sup. tarsal muscles: deeper portion of levator palpabrae: elavates upper eye lids 2) Inferior tarsal muscles: depresses the lower eye lids 3) Orbitalis bridges of the inf. Orbital fissure

Voluntary muscle’s origin

Insertion

Nerve supply # Superior oblique is supplied by trochlear nerve. (SO4) # Lateral rectus is supplied by Abducent nerve. (LR6) # Remaining 5 extraocular muscles sup,inf and medial recti,inf. oblique and levator palpabrae superioris are supplied by occulomotor nerve( III nerve)

Actions of the individual muscles

Single or pure movements are produced by combined actions of muscles eg. Upward rotation or Elevation

SR and IO

Down ward rotation or depression

IR and SO

Medial rotation or adduction Lateral rotation or abduction Intortion Extortion

MR, SR and IR LR, SO and I0 SO and SR IO and IR

Combined movement of eyes Normally, movements of the two eyes are harminously coordinated and it is called conjugate ocular movement. Dissociation movements of the two eyes are called dysjunctive movement. Ant. Post movement of eyeballs are abnormal.

Vessels of the Orbit Origin: is a branch of cerebral part of ICA. Branches: Central Retinal A. 1st branch of opthalmic a. lies below the optic nerve runs forward in the center reach the optic disc. Here it divides into branches for retina. (End artery, no anastamoses occlusion of the artery results blindness)

Branches arising from Lacrimal artery are 1) Lacrimal gland 2) 2 Zygomatic branches Zygomaticofacial Zygomaticotemporal 3) Lat. Palpebral branch supply the eyelids 4) Reccurent meningeal br. to mid. fossa(sup.orb.fis) 5) Muscular branch supplies muscles of orbit.

Branches arising from the main trunk are. 1) Post long and short ciliary arteries supply choroid and iris 2) Supraorbital and supratrochlear supply the skin of the fore head 3) Ant. and post. Ethmoidal artery supply the Ethmoidal sinus. 4) Medial palpebral br. Supply the eye lids 5) Dorsal nasal supply the upper part of nose.

Opthalmic Vein Sup. Opthalmic vein drains into cavernous sinus. Communcate anterorly with the supraorbital and angular veins. Inf. Opthalmic vein drains into cavernous sinus and communi-cates with pterygoid plexus Lymphatic drains into the preauricular parotid L/N

NERVES OF THE ORBIT 1) 2) 3) 4)

5) 6)

Optic nerve. Occulomotor nerve with ciliary ganglion. Trochlear Br. Of Opthalmic and maxillary division of Trigeminal nerve. Abducent Sympathetic nerves.

Optic Nerve Nerve of sight made up of axons of cells in the ganglionic layer of retinaemerges from eyeball runs backward medially and passes through optic canalto enter the middle cranial fossa where it goes to optic chiasm. 4 cm longs: 5mm intracanacular 10mm intracranial 25 mm intraorbital.

Structures: 1.2 million myelinated fibers.53% cross in the optic chiasm. Optic nerve is not a nerve in the strict sense. It is actually a tract. It cannot regenerate after it is cut. Developmental of optic nerve and tract are direct prolangation of the brain.

Relation to the orbit -

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At apex surrounded by recti muscles, ciliary ganglion. Central artery and vein of retina pierce the optic nerve 1.25cm behind the eyeball Crossed superiorly by opthalmic artery, vein and nasociliary n. Crossed inferiorly by the nerve to the medial rectus. Near eyeball, the nerve is surrounded by fat containing ciliary vessels and nerves.

Occulomotor nerve 3rd cranial nerve- distributed to extraocular and intraocular muscles. Since it is somatic nerve, it is series with IV,VI and XII nerve. Nucleus: It is situated in the vetro medial part of central gray matter of mid brain at the level sup. Colliculus. The fibers for the constrictor pupillae for the and for the ciliaries from Edinger Westphal nuceus which forms part of III nerve complex.

Course and Distrubution: -Fiber arises from nuc. and goes to tegmentum and subs. nigra. -At base, nerve is attached to occulomotor sulcus on the medial side of crus cerebri. -It reaches cavernous sinus in Ant.side of sinus divides into upper and lower divisions. -Two divisions of nerve enter orbit through middle part of sup.orbital fissure. -Smaller upper division ascends on lateral side of optic nerve. Supplies SR and levator pal.sup. Larger lower division divides into 3 br. for MR,IR & IO.-is the longest gives motor root to ciliary ganglion.