ORBIT and EYE

Objectives Describe the walls and communications of the orbit Describe the components and functions of the fibrous, vascular and inner layers of the eyeball Describe the origin, insertion and nerve supply of the extraocular muscles Describe the clinical testing of the extraocular muscles Describe the course, branches and distribution of the optic, oculomotor, trochlear, abducens and ophthalmic nerves Describe the origin, course, branches and distribution of the ophthalmic artery Describe location and drainage of the ophthalmic veins Describe the layers of the eyelid Describe the components of the lacrimal apparatus

Bony Orbit pyramidal-shaped space  its long axis is directed posteriorly and medially walls: superior: orbital plate of frontal, lesser wing of sphenoid inferior: orbital surface of body of maxilla, orbital surface of zygomatic bone, orbital process of palatine lateral: orbital surfaces of zygomatic bone and greater wing of sphenoid medial: frontal process of maxilla, lacrimal bone, orbital plate of ethmoid, small part of body of sphenoid

Bony Orbit communications: optic canal: opening between 2 roots of lesser wing  transmits optic nerve and ophthalmic artery superior orbital fissure: opening between lesser and greater wings  transmits superior ophthalmic vein, oculomotor, trochlear and abducens nerves and branches of ophthalmic nerve (frontal, lacrimal and nasociliary) inferior orbital fissure: opening between greater wing and maxilla  transmits infraorbital nerve and vessels, zygomatic nerve and veins communicating inferior ophthalmic vein and pterygoid venous plexus supraorbital notch (or foramen): located at junction of medial and middle thirds of superior orbital margin  transmits supraorbital nerve and vessels

Bony Orbit communications (cont.): infraorbital foramen: located 7-8 mm below inferior orbital margin  transmits infraorbital nerve and vessels from infraorbital canal onto face nasolacrimal canal: downward continuation of fossa for lacrimal sac  communicates orbit with inferior nasal meatus  houses nasolacrimal duct anterior and posterior ethmoidal foramina: located along frontoethmoidal suture  transmit anterior and posterior ethmoidal nerves and vessels, respectively

Eyeball peripheral organ for special sense of sight shaped like a hollow sphere consists of 3 concentric layers (coats/tunics): fibrous layer, vascular layer and inner layer (retina) fibrous layer: has 2 parts: sclera and cornea sclera (“white of the eye”): firm, smooth, opaque fibrous cup which forms posterior 5/6 of fibrous layer  continuous in front with cornea at corneoscleral junction cornea: transparent, anterior 1/6 of fibrous layer  represents a segment of a smaller sphere (compared to sclera)  bulges forward from sclera  has no blood vessels and receives rich sensory nerve supply from ophthalmic nerve

Eyeball vascular layer: has 3 parts: choroid, ciliary body and iris (in posterior-to-anterior direction) choroid: thin, vascular membrane immediately deep to sclera  consists of a dense capillary plexus and small arteries and veins held together by connective tissue with abundant melanocytes ciliary body: raised area in anterior part of vascular layer wedge-shaped in cross-section  inwardly projecting angle of wedge is directed toward lens and connected to it by fibers of suspensory ligament of lens (zonular fibers)

Eyeball Ciliary body (cont.): greatest bulk is contributed by ciliary muscle (muscle of accommodation  reflex helping to maintain a clear visual image as gaze is shifted from a distant to a near point or vice versa) when shifting gaze from a distant to a near point, ciliary muscle contracts and its contraction reduces tension of suspensory ligament of lens  reduces tension exerted by ligament on lens  under less tension, because of its natural elasticity, lens increases its curvature (becomes thicker in anteroposterior direction)  increases refractive power of lens for vision of close objects (opposite happens when shifting gaze from a near point to a distant one) ciliary processes: internal projections of ciliary body  its covering epithelium secretes aqueous humor (watery fluid filling space between cornea and lens)

Eyeball iris: pigmented diaphragm with central aperture (pupil) contains 2 smooth muscles which control pupillary size: sphincter (constrictor) pupillae muscle  formed by circular fibers surrounding margin of pupil  decreases pupillary size dilator pupillae muscle  formed by fibers that radiate from pupillary margin toward outer circumference of iris  increases pupillary size ciliary and sphincter pupillae muscles receive parasympathetic innervation via oculomotor nerve dilator pupillae muscle receives sympathetic innervation from superior cervical ganglion

Eyeball inner layer (retina): optic part  posterior part of retina which covers inner aspect of choroid  contains photoreceptors (rods and cones), 1st and 2nd order neurons of visual pathway, interneurons and supporting cells  ends anteriorly at a jagged border (ora serrata), a short distance behind ciliary body nonvisual (ciliary and iridial) part  thin, anterior part of retina which lines internal aspect of ciliary body and posterior surface of iris  has no nervous elements

Eyeball inner layer (cont.): at posterior pole of eyeball, retina has oval yellowish area (macula lutea) with a central depression (fovea centralis) fovea centralis is the part of retina that provides maximal visual acuity  contains only cones as we move peripherally from fovea centralis, there are less cones and more rods optic disc: located medial to macula lutea  area where axons of ganglion cells of all retina converge to form optic nerve  contains no photoreceptors (blind spot of retina)  branches of central artery and vein of retina spread out from center of optic disc over inner surface of retina

Eyeball space between cornea and lens is divided by iris into 2 compartments: anterior chamber (between cornea and iris) and posterior chamber (between iris and lens)  anterior and posterior chambers communicate with each other via pupil and contain aqueous humor aqueous humor is secreted by epithelium of ciliary processes  passes from posterior chamber into anterior chamber via pupil  drained at irido-corneal angle into scleral venous sinus (canal of Schlemm) glaucoma: condition characterized by increased intraocular pressure due to excessive amount of aqueous humor (usually caused by drainage obstruction)  if left untreated can cause blindness vitreous chamber: space located posterior to lens  filled with transparent semigelatinous material (vitreous humor/body)

Extraocular Muscles 7 in number  6 move eyeball and 7th muscle elevates upper eyelid levator palpebrae superioris (LPS): uppermost of orbital muscles  originates from sphenoid, above optic canal  passes forward under orbital roof  ends anteriorly in a broad tendon  its fibers insert into superior tarsus and skin of upper eyelid superior tarsal muscle: thin lamina of smooth muscle that extends from inferior surface of LPS to superior tarsus nerve supply: LPS  oculomotor nerve; superior tarsal muscle  sympathetic fibers from superior cervical ganglion action: both muscles elevate upper eyelid

Extraocular Muscles rectus muscles: named according to their orientation with respect to eyeball (superior, inferior, medial and lateral) originate from a common tendinous ring which surrounds optic canal and inferomedial part of superior orbital fissure each muscle inserts into sclera, about 6 mm behind corneoscleral junction nerve supply: abducens nerve supplies lateral rectus, oculomotor nerve supplies remaining 3 rectus muscles (superior, inferior and medial)

Extraocular Muscles superior oblique muscle: medially rotates eye lies in superomedial part of orbit originates from sphenoid, superior and medial to optic canal  passes anteriorly and becomes continuous with a tendon  tendon passes through fibrocartilaginous trochlea (pulley) in anteromedial part of orbital roof  tendon then changes direction and passes posteriorly and laterally, under superior rectus muscle, and inserts into sclera of superior, posterolateral aspect of eyeball nerve supply: trochlear nerve

Extraocular Muscles inferior oblique muscle: laterally rotates eye located inferior to eyeball, close to orbital margin originates from orbital surface of maxilla, just lateral to fossa for lacrimal sac  passes posteriorly and laterally, below inferior rectus muscle, and inserts into sclera of inferior, posterolateral aspect of eyeball nerve supply: oculomotor nerve

Clinical Testing of the Muscles that Move Eyeball eye abduction  lateral rectus (abducens nerve) eye adduction  medial rectus (oculomotor nerve) elevation of abducted eye  superior rectus (oculomotor nerve) depression of abducted eye  inferior rectus (oculomotor nerve) elevation of adducted eye  inferior oblique (oculomotor nerve) depression of adducted eye  superior oblique (trochlear nerve)

Optic Nerve begins at optic disc (medial to posterior pole of eyeball)  formed by axons of ganglion cells of retina runs posteriorly and medially in orbit  leaves orbit and enters middle cranial fossa via optic canal. surrounded by sheaths of pia mater, arachnoid and dura mater, which fuse with sclera of eyeball subarachnoid space with its CSF extends from middle cranial fossa around optic nerve as far as eyeball  a rise in pressure of CSF within cranial cavity (increased intracranial pressure) is transmitted to eyeball  causes swelling of optic disc (papilledema)

Arteries of the Orbit main blood supply is provided by ophthalmic artery  infraorbital artery (branch of maxillary a.) also supplies blood to structures close to orbital floor ophthalmic artery: branch of internal carotid artery  enters orbit via optic canal, inferolateral to optic nerve  passes over optic nerve toward medial wall of orbit  passes anteriorly, parallel to medial wall  ends by dividing into two terminal branches: supratrochlear and dorsal nasal arteries  it gives off following branches: central artery of retina: pierces optic nerve with its meningeal sheaths and passes forward in center of nerve, accompanied by central vein of retina  enters eyeball at center of optic disc and its branches spread over internal surface of retina (can be studied in patients using an ophthalmoscope)

Arteries of the Orbit branches of ophthalmic artery (cont.): posterior ciliary arteries: supply eyeball muscular branches: supply extraocular muscles  branches to rectus muscles continue as anterior ciliary arteries (supply eyeball) lacrimal artery: usually largest branch of ophthalmic artery  accompanies lacrimal nerve  gives off branches that accompany zygomaticofacial and zygomaticotemporal nerves supraorbital artery: accompanies supraorbital nerve anterior and posterior ethmoidal arteries: accompany anterior and posterior ethmoidal nerves supratrochlear artery: accompanies supratrochlear nerve dorsal nasal artery: accompanies infratrochlear nerve

Ophthalmic Veins superior ophthalmic vein: communicates anteriorly with facial vein usually joined by inferior ophthalmic vein passes through superior orbital fissure to drain into cavernous sinus inferior ophthalmic vein: communicates with pterygoid venous plexus via veins that pass through inferior orbital fissure usually joins superior ophthalmic vein, but it may drain directly into cavernous sinus

Eyelids movable folds that protect eye palpebral fissure  aperture between upper and lower eyelids layers (from anterior to posterior): skin subcutaneous tissue muscular layer: palpebral part of orbicularis oculi tarsofascial layer: consists of a dense fibrous plate (tarsus/tarsal plate) and a membrane (orbital septum) conjunctiva: mucous membrane that lines posterior surface of eyelid (palpebral conjunctiva) and anterior part of eyeball (bulbar conjunctiva)  lines of reflection from eyelids to eyeball are superior and inferior conjunctival fornices

Lacrimal Apparatus lacrimal gland: located in superolateral part of orbit, just behind superior orbital margin  divided by tendon of levator palpebrae superioris into superior (orbital) and inferior (palpebral) parts  its ducts (about 12) open into superior conjunctival fornix tears move across eyeball toward lacrimal lake (triangular area at medial angle of eye) and are distributed in a uniform layer by blinking  from lacrimal lake tears are drained by lacrimal canaliculi lacrimal canaliculi (superior and inferior): located in medial part of margins of eyelids  begin in 2 small orifices (lacrimal pores/puncta) and end in lacrimal sac lacrimal sac: upper dilated part of nasolacrimal duct  occupies fossa for lacrimal sac in anterior part of medial wall of orbit  inferiorly becomes continuous with nasolacrimal duct  opens into inferior nasal meatus