Dr. H.A.Jaafar Al-Nahrain University

Orbit
Dr. H.A.Jaafar
Al-Nahrain Universitycollege of Medicine
Dept. Of Anatomy
Orbital margin
I. Bony Orbit
A. Orbital margin
Is formed by
1. frontal,
2. maxillary, and
3. zygomatic bones.
B. Walls of orbit
Superior wall or roof:
1. orbital part of frontal bone and
2. lesser wing of sphenoid bone.
Lateral wall:
1. zygomatic bone (frontal process) and
2. greater wing of sphenoid bone.
Inferior wall or floor:
1. maxilla (orbital surface),
2. zygomatic, and
3. palatine bones.
Medial wall:
1. ethmoid (orbital plate),
2. frontal,
3. lacrimal, and
4. sphenoid (body) bones.
Fissures, canals,
and foramina
C. Fissures, canals, and foramina
1. Superior orbital fissure
• Communicates with middle cranial fossa
• is bounded by greater and lesser wings of sphenoid.
• Transmits
1. oculomotor,
2. trochlear,
3. abducens, and
4. ophthalmic nerves (three branches) and ophthalmic veins.
2. Inferior orbital fissure
• Communicates with infratemporal and pterygopalatine fossae.
• Is bounded by :
• greater wing of sphenoid (above) and
• maxillary and palatine bones (below).
• Transmits
1. maxillary (or infraorbital) nerve and its zygomatic branch &
2. infraorbital vessels.
3. Optic canal
• Connects orbit with middle cranial fossa.
• Is formed by two roots of lesser wing of sphenoid
• is situated in posterior part of roof of orbit.
• Transmits optic nerve and ophthalmic artery.
4. Infraorbital groove and infraorbital foramen
• Transmit infraorbital nerve and vessels.
5. Supraorbital notch or foramen
• Transmits supraorbital nerve and vessels.
6. Anterior and posterior ethmoidal foramina
• Transmit anterior and posterior ethmoidal nerves and vessels, respectively.
7. Nasolacrimal canal
• Is formed by
1.
2.
3.
•
maxilla,
lacrimal bone, and
inferior nasal concha.
Transmits nasolacrimal duct from lacrimal sac to inferior nasal meatus.
II. Nerves
II. Nerves
A. Ophthalmic nerve
• Enters orbit through superior orbital fissure
• divides into three branches:
1. Lacrimal nerve
• Enters orbit through superior orbital fissure.
• Enters lacrimal gland, giving rise to branches to lacrimal gland, conjunctiva, and skin
of upper eyelid.
• Its terminal part is joined by zygomaticotemporal nerve that carries postganglionic
parasympathetic and sympathetic GVE fibers.
2. Frontal nerve
• Enters orbit through superior orbital fissure.
• Runs superior to levator palpebrae superioris.
Divides into
1.
supraorbital nerve, which passes through supraorbital notch or foramen
and supplies scalp, forehead, frontal sinus, and upper eyelid, &
2.
supratrochlear nerve, which passes through trochlea and supplies scalp,
forehead, and upper eyelid.
3. Nasociliary nerve
• Is sensory nerve for eye and mediates afferent limb of corneal reflex.
• Enters orbit through superior orbital fissure, within common tendinous ring.
Gives rise to following:
• A communicating branch
to ciliary ganglion.
•
Short ciliary nerves,
which carry postganglionic parasympathetic and sympathetic fibers to ciliary body and iris
and afferent fibers from iris and cornea.
•
Long ciliary nerves,
which transmit postganglionic sympathetic fibers to dilator pupillae and afferent fibers from
iris and cornea.
•
posterior ethmoidal nerve,
which passes through posterior ethmoidal foramen to sphenoidal and posterior ethmoidal
sinuses.
•
anterior ethmoidal nerve,
which passes through anterior ethmoidal foramen to supply anterior ethmoidal air cells.
It divides into
1.internal nasal branches, which supply septum & lateral walls of nasal cavity,
2.external nasal branches, which supply skin of tip of nose.
•
infratrochlear nerve,
which innervates eyelids, conjunctiva, skin of nose, and lacrimal sac.
B. Optic nerve
• Consists of axons of ganglion cells of retina
• leaves orbit by passing through optic canal.
• Carries SSA fibers for vision from retina to brain and mediates afferent limb of
pupillary light reflex.
• Joins optic nerve from corresponding eye to form optic chiasma.
C. Oculomotor nerve
Leaves cranium through superior orbital fissure.
Divides into
1) a superior division, which innervates
i. superior rectus
ii. levator palpebrae superioris muscles,
2)
an inferior division, which innervates
I. medial rectus,
II. inferior rectus, a
III. inferior oblique muscles.
• carries preganglionic parasympathetic fibers (with cell bodies located in EdingerWestphal nucleus) to ciliary ganglion.
D. Trochlear nerve
• Passes through lateral wall of cavernous sinus during its
course.
• Enters orbit by passing through superior orbital fissure
• innervates superior oblique muscle.
E. Abducens nerve
•
Enters orbit through superior orbital fissure
•
supplies lateral rectus muscle.
F. Ciliary ganglion
•
•
Is a parasympathetic ganglion situated behind eyeball,
between optic nerve and lateral rectus muscle
III. Blood
Vessels
III. Blood Vessels
A. Ophthalmic artery
•
Is a branch of internal carotid artery
•
enters orbit through optic canal beneath optic nerve.
Gives rise to ocular and orbital vessels, which include following:
1. Central artery of retina
•
Is most important branch of ophthalmic artery.
•
Travels in optic nerve;
•
it divides into
1. superior branches
2. inferior branches to optic disk, and
•
•
•
each of those further divides into temporal and nasal branches.
Is an end artery that does not anastomose with other arteries,
its occlusion results in blindness.
2. Long posterior ciliary arteries
•
Pierce sclera and supply ciliary body and iris.
3. Short posterior ciliary arteries
•
Pierce sclera and supply choroid.
4. Lacrimal artery
•
Passes along superior border of lateral rectus and supplies lacrimal gland, conjunctiva, and eyelids.
•
Gives rise to two lateral palpebral arteries, which contribute to arcades in upper and lower eyelids.
5. Medial palpebral arteries
•
Contribute to arcades in upper and lower eyelids.
6. Muscular branches
• Supply orbital muscles and give off anterior ciliary arteries, which supply
iris.
7. Supraorbital artery
• Passes through supraorbital notch (or foramen) and supplies forehead
and scalp.
8. Posterior ethmoidal artery
• Passes through posterior ethmoidal foramen to posterior ethmoidal air
cells.
9. Anterior ethmoidal artery
• Passes through anterior ethmoidal foramen to anterior and middle
ethmoidal air cells, frontal sinus, nasal cavity, and external nose.
10. Supratrochlear artery
• Passes to supraorbital margin and supplies forehead and scalp.
11. Dorsal nasal artery
• Supplies side of nose and lacrimal sac.
B. OPHTHALMIC VEINS
1. Superior ophthalmic vein
• Is formed by union of
1. supraorbital,
2. supratrochlear, and
3. angular veins.
• Receives branches corresponding to most of those of ophthalmic
artery,
• receives inferior ophthalmic vein before draining into cavernous sinus.
2. Inferior ophthalmic vein
• Begins by union of small veins in floor of orbit.
• Communicates with
1.
2.
•
pterygoid venous plexus
infraorbital vein
terminates directly or indirectly in cavernous sinus.
A. Innervation of muscles of eyeball
A.
B.
C.
•
SO4,
LR6,
Remainder3,
which means that
1.
2.
3.
superior oblique muscle is innervated by trochlear nerve,
lateral rectus muscle is innervated by abducens nerve,
remainder of these muscles is innervated by oculomotor nerve.
B. Movements of eye
1. Intorsion
• Is a medial (inward) rotation of upper pole (12 o'clock position) of
cornea,
• caused by superior oblique and superior rectus muscles.
2. Extorsion
• Is a lateral (outward) rotation of upper pole of cornea,
• caused by inferior oblique and inferior rectus muscles.
Inf. oblique
Sup. rectus
Sup. rectus
Inf. oblique
Lat.
rectus
Lat.
rectus
Med.
rectus
Sup. oblique
Inf. rectus
RIGHT EYE
Med.
rectus
Inf. rectus
Sup. oblique
LEFT EYE
C. Common tendinous ring
•
Is a fibrous ring that surrounds
I.
optic canal and
II.
medial part of superior orbital fissure.
•
Is site of origin of four rectus muscles of eye
•
transmits following structures enter orbit through superior orbital fissure and common tendinous
ring :
1.
Oculomotor,
2.
nasociliary, and
3.
abducens nerves,
•
enter orbit through optic canal and tendinous ring:
1.
Optic nerve,
2.
ophthalmic artery, and
3.
central artery and vein of retina,
enter orbit through superior orbital fissure but outside tendinous ring.
1.
2.
3.
4.
Superior ophthalmic vein
trochlear,
frontal, and
lacrimal nerves,
V. Lacrimal
Apparatus
V. Lacrimal Apparatus
A. Lacrimal gland
•
•
Lies in upper lateral region of orbit on lateral rectus and levator palpebrae superioris
muscles.
Is drained by 12 lacrimal ducts, which open into superior conjunctival fornix.
B. Lacrimal canaliculi
•
•
Are two curved canals that begin as a lacrimal punctum (or pore) in margin of eyelid and
open into lacrimal sac.
C. Lacrimal sac
•
•
Is upper dilated end of nasolacrimal duct,
opens into inferior meatus of nasal cavity.
D. Tears
Are produced by lacrimal gland.
Pass through excretory ductules into superior conjunctival fornix.
Are spread evenly over eyeball by blinking movements and accumulate in area of lacrimal
lake.
Enter lacrimal canaliculi through their lacrimal puncta (which is on summit of lacrimal papilla)
before draining into lacrimal sac, nasolacrimal duct, and finally inferior nasal meatus.
VI. Eyeball
VI. Eyeball
A. External white fibrous coat
Consists of sclera and cornea.
1. Sclera
• Is a tough white fibrous tunic enveloping posterior
five sixths of eye.
2. Cornea
• Is a transparent structure forming anterior one
sixth of external coat.
• Is responsible for refraction of light entering eye.
B. Middle vascular pigmented coat
•
Consists of
1. choroid,
2. ciliary body
3. iris.
1. Choroid
• Consists of
1. an outer pigmented (dark brown) layer and
2. an inner highly vascular layer, which invests posterior five sixths of eyeball.
• Nourishes retina and darkens eye.
2. Ciliary body
• Is a thickened portion of vascular coat between choroid and iris and
• consists of
•
•
1. ciliary ring,
2. ciliary processes, and
3. ciliary muscle.
ciliary processes are radiating pigmented ridges that encircle margin of lens.
ciliary muscle consists of meridional and circular fibers of smooth muscle innervated by parasympathetic
fibers. It contracts to pull ciliary ring and ciliary processes, relaxing suspensory ligament of lens and
allowing it to increase its convexity.
3. Iris
• Is a thin, contractile, circular, pigmented diaphragm with a central aperture, pupil.
• Contains circular muscle fibers (sphincter pupillae), which are innervated by parasympathetic fibers, and radial fibers
(dilator pupillae), which are innervated by sympathetic fibers.
C. Internal nervous coat
• Consists of retina, which has an outer pigmented layer and an inner nervous layer.
• Has a posterior part that is photosensitive; its anterior part, which is not photosensitive, constitutes inner lining
of ciliary body and posterior part of iris.
1. Optic disk (blind spot)
• Consists of optic nerve fibers formed by axons of ganglion cells. These cells are connected to rods and
cones by bipolar neurons.
• Is located nasal (or medial) to fovea centralis and posterior pole of eye, has no receptors, and is
insensitive to light.
• Has a depression in its center termed physiologic cup.
2. Macula (yellow spot or macula lutea)
• Is a yellowish area near center of retina on temporal side of optic disk for most distinct vision.
• Contains fovea centralis.
3. Fovea centralis
• Is a central depression (foveola) in macula.
• Is avascular and is nourished by choriocapillary lamina of choroid.
• Has cones only (no rods), each of which is connected with only one ganglion cell, and functions in
detailed vision.
4. Rods
• Are approximately 120 million in number and are most numerous about 0.5 cm from fovea centralis.
• Contain rhodopsin, a visual purple pigment.
• Are specialized for vision in dim light.
5. Cones
• Are 7 million in number and are most numerous in foveal region.
• Are associated with visual acuity and color vision.
D. Refractive media
Consist of cornea, aqueous humor, lens, and vitreous body.
1. Cornea
2. Aqueous humor
• Is formed by ciliary processes and provides nutrients for avascular cornea and lens.
• Passes through pupil from posterior chamber (between iris & lens) into anterior chamber
(between cornea and iris) and is drained into scleral venous plexus through canal of
Schlemm at iridocorneal angle.
• Its impaired drainage causes an increased intraocular pressure, leading to atrophy of retina
and blindness.
3. Lens
• Is a transparent avascular biconvex structure enclosed in an elastic capsule.
• Is held in position by radially arranged zonular fibers (suspensory ligament of lens), which
are attached medially to lens capsule and laterally to ciliary processes.
• Flattens to focus on distant objects by pulling zonular fibers and becomes a globular shape
to accommodate eye for near objects by contracting ciliary muscle and thus relaxing
zonular fibers.
4. Vitreous body
• Is a transparent gel called vitreous humor, which fills eyeball posterior to lens (vitreous
chamber between lens & retina).
• Holds retina in place and provides support for lens.
VII. Development of Eye
eye forms from :
1.a neuroectodermal evagination (optic cup and optic stalk) of wall of brain (diencephalon)
2.surface ectoderm (lens placode),
3.mesoderm, and
4.neural crest cells.
A. Neuroectoderm of diencephalon evaginates to form
•optic vesicle, which in turn invaginates to form optic cup and optic stalk. This induces ectoderm to thicken
and form lens placode.
•Optic cup forms retina, iris, and ciliary body.
•Optic stalk forms optic nerve.
B. Surface ectoderm invaginates to form
lens placode, which forms lens and anterior epithelium of corea.
C. Mesoderm forms
sclera, portions of cornea, vitreous body, and extraocular muscles.
D. Neural crest cells form :
choroids, sphincter pupillae muscle, dilator pupillae muscle, and ciliary muscle.
E. Hyaloid artery and vein form
central artery and vein of retina.