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Transcript
The Orbit & Eye
Head & Neck Unit – Lecture 7
‫ حيدر جليل األعسم‬.‫د‬
The Orbit
The Orbits: are a pair of pyramidal cavities
with its base in front and its apex behind.
Boundaries:
• The orbital margin is formed above by the
frontal bone, the lateral margin is formed
by the processes of the frontal and
zygomatic bones, the inferior margin is
formed by the zygomatic bone and the
maxilla, and the medial margin is formed
by the processes of the maxilla and the
frontal bone.
• Roof: orbital plate of the frontal bone.
• Floor: orbital plate of the maxilla.
• Lateral wall: zygomatic bone & greater
wing of sphenoid.
• Medial wall: frontal process of the maxilla,
the lacrimal bone, the orbital plate of the
ethmoid & body of the sphenoid.
The Orbit
Openings into the Orbital Cavity:
1.Orbital opening: About 1/6 of the eyeball is exposed
outside the orbital walls.
2.Supraorbital notch (Foramen): is situated on superior
orbital margin. It transmits supraorbital nerve & vessels.
3.Infraorbital groove and canal: Situated on floor of orbit;
they transmit infraorbital nerve & vessels.
4.Nasolacrimal canal: Located on medial wall of the orbit.
It transmits the nasolacrimal duct.
5.Inferior orbital fissure: Located posteriorly between the
maxilla and the greater wing of the sphenoid. It
transmits the maxillary nerve and its zygomatic branch,
the inferior ophthalmic vein, and sympathetic nerves.
6.Superior orbital fissure: Located posteriorly between
the greater and lesser wings of the sphenoid. It
transmits lacrimal nerve, frontal nerve, trochlear nerve,
oculomotor nerve, abducent nerve, nasociliary nerve &
superior ophthalmic vein.
7.Optic canal: Located posteriorly in the lesser wing of the
sphenoid. It transmits optic nerve & ophthalmic artery.
The Eyelid
The eyelids: are two thin, movable folds that protect the eye from
injury and excessive light by their closure.
The palpebral fissure is elliptical opening between the eyelids.
The conjunctiva is a thin mucous membrane that lines the eyelids
and is reflected at the superior and inferior fornices onto the
anterior surface of the eyeball.
Conjunctival sac: is a potential space formed by conjuctiva and is
open at the palpebral fissure. The upper lateral part of the superior
fornix is pierced by the ducts of the lacrimal gland.
Glands of Zeis: are sebaceous glands of the eyelid & open directly
into the eyelash follicles.
The ciliary glands (glands of Moll) are modified sweat glands that
open separately between adjacent lashes.
The tarsal glands: are long, modified sebaceous glands that pour
their oily secretion onto the margin of the lid.
Lacus lacrimalis: is a small space separate the rounded medial angle
from the eyeball by
Caruncula lacrimalis: is a small, reddish yellow elevation in the
center of lacus lacrimalis.
Plica Semilunaris: is a reddish semilunar fold that lies on the lateral
side of the caruncle.
Papilla Lacrimalis: is a small elevation near medial angle of the eye.
Punctum Lacrimale: is a small hole on the summit of the papilla
Lacrimalis which leads into the canaliculus lacrimalis.
The Eyelid
The orbital septum: is a fibrous sheet attached to periosteum at
the orbital margins & forming the framework of the eyelid. The
orbital septum is thickened at the margins of the lids to form the
superior and inferior tarsal plates.
Lateral palpebral ligament: is a band attaching the lateral ends of
the tarsal plates to a bony tubercle just within the orbital margin.
Medial palpebral ligament: is band attaching the medial ends of
the tarsal plates to the crest of the lacrimal bone.
The superficial surface of the tarsal plates and the orbital septum
are covered by the palpebral fibers of Orbicularis Oculi Muscle.
The aponeurosis of insertion of the levator palpebrae superioris
muscle pierces the orbital septum to reach the anterior surface of
the superior tarsal plate and the skin.
Movements of the Eyelids:
A. They are closed by contraction of the orbicularis oculi and the
relaxation of the levator palpebrae superioris muscles.
B. The eye is opened by the levator palpebrae superioris raising
the upper eyelid.
Lacrimal Apparatus
Lacrimal Gland:
• The lacrimal gland consists of a
large orbital part and a small
palpebral part, which are
continuous with each other around
the lateral edge of the aponeurosis
of the levator palpebrae superioris.
• Situated above the eyeball in the
anterior and upper part of the
orbit posterior to the orbital
septum. The gland opens into the
lateral part of the superior fornix of
the conjunctiva by 12 ducts.
Lacrimal Apparatus
Lacrimal Ducts:
• Tears circulate across the cornea and accumulate
in the lacus lacrimalis. From here, the tears enter
the canaliculi lacrimales through the puncta
lacrimalis.
• The canaliculi lacrimales pass medially and open
into the lacrimal sac, which lies in the lacrimal
groove behind the medial palpebral ligament and
is the upper blind end of the nasolacrimal duct.
• The nasolacrimal duct is about 1.3 cm long and
emerges from the lower end of the lacrimal sac.
The duct descends downward, backward, and
laterally in a bony canal and opens into the inferior
meatus of the nose. The opening is guarded by a
fold of mucous membrane known as the lacrimal
fold. This prevents air from being forced up the
duct into the lacrimal sac on blowing the nose.
Lacrimal Gland - Innervation
• The parasympathetic secretomotor nerve supply is from facial nerve. The
preganglionic fibers are carried by great petrosal nerve & nerve of pterygoid canal to
reach pterygopalatine ganglion (sphenopalatine ganglion). The postganglionic fibers
leave the ganglion and join the maxillary nerve where they pass into its zygomatic
branch and the zygomaticotemporal nerve. Then, they reach the lacrimal gland
within the lacrimal nerve.
• The sympathetic postganglionic nerve supply is from the internal carotid plexus and
travels in the deep petrosal nerve, nerve of pterygoid canal, maxillary nerve,
zygomatic nerve, zygomaticotemporal nerve, and finally lacrimal nerve.
Nerves of the Orbit
A. Nerve passing through optic Canal:
Optic Nerve: It is surrounded by sheaths of pia
mater, arachnoid mater, and dura mater. A rise in
pressure of CSF within cranial cavity; therefore is
transmitted to the back of the eyeball.
B. Nerves passing through upper part of superior
orbital fissure:
1-Lacrimal Nerve: arises from ophthalmic division of
trigeminal nerve & joined by a branch of
zygomatico-temporal nerve, which later leaves it to
enter the lacrimal gland (parasympathetic
secretomotor fibers). It also supplies the skin of the
lateral part of the upper lid.
2-Frontal Nerve: arises from the ophthalmic division
of trigeminal nerve. It divides into supratrochlear
and supraorbital nerves. They supply the upper
eyelid, skin of forehead & also mucous membrane of
frontal air sinus.
3-Trochlear Nerve: supplies superior oblique muscle
Nerves of the Orbit
C. Nerves passing through lower part of superior orbital
fissure:
1- Oculomotor Nerve: supplies superior rectus, medial
rectus, inferior rectus, inferior oblique and levator
palpebrae superioris muscles. It gives off a branch the
ciliary ganglion (Parasympathetic fibers to the sphincter
pupillae and the ciliary muscle).
2- Nasociliary Nerve: arises from ophthalmic division of
trigeminal nerve. It divides into Anterior Ethmoidal and
infratrochlear nerves.
3- Abducent Nerve: supplies only lateral rectus muscle.
Ciliary Ganglion (Parasympathetic):
• It is a parasympathetic ganglion situated in the posterior
part of the orbit. It receives its preganglionic
parasympathetic fibers from the oculomotor nerve. The
postganglionic fibers are carried by short ciliary nerves
to supply the sphincter pupillae and the ciliary muscle.
•Sympathetic fibers pass from internal carotid plexus into
orbit & run through this ganglion without interruption.
Blood Supply of the Orbit
1.Ophthalmic Artery: It is a branch of the internal carotid
artery and enters the orbit through the optic canal. It
runs forward and crosses the optic nerve to reach the
medial wall of the orbit. Branches of the Ophthalmic
Artery
2.Central artery of the retina: is a small branch that enters
the meningeal sheaths of optic nerve to run inside the
optic nerve and enters the eyeball at the center of the
optic disc.
3.Muscular branches to the muscles
4.Ciliary arteries: some enter the eyeball near the
corneoscleral junction; others enter near the optic nerve.
5.Lacrimal artery to the lacrimal gland
6.Supratrochlear and supraorbital arteries.
Ophthalmic Veins:
There are superior & inferior ophthalmic veins that
communicate with facial vein and pterygoid venous plexus,
respectively. Both veins pass backward through the
superior orbital fissure and drain into the cavernous sinus.
The Eyeball
The eyeball is embedded in orbital fat but
separated from it by fascial sheath of the
eyeball.
Fascial Sheath of Eyeball: surrounds the
eyeball from the optic nerve to the
corneoscleral junction. It separates the eyeball
from the orbital fat and provides it with a
socket for free movement.
It is perforated by the tendons of the orbital
muscles and is reflected onto each of them as a
tubular sheath. The sheaths for the tendons of
the medial and lateral recti are attached to the
medial and lateral walls of the orbit by
triangular ligaments called Medial & Lateral
check ligaments.
Suspensory ligament of the eye: is thickening
of the lower part of the fascial sheath, which
passes beneath the eyeball and connects the
check ligaments to suspend the eyeball.
Coats of the Eyeball – Fibrous layer
1- Fibrous Coat: composed of sclera & Cornea
•The Sclera: is posterior opaque part, white in
colour & composed of dense fibrous tissue.
Posteriorly, it is pierced by the optic nerve
and is fused with its dural sheath.
The lamina cribrosa is the area of the sclera
that is pierced by the nerve fibers of the optic
nerve. The sclera is also pierced by the ciliary
arteries and ciliary nerves and their
associated veins (venae vorticosae). The
sclera is directly continuous in front with
cornea at the corneoscleral junction (Limbus).
•The Cornea: is anterior transparent part that
is responsible for refraction of light entering
the eye. It is in contact posteriorly with
aqueous humor. The cornea is avascular and
nourished by diffusion from aqueous humor
and innervated by ciliary nerves.
Coats of the Eyeball – Pigmented Layer
2. Vascular Pigmented Coat: consist of:
A. The Choroid: (outer pigmented layer & inner vascular
layer).
B. The Ciliary Body: composed of ciliary ring, ciliary
processes & ciliary muscle.
•Nerve supply: ciliary muscle by preganglionic
parasympathetic fibers from oculomotor nerve &
postganglionic fibers by short ciliary nerves.
•Action of ciliary muscle: change refractive power of lens by
changing its shape through suspensory fibers of lens.
C. The Iris and Pupil: is a thin, contractile, pigmented
diaphragm with a central aperture (pupil). It divides the
space between lens & cornea into anterior & posterior
chambers.
Iris muscle fibres are involuntary & consist of circular
(Sphincter pupillae) and radiating fibers (Dilator pupillae ).
•Nerve supply: Sphincter pupillae by parasympathetic
oculomotor fibrers (Short ciliary nerves). Dilator pupillae by
sympathetic fibers of long ciliary nerves.
•Action: Sphincter pupillae constricts pupil in bright light &
for accommodation while dilator pupillae dilates pupil in
dim light & in fright.
Coats of the Eyeball – Nervous Layer
3. Nervous Coat (Retina): consists of an
outer pigmented layer and an inner nervous
layer.
The receptor organ is posterior 3/4 of retina
while anterior non-receptive part forms a wavy
ring Ora Serrata, where nervous tissues end.
This anterior part of the retina covers the
ciliary processes and back of the iris.
Macula Lutea: is an oval, yellowish area at the
center of the posterior part of the retina,
which is the area of most distinct vision. It has
a central depression fovea centralis.
Optic disc: is the optic nerve exit and is
completely insensitive to light (the blind spot).
It is about 3 mm medial to macula lutea. The
optic disc is pierced by the central artery of the
retina.
Contents of the Eyeball
The eyeball contains three refractive media: Aqueous humor, Vitreous body & lens.
•Aqueous Humor: It is a clear fluid filling anterior and posterior chambers of the eyeball. It is secreted
from the ciliary processes to enter the posterior chamber & flows into the anterior chamber through
the pupil and then is drained away through the spaces at the iridocorneal angle into Canal of
Schlemm. Obstruction to this drainage results in a rise in intraocular pressure called (Glaucoma).
•Function of Aqueous Humor is to maintain optical shape of the eyeball and to nourish the cornea
and the lens and removes the products of metabolism.
•Vitreous Body: it is a transparent gel filling the eyeball behind the lens. The hyaloid canal is a
rudimentary narrow channel running through vitreous body from optic disc to posterior surface of
lens (filled by hyaloid artery in fetus).
•Function of Vitreous Body is to
supports posterior surface of lens,
assists in holding the retina against the
pigmented part of the retina &
contribute slightly to the magnifying
power of the eye.
The Lens: is a transparent, biconvex
structure enclosed in a transparent
elastic capsule. It is encircled by and
attached to the ciliary processes by
suspensory ligament of the lens.
Extrinsic Muscles of the Eye
• They are 6 skeletal striated voluntary
muscles
• The are all supplied by oculomotor nerve
except superior oblique muscle by
trochlear nerve and lateral rectus by
abducent nerve.
• They are responsible for movement of the
eyeball in different directions and
paralysis of any one may cause squint of
the eye.
1- Superior Rectus
2- Inferior Rectus
3- Medial Rectus
4- Lateral Rectus
5- Superior Oblique
6- Inferior Oblique
Actions of the Extra-ocular muscles
End of the Lecture
GOOD LUCK