Download 8-Orbit II

ORBIT II
Dr. Mujahid Khan
Blood Supply
Ophthalmic Artery:
•
It is a branch of Internal Carotid Artery
•
Emerges from cavernous sinus
•
Runs forward lateral to the optic nerve
•
Reaches the medial wall of the orbit
•
Gives away several branches
Central Artery of Retina
•
Is a small branch
•
Pierces the meningeal sheath of optic
nerve & gain entrance to the nerve
•
Enters the eyeball at the centre of optic
disc
•
Divides into 2 branches called end arteries
Ciliary Arteries
•
Can be divided in two groups
•
Anterior group enters the eyeball near the
corneoscleral junction
•
Posterior group enters the eyeball near the
optic nerve
Lacrimal Artery
•
It supplies the lacrimal gland
Supratrochlear & Supra orbital
Arteries
•
Are distributed to the skin of the forehead
Ophthalmic Veins
•
Superior ophtalmic vein communicates in
front with the facial vein
•
Inferior ophthalmic vein communicates
with the pterygoid plexus through the
inferior orbital fissure
•
Both the veins pass backward through
superior orbital fissure & drain into
cavernous sinus
Lymph vessels
•
No lymph nodes or vessels are present in
the orbital cavity
The Eye
•
Eyeball consists of 3 coats:
•
The fibrous coat
•
The vascular pigmented coat
•
The nervous coat
Fibrous Coat
•
Made up of posterior opaque part, the
sclera & anterior tranparent part cornea
Sclera
•
Composed of dense fibrous tissue
•
Pierced by optic nerve posteriorly and is fused
with the dural sheath of the nerve
•
Lamina Cribrosa is the area of sclera that is
pierced by optic nerve fibers
•
Also pierced by ciliary arteries & nerves
•
Is continuous in front with the cornea
Cornea
•
Is transparent
•
Responsible for refraction of light entering
the eye
•
It is in contact with the aqueous humor
posteriorly
Vascular Pigmented Coat
•
Consists from behind forward:
•
Choroid
•
Ciliary body
•
Iris
Choroid
•
Is composed of an outer pigmented layer
and an inner highly vascular layer
Ciliary Body
•
•
Is continuous posteriorly with choroid
Anteriorly lies behind the peripheral
margin of iris
•
Composed of:
•
Ciliary ring
Ciliary process
Ciliary muscle
•
•
•
Ciliary ring is the posterior part of the
body, has shallow grooves, Ciliary striae
•
Ciliary processes are radially arranged
folds connects the suspensory ligaments
of the lens
•
Ciliary muscle is composed of meridianal
and circular fibers of smooth muscles
Iris
•
Is a thin, contractile, pigmented diaphragm
•
Has central aperture called pupil
•
Is suspended in the aqueous humor between
the cornea and lens
•
Its periphery is attached to the anterior surface
of the ciliary body
•
Divides the space between cornea and lens into
anterior & posterior chambers
Nervous Coat or Retina
•
Consists of an outer pigmented layer & inner
nervous layer
•
Its outer surface is in contact with choroid
•
Inner layer in contact with the vitreous body
•
Posterior three-fourths is the receptor organ
•
Macula lutea is the oval yellowish area in the
center of the posterior part
•
Fovea centralis is the central depression
Retina
•
Optic nerve leaves the retina to medial
side of macula lutea by the optic disc
•
Optic disc is depressed at its center,
where it is pierced by central artery
•
Optic disc is insensitive to light and
referred as blind spot
•
Optic disc is seen to be pale pink with
ophthalmoscope examination
Optic Nerve
•
Enters the orbit from middle cranial fossa
by passing through the optic canal
•
Accompanied by ophthalmic artery
•
It is surrounded by sheaths of pia,
arachnoid and dura maters
•
It runs forward and laterally within the
cone of the recti muscles
Optic Nerve
•
Pierces the sclera at a point medial to the
posterior pole
•
The meninges fuse with the sclera
•
The subarachnoid space extends forward as far
as the eyeball
•
A rise in pressure of the CSF within the cranial
cavity is transmitted to the back of the eyeball
Nasociliary Nerve
•
Arises from the ophthalmic division of the
trigeminal nerve in the lateral wall of the
cavernous sinus
•
Enters the orbit through the lower part of the
superior orbital fissure
•
Crosses above the optic nerve with the
ophthalmic artery
•
Ends by dividing into the anterior ethmoidal and
infratrochlear nerves
Branches of Nasociliary Nerve
•
Communicating branch to the ciliary ganglion
•
The long ciliary nerves (2-3 in number)
•
Posterior ethmoidal nerve
•
Infratrochlear nerve
•
Anterior ethmoidal nerve
•
External nasal nerve
Ciliary Ganglion
•
It is about the size of a pinhead
•
It is a parasympathetic ganglion
•
Situated in the posterior part of the orbit on the lateral
side of the optic nerve
•
Receives its preganglionic parasympathetic fibers from
the oculomotor nerve via nerve to inferior oblique
•
The postganglionic fibers leave the ganglion in the short
ciliary nerves
Contents of the Eyeball
•
Aqueous Humor
•
Vitreous body
•
lens
Aqueous Humor
•
Clear fluid fills the ant. & post. Chambers
•
Is a secretion from ciliary processes
•
Drained away through canal of Shlemm
•
Obstruction to its draining results in glaucoma
•
Glaucoma causes degenerative changes in
the retina
Aqueous Humor
•
Supports the wall of the eyeball
•
Maintains its optical shape
•
Nourishes the cornea and lens
•
Removes the products of metabolism
Vitreous Body
•
Is a tranparent gel
•
Fills the eyeball behind the lens
•
Hyaloid canal is a narrow channel runs through
it extends from optic disc to posterior surface of
the lens
•
Canal is filled with hyaloid artery in fetus
•
Contribute in the magnifying power of eye
•
Supports posterior surface of lens
Lens
•
Is a transparent, biconvex structure
•
Enclosed in a transparent capsule
•
Situated behind the iris & in front of vitreous
•
Encircled by ciliary process
•
Assumes globular shape due to tense elastic
capsule
•
Its circumference attached to the ciliary process
by suspensory ligament
Lens
•
Suspensory ligament keeps the elastic
lens flattened
•
Ciliary muscle contracts to accommodate
the eye for close objects
•
Lens becomes dense & less elastic in
advance age resulting in presbyopia
•
Glasses are used to overcome presbyopia