Transcript Orbital anatomy

Orbital and Ocular Anatomy
Abdulrahman Al-Muammar, MD, FRCSC
King Saud University
Periorbital Sinuses
The eyes lie within two bony
orbits, located on either side of
the root of the nose.
They border the nasal cavity
anteriorly and the ethmoidal air
cells and the sphenoid sinus
posteriorly.
The lateral walls border the
middle cranial, temporal, and
pterygopalatine fossae.
Superior to the orbit are the
anterior cranial fossa and the
frontal and supraorbital sinus.
The maxillary sinus and the
palatine air cells are located
inferiorly.
Orbital Volume
The volume of each adult orbit
is slightly less than 30 cc
The orbital entrance averages
about 35 mm in height and 45
mm in width. The maximum
width is about 1 cm (behind the
anterior orbital margin)
In adults, the depth of the orbit
varies from 40 to 45 mm from
the orbital entrance to the orbital
apex
Both race and sex affect each of
these measurements.
Bony Orbit
Seven bones make
up the bony orbit:
Frontal
Zygomatic
Maxillary
Ethmoidal
Sphenoid
Lacrimal
Palatine
Orbital Roof
The orbital roof
formed from both
the orbital plate of
the frontal bone and
the lesser wing of
the sphenoid bone.
Lacrimal gland
Fovea trochlearis
Medial Orbital Wall
Then medial wall of the
orbit is formed from four
bones:
Frontal process of the
maxillary
Lacrimal
Orbital plate of the
ethmoidal
Lesser wing of the
sphenoid
Lacrimal fossa
Lamina papyracea
Orbital Floor
The floor of the orbit
is formed from three
bones:
Maxillary
Palatine
Orbital plate of the
zygomatic
Infraorbital groove
Inferior oblique
muscle
Lateral Orbital Wall
Formed from two
bones:
Zygomatic
Greater wing of the
sphenoid
Thickest and
strongest
Lateral orbital
tubercle (Whitnall’s
tubercle)
Orbital Foramina
The optic foramen
The supraorbital foramen, or
notch
The anterior ethmoidal
foramen
The posterior ethmoidal
foramen
The zygomatic foramen
Nasolacrimal duct
Infraorbital canal
Superior orbital fissure
Inferior orbital fissure
Extraocular Muscles
The four recti and
two oblique muscles
All are supplied by
oculomotor nerve III
except superior
oblique (Trochlear
N) and lateral rectus
(Abducens)
Optic nerve
The optic nerve
consists of more
than 1 million axons
that originate in the
ganglion cell layer of
the retina and
extend toward the
occipital cortex
Optic Nerve
The optic nerve may be divided
into the following topographic
areas:
Intraocular portion of the optic
nerve: optic disc, or nerve
head; prelaminar; and laminar
portions
Intraorbital portion (located
within the muscle cone)
Intracanalicular portion (located
within the optic canal)
Intracranial portion (ending in
the optic chiasm)
Optic Chiasm
The chiasm measures
approximately 12 mm wide,
8 mm long in the
anteroposterior direction,
and 4 mm thick. The exact
location of the chiasm with
respect to the sella is
variable. Most of the time it is
directly superior
Within the chiasm, the fibers
coming from the nasal retina
(approximately 53% of total
fibers) cross to the opposite
side to join the
corresponding contralateral
fibers
Optic Tract
Each optic tract
contains ipsilateral
temporal and
contralateral nasal
fibers from the optic
nerves . Fibers (both
crossed and uncrossed)
from the upper retinal
projections travel
medially in the optic
tract; lower projections
move laterally.
Lateral geniculate body
The lateral geniculate body,
or nucleus, is the synaptic
zone for the higher visual
projections
It has six alternating layers
of gray and white matter.
Layers 1, 4, and 6 of the
lateral geniculate body
contain axons from the
contralateral optic nerve.
Layers 2, 3, and 5 arise from
the ipsilateral optic nerve
Optic radiations
The optic radiations connect
the lateral geniculate body
with the cortex of the
occipital lobe
The fibers of the optic
radiations leave the lateral
geniculate body and run
around the temporal horn of
the lateral ventricle,
approaching the anterior tip
of the temporal lobe (the socalled loop of Meyer)
Visual cortex
The visual cortex, the thinnest
area of the human cerebral
cortex
Macular function is extremely
well represented in the visual
cortex and occupies the most
posterior position at the tip of
the occipital lobe
The posterior cerebral artery, a
branch of the basilar artery,
supplies the visual cortex
almost exclusively. The blood
supply to the occipital lobe does
show anatomical variation,
however, with the middle
cerebral artery making a
contribution in some persons.
Cranial Nerve III (Oculomotor)
It supplies all the extraocular muscles
except the superior oblique and the
lateral rectus
It also carries cholinergic innervation to
the pupillary sphincter and the ciliary
muscle
Cranial Nerve III
The CN III nucleus consists of several
distinct, large motor cell subnuclei, each
of which subserves the extraocular
muscle it innervates
The Edinger-Westphal nucleus provides
the parasympathetic preganglionic
efferent innervation to the ciliary muscle
and pupillary sphincter
Cranial Nerve III
CN III usually divides into
superior and inferior
divisions after passing
through the annulus of Zinn
in the orbit
The superior division of CN
III innervates the superior
rectus and levator palpebrae
muscles. The larger inferior
division splits into three
branches to supply the
medial and inferior rectus
muscles and the inferior
oblique.
Cranial Nerve III
The parasympathetic
fibers wind around the
periphery of the nerve
Enter the inferior
division, and course
through the branch that
supplies the inferior
oblique muscle. They
join the ciliary ganglion
They synapse with the
postganglionic fibers,
which emerge as many
short ciliary nerves
Cranial Nerve IV (Trochlear)
Cranial nerve IV has the
longest intracranial course
The CN IV the only cranial
nerve that is completely
decussated and the only
motor nerve to exit dorsally
from the nervous system.
CN IV enters the orbit
through the superior orbital
fissure outside the annulus
of Zinn and runs superiorly
to innervate the superior
oblique muscle
Cranial Nerve V (Trigeminal)
The largest cranial nerve
Possesses both sensory and motor divisions
The sensory portion subserves the greater
part of the scalp, forehead, face, eyelids, eye,
lacrimal gland, extraocular muscles, ear, dura
mater, and tongue
The motor portion innervates the muscles of
mastication through branches of the
mandibular division
Divisions of Cranial Nerve V
Ophthalmic
Frontal
Lacrimal
Nasociliary
Maxillary
Mandibular
Cranial Nerve VI (Abducens)
The nucleus of cranial nerve VI is situated in
the floor of the fourth ventricle, beneath the
facial colliculus, in the caudal pons
CN VI runs below and lateral to the carotid
artery and may transiently carry sympathetic
fibers from the carotid plexus
It passes through the superior orbital fissure
within the annulus of Zinn and innervates the
lateral rectus muscle on its ocular surface
Arterial system
Internal carotid artery
Ophthalmic artery
Central retinal A
Short post ciliary A
Long post ciliary A
Anterior ciliary A
Lacrimal A
Superior muscular A
Inferior muscular A
Posterior ethmoidal A
Anterior ethmoidal A
Supraorbital A
Supratrochlear A
Venous system
Central retinal V
Superior vortex V
Superior episcleral plexus
Inferior vortex V
Inferior episcleral plexus
Pterygoid plexus
Superior
ophthalmic V
Cavernous
sinus
Jugular v
The Eye
The adult human
eye averages 24
mm in diameter
The eye reaches
maximum size
before puberty. The
transverse vertical
diameter is less
variable.
Cornea
The cornea occupies the
center of the anterior pole of
the globe. In the adult, it
measures about 12 mm in
the horizontal meridian and
about 11 mm in the vertical
The cornea is transparent
and form a positive lens of
about 40 D and constitute
the main refractive element
of the eye
Cornea
Epithelium
Bowman’s layer
Stroma
Descemet’s
membrane
Endothelium
Sclera
Sclera is opaque
and white
The sclera covers
the posterior four
fifths of the surface
of the globe, with an
anterior opening for
the cornea and a
posterior opening for
the optic nerve
Limbus
Transition zone
between the
peripheral cornea
and the anterior
sclera
Conjunctiva
Mucous membrane with
non keratinized
squamous epithelium
and goblet cells
Thin, richy vascularized
substantia propria
Can be divided into
three geographic zones:
Palpebral
Forniceal
Bulbar
Anterior chamber
The anterior chamber is
bordered anteriorly by
the cornea and
posteriorly by the iris
diaphragm and the pupil
The depth of the
anterior chamber varies
The anterior chamber is
filled with aqueous
humor, which is
produced by the ciliary
epithelium
Anterior chamber
The fluid passes through the pupil
aperture and drains chiefly by the
conventional pathway through the
trabecular meshwork
The anterior chamber angle, which
lies at the junction of the cornea and
the iris, consists of the following
structures :
Schwalbe's line
Schlemm's canal and the trabecular
meshwork
Scleral spur
Anterior border of the ciliary body
Lens
The lens is a biconvex
structure located directly
behind the posterior
chamber and pupil
It is the lesser of the two
refractive elements in the
dioptric system
The equatorial diameter in
adult is about 9-10 mm
The anteroposterior width of
the lens is about 6 mm
The lens has certain unusual
features. It lacks innervation
and is avascular.
Uveal Tract
The uveal tract is the
main vascular
compartment of the
eye. It consists of three
parts:
Iris
Ciliary body (located in
the anterior uvea)
Choroid (located in the
posterior uvea)
Iris
Ciliary Body
The ciliary body, which
is triangular in cross
section. The apex of the
ciliary body is directed
posteriorly toward the
ora serrata. Its base
gives rise to the iris.
The only attachment of
the ciliary body to the
sclera is at its base, via
its longitudinal muscle
fibers, where they insert
into the scleral spur.
Ciliary body
The ciliary body has
three principal
functions:
aqueous humor
formation and lens
accommodation
It also plays a role in
the trabecular and
uveoscleral outflow
of aqueous humor
Accommodation
Choroid
The choroid, the posterior
portion of the uveal tract,
nourishes the outer portion of
the retina. It averages 0.25 mm
in thickness and consists of
three layers of vessels:
The choriocapillaris, the
innermost layer
A middle layer of small vessels
An outer layer of large vessels
Retina
The fundus is the part of the
eye that is visible on
ophthalmoscopy, including
the retina and its vessels
and the optic nerve head (or
optic disc)
The macula, 5–6 mm in
diameter, lies between the
temporal vascular arcades.
At the macula's center lies
the fovea, rich in cones and
responsible for color vision
and the highest visual acuity
Vitreous
The vitreous cavity occupies four
fifths of the volume of the globe
The transparent vitreous humor is
important to the metabolism of the
intraocular tissues because it
provides a route for metabolites
used by the lens, ciliary body, and
retina
Its volume is close to 4.0 ml
Although it has a gel-like structure,
the vitreous is 99% water
Its viscosity is approximately twice
that of water, mainly because of the
presence of the
mucopolysaccharide hyaluronic acid
Ocular Embryology
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