Download Anatomy of the Orbit 26 (2)

Anatomy of the Orbit
Objectives
1. Describe the location of the orbit.
2. Make a list of structures making the orbit starting
from orbital margin.
3. Define each component.
4. Describe openings into orbital cavity..
5. Describe muscles of the orbit, their cone
arrangement, origin, insertion, nerve supply and
their function.
6. Describe the visual pathway
Bony Orbit
• Seven bones make up
the bony orbit:
– Frontal
– Zygomatic
– Maxillary
– Ethmoidal
– Sphenoid
– Lacrimal
– Palatine
The basic shape of the orbit is a
pyramid:
The medial walls are parallel
The depth is 1.5 x base
Orbital Roof
• The orbital roof
formed from both the
orbital plate of the
frontal bone and the
lesser wing of the
sphenoid bone.
Lacrimal Fossa
Trochlear Fossa or fovea
Supraorbital Notch
• Lacrimal gland
Medial Orbital Wall
• Then medial wall of the
orbit is formed from
four bones:
1-Frontal process of
maxillary
2-Lacrimal bone
3-Orbital plate of
ethmoid
4-Lesser wing of
sphenoid
• Lacrimal fossa
Orbital Floor
• The floor of the
orbit is formed
from three bones:
– Maxillary
– Palatine
– Orbital plate of
zygomatic bone2
• Infraorbital groove
Lateral Orbital Wall
• Formed from two
bones:
– Zygomatic
– Greater wing of
sphenoid
• Thickest and
strongest
The Lateral Wall
Orbital Foramina
• The optic foramen
• The supraorbital foramen,
or notch
• Nasolacrimal duct
• Infraorbital canal
• Superior orbital fissure
• Inferior orbital fissure
Main components of fissures
EXTRA-OCULAR
MUSCLES:
• (7 muscles).
• 1-Levator palpebrae
superioris
• 4 Recti muscles:
Medial &lateral
&superior &inferior
• 2 Oblique muscles:
(superior and
inferior)
• NB. All muscles of
the eye are supplied
by the oculomotor
nerve , EXCEPT LR6 +
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.
Eyeball
The eyeball is formed
of:
• Cornea
• Sclera
• Conjunctiva
• Anterior Chamber
• Iris/Pupil
• Posterior Chamber
• Lens
• Vitreous
• Choroid
• Ciliary body
• Retina
Eyelids
In addition to tear spreading,
the eyelid is primarily
responsible for corneal nutrition
.
Also provides protection to
cornea
Lashes offer additional
protection
When eye is open, the upper lid
covers about 1/6th of the cornea
& the lower lid just touches the
limbus.
The two lids meet each other at
medial and lateral angles(or
outer & inner canthi).
• In addition, the upper lid also
contains the orbicularis oculi
supplied by Facial and
levator palpebrae superioris
muscle (LPS) supplied by
Occulomotor.
• Eyelids are closed by
Orbicularis oculi and opened
by LPS..(Facial Palsy)
• LPS arises from apex of the
orbit and is inserted by three
parts on1- the skin of lid,
2-anterior surface of tarsal
plate and
3-conjunctiva of superior
Lacrimal Apparatus
The lacrimal apparatus consists
of
A-lacrimal gland
B-lacrimal passages:
1- Lacrimal sac
2- Lacrimal canaliculi
3- Nasolacrimal duct
Lacrimal gland –consists of 2
parts
A-orbital lobe situated in the
lacrimal fossa in the outer part
of the orbital roof.
B-palpebral lobe situated in the
outer part above the superior
fornix
Lacrimal System/Tear Film
• Lacrimal system is responsible for
tear production and drainage
• Tears are made up of 3 layers :
• Created primarily by lacrimal
apparatus and meibomian glands
• Lubricate the eyeball, provides
oxygen/nutrition for cornea, has
antibacterial properties and helps
wash away debris
• Also have unique composition
which keeps surface of cornea
moist
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
• Made up of 5 layers
• Specialized Transparent Tissue
– No blood vessels
• Primarily responsible for refracting
light : more than the lens
• More nerve endings than anywhere
else in the body
– Protection to the eye
• The only part of the eye that is
transplanted from one person to
another
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
• Called the whites of the eye
• Made up of 3 layers
• Tough, fibrous tissue: site of
extra-ocular muscle
attachment
• Opaque...allows NO light to
enter
Limbus
• The limbus is the
border of the cornea
and the sclera.
• It is the transition zone
between the peripheral
cornea and the anterior
sclera
Conjunctiva
• Mucous membrane with
non keratinized
squamous epithelium
and goblet cells
• Thin, richly 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
Lens
It is the lesser of the two
refractive elements in the
dioptric system
It lacks innervation and is
avascular.
Transparent, biconvex structure,
held in place by ciliary zonules
attached to (suspensory
ligaments)
Composed of 6 layers
Refracts light
Nutrition comes from aqueous
humor…
Insoluble deposits of proteins
build up over time = Cataracts :A
clouding of the lens and capsule
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
• The colored part of the
eye…unique to every
individual like a fingerprint
– Color is dependent on the
amount of pigment
• A diaphragm, the iris has tiny
muscles :Dilator pupillae and
Sphincter pupillae ,that control
the light levels in the eye
• Has 2 layers
• Pupil is located in the center of
the iris
– pupil = hole: it is not an eye
structure per se
Ciliary Body
The ciliary body, 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
• Has three parts including:
The ciliary muscle is ring
shaped muscle that controls
the shape of the lens
(accommodation)
The ciliary process is the
attachment site for the
zonules and produces the
aqueous in the pars plicata
The ciliary ring is attached to
the choroid and is composed
of the pars plana. The pars
plana has no known function
in the post-fetal eye thus this
is a safe area through which
surgical instruments may be
inserted
It Connects the choroid with the iris
The ciliary body has three
principal functions:
1- aqueous humor
formation and lens
accommodation
2- It also plays a role in
the outflow of aqueous
humor and
3- 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
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
Ora Serrata
• A serrated juncture
between the retina and
ciliary body marking
the transition between
non-sensitive tissue
and the retinal portion
with many layers and
specialized
photoreceptor cells
Fundus
• 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. At the macula's
center lies the fovea, rich in
cones and responsible for
color vision and the highest
visual acuity.
• It is the Point of sharpest
vision
Retina
• Most internal layer of eye, facing
the vitreous
• Converts light energy into
electrical energy which is then
sent to the brain via the optic
nerve
• Actually an extension of brain
tissue
• Composed of 10 layers…contains
photoreceptors: cones, near
center (responsible for seeing
detail and color) and rods, in
periphery (responsible for seeing
in low light and seeing
movement)
• Blind spot