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Module 49: The Orbit
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Module 49: The Orbit
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Contents:
Anatomy
Regions of the orbits
Openings on the orbits
Sinuses
Imaging of the orbits
X-ray
CT scan
MRI
Ultrasonography
Diseases of the orbital region
Orbital cellulitis
Idiopathic orbital inflammation
Vasculitis
Tumors
History Taking
Clinical Examination
Proptosis (exophthalmos)
Name
Anatomy
E-mail
The bony orbit provides protection for the eyeball and a place to hang out (so to
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Module 49: The Orbit
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speak). The orbit is shaped roughly like a pyramid, with the base of the pyramid at
the front (on the face) and the apex in the back (toward the brain). The orbit is
lined by fatty tissue, which provides lubrication for movement within the orbit. The
eyeball is suspended by the extraocular muscles within the orbit. The model
below gives us an idea of the structure. Move your mouse over the image to
remove the globe and some of the extraocular muscle structure.
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Figure 49-1
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substance and presentation.
JCAHPO® , COA ® , COT ® , a
COMT ® are registered trade
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There are four basic regions to the orbit: the roof, the floor, the medial wall, and
the temporal wall. There are 7 bones that make up the orbit. Unfortunately for
test takers, the bones are not nicely divided into regions. As shown on the
schematic below, the orbital bones connect together like a puzzle. The 7 bones
are as follows, and are identified on the schematic by colors and their first letters. Move your mouse over the schematic to view an orientation photo.
frontal
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maxilla
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zygoma
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reserved. No part of this site
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palantine
The white circle on the schematic indicates the location of the orbital rim. Notice
publisher except for brief
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Module 49: The Orbit
that the sphenoid bone (green) has two "wings", the greater wing and the lesser
wing. The hole (black) in the lesser wing is the optic foramen, through which the
optic nerve and the ophthalmic artery pass. The space (black) between the two
wings of the sphenoid is the superior orbital fissure, through which pass cranial
nerves III, IV, V, and VI.
quotations. Figure 49-2
The regions of the orbit are all made up of one or more of the orbital bones:
The floor - Three bones make up the floor: the maxilla (or maxillary), the
zygoma (or zygomatic), and the palantine. The maxillary bone occupies the
most space on the floor. The orbital floor is the weakest region of the orbit. A
concussive force, such as a fist to the eye, can fracture the orbit floor and
entrap the inferior rectus muscle. The is called a blow-out fracture. A blowout fracture is characterized by a history of concussive trauma, swelling of the
soft tissues of the orbit, and the inability of the eye to look upward due to the
entrapped inferior rectus muscle. Fortunately, most blow-out fractures
resolve without the need for surgery. When the swelling goes down, the
muscle usually becomes free.
The roof - The frontal bone forms the roof of the orbit.
The medial wall - Four bones make up the medial wall of the orbit: the
maxilla, lacrimal, ethmoid, and sphenoid (lesser wing) bones.
The lateral wall - The zygomatic bone makes up the anterior lateral wall, and
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Module 49: The Orbit
the greater wing of the sphenoid bone makes up the posterior lateral wall. The zygoma is also part of the jaw.
Openings in the orbit
Optic foramen (or optic canal) - The optic nerve enters the eye through the
optic foramen, which is a hole at the apex (back) of the orbit. If you observe
the upper left corner of the image in Figure 49-1 while moving the mouse
pointer over the image, you can see how the nerve fits through this hole.
Orbital fissures - The superior and inferior orbital fissures are "cracks" at the
back of the orbit. These are shown as black areas in the center of Figure 492. Cranial nerves III, IV, V, and VI, and the superior ophthalmic vein pass
through the superior fissure. The inferior ophthalmic vein passes through the
inferior fissure.
Supraorbital foramen - There is a hole at the top of the orbit which is called
the superorbital foramen, which is more like a notch located just under the
eyebrow. The supraorbital nerve, the supraorbital artery, and the supraorbital
vein pass through this notch. Infraorbital foramen - This is a hole in the high cheek area through which
pass the infraorbital nerve, the infraorbital artery, and the infraorbital vein.
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Sinuses
The paranasal sinuses are air filled spaces within the bones of the face. The
spaces open into the nasal cavity and they surround the orbit except on the
temporal side. In the x-ray image below, the orbits are identified with the letter
"O", the maxillary sinuses are labeled with "M", and the ethmoid sinuses are
labeled with "E". Sphenoid and frontal sinuses are not shown. Inflammation,
blockage, and drainage of the sinuses are commonly associated with allergies
and colds.
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Module 49: The Orbit
Imaging of the Orbits
Abnormalities of the orbits occur from congenital defects, inflammation, trauma,
and tumors. There are a variety of imaging modalities that the physician can use to evaluate
the orbital regions:
X-ray
Computerized Axial Tomography (CT scan)
Magnetic Resonance Imaging (MRI)
Ultrasonography
X-ray Imaging
An X-ray is a form of radiation. X-ray
imaging involves sending a small burst
of x-ray radiation through the body. Xrays are absorbed by varying degrees
by parts of the body. The radiation is
absorbed to a high degree by bones, to
a lesser degree by soft tissues, and not
at all by air spaces. The X-rays that
pass through the body are captured on
special imaging plates (it used to be
film). Since bones absorb a greater
degree of the radiation, the image of
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Module 49: The Orbit
bones will appear whitish. Air spaces
will appear black, and soft tissue will
appear as shades of gray.
X-rays provide information about the integrity of bony structures in cases of
trauma, and x-rays are good at imaging highly x-ray opaque objects such as the
metallic foreign body imaged below by x-ray. X-rays are not sensitive enough to image small fractures. X-rays are not
particularly good for imaging soft tissues. Single X-rays are not used much
anymore for orbital evaluation, having been replaced by the CT Scan, which
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creates multiple X-ray cuts.
CT Scan (CAT scan)
"CT" stands for computed tomography. Sometimes it is referred to as
"Computerized Axial Tomography"
(CAT) scanning. Tomography means
"to image by slicing". The CT scanner
takes a number of X-ray "slices" of the
body which are then joined together by
computer into cross-sectional and 3-D
views of the body. The CT scan
provides greater image resolution
compared to conventional X-ray
imaging.
Small fractures and soft tissue are imaged in more detail with a CT scan
compared to conventional X-ray imaging.
Below is an image of the orbits taken with a CT scanner.
Magnetic Resonance Imaging (MRI)
MRI uses a magnetic field, radio
waves, and a computer to produce
images of the internal structures of the
body. No radiation is used. Currently
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Module 49: The Orbit
MRI provides the most detailed images
of the structures inside the head. In
order to obtain good quality images,
the patient must hold very still.
MR imaging is more expensive than CT scanning, it takes more time, and the
results may not be immediately available. These factors make CT scanning more
practical in trauma cases. The MRI may adversely affect the function of a medical
device (such as a pacemaker). The MRI may cause a metallic material in the
body to move and/or heat up.
The image below gives you an idea of the fantastic detail that MRI can provide.
Costs vary widely, but to give you an idea an X-ray of the orbits may cost as little
as $40, a CT scan about $200, and an MRI about $400.
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Module 49: The Orbit
Ultrasonography
Ultrasonography uses sound waves to
image the globe and, to a limited
extent, the orbits. It is most useful for
the ophthalmologist as a tool to image
inside the globe when no view of the
vitreous and/or the retina is available,
usually due to a dense cataract or a
vitreous hemorrhage. It is less useful
as an imaging device for the orbital
area. The ultrasound is useful as a
screening device for orbital disease.
CT scanning and MRI provide more
detailed imaging of the orbit. Below is an ultrasound image of a mucocele of the frontal sinus (M). The vitreous
inside the globe is the black (low reflective) area labeled with the "V". Orbital fat is
highly reflective of the ultrasound beam and the fat is visible as the white area.
Diseases of the Orbital Region
This discussion is not meant to be a comprehensive study of orbital diseases. It is
not even a complete listing of orbital diseases. The goal is to familiarize you with
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some of the terminology of orbital diseases.
Diseases of the orbital region include orbital cellulitis, idiopathic orbital
inflammation, thyroid orbitopathy (Graves disease), vasculitis, and a variety of
tumors.
Orbital cellulitis is the most common cause of proptosis in childhood. The
source of infection is usually a paranasal sinusitis. The patient presents with
swelling of the orbital soft tissues, pain, and fever. There is usually restricted eye
movement and there may be decreased vision. Complications can be serious with
up to 11% of cases resulting in vision loss. Treatment includes hospitalization with
the administration of an appropriate intravenous antibiotic. Surgical drainage of an
abscess is sometime required.
Idiopathic orbital inflammation can be acute or chronic, and it can involve
frequent relapses. "Idiopathic" means "of unknown cause". It can be unilateral or
bilateral, and it can involve any of the orbital tissues. Symptoms can include pain,
swelling, proptosis, limited eye movement, and vision loss. Tissue biopsy reveals
fibrosis of the tissue with infiltration of lymphocytes, plasma cells, and
eosinophils. Treatment involves systemic steroids, and may include radiation or
orbital decompression.
Thyroid orbitopathy (Grave's disease) is the most common cause of proptosis
in adults. The age of onset is usually 20 to 45 years old. It affects 8x more women
than men. It is a systemic disease with most cases due to hyperthyroid. Clinical
symptoms can include exophthalmos, eyelid retraction, lid lag, lagophthalmos (the
lids cannot close completely), diplopia due to restricted muscle movement, edema
of the eyelid, and swelling of the conjunctiva (chemosis). The optic nerve can be
damaged due to excessive pressure on the nerve (compressive optic
neuropathy). Symptoms are caused by enlargement of the extra-ocular muscles
due to infiltration. Non-surgical treatment may include lubrication of the eyeball
and systemic prednisone. Surgical treatments may include orbital decompression,
EOM surgery, and lid retraction repair. Radiation may be used for refractory
(unresponsive to treatment) cases.
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Above: Exophthalmos, and eyelid retraction secondary to thyroid orbitopathy.
Above: CT scan showing exophthalmos and enlarged extraocular muscles,
particularly the medial rectus muscles (arrows).
Vasculitis of the orbital region includes giant cell arteritis. Giant cell arteritis
(GCA) is an inflammation of the lining of the artery. It most often affects the
arteries in the head, especially the temples. It is sometimes called temporal
arteritis. The average age of onset is 70, and it rarely occurs in people below the
age of 50. It affects twice as many women as men, and the vast majority are
white. About half the people with GCA also have polymyalgia rheumatica (an
arthritic condition). Symptoms can include head pain, especially tenderness at the
temples, double vision, decreased vision, jaw pain, fever, and pain and stiffness in
the neck, arms and hips. The condition can cause an aneurysm, stroke, or
blindness. Blindness results from decreased blood flow to the eye. The condition
is treated with high dose steroids.
Tumors of the orbital region include developmental pediatric tumors, metastatic
pediatric tumors, metastatic adult tumors, vascular tumors, neural tumors, lacrimal
gland tumors, lymphoproliferative lesions, mesenchymal tumors, and secondary
orbital tumors. Specific tumors in each category are listed below. You should
read each name so that you become familiar with the terminology. Do an internet
search on the term if you are interested in more information.
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Developmental pediatric tumors include the following:
dermoid cyst
lipodermoid
teratoma
Metastatic pediatric tumors include:
neuroblastoma
leukemia
Mesenchymal tumors include:
rhabdomyosarcoma (most common primary orbital malignancy in children)
Metastatic adult tumors of the orbit are rare. A metastatic tumor is a tumor that
has spread from another source. Intraocular metastases are ten times more
common. The most common source of metastatic tumors for women is breast
cancer. The most common source for men is lung cancer.
Vascular tumors include the following:
capillary hemangioma
lymphangioma
cavernous hemangioma (this is the most common benign orbital tumor in
adults)
hemangiopericytoma
AV malformation
AV fistula
Varices
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Neural tumors include the following:
optic nerve glioma
meningioma
neurofibromatosis
neurofibroma
schwannoma (neurilemmoma)
Lacrimal gland tumors include the following:
pleiomorphic adenoma
adenoid cystic carcinoma
nonepithelial (infiltrative) lesions
Lymphoproliferative lesions include:
lymphoid hyperplasia
malignant lymphoma
Secondary orbital tumors include:
sinus tumors (mucocele, carcinoma)
eyelid tumors
intraocular tumors with orbital extension
History taking related to orbital disease
As related to orbital disease, the following considerations are of particular
importance:
Is this the first time the patient has seen a doctor? Was the patient referred
by another doctor (get details)? If seen by another doctor, where there
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diagnostic studies done? If so, how can the studies be obtained? If a
diagnosis has been made, what is the diagnosis?
How long has the patient had the problem (hours, days, weeks, months,
years)?
Has there been trauma associated with the condition? If so, what are the
details?
Has there been any other physical condition or sickness recently?
Is there pain associated with the condition? If so, how intense? Where is the
pain located? Is it constant, or does it come and go? Has it been staying the
same, getting better, or getting worse? Does anything relieve the pain? Is the
pain worse in certain circumstances? Is the patient taking pain medication? Does the medication help?
Has the patient's vision been affected? To what degree? Is it getting better or
worse? When did the patient first notice a vision problem? Does the patient
have double vision? If so, when did it start? Is there double vision only when
looking in a particular direction?
Has there been a change in appearance? If so, how has it changed and when
did it change?
The clinical exam for orbital disease
The clinical exam may involve a complete eye exam with dilation, if this has not
recently been done. Specific to orbital disease, the physician will be examining
the area around the globe for "periorbital" changes. The conjunctiva will be
examined for changes in coloration, lesions, swelling, and unusual blood vessel
formations. The lids will be examined for lesions, retraction, swelling, and unusual
formations. The skin will be examined for ecchymosis, other discolorations,
lesions, swelling, and unusual formations. Eccymosis is a purplish discoloration of
the skin caused by blood that escapes from blood vessels under the skin (a bruise
from trauma is an example).
The physician my examine by palpation, using his fingers to feel for abnormal
structures in the periorbital area. Palpation can also be used to gently push the
globe toward the back of the socket (retrodisplacement) to detect resistance to
movement which may mean that there is an obstruction behind the globe.
The physician will observe and sometimes palpate for pulsation of blood vessels,
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which may indicate high blood flow in a vascular lesion. The doctor may also
listen for bruits (rhymes with Louie), which is an abnormal blowing sound over a
peripheral blood vessel, which can be an indicator of a fistula. A fistula is an
abnormal passageway between two organs.
Proptosis (exophthalmos)
The physician will also be looking for, and sometimes measuring, proptosis. The
short definition of proptosis is abnormal protrusion of the eyeball. The terms
exophthalmos and proptosis are often used interchangeably. Some use
exophthalmos to mean abnormal protrusion secondary to Grave's disease and
proptosis to mean abnormal protrusion secondary to any other cause (e.g. a
tumor).
Proptosis is measured from the bony orbital rim to the apex of the cornea:
Normal has been defined as protrusion in the 16 to 20mm range, although
exophthalmos and proptosis are sometimes defined to be protrusion greater than
18mm. In the clinical situation, the definition is not of much importance unless the
measurement is significantly greater than 20. On the first visit, the doctor may
want to get a baseline measurement which is subsequently compared to
measurements on future visits in order to monitor change over time. The patient
with significant proptosis does not need a measurement for confirmation of the
condition, the obvious 'bug eyed" appearance speaks for itself.
Proptosis can be monocular or binocular. Exophthalmos from Grave's disease is
usually bilateral. Proptosis from an orbital tumor is usually monocular. The globe
can be displaced straight out (axial proptosis) or it can be displaced in non-axial
directions. Axial displacement occurs from diffuse enlargement of the orbital soft
tissues and/or EOMs, or from a lesion in the orbital cone (directly behind the
globe). Non-axial displacement occurs when the globe is pushed away from the
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Module 49: The Orbit
sight of a lesion. For example, a downward/medial displacement can occur in the
presence of a lacrimal gland tumor.
The doctor must differentiate between true proptosis and pseudoproptosis. Very
nearsighted eyes (long axial length) can appear to be proptotic. A fellow eye can
falsely appear to be proptotic when the other eye is "sunken in" perhaps due to
enophthalmos, an orbital bone asymmetry post trauma, or a palebral fissure
asymmetry.
The ophthalmic assistant or technician can be assistance with the orbital eye
exam by measuring eye protrusion with the exophthalmometer. For a discussion
on the use of this instrument, see Module 29, Section 5.
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