The Orbit
Anatomy
The orbit is a pear-shaped cavity, the stalk of which is the optic canal.
• The roof consists of two bones: the lesser wing of the sphenoid and the
orbital plate of the frontal bone. It is located subjacent to the anterior
cranial fossa and the frontal sinus. A defect in the orbital roof may cause
pulsatile proptosis due to transmission of cerebrospinal fluid pulsation to the
orbit.
• The lateral wall also consists of two bones: the greater wing of the sphenoid
and the zygomatic. The anterior half of the globe is vulnerable to lateral
trauma since it protrudes beyond the lateral orbital margin.
• The floor consists of three bones: the zygomatic, maxillary and palatine. The
posteromedial portion of the maxillary bone is relatively weak and may be
involved in a ‘blowout’ fracture. The orbital floor also forms the roof of the
maxillary sinus so that maxillary carcinoma invading the orbit may displace the
globe upwards.
• The medial wall consists of four bones: maxillary, lacrimal, ethmoid and
sphenoid. The lamina papyracea, which forms part of the medial wall, is paper-
thin and perforated by numerous foramina for nerves and blood vessels.
Orbital cellulitis is therefore frequently secondary to ethmoidal sinusitis.
• The superior orbital fissure is a slit linking the cranium and the orbit,
between the greater and lesser wings of the sphenoid bone; through it pass
numerous important structures.
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The superior portion contains the lacrimal, frontal and trochlear nerves, and
the superior ophthalmic vein.
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The inferior portion contains the superior and inferior divisions of the
oculomotor nerve, the abducens and nasociliary nerves, and sympathetic fibres
from the cavernous plexus.
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Inflammation of the superior orbital fissure and apex (Tolosa–Hunt syndrome)
may therefore result in a multitude of signs including ophthalmoplegia and
venous outflow obstruction.
• The inferior orbital fissure lies between the greater wing of the sphenoid
and the maxilla, connecting the orbit to the pterygopalatine and infratemporal
fossae. Through it run the inferior ophthalmic vein.
Clinical signs of orbital disease:
1.soft tissue involvement: lid and periorbital edema, ptosis (mechanical ptosis
due to swelling leading to heaviness of the lid) , conjunctival chemosis (edema)
and conjunctival injection.
2. proptosis: it is an abnormal protrusion of the globe which may be caused by
retro bulbar lesion which push globe forward or less frequently a shallow orbit
which is usually congenital. When it is asymmetrical it is best detected by
looking down on the patient from above and behind.
•
Direction of proptosis may indicate the possible pathology.eg a SOL
within the extra ocular muscle cone (optic nerve glioma) causes axial
proptosis whereas an extraconal mass would push the globe away from
its site causing eccentric proptosis e.g. lacrimal gland adenoma.
•
Severity of proptosis can be measured by a simple plastic ruler resting
on the lateral orbital margin or using an Hertel exopthalmometer (a
plate attached to it 2 mirrors placed at 45 degree). normally ,the apex
of the cornea is about 20mm anterior to lateral orbital margin, and
anything more than 21 mm is considered proptosis, and >2mm difference
between the two eye balls is suspicious regardless to the absolute value.
Proptosis can be graded as mild (21-23mm), moderate (24-27mm) or
severe (28mm and more).
•
Pseudoproptosis or false impression of proptosis may be due to facial
asymmetry, severe ipsilateral enlargement of the eye ball (high myopia
or buphthalmos), ipsilateral lid retraction or contra lateral
enophthalmos.
3. Enophthalmos: recession of the globe within the orbit.
Causes: a. structural abnormalities of the orbital walls e.g. blow out
fracture. b. atrophy of the orbital contents e.g. following radiotherapy. c.
cicatrizing orbital lesions e.g. schirrous carcinoma.
Pseudo enophthalmos may be caused by microphthalmia or pthiasis bulbi.
4.ophthalmoplegia: defective ocular motility may be caused by an orbital mass,
restrictive myopathy as in thyroid eye disease, ocular motor nerve lesion or
entrapment of the muscle or its fascia in a blowout fracture.
5.visual dysfunction: impaired vision can be caused by: A/ Exposure
keratopathy secondary to severe proptosis. B/ Compressive optic
neuropathy. C/ Choroidal folds
6.ocular signs:
•
Optic disc changes such as optic atrophy which is usually preceded by
swelling. It is due to compressive optic neuropathy
•
Choroidal folds seen as striae or lines at the posterior pole due to
pressure by orbital mass. they sometimes proceed the onset of proptosis
•
Retinal vascular changes such as venous dilatation and tortuosity or
vascular occlusion
8.dynamic properties
•
Increased venous pressure by Valsalva maneuver or jugular compression
may exacerbate proptosis secondary to orbital venous anomalies.
•
Pulsation of the orbital contents or the globe can accompany an
arteriovenous communication or orbital roof defect
•
Bruit is a sign of carotid-cavernous fistula
Special investigations:
The following investigations can help to locate an orbital lesion or to define the
consistency of a SOL: 1.plain radiography. 2.CT scan. 3.MRI. 4.Fine needle
biopsy under CT guidance.
THYROID EYE DISEASE
Thyroid eye disease (TED), also known as thyroid-associated orbitopathy and
Graves ophthalmopathy, is a very common orbital disorder, and is the most
common cause of both bilateral and unilateral proptosis in an adult.
Risk factors for ophthalmopathy
Once a patient has Graves disease, the major clinical risk factor for developing
TED is smoking. Women are five times more likely to be affected by TED than
men. Radioactive iodine used to treat hyperthyroidism can worsen TED. TED
can also, though less commonly, occur in euthyroid and hypothyroid (including
treated hyperthyroid) patients. It can sometimes be the presenting
manifestation of thyroid-related disease.
Pathogenesis of ophthalmopathy
Thyroid ophthalmopathy involves an organ-specific autoimmune reaction in
which an antibody that reacts against thyroid gland cells and orbital
fibroblasts leads to inflammation of extraocular muscles, interstitial tissues,
orbital fat and lacrimal glands characterized by pleomorphic cellular
infiltration, associated with increased secretion of glycosaminoglycans and
osmotic imbibition of water. There is an increase in the volume of the orbital
contents, particularly the muscles, which can swell to eight times their normal
size. There may be a secondary elevation of intraorbital pressure, and the
optic nerve may be compressed. Subsequent degeneration of muscle fibres
eventually leads to fibrosis, which exerts a tethering effect on the involved
muscle, resulting in restrictive myopathy and diplopia.
Clinical features:
TED typically proceeds through a congestive (inflammatory) stage in which the
eyes are red and painful; this tends to remit within 1–3 years and only about
10% of patients develop serious longterm ocular problems. A fibrotic
(quiescent) stage follows in which the eyes are white, although a painless
motility defect may be present. Clinical features broadly can be categorized
into (i) soft tissue involvement, (ii) lid retraction, (iii) proptosis, (iv) optic
neuropathy and (v) restrictive myopathy.
(I) Soft tissue involvement:
• Symptoms. Grittiness, red eyes, lacrimation, photophobia, puffy lids and
retrobulbar discomfort.
• Signs may include:
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Epibulbar hyperaemia.
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Periorbital swelling is caused by oedema and infiltration behind the orbital
septum; this may be associated with chemosis and prolapse of retroseptal fat
into the eyelids.
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Tear insufficiency and instability is common.
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Corneal signs are exacerbated by lid retraction and can include punctate
epithelial erosions, superior limbic keratoconjunctivitis, and occasionally
bacterial keratitis, thinning and scarring.
(II) Lid retraction:
Retraction of upper and lower lids occurs in about 50% of patients with Graves
disease. Humorally induced overaction of Müller muscle is postulated to occur
as a result of sympathetic overstimulation secondary to high levels of thyroid
hormones. Fibrotic contracture of the levator palpebrae and inferior rectus
muscles associated with adhesion to overlying orbital tissues is another
probable mechanism, together with secondary overaction in response to hypo-
or hypertropia produced by fibrosis.
• Symptoms. Patients may complain of a staring or bulging eyed appearance,
difficulty closing the eyes and ocular surface symptoms.
• Signs
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The upper lid margin normally rests 2 mm below the limbus. Lid retraction is
suspected when the margin is either level with or above the superior limbus,
allowing sclera to be visible (‘scleral show’).
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The lower eyelid margin normally rests at the inferior limbus; retraction is
suspected when sclera shows below the limbus. Lid retraction may occur in
isolation or in association with proptosis, which exaggerates its severity.
(III) Proptosis :
• Symptoms are similar to those of lid retraction.
• Signs. Proptosis is axial, unilateral or bilateral, symmetrical or asymmetrical,
and frequently permanent. Severe proptosis may compromise lid closure and
along with lid retraction and tear dysfunction can lead to exposure
keratopathy, corneal ulceration and infection.
(IV) Restrictive myopathy:
Between 30% and 50% of patients with TED develop ophthalmoplegia and this
may be permanent. Ocular motility is restricted initially by inflammatory
oedema, and later by fibrosis.
• Symptoms. Double vision, and often discomfort in some positions of gaze.
• Signs, in approximate order of frequency:
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Elevation defect caused by fibrotic contracture of the inferior rectus, is
the most common motility deficit.
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Abduction defect due to fibrosis of the medial rectus, which may simulate
sixth nerve palsy.
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Depression defect secondary to fibrosis of the superior rectus.
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Adduction defect caused by fibrosis of the lateral rectus.
(V) Optic neuropathy:
Optic neuropathy is a serious complication caused by compression of the
optic nerve or its blood supply at the orbital apex by the congested and
enlarged recti and swollen orbital tissue. Such compression, which may occur
in the absence of significant proptosis, may lead to severe visual impairment
if adequate and timely treatment is not instituted.
• Symptoms. Impairment of central vision occurs in conjunction with other
symptoms of TED.
• Signs. A high index of suspicion should be maintained for optic neuropathy:
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Visual acuity (VA) is usually reduced.
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Colour desaturation.
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There may be diminished light brightness appreciation.
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A relative afferent pupillary defect.
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Visual field defects can be central or paracentral and may be combined with
nerve fibre bundle defects. These findings, in concert with elevated IOP, may
be confused with primary open-angle glaucoma.
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The optic disc may be normal, swollen or, rarely, atrophic.
Investigation
Investigations other than blood tests for thyroid disease are not necessary if
the diagnosis is evident clinically, but the exclusion of other conditions is
sometimes indicated. Visual field testing is carried out if there is a suspicion
of optic nerve compromise. MRI, CT and ultrasonographic imaging of the orbits
are indicated in some circumstances, such as helping to confirm an equivocal
diagnosis by identification of the typical pattern of extraocular muscle
involvement in TED, consisting of muscle belly enlargement with tendon
sparing. Imaging is also used in the assessment of optic nerve compression and
prior to orbital wall surgery. Visual evoked potentials are sometimes utilized in
optic neuropathy.
Treatment
Treatment can be classified into that of mild disease (most patients),
moderate to severe active disease, and treatment of post inflammatory
complications. The first measure taken in all cases should be the cessation of
smoking. Thyroid dysfunction should also be managed adequately; if radioiodine
treatment is administered in patients with pre-existing TED, a short course of
oral steroids should be given in concert.
• Mild disease
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Lubricants for superior limbic keratoconjunctivitis, corneal exposure and
dryness.
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Topical anti-inflammatory agents (steroids, NSAIDs, ciclosporin).
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Head elevation with three pillows during sleep to reduce periorbital oedema.
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Eyelid taping during sleep may alleviate mild exposure keratopathy.
Moderate to severe active disease
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Systemic steroids are the mainstay of treatment for moderate to severe
disease. Oral prednisolone may be given initially, and tapered depending on
response. Intravenous methylprednisolone is often reserved for acute
compressive optic neuropathy.
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Orbital steroid injections are occasionally used in selected cases to
minimize systemic side effects, but are typically considerably less effective
than systemic treatment.
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Low-dose fractionated radiotherapy may be used in addition to steroids or
when steroids are contraindicated or ineffective, but because of the delayed
effect is not used as the sole treatment of acute optic nerve compression. A
positive response is usually evident within 6 weeks, with maximal improvement
by 4 months; around 40% will not respond. Adverse effects include cataract,
radiation retinopathy, optic neuropathy and an increased risk of local cancer;
the threshold for its use should be higher in younger patients and diabetics,
the latter because of a possibly increased risk of retinopathy.
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Combined therapy with irradiation, azathioprine and low-dose prednisolone
may be more effective than steroids or radiotherapy alone.
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Optic neuropathy, and less commonly intractable corneal exposure, requires
aggressive treatment. Pulsed intravenous methylprednisolone is commonly used,
followed by oral prednisolone. Orbital wall decompression and/or orbital apex
decompression may be considered if steroids are ineffective or
contraindicated. Orbital radiotherapy may also be administered, but is
generally only used as an adjunct to other modalities.
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Drugs targeting the immune response in TED are used like rituximab.
• Post-inflammatory complications. Eyelid surgery should be performed only
after any necessary orbital and then strabismus procedures have been
undertaken, as orbital decompression may impact both ocular motility and
eyelid position, and extraocular muscle surgery may affect eyelid position.
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Proptosis. After active inflammation has remitted, Surgical decompression
increases the volume of the orbit by removing the bony walls and may be
combined with removal of orbital fat. One-wall; two-wall; three-wall and four-
wall decompression may be done.
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Restrictive myopathy. Surgery is required in most cases, provided the
inflammatory stage has subsided and the angle of deviation has been stable
for at least 6–12 months. Recession of the inferior and/or medial recti is the
most commonly indicated surgery.
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Lid retraction. Mild lid retraction frequently improves spontaneously so
does not require treatment. Botulinum toxin injection to the levator
aponeurosis and Müller muscle may be used. Müllerotomy is effective for mild
lid retraction, but more severe cases may also require recession/disinsertion
of the levator aponeurosis and the suspensory ligament of the superior
conjunctival fornix.
Preseptal cellulitis
Preseptal cellulitis is an infection of the subcutaneous tissues anterior to the
orbital septum. It is considerably more common than orbital cellulitis, and
though regarded as less serious, can still be associated with severe
complications such as abscess formation, meningitis and cavernous sinus
thrombosis. Rapid progression to orbital cellulitis may occasionally occur.
Organisms typically responsible are Staphylococcus aureus and Streptococcus
pyogenes, with causes including skin trauma such as laceration or insect bites,
spread from focal ocular or periocular infection such as an acute hordeolum,
dacryocystitis, conjunctivitis or sinusitis, and haematogenous spread from
remote infection such as the upper respiratory tract or middle ear.
Diagnosis
The condition manifests with a swollen, often firm, tender red eyelid that may
be very severe; however, in contrast to orbital cellulitis, proptosis and
chemosis are absent, and visual acuity, pupillary reactions and ocular motility
are unimpaired. The patient is often pyrexial. Imaging with MRI or CT is not
indicated unless orbital cellulitis or a lid abscess is suspected, or there is a
failure to respond to therapy.
Treatment
Treatment is with oral antibiotics such as co-amoxiclav. Severe infection may
require intravenous antibiotics.
Bacterial orbital cellulitis
Bacterial orbital cellulitis is a serious infection of the soft tissues behind the
orbital septum, which can be sight- and life-threatening. It can occur at any
age but is more common in children. Streptococcus pneumoniae,
Staphylococcus aureus, Streptococcus pyogenes and Haemophilus influenzae
are common causative organisms, with infection originating typically from the
paranasal (especially ethmoid) sinuses. Infection can also spread from
preseptal cellulitis, dacryocystitis, midfacial skin or dental infection, and can
follow trauma, including any form of ocular surgery. Blood-borne spread from
infection elsewhere in the body may occur.
Clinical features
• Symptoms consist of the rapid onset of pain exacerbated by eye movement,
swelling of the eye, malaise, and frequently visual impairment and double vision.
There is commonly a recent history of nasal, sinus or respiratory symptoms.
• Signs
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Pyrexia, often marked.
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VA may be reduced and colour vision impaired, raising the possibility of
optic nerve compression; the presence of a relative afferent pupillary defect
in a previously normal eye makes this almost certain.
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Tender, firm, erythematous and warm eyelids, with periocular and
conjunctival (chemosis) oedema, conjunctival injection and sometimes
subconjunctival haemorrhage; the signs are usually unilateral, though oedema
may spread to the contralateral eyelids.
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Proptosis is common in established infection, but is often obscured by lid
swelling; it may be non-axial (dystopia), particularly if an abscess is present.
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Painful ophthalmoplegia.
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Choroidal folds and optic disc swelling may be present on fundus
examination.
Investigations may include:
• White cell count.
• Blood cultures.
• Culture of nasal discharge.
• High-resolution CT of the orbit, sinuses and brain.
• Lumbar puncture if meningeal or cerebral signs develop.
Treatment
• Hospital admission is mandatory, with urgent otolaryngological assessment
and frequent ophthalmic review.
• Antibiotics are given intravenously, ceftazidime is a typical choice,
supplemented by oral metronidazole to cover anaerobes.
• Monitoring of optic nerve function is performed at least every 4 hours
initially by testing VA, colour vision, light brightness appreciation and pupillary
reactions. Deterioration should prompt the consideration of surgical
intervention.
• Surgery. Drainage of an orbital abscess should be considered at an early
stage; drainage of infected sinuses should be considered if there is a lack of
response to antibiotics, or if there is very severe sinus disease. Biopsy of
inflammatory tissue may be performed for an atypical clinical picture. Severe
optic nerve compression may warrant an emergency canthotomy/cantholysis.
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