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.
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.
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• 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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