Orbit Flashcards
Orbit anatomy
Look at diagram
Know bones surrounding orbit and the orbital openings
What is the orbital septum?
-The orbital septum is located anterior to the orbit and extends from the orbit
rims to the eyelid.
- It is a membranous sheet that forms the fibrous part of the eyelids.
- It is an important landmark as it marks the border between the periorbital
(preseptal) and orbital (postseptal) regions
Risk factors for thyroid eye disease
● Smoking
● Females
● HLA-DR3 and HLA-B8
Pathophysiology of Thyroid Eye Disease?
-Sympathetic overstimulation of the Müller muscle due to high levels of thyroid hormones causing eyelid retraction.
-Fibroblastic deposition of glycosaminoglycans into the EOM producing oedema and eventual fibrosis of EOM. This leads to:
-Impaired movement of EOM (restrictive myopathy).
-Exophthalmos which exposes the cornea causing dryness, irritation and exposure keratitis.
-Lid retraction due to fibrosis of levator palpebrae.
-Increased pressure on the optic nerve causing optic neuropathy.
-Impaired venous drainage leading to conjunctival and periorbital oedema and conjunctival injection
Clinical features of Thyroid eye disease
- Unilateral/bilateral axial proptosis, redness, chemosis and ocular irritation.
- Lid retraction (Dalrymple sign).
- Lid lag on downgaze (Von Graefe sign).
- ‘Staring’ appearance (Kocher sign).
- Restrictive myopathy: EOM is usually affected in the following order:
inferior rectus (IR), medial rectus (MR), superior rectus (SR), levator
palpebrae, lateral rectus (LR). - Choroidal folds (rare)
Investigations for Thyroid eye disease
- Thyroid function tests.
- Imaging
- CT or MRI are indicated if orbital decompression is planned, to help confirm
an equivocal diagnosis or if there is asymmetry on exophthalmometry. - Shows thickening of EOM bellies (most commonly IR and MR) with
characteristic tendon sparing. - Visual field testing is indicated, especially if optic neuropathy is suspected
Management for Thyroid eye disease
General measures
● Smoking cessation.
● Achieve euthyroid status.
Mild disease
● Watchful waiting.
● Ocular lubricants during day and overnight to avoid dryness and ulceration
of the cornea.
50 Orbit
● Topical ciclosporin to reduce ocular irritation.
● Overnight lid taping for mild exposure keratopathy.
● Selenium supplements can improve the course of TED (2).
Moderate-severe disease
● IV methylprednisolone ± oral prednisolone: Bisphosphonates should be
considered in patients receiving steroid therapy due to risk of osteoporosis.
It is important to check liver function in patients receiving high doses of IV
steroids.
● Orbital radiotherapy: Can be used in combination with steroids or when
steroids are contraindicated in patients with active TED complaining of
diplopia or restricted eye movements. Orbital irradiation can increase risk of
retinopathy in diabetic and hypertensive patients.
● Surgery
● Surgery is indicated after inflammatory phase subsides (i.e. in the
inactive phase), in cases of optic neuropathy, significant proptosis,
persistent diplopia or severe lid retraction.
● The following order is recommended if surgery is indicated:– Orbital decompression– Strabismus surgery– Eyelid surgery
Thyroid eye disease complications
- Dysthyroid optic neuropathy: Causes severe sight-threatening TED, suspect
if there are changes in colour vision or VA with presence of optic disc swelling and relative afferent pupillary defect (RAPD). Treatment is with IV steroids and orbital decompression (if unresponsive to IV steroids).
● Exposure keratopathy: Manage with lubricants, surgery (e.g. tarsorrhaphy)
or botulinum toxin injections.
● Superior limbic keratoconjunctivitis: A common association with TED
What is a Rhabdomyosarcoma?
Rhabdomyosarcoma is considered the most common primary orbital malignancy
in children. The mean age of onset is 8 years. The most common affected areas
are the genitourinary system and the head and neck (including orbit).
Histopathology of Rhabdomyosarcoma
This tumour has the ability to differentiate into striated muscle from undifferentiated mesenchymal cells. Embryonal is the most common subtype and is characterized by elongated spindle-shaped cells (‘strap cells’)
Clinical Features of Rhabdomyosarcoma
- Rapidly progressive unilateral proptosis.
- Most common location in the orbit is superonasal.
- Diplopia may occur
Investigation of Rhabdomyosarcoma
- MRI or CT: Shows a circumscribed mass ± bone erosion.
- Biopsy
Orbital cellulitis
Infection deep to the orbital septum
Features: proptosis, chemosis, limited eye movement.
Investigations: CT scan
Mx: IV antibiotics (ceftriaxone + flucloxacillin + metronidazole).
What is a Cavernous sinus Thrombosis?
Cavernous sinus thrombosis refers to a clot formation within the sinus and is mainly due to a spreading infection from the paranasal sinuses, ear or pre existing orbital cellulitis.
CLINICAL FEATURES
● Rapid-onset headache, nausea, vomiting, chemosis and dVA.
● Unilateral or bilateral proptosis.
● Diplopia due to CNIII, CNIV or CNVI compression. CNVI is first to be affected, as it lies freely within the cavernous sinus, causing a lateral gaze palsy.
Management of cavernous sinus thrombosis?
- Intravenous antibiotics, steroids and/or low-molecular-weight heparin.
- Surgical drainage
Investigations for cavernous sinus thrombosis
MRI and MRI venography to confirm diagnosis
What is a neuroblastoma?
This is the most common extracranial solid tumour in children and is derived from the neural crest cell of the sympathetic nervous system. It most commonly occurs in the adrenal medulla secreting catecholamines but can also involve the head, neck, chest abdomen or spine. It usually metastasises to the orbit.
● Histology: Homer-Wright rosettes.
● Clinical features: Child with unilateral/bilateral proptosis and periorbital ecchymosis (racoon eyes). Differential for basal skull fracture.
