Orbit Flashcards
how many bones in the orbit
7
2 bones forming roof of orbit
frontal bone
lesser wing of sphenoid
2 bones forming lateral wall of orbit
zygomatic bone
greater wing of sphenoid
3 bones forming floor of orbit
zygomatic bone
maxillary bone
palatine bone
4 bones forming medial wall of orbit
maxillary
lacrimal
sphenoid
ethmoid
what is the lamina papyracea
paper-thin plate which covers the ethmoidal cells and forms a part of the medial wall - can act as a route of entry for infection from the ethmoid sinus
3 orbital openings
optic foramen
superior orbital fissure (SOF)
inferior orbital fissure
where is the optic foramen and what does it transmit
within lesser wing of sphenoid
transmits optic nerve and ophthalmic artery into middle cranial fossa
where is the SOF and what are the 2 parts
between greater and lesser wings of sphenoid - superior and inferior part
what does the superior part of the SOF contain
superior ophthalmic vein
lacrimal nerve (CNV1)
frontal nerve (CNV1)
CNIV
what does the inferior part of the SOF contain
CNIII
nasociliary nerve (CNV1)
CNVI
where is the inferior orbital fissure and 3 things it contains
between maxilla and greater wing of sphenoid bone
infraorbital nerve (CNV2) zygomatic nerve (CNV2) inferior ophthalmic vein
what is the annulus of Zinn
common tendinous ring surrounding the optic canal and inferior part of the SOF - marks the origin of the 4 recti muslces
what 4 things run through the annulus of Zinn
CNII
CNIII
CNVI
nasociliary nerve
what does retrobulbar anaesthetic block do
affects the nerves inside the common tendinous ring / annulus of Zinn
where is the orbital septum located
anterior to the orbit and extends from the orbit rims to the eyelid - marks the border between the periorbital (preseptal) and orbital (postseptal) regions
what is the orbital septum
membranous sheet that forms the fibrous part of the eyelids
most common cause of unilateral and bilateral axial proptosis in adults
thyroid eye disease (TED) - usually associated with hyperthyroidism but can also involve hypo or euthyroid
2 phases of TED
active inflammatory phase (months-years) - eyes red and painful
inactive fibrotic phase - involves extraocular muscles and connective tissues
3 risk factors for TED
smoking
female
HLA-DR3 and HLA-B8
pathophysiology of TED
sympathetic overstimulation of Müller muscle due to high levels of thyroid hormones causing eyelid retraction
fibroplastic deposition of glycosaminoglycans into the EOM producing oedema and eventual fibrosis of EOM
3 things occurring in TED as a result of fibrosis of EOM
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 = optic neuropathy
impaired venous drainage = conjunctival and periorbital oedema and conjunctival injection
what is Dalrymple sign in TED
lid retraction
what is von Graefe sign in TED
lid lag on downgaze
what is Kocher sign in TED
‘staring’ appearance
usual order of EOMs affected in TED (restrictive myopathy)
inferior rectus (IR) medial rectus (MR) superior rectus (SR) levator palpebrae lateral rectus (LR)
1 rare clinical feature in TED
choroidal folds
3 investigations for TED
thyroid function tests
imaging (CT/MRI if orbital decompression is planned)
visual field testing, especially if ON suspected
what does CT/MRI usually show in TED
thickening of EOM bellies (most commonly IR and MR) with characteristic tendon sparing
3 classifications of TED
severe sight threatening (optic neuropathy)
moderate-severe (exophthalmos >3mm, lid retraction >2mm and/or diplopia)
mild disease
2 general measures for managing TED
smoking cessation
achieve euthyroid status
5 ways to manage TED mild disease
watchful waiting
ocular lubricants
topical ciclosporin (reduce ocular irritation)
overnight lid taping (for mild exposure keratopathy)
selenium supplements
3 ways to manage TED moderate-severe
IV methylprednisolone +/- oral prednisolone
orbital radiotherapy (can be used in combination with steroids)
surgery
5 times surgery is indicated in TED moderate-severe
after inflammatory phase subsides cases of optic neuropathy significant proptosis persistent diplopia severe lid retraction
3 complications and associations with TED
dysthyroid optic neuropathy - causes severe sight-threatening TED
exposure keratopathy
superior limbic keratoconjunctivitis (common)
when to suspect dysthyroid optic neuropathy
changes in colour vision or VA with presence of optic disc swelling and RAPD
treatment of dysthyroid optic neuropathy
IV steroids and orbital decompression (if unresponsive to IV steroids)
3 ways to manage exposure keratopathy
lubricants
surgery e.g. tarsorrhaphy
botox injections
what is preseptal cellulitis
infection of soft tissues anterior to orbital septum
what is orbital cellulitis
infection of soft tissues posterior to orbital septum
