Lecture 20 mechanical limitations Flashcards
What is the definition of mechanical limitation?
Restriction of ocular motility caused by elements within the orbit which interfere with muscle contraction and relaxation preventing movement
What is the main feature of a mechanical limitation on ocular motility?
duction=version
This means there is no further improvement of eye movement when one eye is occluded compared to when both eyes are open.
What are the characteristics of a mechanical limitation?
*Positive forced duction test (FDT)
* Restriction of globe associated with narrowing palpebral aperture. Occurs when gaze is directed away from the site of the leash. Best seen by viewing affected eye from the side.
*Reversal of deviation in opposite directions of vertical and horizontal gaze. Also seen in 3rd CNP, myasthenia gravis, multiple CNP
*Limited muscle sequalae (often confined to overaction contralateral synergist in unaffected eye)
Any restraint interfering with muscle function can be direct or indirect.
describe these restraints
Direct
-tight or shortened muscle/tendon e.g., tightened conjunctiva or surrounding connecting tissue
- limit movement when the gaze is directed AWAY from the leash
-more common in clinical practice
Indirect
-blocking movement e.g., enlarged retinal explants of adhesion between conjunctiva and orbit following trauma
-limit eye movement when gaze is directed TOWARDS the leash
Which px does thyroid eye disease occur in?
*Common in hyperthyroid patients (85%)
*Can also present in hypothyroidism (10%)/euthyroid patients (5%)
* px who are having had thyroidectomy
What is the pathology behind thyroid eye disease?
*Inflammatory process affecting EOM and eyelids
*EOM bellies become enlarged
*Inflammation of EOM causes fibrosis and leads to limited eye movement
*Increased soft tissue volume causes proptosis.
What are the clinical characteristics of TED?
*Progressive active stage is characterised by inflammation and orbital tissue remodelling
*Conjunctival congestion
*Restricted strabismus
*Conjunctival injection sometimes over the site of rectus muscle insertion
*Chemosis
*Oedema of the lids
*Over time (1-2 yrs), inflammatory signs lessen
*EOM become restricted and fibrotic. (Commonly bilateral and symmetrical but can be unilateral+asymmetrical)
*Diplopia occurs due to asymmetrical limitations of OM
What are the examination signs of TED?
*Upper lid retraction: accentuated by proptosis and in attempted up gaze when the inferior recti are tight
*Reduced frequency of blinking (need lubricating drops daily)
*Lid lag on down gaze
*Staring appearance
*Exophthalmos
What modifiable factor increases risk of TED?
smoking
How should you investigate TED?
MRI/CT scan to exclude orbital tumours
check VA and colour vision (optic nerve compression by enlarged EOM can cause sight loss)
WHat can you expect to find on cover test in someone with TED?
*IR fibrosis causes limited elevation: hypotropia in PP
*Tight IR causes small degree of excyclotorsion, especially on attempted elevation
*MR fibrosis causes limited abduction: esotropia
*Common to have eso and hypo deviation together
*Deviation can be manifest or latent
*May or may not have abnormal head posture
What is the optometric management of TED?
*Preservation of sight is priority: need to monitor vision and colour vision routinely
*Watch for stabilisation ocular motility
*Centralise and enlarge BSV field so AHP not needed: prisms, bangerter foil on glasses/patch
What is the medical management of ted?
Topical therapy
*Artificial tears and decongestants. Useful for chemosis and conjunctival injection.
*May need to tape eyes closed at night
*May benefit from tinted specs if there distressed by their proptosis
*Selenium supplementation: trace mineral rich in natural sources found in seafood, muscle meat and Brazil nuts has been shown to slow progression in px with mild thyroid issues or reducing ocular involvement in TED.
High dose Steroids
*Are not disease modifying
*Reduces inflammation in active phase until body passes into stable phase.
*Reducing inflammation reduces the pressure on the optic nerve.
*Intravenous steroids more effective than oral steroids. More rapid onset.
*Reduce soft tissue swelling, EOM restriction and relieve optic nerve compression
Radiotherapy treatment
*Helpful in px with persistent inflammation in active disease
*Synergistic with steroids. Combined effect is better than them alone
*Used in early stages of disease due to sensitivity of orbital lymphocytes to radiation.
Immunosuppressive therapy
*Improves congestive changes
What is the surgical management of TED?
decompression surgery
strabismus surgery-cosmetic
lid surgery
What is the aetiology of orbital injuries?
*Blunt trauma to orbit by objects of diameter more than 5cm.
