mechanical limitations - MEH Flashcards
define a mechanical limitation
Restriction of ocular motility casued by elements within the orbit which interfere with muscle contraction and relaxation preventing movement
when you have a mechanical limitation what is duction equal to?
version
what does duction = version mean?
eye does not move when the other eye is occluded (i.e not an underaction)
what is a leash?
restraint interfering with muscle function
what are the 2 types of leash?
direct or indirect
what is a leash also known as ?
tether
what is a direct leash?
tight or shortened muscle/tendon
OM is limited when gaze is directed … from the leash (direct leash)
away
OM is limited when gaze is directed … the leash (indirect leash)
towards
what is an indirect leash?
blocking movement
examples of an indirect leash?
retinal explant or adhesions between the conjunctiva and orbit following trauma
characteristics of mechanical restrictions
1.+ve forced duction test
2.restriction of the globe
3.reversal of deviation in opposite gazes
4.limited muscle sequalae (steps 1&2)
what is thyroid eye disease also known as?
graves ophthalmopathy
there is an increased prevalence of co-existing autoimmune disorders in those with TED. what other condition should you consider?
myasthenia gravis
TED : autoimmune disease in which the eye muscles and fatty tissue behind the eye become inflamed
what is the pathology of TED?
- inflammatory process causes EOM belly to become enlarged
- this causes fibrosis leading to limited eye movement
- increased amount of soft tissue leads of proptosis
what does NO SPECS stand for?
1.No signs or symptoms
2.Only signs, no symptoms
3.Soft tissue involvement (signs & symptoms)
5.Proptosis
6.Extraocular muscle involvement
7.Corneal involvement
8.Sight loss (optic nerve involvement)
what is NO SPECS?
grades for clinical severity
how long does the active period of TED last for?
2 years
when is treatment given for TED?
within the active phase
what is important to remember about NO SPECS?
does not provide a means of distinguishing inflammatory progressive from non-inflammatory stationary
name the clinical characteristics of TED?
- inflamamtory signs of the eye and orbit
- conjunctival injection sometimes over the site of rectus muscle insertion
- chemosis
- lid oedema
- exophthalmos
OVER TIME: - EOM become restricted and fibrotic
- diplopia due ot asymmetrical limitations of OM
name some examination signs of TED?
- upper lid retraction
- reduced blinking freq
- lid lag on downgaze
- staring appearance
- exophthalmos
what increased the risk of TED by 7x?
smoking
what is the HES investigation of TED?
thyroid function tests (TSH, T3 , T4 levels)
CT scans and MRI scans useful in active disease (esp in unilateral proptosis to exclude orbital tumour)
why is VA affected in TED?
optic nerve gets compressed by grossly enlarged EOM
corneal involvement due to exposure
what are important tests to do in someone with TED?
VAs, cover test and colour vision testing
what is revealed on cover test? TED
hypotropia (due to IR fibrosis)
excyclotorsion (tight IR) esp on attempted elevation
eso devation (due to limited abduction caused by MR fibrosis)
potential AHP
what is a commonly found deviation on cover test?
eso + hypo