Incomitancy investigation Flashcards
1
Q
what is incomitancy
A
Strabismus which varies in size with position of gaze
2
Q
list 4 things about incomitancy
A
- Manifest or latent
if latent in primary position often becomes larger or manifest as eyes move into other positions of gaze - Congenital or acquired in aetiology
- Unilateral or bilateral (unilateral more common)
- Angle may vary with the eye used for fixation
3
Q
how must you monitor a px whose latent in primary position but becomes manifest as their eyes move into other positions of gaze
A
monitor the change with a prism bar
4
Q
describe the incomitancy in a 6th nerve palsy
A
- Right gaze, eyes are straight with binocular single vision (BSV)
- Left gaze diplopia due to left esotropia
- The angle measured in left side gaze compared to primary position is larger than the angle you would measure in right gaze
5
Q
give an example of a condition and describe what it is, where incomitancy effects the vertical muscle
A
- Brown’s syndrome
- Caused by the shortening of the SO tendon
- When px looks upward in adduction, the short SO prevents the eye from elevating
- So px ends up with a large vertical deviation which doesn’t occur in down gaze
6
Q
when may incomitancy be present in congenital cases and why
A
- may present at any age, not always starting from birth, can even come during 20’s - 30’s or first 6 months
- due to some sort of neurogenic problem from 3rd, 4th or 6th nerve
7
Q
what will you do if you see a patient with a congenital incomitancy
A
depending on signs and symptoms may refer to HES
8
Q
what is acquired incomitancy and what is it associated with
A
- when the incomitancy comes suddenly
- associated with neurological damage and significant medico-legal implications who may require medical intervention and intervention to manage the squint in the long run
9
Q
what will you do if you see a patient with an acquired incomitancy
A
referral is essential
10
Q
what is the aetiology of incomitancy classified as and what 4 are these
A
- classified according to the underlying cause:
- Neurogenic (strabismus due to nerve lesion)
or - Myogenic (lesion directly affecting the muscle)
or - Mechanical (lesion within the orbital that interferes with muscle action)
or - Congenital or acquired incomitant squint
11
Q
what is a neurogenic cause of a incomitancy also known as
A
- Also known as paralytic
- paralysis – total failure of nerve; paresis – partial failure; palsy covers both
12
Q
list 4 possible places lesions can occur with a neurogenic incomitancy
A
- infranuclear
- nuclear
- internuclear
- supra nuclear
13
Q
a neurogenic incomitancy can be __________ or __________
A
a neurogenic incomitancy can be congenital or acquired
14
Q
list 4 acquired causes of a neurogenic incomitancy
A
- vascular - hypertension, diabetes, aneurysm
- head trauma – road traffic accident, falls from horse
- tumour - intracranial
- inflammation – meningitis, encephalitis, multiple sclerosis
15
Q
at which distance does a LR palsy affect more and why
A
- affects abduction more at distance than near
- because our LR aren’t very involved in focussing at near
16
Q
what is the most common type of classification of acquired aetiology of incomitancy and name an example of a condition
A
- Myogenic (lesion directly affecting the muscle)
- Myasthenia gravis
17
Q
what effect to the muscle does a mechanical lesion cause and name examples of some conditions that cause this to happen
A
- Lease or tether effect
- Acquired – thyroid eye disease, orbital bone fractures, space-occupying lesion within orbit
18
Q
what is the common aetiology of a congenital incomitancy
A
commonly is developmental failure affecting muscle / tendon
19
Q
what is the common aetiology of a acquired incomitancy
A
abnormality of nerve
20
Q
why do we need to investigate the signs of an incomitancy
A
to see if we can manage for the long term, or if the patient needs a hospital investigation
21
Q
what is seeing the signs of muscle sequelae important for
A
understanding and diagnosis of incomitant strabismus
22
Q
whats is Hering’s law
A
Equal and simultaneous contraction of contralateral synergist muscles (related to both eyes)
23
Q
what is Sherrington’s law
A
Agonist muscle contracts with equal and simultaneous relaxation of direct antagonist (same eye)
24
Q
list the muscle sequelae for a RSO under action
A
- Primary muscle underaction (RSO)
- Overaction (contracture) of contralateral synergist (LIR)
- Overaction (contracture) of direct antagonist (RIO)
- Secondary inhibitional palsy of antagonist to contralateral synergist (LSR)
25
which stages of muscle sequelae don't need emergency care
later stages - which indicates it was long standing
26
with which 2 classifications of aetiology does a full muscle sequelae develop with time
neurogenic and myogenic incomitance
27
what is difficult to differentiate with a congenital muscle sequelae
primary from secondary palsy e.g. SO vs SR
28
how far does a muscle sequelae usually go with a mechanical aetiology
just up till the first stage, wont see much of a secondary stage
29
describe three characteristics of a RLR under action which may be due to a 6th nerve trauma
- Esophoria/esotropia, worse on distance fixation and in direction of action of RLR– i.e. to RT
- Horizontal diplopia worse in dextroversion (gaze towards the RHS)
- also >FR since recently acquired (secondary deviation)
you get a big squint with the affected eye in recent muscle sequelae
30
explain how you will distinguish if the origin of a RLR under action is mechanical or neurogenic
- cover up the left eye and move the torch even further out to get the px to move their eye further out
- if the corneal reflections have moved and you observe better excursions monocularly then = neurogenic
- if it was mechanical, then you won't see a change in the corneal reflections
- this is how you differentiate between a 6th nerve palsy or a problem with the muscle
- as with a mechanical problem, the eyes won't move further out monocularly or binocularly
31
describe three characteristics of a LIR under action which may be myogenic and caused by Myasthenia gravis
- L hyperphoria / tropia (L/R) in primary position, increasing in size in laevodepression
- Vertical diplopia > in laevodepression
- Also >FL since recently acquired (secondary deviation)
32
describe three characteristics of limited elevation of both eyes but > RE, due to TED
- R hypophoria/tropia (L/R) in primary position, increasing on elevation
- Vertical diplopia > in elevated positions (due to tight IR)
- Also >FR (secondary deviation)
33
describe three characteristics of a right orbital floor fracture
- LE goes higher than RE on up gaze
- BSV in primary position
- RE goes less lower than LE on downsize
so right eye doesn't go down or up fully
34
in an incomitant squint, when is the angle maximum and explain how you will analyse this in vertical deviations
- when the eyes are in the affected gaze position
- consider the position of gaze in which the VERTICAL action of the muscle is greatest
E.g. obliques in adduction, vertical recti in abduction
35
what are the 4 aims of investigating an incomitancy
- Differential diagnosis
Mechanical vs non-mechanical (neurogenic or myogenic)
Congenital, longstanding vs. acquired
- Assess stability or monitor change of ophthalmoplegia
- Presence and strength of binocular vision
- Temporary management i.e. referring on or making more comfortable
36
The greater the degree of incomitance....
the more recent the onset – i.e. the angle of deviation varies++ in different positions of gaze and fixing with the affected or unaffected eye
37
In mechanical incomitance the limitations are seen in...
affected eye with the corresponding overactions in the unaffected eye in the same direction of gaze (i.e. the contractures due to Hering’s law)
i.e. you don't get the same amount of muscle sequelae
38
when can signs and symptoms occur with a congenital incomitancy
Signs and symptoms can occur at any age and were always aware that they had a squint/lazy eye
39
what consequences will an acquired aetiology of incomitancy have
- Significant and life threatening consequences and referral to ophthalmologist is essential
- Medico-legal implications
40
list 3 possible cosmetic appearances of a congenital incomitancy
- abnormal head movements
- squint
or
- head posture
41
what symptoms will a patient with congenital incomitancy have, and name some examples
- Symptoms of decompensation:
- Blurred vision, diplopia but often suppress, increasing squint, headaches
- In childhood may not be symptomatic as suppressing
- General health may be a trigger i.e. physical poor health
42
a __________ presentation of incomitancy may be opportunistic, whereby the patient is ___________
a congenital presentation of incomitancy may be opportunistic, whereby the patient is asymptomatic
43
list 5 signs/symptoms of an acquired incomitancy
- Diplopia
can describe if horizontal or vertical, RARELY torsional i.e. the patient knows they got diplopia
- BSV present if move head in a specific way
- Possible pain on eye movements e.g. from TED/inflammation of eye muscles
- Known onset – neurosurgery, stroke, trauma
- Previous episodes e.g. remitting and recurring in patients with diabetes/microvascular disease
44
list 3 causes of a non-ocular AHP
- Shyness
- Abnormalities of neck muscle or cervical vertebrae
- Unilateral deafness
45
list 6 reasons why an AHP is used
- Used to compensate (entirely or partially) for the deviation
- Development or maintenance of BSV
- Centralise field of BSV or visual field
- Avoid direction of gaze in which pain or discomfort
- Null zone for nystagmus
- Ptosis i.e. lift chin up, so they look underneath the lid
46
if a patient has diplopia in every direction of gaze e.g. total 3rd nerve palsy, why may they use an AHP
to use the nose as an occluder e.g. lift chin up or down
47
what is an AHP
Compensatory head posture (CHP) to place eyes in a position of gaze where deviation least
48
list the 3 components of an AHP
- Face turn (FT)
- Head tilt to one shoulder (HT)
Cyclotropia
Vertical deviation
- Chin up or down
49
what is the rules of an AHP for horizontal deviations e.g. an eso which is larger in left gaze
ESO > on left gaze (laveoversion) = face turn (FT) to left puts eyes into right gaze (dextroversion)
e.g. a classic 6th nerve palsy or a Mr/LR trauma
50
what are the rules of an AHP for a vertical deviation e.g. a RSR under action
- FT in direction of vertical action of muscle e.g. RSR – FT to right
- HT towards lower eye (may also compensate for torsion) e.g. RSR – HT to right
- Chin in direction of worst affected gaze position e.g. RSR, chin up (eyes down)
51
what will be the AHP for a child with type B Duane's syndrome and right eye affected
- Face turn right to move eyes to left
| - Without AHP in primary position: RET
52
which type of patients are usually unaware of their AHP
Congenital incomitance patients
53
how can you investigate if a px has an AHP from congenital incomitance
- Family album tomography (FAT) - this way you can see if the e.g. 4th nerve is decompensating or whether it is a general health problem such as undiagnosed diabetes or hypertension. ask px to bring an old photo in to see if they always had that AHP
- If you straighten head the patient feels that the head is not in a comfortable position and hard to maintain, at times may complain of diplopia with head straight
54
which 2 types of patients may be aware of their AHP and what may they complain of
- Decompensating congenital conditions or recently acquired may be aware of AHP
- may complain of neck ache as AHP increases to try to maintain control of deviation
55
list 3 reasons where it may not be possible to benefit from an AHP
- In large angle acquired incomitance
- Diplopia may be too variable
Total third nerve palsy
Use nose to occlude diplopia
- Can’t overcome significant torsion of 6-8 degrees
56
list 4 things you can do to assess the incomitancy of a px
- cover test
- ocular motility
- diplopia chart
- hess chart
57
list 3 things you will do when assessing incomitancy with a cover test
- Test with and without AHP in primary position
- For 1/3m and 6m
- Record results with and without AHP
and establish if doing for a ocular or non ocular cause
58
list 4 things you will do when assessing incomitancy with ocular motility and how must you do the ocular motility and why
- Test without AHP
- Smooth pursuits
- Versions and ductions
- Saccades
- head must be straight for testing OM, as the AHP may mask these vertical or horizontal movements/deviations
59
at which position is it better to do the cover test first when assessing incomitancy and why
- better to do before straightening the AHP
- because if you straighten their head then ask them to go back to the way they held their head/AHP, if they got poor fusion range, then your not going to know what the AHP is for
60
list 5 facts about deviation and ocular motility due to neurogenic cause
- Deviation in primary position reflects the extent of palsy e.g. large deviation in pp reflects the extent of the palsy and means theyre likely to have a great under action of that primary acting muscle
- Duction movement is greater than versions
- Saccadic movement may be slow in paretic eye
- No globe retraction
- AHP tilt common in vertical muscle palsies
61
list 5 facts about deviation and ocular motility due to mechanical causes
- Often small deviation in primary position
- Duction movement same as versions
- Saccadic movement the velocity is normal until point of limitation occurs
- Maybe globe retraction, pain or discomfort
- AHP tilt is rare
62
why is there often a small deviation in primary position with mechanical incomitancy compared to larger ones seen in neurogenic
- because they only have one stage of muscle sequelae, so if they can't depress their eye, the only muscle sequelae you will see is the overreaction of the other eye to try and compensate
- their CT in primary position tends to be more subtle
- this is another way you can differentiate this between a neurogenic cause
- the small deviation also means that an AHP is more likely seen in neurogenic and less in mechanical causes
63
what do patients with a long standing neurogenic muscle sequelae tend to have and how do you see this
- large fusion range
| - seen with prism bars
64
what does a diplopia chart do and how is it used
- it maps out the 9 positions of gaze and any double vision
- put on red and green glasses so px can see crossed or uncrossed diplopia
- larger separation of lines shows in which gaze the larger problem is in
65
why use a Hess chart to assess incomitancy
As it allows ocular movements to be represented graphically using a Hess or Lees test
66
how is a Hess chart used i.e. what will you instruct your patient
Patient asked to identify position of fixation spots in different gaze positions and results plotted on paper chart
67
list 3 things a patient must have to be able to use a Hess chart to assess their incomitancy
- Foveal fixation
- Normal retinal correspondence
- Sufficient vision in either eye to locate fixation spots
68
list 3 values of using a Hess chart to assess incomitancy
- Demonstrate muscle sequelae
- Assists in differential diagnosis
congenital vs recent acquired
Mechanical vs neurogenic vs myogenic
- Shows which eye is affected
69
list 4 things that the interpretation of the Hess chart shows
- Indicate stability, recover, deterioration
- Shows approx angle of deviation in any gaze position
- Position
Central dot indicates deviation in primary positions
Each square is equal to 5 degrees = can judge the angle without doing a PCT
Position of fields reflects position of the eyes i.e. higher field belongs to higher eye
- Size
Smaller field belongs to the affected eye
- Shape of outer field
Sloping fields denote A or V pattern
70
list 5 things that the size of the field shows in a Hess chart
- Smaller field belongs to the affected eye
- Under action is seen with an inward displacement of dots (max. displacement is due to affected muscle)
- Look for muscle sequelae
In the smaller field – overaction of direct antagonist
In the larger field – look for overaction contralateral synergist and secondary inhibitional palsy
So you can establish whats the primary under acting muscle, showing Herrings and Sherringtons law
- Narrow field restricted in opposing directions denotes a mechanical restriction of motility
- Equal size field denotes
Symmetrical limitation of OM of both eyes
Non-paralytic strabismus (or one that has become concomitant with time)
71
what does a Hess chart not show and why
- does not show torsion
| - because the px is looking at a single spot so can't see if its rotated
72
what is the field of BSV measured using
an arc perimeter
73
what does the field of BSV demonstrate
the area of BSV
74
how is a field of BSV used
- px looks at a spot
- px to tell you when it becomes double
- rotate it 360 degrees
- repeat on px evetytime to ensure stability
- if theres a change, this suggests something is going on and must refer px to Hes
- if constant and asymptomatic then you can monitor that patient in an optical point of view
