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Incomitancy - MEH Flashcards

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1
Q

What is the definition of incomitancy?

A

The angle of deviation varies in size (can be larger or smaller) in different positions of gaze + the angle of deviation is greatest in the direction of limitation of eye movement

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2
Q

What are two ways to classify incomitancy?

A

Acquired and congenital

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3
Q

What is essential with acquired incomitancies?

A

Referral is essential as it requires further investigation

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4
Q

What are four ways incomitant strabismus is classified?

A
  • Neurogenic
  • Myogenic
  • Mechanical
  • Dysinnervational
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5
Q

How is a neurogenic incomitant strabismus caused?

A

A lesion with the nerve supplying the muscle

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6
Q

How is a myogenic incomitant strabismus caused

A

A lesion directly affecting the muscle itself

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7
Q

How is a mechanical incomitant strabismus caused?

A

A lesion within the orbit that interferes with muscle action

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8
Q

How is a dysinnervational incomitant strabismus caused

A

Resulting in developmental error in innervation of the muscle

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9
Q

Which two incomitant strabismus’ are similar ?

A

Neurogenic and myogenic
Mechanical and dysinnervational

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10
Q

What are three examples of a neurogenic strabismus?

A

III, IV and VI cranial nerve palsies
Double elevator palsy
Double depressor palsy

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11
Q

What are characteristics of a left 4th nerve palsy?

A

Left hypertropia which increases as px looks to the right and decreases when px looks to the left

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12
Q

What are examples of myogenic strabismus?

A

Myaesthenia Gravis and chronic progressive external ophthalmoplegia (CPEO)

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13
Q

What are three examples of mechanical strabismus?

A
  1. Browns Syndrome
  2. thyroid eye disease
  3. orbital fracture
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14
Q

What are two examples of dysinnervational disorders?

A

Duanes retraction syndrome, and congenital fibrosis of EOM

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15
Q

What is sheringtons law?

A

Unilocular law which involves the agonist muscle contracting with equal and simultaneous relaxation of the direct antagonist

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16
Q

What is Hering’s law?

A

Binocular law of which equal and simultaneous contraction of contralateral synergist muscle (the opposite eye)

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17
Q

Can you name where the muscles are acting in each gaze?

A

No? You are gonna fail if you do not know this simple stuff

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18
Q

What are the four steps of a muscle sequelae ?

A

1) Primary muscle u/a
2) O/a of contralateral synergist (the other eye)
3) O/a of ipsilateral direct antagonist (same eye)
4) U/a of antagonist of contralateral synergist

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19
Q

Does a full muscle sequelae develop over time or over a acute onset in neurogenic and myogenic incomitant strabismus?

A

Over time

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20
Q

Why is hard to differentiate the primary under actor from congenital palsies?

A

Due to a fully developed sequelae difficult to differentiate which is the primary under actor and underacting antagonist contralateral synergist

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21
Q

What are four things we must address which doing an orthoptic assessment for a incomitant strabismus?

A

1) Make a differential diagnosis
2) Asses stability or monitor change of ophthalmoplegia
3) Presence and strength of BSV
4) Management both temporary and long term

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22
Q

What tests would you do for someone with an incomitant strabismus and what would each of them indicate ?

A
  • Observations (facial asymmetry & CHP)
  • Ocular motility (pain on eye movement + globe retraction)
  • PCT in 9 positions of gaze
  • Synoptophore (torsion would be seen)
  • BSV ( particular attention to fusional amplitude)
  • Hess chart
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23
Q

What three signs would someone with a COMPENSATED incomitant strabismus show?

A
  • Asymptomatic of diplopia
  • Adopts CHP
  • Increased fusional amplitude
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24
Q

What three signs would someone with a DECOMPENSATED incomitant strabismus show?

A
  • Manifest deviation
  • Diplopia with aesthenopic sx
  • Suppression but this is more likely to occur with longstanding/children
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25
Is a CHP in just acquired, just congenital or both?
Both
26
What are six reasons for why a CHP is used?
- Achieve SV - Centralise field of BSV - Avoid area where there is dipl/pain/discomfort - Increased separation if diplopic images - Ptosis - Nystagmus
27
What are three components of a CHP?
- Face turn - Head tilt (overcome height or torsion) - Chin elevation of depression
28
What CHP would someone with a horizontal deviation have?
Adopt a face turn
29
What CHP would someone with a vertical deviation have?
FT in direction of vertical action Head tilt towards lower eye Chin in direction of worst affected gaze position
30
Should a CT be assessed or without a head posture?
Both
31
Should OM be tested with or without a head posture?
Without
32
What are five characteristics of a neurogenic incomitancy? (Like deviations and stuff)
- Deviation in pp reflects extent extent of palsy - Duction > versions - Saccadic movement may be slow in paretic eye - No globe retraction - AHP tilt in vertical palsies
33
What are five characteristics of a mechanical incomitancy? (Like deviations and stuff)
- Small deviation in pp - Duction = versions - Saccadic movement the velocity is normal until point of limitation occurs - May have globe retraction, pain or discomfort - AHP tilt rare
34
What are the three purposes of a Hess chart?
- Allows ocular movements to be represented graphically - Demonstrates muscle sequelae - Assists in differential diagnosis
35
What a three conditioNS in Hess charts?
- Px must have foveal fixation - NRC - Sufficient vision in either eye to locate fixation points
36
How many degrees are represented in each square of a Hess chart?
5
37
Which eye does a smaller field belong to?
Affected eye
38
How is an under action represented in a Hess chart?
Inward displacement
39
How is a mechanical restriction represented on a Hess chart?
Narrow field restricted in opposing directions
40
What does an equal sized field on a Hess chart denote?
Symmetrical limitation in BE/ non paralytic strab/ spread of concomitance
41
What chart can be used to plot separation of images?
Diplopia chart
42
What does a field of BSV demonstrate and how is it measured and represented?
Area of BSV, measured using the arc perimeter and the area of bsv is marked with hatching
43
Do you know how to differential diagnose between congential and acquired?
44
Do you know how to differentially diagnose between neurogenic and mechanical?
45
Not a flash card but go through the px scenarios in the incomitancy lecture slides.
Not a flash card but go through the px scenarios in the incomitancy lecture slides.
46
Will a px with congenital incomitancy experience diplopia?
No or may be intermittent
47
Will a px with an acquired incomitancy experience diplopia?
Yes and will be able to tell u exact onset
48
Will a px with a congenital incomitancy be aware of a CHP?
No but they have one
49
Will a px with a aquired incomitancy be aware of a CHP?
Yes and find is uncomfortable to maintain
50
Will a px with a congenital incomitancy have a full muscle sequelae?
Yes, difficult to find under actor on Hess
51
Will a px with a aquired incomitancy have a full muscle sequelae?
No, normally just step 1 & 2 (easy to see on Hess)
52
Will a px with a congenital incomitancy have a normal fusional amplitude range?
No they would have extended ranges for vertical deviations (like a SO palsy)
53
Will a px with an acquired incomitancy have a normal fusional amplitude range?
Yes
54
Will a px with a congenital incomitancy suppress?
Yes with intermittent diplopia
55
Will a px with an aquired incomitancy suppress?
No unless very poor vision
56
In congenital SO palsy, would torsion be noted?
No
57
In acquried SO palsy, would torsion be noted?
Yes
58
Would there be a PP deviation in neurogenic incomitancies?
Yes, Marked
59
Would there be a PP deviation in mechanical incomitancies?
Yes, but small
60
Does diplopia remain the same or reverse in neurogenic incomitancies?
Remains the same
61
Does diplopia remain the same or reverse in mechanical incomitancies?
Can reverse
62
With neurogenic incomitancies, what is the relationship between duction and versions?
Movement is greater on duction then versions
63
With mechanical incomitancies, what is the relationship between duction and versions?
Ductions and versions same
64
With a neurogenic incomitancy, is a Hess chart compressed or equally spaced?
Equally spaced, but slightly smaller for the affected eyes
65
With a mechanical incomitancy, is a Hess chart compressed or equally spaced?
Compressed
66
With a neurogenic incomitancy, will a px experience pain?
Uncommon
67
With a mechanical incomitancy, will a px experience pain?
Yes, it is Common
68
Will IOP change and if so by how much with a neurogenic incomitancy?
Remains Unchanged
69
Will IOP change and if so by how much with a mechanical incomitancy?
Rises by 5mmHg when looking AWAY from limitation
70
Is this mechanical or neurogenic?
Mechanical
71
Is this mechanical or neurogenic?
Neurogenic but not fully developed
72

Binocular Vision (30 decks)

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