Incomitancy - MEH Flashcards
What is the definition of incomitancy?
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
What are two ways to classify incomitancy?
Acquired and congenital
What is essential with acquired incomitancies?
Referral is essential as it requires further investigation
What are four ways incomitant strabismus is classified?
- Neurogenic
- Myogenic
- Mechanical
- Dysinnervational
How is a neurogenic incomitant strabismus caused?
A lesion with the nerve supplying the muscle
How is a myogenic incomitant strabismus caused
A lesion directly affecting the muscle itself
How is a mechanical incomitant strabismus caused?
A lesion within the orbit that interferes with muscle action
How is a dysinnervational incomitant strabismus caused
Resulting in developmental error in innervation of the muscle
Which two incomitant strabismus’ are similar ?
Neurogenic and myogenic
Mechanical and dysinnervational
What are three examples of a neurogenic strabismus?
III, IV and VI cranial nerve palsies
Double elevator palsy
Double depressor palsy
What are characteristics of a left 4th nerve palsy?
Left hypertropia which increases as px looks to the right and decreases when px looks to the left
What are examples of myogenic strabismus?
Myaesthenia Gravis and chronic progressive external ophthalmoplegia (CPEO)
What are three examples of mechanical strabismus?
- Browns Syndrome
- thyroid eye disease
- orbital fracture
What are two examples of dysinnervational disorders?
Duanes retraction syndrome, and congenital fibrosis of EOM
What is sheringtons law?
Unilocular law which involves the agonist muscle contracting with equal and simultaneous relaxation of the direct antagonist
What is Hering’s law?
Binocular law of which equal and simultaneous contraction of contralateral synergist muscle (the opposite eye)
Can you name where the muscles are acting in each gaze?
No? You are gonna fail if you do not know this simple stuff
What are the four steps of a muscle sequelae ?
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
Does a full muscle sequelae develop over time or over a acute onset in neurogenic and myogenic incomitant strabismus?
Over time
Why is hard to differentiate the primary under actor from congenital palsies?
Due to a fully developed sequelae difficult to differentiate which is the primary under actor and underacting antagonist contralateral synergist
What are four things we must address which doing an orthoptic assessment for a incomitant strabismus?
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
What tests would you do for someone with an incomitant strabismus and what would each of them indicate ?
- 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
What three signs would someone with a COMPENSATED incomitant strabismus show?
- Asymptomatic of diplopia
- Adopts CHP
- Increased fusional amplitude
What three signs would someone with a DECOMPENSATED incomitant strabismus show?
- Manifest deviation
- Diplopia with aesthenopic sx
- Suppression but this is more likely to occur with longstanding/children
Is a CHP in just acquired, just congenital or both?
Both
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
What are three components of a CHP?
- Face turn
- Head tilt (overcome height or torsion)
- Chin elevation of depression
What CHP would someone with a horizontal deviation have?
Adopt a face turn
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
Should a CT be assessed or without a head posture?
Both
Should OM be tested with or without a head posture?
Without
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
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
What are the three purposes of a Hess chart?
- Allows ocular movements to be represented graphically
- Demonstrates muscle sequelae
- Assists in differential diagnosis
What a three conditioNS in Hess charts?
- Px must have foveal fixation
- NRC
- Sufficient vision in either eye to locate fixation points
How many degrees are represented in each square of a Hess chart?
5
Which eye does a smaller field belong to?
Affected eye
How is an under action represented in a Hess chart?
Inward displacement
How is a mechanical restriction represented on a Hess chart?
Narrow field restricted in opposing directions
What does an equal sized field on a Hess chart denote?
Symmetrical limitation in BE/ non paralytic strab/ spread of concomitance
What chart can be used to plot separation of images?
Diplopia chart
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
Do you know how to differential diagnose between congential and acquired?
Do you know how to differentially diagnose between neurogenic and mechanical?
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.
Will a px with congenital incomitancy experience diplopia?
No or may be intermittent
Will a px with an acquired incomitancy experience diplopia?
Yes and will be able to tell u exact onset
Will a px with a congenital incomitancy be aware of a CHP?
No but they have one
Will a px with a aquired incomitancy be aware of a CHP?
Yes and find is uncomfortable to maintain
Will a px with a congenital incomitancy have a full muscle sequelae?
Yes, difficult to find under actor on Hess
Will a px with a aquired incomitancy have a full muscle sequelae?
No, normally just step 1 & 2 (easy to see on Hess)
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)
Will a px with an acquired incomitancy have a normal fusional amplitude range?
Yes
Will a px with a congenital incomitancy suppress?
Yes with intermittent diplopia
Will a px with an aquired incomitancy suppress?
No unless very poor vision
In congenital SO palsy, would torsion be noted?
No
In acquried SO palsy, would torsion be noted?
Yes
Would there be a PP deviation in neurogenic incomitancies?
Yes, Marked
Would there be a PP deviation in mechanical incomitancies?
Yes, but small
Does diplopia remain the same or reverse in neurogenic incomitancies?
Remains the same
Does diplopia remain the same or reverse in mechanical incomitancies?
Can reverse
With neurogenic incomitancies, what is the relationship between duction and versions?
Movement is greater on duction then versions
With mechanical incomitancies, what is the relationship between duction and versions?
Ductions and versions same
With a neurogenic incomitancy, is a Hess chart compressed or equally spaced?
Equally spaced, but slightly smaller for the affected eyes
With a mechanical incomitancy, is a Hess chart compressed or equally spaced?
Compressed
With a neurogenic incomitancy, will a px experience pain?
Uncommon
With a mechanical incomitancy, will a px experience pain?
Yes, it is Common
Will IOP change and if so by how much with a neurogenic incomitancy?
Remains Unchanged
Will IOP change and if so by how much with a mechanical incomitancy?
Rises by 5mmHg when looking AWAY from limitation
Is this mechanical or neurogenic?
Mechanical
Is this mechanical or neurogenic?
Neurogenic but not fully developed
