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Strabismus & Ocular Motility > Investigation of Neurogenic Palsies > Flashcards

Investigation of Neurogenic Palsies Flashcards

1
Q

What does ‘concomitant’ mean?

A

The angle of deviation is the same fixing either eye and in all positions of gaze

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2
Q

What does ‘Incomitant’ mean?

A

The angle of deviation varies depending on the eye used for fixation and direction of gaze.

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3
Q

What can ‘incomitant’ deviations be caused by?

A
  • Neurogenic palsy
  • Restrictive Eye Movements
  • Myogenic
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4
Q

What is a Neurogenic Palsy?

A

Nerve supply to muscle affected; may affect one individual muscle or group of muscles

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5
Q

Which eye should you hold the prism over in a PCT?

A

The affected eye.

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6
Q

What is the ‘primary’ vs. ‘secondary’ deviation in an incomitant deviation?

A

Primary deviation:
fixing with unaffected eye

Secondary deviation:
fixing with affected eye

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7
Q

In an incomitant deviation, why does the secondary deviation measure more than the primary?

A

This is due to the extra innervation required of the paretic muscle to fixate when the fellow eye is covered. The non-paretic eye will then overact (behind the cover) due to the extra innervation (Hering’s Law) and will have a greater compensatory movement once the cover is removed.

So:
Extra innervation to the paretic muscle is required to fixate.

The non-paretic eye will consequently overact behind the cover due to Herring’s Law.

There will be greater compensatory movement when the cover is removed.

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8
Q

What are the more frequent reasons for developing an AHP?

A

Most frequently:
- To place eyes in position of least deviation

  • Maintain and develop BSV
  • Centralise field of BSV

Less frequently:
- To place eyes in position of greatest deviation

  • Greatest separate of two images
  • Ignore diplopia
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9
Q

What is AHP also known as?

A

Compensatory Head Posture

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10
Q

When we tilt our head what happens to our eyes in terms of torsion?

A

Ipsilateral eye to tort intorts and contralateral eye extorts

i.e. when tilting to the right the right eye intorts and the left eye extorts

So, if left extorsion is present in a deviation the patient will tilt to the right to get the fellow eye to intort to match the position

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11
Q

When we tilt our head what happens to our eyes in terms of vertical movement?

A

As we tilt our head the ipsilateral eye moves up and the contralateral eye moves down

i.e. when tilting to the right the right eye moves up and the left eye moves down

So, if someone had a left over right vertical deviation they may tilt to the right to counteract by bringing the right eye up to the same level

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12
Q

What AHP is most likely in a patient with a left SR weakness?

A

LSR elevates, adducts and intorts so results in a left hypo and a left XT
The positions where the SR elevates the eye is where there’s the largest u/a

To avoid this you would want to head turn left and do a chin up AHP

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13
Q

What AHP is most likely in a patient with a left 4th nerve palsy?

A
  • Head tilt right
  • Head turn right
  • Chin down
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14
Q

What AHP is most likely in a patient with a right 6th nerve palsy?

A
  • Head turn right
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15
Q

During a CT what should you consider?

A
  • Deviation in the primary position
  • Fixing with unaffected eye (primary deviation)
  • Fixing with affected eye (secondary deviation)
  • Abnormal head posture (compensatory head posture) to avoid deviation

Record AHP
N.B. Covering eye removes reason for AHP
Record CT first with AHP N&D
Then record without AHP

Record Size and Type of deviation

Also note:
Degree of incomitance fixing either eye
Difference in vertical deviation between N & D
- obliques larger at near
- recti larger at distance

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16
Q

Why do we need to care about distance in vertical deviations?

A
  • Obliques larger at near
  • Recti larger at distance
17
Q

When should we check for AHP?

A

Check AHP prior to CT

18
Q

What do we need to measure in an incomitant deviation?

A
  • With / without AHP – latter more repeatable former only possible if longstanding
  • With /without refractive correction; if indicated (need to consider if they can fix without glasses and if their glasses have been decentred with prisms already)
  • Near / distance
  • Nine/Five positions of gaze
    Synoptophore
    PCT
19
Q

What should we check about patients glasses?

A

If verifocals, bifocals or if they’ve got prisms incorporated

20
Q

How can we measure torsion?

A

Torsion
- Synoptophore
- Double Maddox Rod
- Torsionometer? (Considered less reliable)
- Awaya Cyclo

Maddox Rod
Subjective, good for small vertical deviations

21
Q

During OM testing what do we need to check?

A
  • Versions - movement of the two eyes in the same direction,
  • Ductions – movement of one eye from PP
  • Interpret development of muscle sequelae

Include the different eye movement systems:
- Smooth pursuit
- Saccades (can cover one eye if diplopia is bad)
- OKN
- VOR

22
Q

What do we need to look for during OMs?

A
  • Smoothness of movements during pursuit
  • Head movements in child may indicate avoidance of affected movement
  • Pupils
  • Lid position, changes on movement
  • Globe position, changes
  • Nystagmus
23
Q

How to tell if a deviation is longstanding?

A
  • AHP
  • Extended Vertical PFR
  • Facial Asymmetry
24
Q

If a patient with a large standing intermittent XT develops a CNVI palsy, what is the patients deviation?

A

Expected deviation not always found due to a pre-existing deviation!

Could have diplopia in the new position of gaze compared to their previous long-standing XT that is likely being suppressed

Need to apply the palsy to the patients baseline which isn’t always orthophoric!

25
Q

Why might a patient with a neurogenic palsy have reduced VA?

A

They should have a normal VA so if they don’t it may be due to:

  • Previously present e.g old amblyope
  • Traumatic mydriasis
  • Related to neurogenic condition e.g retrobulbar neuritis in MS
  • If recent, can contribute to decompensation of longstanding palsy
  • Co-incidental pathological cause
26
Q

Why might a patient with a neurogenic palsy not have BSV/ potential BSV?

A

If they didn’t have previous ocular issues they should have normal BSV/potential BSV. If they don’t then they may have had a previous deviation with suppression or ARC (diplopia may occur with change in angle) or due to a traumatic loss of fusion

27
Q

Define ‘Underaction’

A

Underaction: Reduced ocular rotation which improves on testing ductions, often associated with neurogenic palsy

28
Q

Define ‘Overaction’

A

Excessive action of a muscle caused by increased innervation as a consequence of palsy or limitation to the ipsilateral antagonist or contralateral synergist

29
Q

Define ‘Restriction’

A

A term to describe abnormal ocular rotation where the movement does not improve fully when testing ductions and is often associated with mechanical aetiology

30
Q

Define ‘Limited Eye Movement’

A

A description of abnormal ocular rotation.

31
Q

What does the Lee’s Screen test?

A
  • Measurement of deviation in nine positions of gaze (up to 30°)
  • Compares one eye to fellow eye
  • Aids identification of affected eye and muscle
32
Q

Why is the Lee’s Screen useful?

A
  • Aids differential diagnosis of neurogenic limitations and restrictive eye movements (mechanical)
  • Illustrates degree of concomitance
  • Used for monitoring patient
33
Q

How do we measure torsion using the Lee’s Screen?

A
  • Torsion can only be measured with a special adaptation (but you’re better off using double Maddox or Synoptophore)
  • Not good for bilateral conditions (uniocular field of fixation is a better test to use)
34
Q

What is the Field of BSV test? How is it useful?

A
  • Records area in which BSV is maintained
  • Excellent to record the eye movements when ductions are affected
  • Compare pre and post sx

-A good representation of eye movements in bilateral conditions and mechanical limitations such as Graves’ orbitopathy

Strabismus & Ocular Motility (8 decks)

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