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Strabismus & Ocular Motility > Muscle Sequelae, Hess Charts & Diplopia Charts > Flashcards

Muscle Sequelae, Hess Charts & Diplopia Charts Flashcards

1
Q

How do we see a mechanical strabismus on a Hess Chart?

A

The fields are vertically compressed

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2
Q

Hess Chart Practice

A

https://www.mrcophth.com/commonhesschart/ds.html

https://www.slideshare.net/slideshow/hess-chart-76422300/76422300

https://cybersight.org/library/lecture-evaluation-and-surgical-management-of-superior-oblique-palsy-2020-update-qa-and-case-discussion/

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3
Q

Diplopia Chart Practice

A

https://www.eophtha.com/posts/diplopia-charting-a-ready-reckoner-for-the-postgraduates

https://www.youtube.com/watch?v=nNXvsNHnFmQ

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4
Q

What are the methods of plotting a Hess Chart?

A

Lees Screen
Mirror to dissociate eyes
Hess Screen
Grey background, red & green goggles & lights
Lancaster – Hess test (Lancaster red-green test)

Computerised versions
PC Hess Screen (Thomson Software)
Digital Hess Screen
Ocular Motility Analyzer (OMA)

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5
Q

What eye are we plotting on a Hess Chart when fixing with the right eye?

A

Movement of the LE

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6
Q

How much is each square of a Hess Chart worth in degrees?

A

Each square is 5 degrees meaning the inner field is 15 degrees and outer field is 30 degrees

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7
Q

What is the testing distance for a Hess Chart?

A

50cm

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8
Q

What are the 10 steps for interpreting a Hess Chart>

A
  1. Compare charts of the two eyes – position, shape & size
    Higher field – higher eye
    Inward shifted field – eso deviation
  2. Size of overall field
    (smaller field = ‘affected eye’)
  3. Primary position deviation
    (can’t tell if manifest or latent, the primary deviation is when fixing with the unaffected eye, the secondary deviation is when fixing with the affected eye and size of deviation)
  4. Underaction
    Inward displacement of dots, max displacement is in the main action of the affected muscle, primary underaction
  5. Overaction
    Outward displacement of dots, max displacement in direction of main action of overacting contralateral synergist
  6. Muscle Sequelae
    Might not get all 4 steps of muscle sequelae as this develops over time.
  7. Mechanical vs. Neurogenic Differential Diagnosis
    Mechanical is flattened or narrow field
    Reversal of deviation between the eyes
  8. Equal Size Fields
    Symmetrical limitation of movement
    Longstanding muscle palsy with developed muscle sequelae - concomitance
  9. Sloping Fields
    A or V patterns
    Do not show torsion (need a linear pointer to do so)
  10. Interpretation at one point in time
    Comparison over time
    Viewed with OM, field of BSV, field of uniocular fixation, measurements
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9
Q

If the primary position of the two eyes look different on a Hess Chart what does it suggest the deviation is?

A

Incomitant

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10
Q

How can you tell on a Hess Chart if the deviation is incomitant?

A

If the primary position of the two eyes looks different on a Hess Chart

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11
Q

How do you work out which is the ‘affected’ eye on a Hess Chart?

A

Smaller field has

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12
Q

When we’re fixing with the unaffected eye what are we plotting on the Hess Chart?

A

Primary deviation

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13
Q

When we’re fixing with the affected eye what are we plotting on the Hess Chart?

A

Secondary deviation

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14
Q
A
  1. Underactions = RLR largest so this is the primary underaction 2. Overactions = LMR (contralateral synergist)3. o/a Ipsilateral Antagonist overaction = RMR4. u/a Contralateral Antagonist = not yet happened because the LLR is unaffected
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15
Q

What does a Neurogenic field look like on a Hess Chart?

A
  • Largest deviation in the direction of the affected muscle
  • Field shifted and misplaced, rather than constricted
  • Equal spacing between inner and outer fields
  • Full muscle sequelae develops
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16
Q

What can look like a mechanical issue (squashed Hess chart) but isn’t?

A

3rd Nerve Palsy

17
Q

What wont show up on a Hess Chart?

A

Remember – bilateral symmetrical OM defects will not show up on a Hess chart

You are plotting the movements of one eye relative to the other eye – so this will only show up any asymmetry between the two eyes

18
Q

What must the patient have to be able to complete a Hess Chart?

A
  • Must not have suppression
  • Must have NRC
    (A pre-existing deviation with abnormal correspondence will mean you are plotting a Hess with fovea of non-squinting eye corresponding to pseudofovea of squinting eye)
19
Q

What’s an Agonist?

A

The primary muscle

20
Q

What’s an Antagonist?

A

EOM whose action opposes the action of the contracting muscle

21
Q

What’s a Synergist muscle?

A

Contralateral EOM that work together

22
Q

What is Sherrington’s Law?

A

Uniocular law

When increased innervation is sent to a muscle to contract, an equivalent decrease in innervation is received by the direct antagonist

This means the direct antagonist muscle is relatively relaxed

23
Q

What is Hering’s Law?

A

Binocular law

When an impulse goes to a muscle causing it to contract, a simultaneous and equal impulse is sent to its contralateral synergist to contract

24
Q

What is the pattern of muscle sequelae?

A
  1. Primary underaction
  2. Overaction of the contralateral synergist
    - Hering’s law of equal innervation
  3. Overaction/contracture of the ipsilateral antagonist
    - Sherrington’s law of reciprocal innervation
  4. Secondary inhibition (underaction) of the contralateral antagonist
    - Hering’s law of equal innervation
    The contracted ipsilateral antagonist requires less innervation
25
Q

What happens when muscle sequalae develops?

A

Takes time & the longer that it is left the less incomitant it looks and so ends up looking more concomitant due to the muscle sequelae

Fixing with affected eye > fixing with unaffected eye (secondary dev > primary dev)
If similar in primary deviation (fixing with unaffected eye) and secondary deviation (fixing with affected eye) then it’s a long standing problem from muscle squealae

26
Q

What subjective tests can we do to plot diplopia?

A

Diplopia Charts
Subjective report of diplopia – red & green goggles
Fixing linear light source (vertical) at 50cm

27
Q

When are diplopia charts used most to plot diplopia?

A

Impaired mobility
Bilateral, asymmetrical 4th nerve palsies

28
Q

How do we interpret diplopia charts?

A

Crossed / homonymous = XT
Uncrossed / heteronymous = ET

Higher image is from lower eye = Hypo (HoT)
Lower image is from higher eye = Hyper (HT)

Extorted eye sees intorted image (incyclo T)
Intorted eye sees extorted image (excyclo T)

Greatest separation of diplopia = inconcomitant, larger deviation

29
Q

How can we tell if a deviation is inconcomitant on a diplopia chart?

A

Greater separation of diplopia in different positions of gaze

Strabismus & Ocular Motility (8 decks)

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