Alphabet Patterns Flashcards
What is a physiological V pattern defined as?
A physiological tendency for divergence on elevation. To be physiological we’d be looking at a <15 difference from depression to elevation
What is a pathological V pattern defined as?
> 15PD difference from depression to elevation
What is a pathological A pattern defined as?
> 10PD from elevation to depression
What are the alphabet patterns?
V, A, X, Y, Inverted Y & Diamond
What is this pattern?
5BO Elevation
15BO pp
30BO Depression
V Eso
What is this pattern?
30BO Elevation
15BO pp
5BO Depression
A Eso
What is this pattern?
5BI Elevation
15BI pp
30BI Depression
A Exo
What is this pattern?
30BI Elevation
15BI pp
5BI Depression
V Exo
What is this pattern?
35BI Elevation
25BI pp
10BI Depression
V Exo
What is this pattern?
10BO Elevation
25BO pp
35BO Depression
V Eso
What is this pattern?
10BI Elevation
25BI pp
35BI Depression
A Exo
What is this pattern?
35BO Elevation
25BO pp
10BO Depression
A Eso
What is the prevalence of A or V patterns in horizontal strabismus?
12 - 50%
V 2x as common as A
A Exo more common than A Eso
What is Antimongoloid?
Downward slanting palpebral fissures
What pattern is someone with Antimongoloid likely to have?
More likely to have a V pattern
What is Mongoloid?
Upward slating palpebral fissures
What pattern is someone with Mongoloid likely to have?
More likely to have an A pattern
What orbital anomalies often display A and V-patterns?
Craniosynostosis (abnormally shaped skulls due to premature fusion of sagittal and frontal sutures at birth), such as Crouzon, Apert and Pfeiffer syndromes and plagiocephaly, often display A- and V-patterns owing to orbital anomalies
What pattern is associated with an ET with IO o/a?
V Pattern
What pattern is associated with an XT with IO o/a?
V Pattern
What pattern is associated with an XT with SO o/a?
A pattern
What pattern is associated with an ET with SO o/a?
A pattern
(as more divergence looking down)
What vertically acting muscle weakness is a V Eso associated with?
SO weakness
What vertically acting muscle weakness is a V Eso associated with? What happens in depression and in elevation?
SO weakness
In depression: –> less abduction + o/a of IR = increased adduction
In elevation: o/a of IO gives relatively more abduction + u/a of SR = less adduction
What vertically acting muscle weakness is a V Exo associated with?
SR weakness
What vertically acting muscle weakness is a V Exo associated with? What happens in depression and in elevation?
SR weakness
In elevation: –> less adduction + o/a of IO = increases abduction
In depression: o/a of IR gives relatively more adduction & u/a of SO = less abduction
What vertically acting muscle weakness is an A Eso associated with?
IO weakness
What vertically acting muscle weakness is a A Eso associated with? What happens in depression and in elevation?
IO weakness
In elevation: –>less abduction + o/a of SR = increases adduction
In depression: o/a of SO gives relatively more abduction + u/a of IR = less adduction
What vertically acting muscle weakness is a A Exo associated with?
IR weakness
What vertically acting muscle weakness is a A Exo associated with? What happens in depression and in elevation?
IR weakness
In depression: –>less adduction + o/a of SO = increases abduction
In elevation: o/a of SR cause relatively more adduction & u/a of IO = less abduction
Are A or V patterns most common in unilateral or bilateral weakness?
Bilateral weakness
In a V eso what horizontal muscle is o/a or u/a?
o/a of MR
In an A eso what horizontal muscle is o/a or u/a?
u/a of MR
In a V exo what horizontal muscle is o/a or u/a?
o/a of LR
In a V eso what horizontal muscle is o/a or u/a?
u/a of LR
Why is it that exo’s are associated with LR and eso’s with MR?
Theory is based on the hypothesis:
- Lateral recti work more for distance and on elevation
- Medial recti work more for near and on depression
In a V Exo where is the LR insertion?
Too low
In a V Exo if the LR is too low what does this mean?
It causes more slack of LR muscle on depression (i.e. less divergence) and on elevation LR are at an increased mechanical advantage, causing increased divergence.
This weakens the primary action of the muscle in downgaze and increases it in upgaze.
In a V Eso if the MR is too high what does this mean?
It causes more slack of MR on elevation (i.e. less convergence) and on depression the MR are at an increased mechanical advantage, causing increased convergence.
If a medial rectus muscle is infraplaced, a new force vector for depression will be created.
In an A Eso if the LR is too high what does this mean?
It causes more tension of the LR on depression (i.e. more abduction/divergence) and on elevation causes more slack of the LR (i.e. less abduction/divergence) =
More convergence in elevation and less convergence in depression
In an A Exo if the MR is too low what does this mean?
It causes more tension of the MR in elevation (i.e. more convergence) but causes the MR to be more slack in depression (i.e. less convergence)
More convergence in elevation and less convergence in depression
What does an oblique muscle insertion being too anterior mean?
It weakens it
What does an oblique muscle insertion being too posterior mean?
It strengthens it
What oblique muscle insertion could a V Eso have?
SO too anterior
What does it mean if a V Eso has a SO that’s too anterior?
The abducting force of the SO is weakened and as this works mainly in depression there is relatively more convergence in depression, therefore giving a V Eso pattern
What oblique muscle insertion could a V Exo have?
IO too posterior
What does it mean if a V Exo has a SO that’s too posterior?
The abducting force of the IO is strengthened and as this works mainly in elevation there is relatively more divergence in elevation, therefore giving a V Exo pattern
What oblique muscle insertion could an A Eso have?
IO too anterior
What does it mean if an A Eso has a IO that’s too anterior?
The abducting force of the IO is weakened and this works mainly in elevation so there is relatively more convergence in in elevation therefore giving an A pattern Eso
What oblique muscle insertion could an A Exo have?
A SO that’s too posterior
What does it mean if an A Exo has a SO that’s too posterior?
The abducting force of the SO is strengthened, and as this mainly works in depression, there is relatively more divergence in depression, therefore giving an A Exo pattern
How might vertical recti muscles be abnormally positioned in a V eso?
IR insertion too nasal (medial) –> increase in adduction by IR on depression
How might vertical recti muscles be abnormally positioned in a V exo?
SR insertion too temporal –> less adduction by SR on elevation
How might vertical recti muscles be abnormally positioned in a A eso?
SR insertion too nasal –> increase in adduction by SR on elevation
How might vertical recti muscles be abnormally positioned in a A exo?
IR insertion too temporal –> less adduction by IR on depression
In eso deviations are the vertical recti muscle insertions too medial or too temporal?
Too medial
In exo deviations are the vertical recti muscle insertions too medial or too temporal?
Too temporal
How might Sagittalisation affect vertical actions of muscles and cause an A or V pattern?
A dysfunction of the oblique muscles caused by differences b/w the planes of SO and IO
The normal axes of the SO and Io muscles are approx parallel. If one insertion is more posterior than normal the muscles axis lies in a more sagittal plane i.e. It is closer to the anterior posterior axis of globe.
The need to compensate for the cyclo-deviation caused will alter the degree of contraction by the vertical muscles and therefore, also influence their vertical actions. Thus causing an A or V pattern.
What does sagittalisation of the IO mean?
The angle between the IO and visual axis is reduced compared to the angle between visual axis and SO due to the origin being too anterior or the insertion too posterior
What does sagittalisation of the IO cause?
It reduces the IO’s torsional action thus causing incyclotropia.
As the IO and IR contract to try to compensate for this which results in excessive adduction on depression and excessive abduction on elevation often then showing as an o/a IO with a V pattern
What sagittalisation can cause a V-pattern?
Sagittalisation of IO cause o/a of IO and increased abduction on upgaze
What sagittalisation can cause an A-pattern?
Sagittalisation of SO causes o/a of SO and increase in abduction on downgaze
What are muscle pulleys?
Connective tissue pulleys have been identified as functional mechanical origins of the EOM. Normally stable during gaze shifts.
What happens when muscle pulleys are not where we except them to be in terms of the MR and LR?
A-exo (MR lower than LR)
V-exo (MR higher than LR)
Clark et al. (1998)
What is the association of torsion to alphabet patterns?
Association of excyclotorsion with V pattern and incyclotorsion with A pattern
What torsion does a V pattern cause? Where might the LR pulley be?
V-pattern characterised by excyclorotation of the orbits; LR pulley is located too low relative to the medial rectus pulley (Demer, 2014)
What can loss of fusion lead to in terms of torsion and alphabet patterns?
Guyton (1988, 1992), Deng et al (2013) loss of fusion predisposes the oculomotor system to cyclodeviations of the eyes which in turn causes A and V patterns
What might mongoloid lead to in terms of alphabet patterns and muscle actions?
A pattern and SO over-action
What might antimongoloid lead to in terms of alphabet patterns and muscle actions?
V pattern and IO over-action
How is Down’s Syndrome related to alphabet pattern and muscle actions?
Downs syndrome is often associated with A pattern esotropia and SO o/a
What elevators are affected in V patterns?
Elevators: o/a of IO and u/a of SR =
Greater relative divergence
What depressors are affected in V patterns?
u/a of SO and o/a of IR =
Greater relative convergence
What elevators are affected in A patterns?
Elevators: u/a of IO and o/a of SR =
Greater relative convergence
What depressors are affected in A patterns?
Depressors: o/a of SO and u/a of IR =
Greater relative divergence
What tests can you use to diagnose an alphabet pattern?
- CT & OMs
- Measurements in PP, direct elevation and depression
- PCT
6m to eliminate accommodation. May also want to measure at 1/3m if interested in what happens when accommodate. - Synoptophore
- Lees screen
- Field of BSV
Why would we want to manage an alphabet pattern?
- To create a larger and more useful field of BSV
- To achieve a better ocular alignment
- To reduce the risk of consecutive exotropia and give a more stable angle
What do we need to gain from the investigation into alphabet patterns?
- Symptomatic
Diplopia, Constant, Intermittent e.g. Decompensate on prolonged reading,
Asthenopic - Ocular alignment
- Objective assessment of torsion
Indirect ophthalmoscopy or fundus photography - Potential for BSV or retaining BSV
- Assess risk of over-correcting a patient requiring strabismus surgery
- Assess value of combining strabismus surgery & correcting alphabet pattern at the same time
What surgery do we need to do in alphabet patterns?
Surgery may depend on aetiology or the presence of significant oblique over-actio
What are some surgical principles when it comes to whether to operate on vertical or horizontal muscles?
If associated vertical muscle over- & under-actions: operate on vertical muscles
If no/ mild vertical muscle over- & under-actions: operate on horizontal muscles
What is the aim of surgery in V pattern with IO over-action?
Weakening of the IO muscle allows more convergence on elevation i.e. cause SR over-action increased ad-duction due to the o/a they have of the IO
What are the surgical options for V pattern IO overaction?
- IO recession
- IO myectomy
- Anterior transposition of IO
Horizontal surgery (recess/resect) performed at same time or subsequent sitting
Anterior transposition of IO as advocated by Gobin now mostly used in DVD
In acquired bilateral SO palsy with V-Eso
- Harado-Ito or SO tuck will reduce V pattern
What surgery to we do in acquired bilateral SO palsy with V-Eso?
Harado-Ito or SO tuck will reduce V pattern
What is the aim of A pattern with SO overaction?
Weakening the SO muscle allows more convergence on depression i.e. cause IR over-action = increased adduction
What are the surgical options of an A pattern with SO overaction?
- SO posterior tenectomy
- SO posterior tenotomy
- SO z-tenotomy
- SO split lengthening
- SO tendon spacer (silicon expander; makes tendon longer)
- Operate on both SO if moderate/marked o/a of SO
- Alternative
Bilateral IR resection
Horizontal surgery (recess/resect) performed at same time or subsequent sitting
Combining SO Z-tenotomy, SO posterior tenectomy or tenotomy, and recess/resect of horizontal rectus muscles
What is the aim of A pattern with SR overaction?
Weakening of both SR muscles allows more divergence on elevation i.e. cause IO over-action increased ab-duction
What are the surgical options of A pattern with SR overaction?
Bilateral SR recession but could also do a bilateral IO recession
When might we transpose horizontal muscles?
We can do a bilateral recession and transposition of muscles by moving the LR in exo deviations and the MR in eso deviations
We move it in the direction of the greatest deviation so:
- Insertion of MR moved towards apex (less convergence this way)
- Insertion of LR moved towards wide end
When moving the insertion down it cause the action of that muscle to be more slack on depression
When transposing the MR where do we move it towards?
Towards apex to cause less convergence
When transposing the LR where do we move it towards?
Towards the wide end
When we move the insertion down what does it cause of the muscle?
When moving the insertion down it cause the action of that muscle to be more slack on depression
What muscle do we transpose, and where, in V Eso’s?
Transpose MR insertion downwards
What muscle do we transpose, and where, in A Eso’s?
Transpose MR insertion upwards
What muscle do we transpose, and where, in V Exo’s?
Transpose LR insertion upwards
What muscle do we transpose, and where, in A Exo’s?
Transpose LR insertion downwards
When might be transpose horizontal muscles instead of other surgical options?
Advocated if no or minimal oblique muscle over- and under-actions
Also possible to combine recess/resect procedure, moving one up & one down
Complications: risk of torsional disturbances if work on one eye
What are the risks of transposing horizontal muscles?
Complications: risk of torsional disturbances if work on one eye
What is it called when we combine horizontal surgery with the slanting of muscle insertions?
Boyd’s technique
When might we use the surgical technique of slanting horizontal muscle insertions?
Advocated in the absence of marked over-actions of the oblique muscles
What complications are there from slanting of muscle insertions?
- Correcting A-exo can result in SO weakening
- Vertical displacement of horizontal muscles may induce torsion
How does horizontal muscle insertion work as a surgical technique?
Horizontal muscle tension is stronger at upper margin than at lower margin on elevation.
What horizontal slanting surgery do we do to reduce V exo?
Upper margin of LR recessed > than lower margin to reduce V-exotropia
i.e. less ab-duction on elevation: close V
What horizontal slanting surgery do we do to reduce A exo?
Lower margin of LR recessed > than upper margin to reduce A-exotropia
i.e. less ab-duction on depression: close A
What horizontal slanting surgery do we do to reduce A eso?
Upper margin of MR recessed > than lower margin to reduce A-esotropia
i.e. less ad-duction on elevation: opens A
What horizontal slanting surgery do we do to reduce V eso?
Lower margin of MR recessed > than upper margin to reduce V-esotropia
i.e. less ad-duction on depression: opens V
When might a surgery be modified to prevent an A exo post-op?
- When performing horizontal muscle surgery
- Consecutive XT may be associated with A-patterns due to SO overaction
- Large recession of IR for Graves Orbitopathy moves insertions nasally which will prevent A exo post-op
How might we modify a horizontal muscle surgery to prevent an A exo post-op?
- Abnormally low insertion of MR is noted. This muscle may be transposed upwards.
- If the insertion of the LR muscle is found to be abnormally high this muscle may be transposed downwards.
- This will minimise the risk of an A-exo post-operatively
How might we modify a surgery in a consecutive XT that’s associated with A pattern due to SO o/a to prevent an A exo post-op?
Combined horizontal muscle surgery with SO weakening procedure may reduce the risk of A exo post-operatively
How might we modify a surgery in a large recession of IR for Graves Orbitopathy to prevent an A exo post-op?
Moving insertions nasally will prevent an A exo post-op
i.e. moving insertion nasally increases ad-duction, moving insertion temporally decreases ad-duction
A V-Eso is caused by what?
Overaction of MR
If an oblique muscle is positioned too anterior it results in what?
The abducting force of SO is weakened and leads to a V eso
What is sagittalisation of the SO? What does it lead to?
The angle between the SO and visual angle is reduced compared to angle for IO, and leads to SO and SR contract to compensate for the torsion and causes SO over-action and A-pattern
What surgery do we do for a V-eso?
Transpose MR upwards
What surgery do you do in an A-eso?
Bilateral LR recession and IR recession
5BO
15BO
35BO
What’s the pattern?
V Eso
5 BI
18BI
25BI
What’s the pattern?
A Exo
What causes a V-pattern?
IO o/a and SR u/a
What can cause an A-pattern?
SR o/a and IR u/a
What can a V eso be caused by?
o/a of MR
What does it mean if the MR is inserted too high?
Causes slacking of the muscle in elevation
An ET with a MR inserted too high causes what pattern?
V-pattern
XT when LR is inserted too low causes what pattern?
V-pattern
If an oblique muscle is positioned too anterior what does it result in?
The abducting force of SO is weakened = V Eso
Sagittalisation of the SO causes what?
The angle between SO and visual angle is reduced compared to angle for IO, and leads to SO and SR contraction to compensate for the torsion and causes SO o/a and A-pattern
V-pattern Surgery?
Anterior transposition of IO
A-pattern Surgery?
SO tenotomy
Surgery for V Eso?
Bilateral MR recessions and IO myectomy
Surgery for A Exo?
LR recess/MR resect and SO tendon spacer
