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Strabismus > A&V patterns 1 > Flashcards

A&V patterns 1 Flashcards

1
Q

What are the types of alphabet patterns

A

X, Y, ◊, A, V

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2
Q

A and V patterns if patient has a

A

bilateral weakness

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3
Q

Cause of alphabet patterns

A

If insertion is not where expected

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4
Q

Is there a of the horizontal deviation in elevation and depression

A

YES , 15 dioptres

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5
Q

Physiological V pattern

A
  • Physiological tendency for divergence on elevation
  • <15∆ difference from depression to elevation
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6
Q

Pathological V pattern

A
  • > 15∆ difference from depression to elevation
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7
Q

Pathological A pattern

A
  • > 10∆ difference from elevation to depression
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8
Q

Likelihood of V compared to A pattern

A

V is twice as common as the A pattern and an A-exo is more common than A-eso

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9
Q

The primary horizontal deviation determines the alphabet classification

A

— V esotropia (V eso)
— V exotropia (V exo)
— A esotropia (A eso)
— A exotropia (A exo)

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10
Q

What type of eso is
5D Elevation
15D PP
30D Depression

A

V ESO

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11
Q

What type of eso is

30D Elevation
15D PP
5D Depression

A

V eso

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12
Q

What type of eso is this
30D Elevation
15D PP
5D Depression

A

A ESO

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13
Q

What type of EXO is this
5D Elevation
15D PP
30D Depression

A

A EXO

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14
Q

V ESO is more

A

convergent looking down

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15
Q

Antimongoloid downward slanting palpebral fissures

A

V pattern more likely

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16
Q

Mongoloid upward slanting palpebral fissures

A

A pattern more likely

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17
Q

Craniosynotosis

A

A birth defect in which the bones in a baby’s skull join together too early. This happens before the baby’s brain is fully formed. As the baby’s brain grows, the skull can become more misshapen. Can have A or V pattern. Craniosynostosis, such as Crouzon, Apert and Pfeiffer syndromes and plagiocephaly, often display A- and V-patterns owing to orbital anomalies

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18
Q

Aetiology of craniosynostosis

A

Most popular in literature- Abnormal oblique muscle function
The aetiology of alphabet patterns is not fully understood and there is disagreement in the literature!
Most popular theory is abnormal oblique muscle function as the cause of A and V patterns
Another theory- abnormal insertion of muscles

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19
Q

Saggitalisation definition

A

muscle is closer to the anterior/posterior axis of the globe

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20
Q

Desaggitalisation definition

A

muscle is further from the anterior/posterior axis

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21
Q

Muscle pulleys definition

A

The 4 rectus muscles are surrounded by fibroelastic pulleys that maintain the position of the EOMs relative to the orbit. The pulleys consist of collagen, elastin, and smooth muscle, enabling them to contract and relax.

22
Q

Muscle actions

A

Superior intort, Recti adduct, Obliques abduct

23
Q

What are the 1st, 2nd and 3rd actions of SO muscle?

A

Depress, abduct and intort

24
Q

What are the 1◦, 2◦ and 3◦ actions of the inferior oblique muscle?

A

Elevate, abduct and extort

25
Q

Esotropia with IO over-action can have associated?

A

V pattern- Eso deviation greater on depression than elevation: Elevate, abduct and extort
V pattern more divergence looking up than down

26
Q

Exotropia with IO over-action can have associated

A

V pattern

27
Q

Esotropia with SO over-action can have associated

A

A pattern- SO abductor on down gaze so A pattern and IO underacts

28
Q

Exotropia with SO over-action can have associated

A

A Pattern- MORE divergence on down gaze

29
Q

V eso features

A

SO WEAKNESS
— In depression: less abduction + o/a of IR increases adduction
— In elevation: o/a of IO gives relatively more abduction + u/a of SR less adduction
— V eso has an o/a of MR
— M.R. Insertion too high
— Cause more slack of MR on elevation (i.e. less convergence) and on depression the MR are at an increased mechanical advantage, causing increased convergence
— IR insertion too nasal (medial)  increase in adduction by IR on depression
— : SO 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. underaction

30
Q

V exo features-which muscle is weak

A

SR WEAKNESS
— 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
— L.R. Insertion too Low
— Cause more slack of LR muscle on depression (i.e. less divergence) and on elevation LR are at an increased mechanical advantage, causing increased divergence
— SR insertion too temporal  less adduction by SR on elevation
— IO 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. Overaction

31
Q

A eso features

A

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
— A Eso L.R. Insertion too high
— SR insertion too nasal increase in adduction by SR on elevation
— IO too anterior

32
Q

A exo features-which muscle underacts

A

— 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
— A Exo M.R. Insertion too low
— IR insertion too temporal less adduction by IR on depression
— SO too posterior

33
Q

Oblique muscle insertions- too anterior

A

weakens muscle

34
Q

Oblique muscle insertions- too posterior

A

strengthens muscle

35
Q

Abnormal horizontal muscle function

A

— Over-actions or weakness (under-actions)
— Theory is based on the hypothesis:
— Lateral recti work more for distance and on elevation
— Medial recti work more for near and on depression
— Eso deviation interested in action of MR
— Exo deviation interested in action of LR

36
Q

Eso deviation interested in…

A

medial rectus muscles which causes the convergent position

37
Q

V exo can be caused by

A

o/a of LR

38
Q

A eso can be caused by

A

u/a of MR

39
Q

A exo can be caused by

A

u/a of LR

40
Q

Saggitalisation- Gobin(1967)

A

if the normal parallelism of obliques is disrupted due to the angle at the origin or insertion then torsion occurs.
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. The type depends on the underlying deviation.

41
Q

What happens in saggitalisation of IO and causes

A

The angle between the IO and visual axis is reduced compared to the angle between visual axis and SO
This may be due to insertion being too anterior or insertion too posterior

42
Q

Saggitalisation of IO causes

A

Sagittalisation reduces the IO’s torsional action (i.e. extorsion) and **incyclotropia occurs **
To compensate for this, the IO & IR contract and overact to compensate for this giving excessive adduction on depression and excessive abduction on elevation
This will often show as an o/a IO and a V pattern

43
Q

Sagittalisation of which muscle causes an A pattern

A

sagittalisation of SO causes o/a/of SO and increase in abduction on downgaze

44
Q

Sagittalisation of which muscle causes a V pattern

A

Sagittalisation of IO cause o/a of IO and increased abduction on upgaze

45
Q

Function of muscle pulleys

A

Connective tissue pulleys have been identified as functional mechanical origins of the EOM. Normally stable during gaze shifts.

46
Q

What does MRI reveal about LR pulleys

A

MRI has revealed substantial shift of the LR pulley opposite to the direction of vertical gaze in a patient with an X pattern (Oh et al. 2002)

47
Q

Abnormal EOM pulleys and alphabet patterns

A

— Association of excyclotorsion with V pattern and incyclotorsion with A pattern
— Paysse et al. (2002) examined patients with A-eso associated with SO o/a and up-slanting palpebral fissures They proposed the orbital developmental abnormality, characterised by incyclorotation of the orbits with resultant heterotopy (misplacement) of the rectus muscle pulleys i.e. MR pulley is located too low and LR pulley too high causing the eye to be incyclorotated causes an A-pattern
— Demer (2010) agrees A-patterns can be caused by rectus pulley instability where incyclorotation of the entire rectus pulley array occurs
— V-pattern characterised by excyclorotation of the orbits; LR pulley is located too low relative to the medial rectus pulley (Demer, 2014)
— 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

48
Q

What conditions cause alphabet patterns

A
  • Up-ward slanting palpebral fissures (Mongoloid)- A pattern and SO over-action
  • Down-ward slanting palpebral fissures (Anti-mongoloids) - V pattern and IO over-action
  • Downs syndrome is often associated with A pattern esotropia
  • Ocular syndromes e.g. Duanes, Browns syndrome are associated with A pattern
  • DVD

example pictures in slides

49
Q

V EXO is

A

more divergent looking up

50
Q

A ESO

A

more convergent looking up

51
Q
A

Strabismus (46 decks)

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