A&V patterns 1 Flashcards
What are the types of alphabet patterns
X, Y, ◊, A, V
A and V patterns if patient has a
bilateral weakness
Cause of alphabet patterns
If insertion is not where expected
Is there a of the horizontal deviation in elevation and depression
YES , 15 dioptres
Physiological V pattern
- Physiological tendency for divergence on elevation
- <15∆ difference from depression to elevation
Pathological V pattern
- > 15∆ difference from depression to elevation
Pathological A pattern
- > 10∆ difference from elevation to depression
Likelihood of V compared to A pattern
V is twice as common as the A pattern and an A-exo is more common than A-eso
The primary horizontal deviation determines the alphabet classification
V esotropia (V eso)
V exotropia (V exo)
A esotropia (A eso)
A exotropia (A exo)
What type of eso is
5D Elevation
15D PP
30D Depression
V ESO
What type of eso is
30D Elevation
15D PP
5D Depression
V eso
What type of eso is this
30D Elevation
15D PP
5D Depression
A ESO
What type of EXO is this
5D Elevation
15D PP
30D Depression
A EXO
V ESO is more
convergent looking down
Antimongoloid downward slanting palpebral fissures
V pattern more likely
Mongoloid upward slanting palpebral fissures
A pattern more likely
Craniosynotosis
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
Aetiology of craniosynostosis
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
Saggitalisation definition
muscle is closer to the anterior/posterior axis of the globe
Desaggitalisation definition
muscle is further from the anterior/posterior axis
Muscle pulleys definition
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.
Muscle actions
Superior intort, Recti adduct, Obliques abduct
What are the 1st, 2nd and 3rd actions of SO muscle?
Depress, abduct and intort
What are the 1◦, 2◦ and 3◦ actions of the inferior oblique muscle?
Elevate, abduct and extort
Esotropia with IO over-action can have associated?
V pattern- Eso deviation greater on depression than elevation: Elevate, abduct and extort
V pattern more divergence looking up than down
Exotropia with IO over-action can have associated
V pattern
Esotropia with SO over-action can have associated
A pattern- SO abductor on down gaze so A pattern and IO underacts
Exotropia with SO over-action can have associated
A Pattern- MORE divergence on down gaze
V eso features
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
V exo features-which muscle is weak
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
A eso features
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
A exo features-which muscle underacts
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
Oblique muscle insertions- too anterior
weakens muscle
Oblique muscle insertions- too posterior
strengthens muscle
Abnormal horizontal muscle function
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
Eso deviation interested in…
medial rectus muscles which causes the convergent position
V exo can be caused by
o/a of LR
A eso can be caused by
u/a of MR
A exo can be caused by
u/a of LR
Saggitalisation- Gobin(1967)
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.
What happens in saggitalisation of IO and causes
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
Saggitalisation of IO causes
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
Sagittalisation of which muscle causes an A pattern
sagittalisation of SO causes o/a/of SO and increase in abduction on downgaze
Sagittalisation of which muscle causes a V pattern
Sagittalisation of IO cause o/a of IO and increased abduction on upgaze
Function of muscle pulleys
Connective tissue pulleys have been identified as functional mechanical origins of the EOM. Normally stable during gaze shifts.
What does MRI reveal about LR pulleys
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)
Abnormal EOM pulleys and alphabet patterns
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
What conditions cause alphabet patterns
- 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
V EXO is
more divergent looking up
A ESO
more convergent looking up
