alphabet pattern Flashcards
what is a v pattern
there is difference of the horizontal deviation in elevation and depression
physiological v pattern - physiological tendency for divergence on elevation
15 diopter difference from depression to elevation
pathological v pattern - more than 15 diopters difference from depression to elevation
what is a pathological a pattern
more than 10 diopters difference from elevation to depression
what are examples of a and v patterns
V Eso
5∆
Elevation
15∆
PP
30∆
Depression
V Exo
30∆
Elevation
15∆
PP
5∆
Depression
what is an example of an eso in elevation primary position and depression
30 diopters elevation
15 diopters primary position
5 diopters depression
what is an example of an a exo
5 dioptres elevation
15 diopters primary position
30 diopters depression
what is the prevalence of a and v patterns
Prevalence of A or V patterns with horizontal strabismus range between 12%-50%
V is twice as common as the A pattern
A-exo is more common than A-eso
Antimongoloid downward slanting palpebral fissures
V pattern
Mongoloid upward slanting palpebral fissures
A pattern
Craniosynostosis, such as Crouzon, Apert and Pfeiffer syndromes and plagiocephaly, often display A- and V-patterns owing to orbital anomalies
what is the prevalence of a and v patterns
The reported prevalence in the literature of associated A or V patterns with horizontal strabismus range between 12%-50%
Unable to find in literature if V eso is more common than V exo
what is the aetiology of a and v patterns
Disagreement in literature
Most popular theory
Abnormal oblique muscle function
Other theories
Weakness of vertical muscle function
Abnormal horizontal muscle function
Abnormal position of oblique muscle insertion
Abnormal position of vertical rectus muscle insertion
Sagittalisation
Muscle pulleys
what is the aetiology of a and v patterns
Disagreement in literature
Most popular theory
Abnormal oblique muscle function
Other theories
Weakness of vertical muscle function
Abnormal horizontal muscle function
Abnormal position of oblique muscle insertion
Abnormal position of vertical rectus muscle insertion
Sagittalisation
Muscle pulleys
what are the primary secondary and tertiary actions of the superior oblique muscle
depress , abbduct and intort
what are the primary secondary and tertiary actions of the inferior oblique muscle
elevate abduct and extort
what can a esotropia with an inferior oblique overaction be associated with
eso deviation greater on depression than elevation , elevate , abduct and extort - v pattern
an exotropia with inferior oblique over action can have associated
v pattern
an esotropia with a superior oblique over action can have associated
a pattern
an exotropia with a superior oblique over action can have an associated
a pattern
if you have a v eso what muscle weakness Is present
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
if you have a v exo what muscle weakness do you have a
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
if you have a a eso what muscle weakness do you have
inferior oblique 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
if someone has a A exo what muscle weakness do they have
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
in what type of weakness do a or v patterns occur
a or v patterns occur most commonly in bilateral weakness
what is abnormal horizontal muscle function caused by
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
V eso:
o/a of MR
v exo can develop as a result of
over action of the lateral rectus
an a type eso can develop as a result of
underaction of the medial rectus
what can an a exo develop as a result of
under action of the lateral rectus
what does abnormal insertion of horizontal muscles cause
V Exo 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
V Eso 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
A Eso L.R. Insertion too high
A Exo M.R. Insertion too low
what does abnormal insertion of oblique muscle cause
Insertion too anterior (weakens) or too posterior (strengthens) muscle
V Eso: 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
V Exo: 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
A Eso IO too anterior
A Exo SO too posterior
what does abnormal position of vertical rectus muscle insertion cause
V eso:
IR insertion too nasal (medial) increase in adduction by IR on depression
V exo:
SR insertion too temporal less adduction by SR on elevation
A eso:
SR insertion too nasal increase in adduction by SR on elevation
A exo
IR insertion too temporal less adduction by IR on depression
Eso-deviation insertion too medial & exo-deviation too temporal
what is saggitlisation
Gobin describes 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
what does the saggitlisation of the inferior oblique cause
The angle between the IO and visual axis is reduced compared to the angle between visual axis and SO
This may be due to origin too anterior or insertion too posterior
Sagittalisation reduces the IO’s torsional action (i.e. extorsion) and incyclotropia occurs
The IO & IR contract 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
what are the correlations between abnormalitieds in pulley position and alphabet patterns
Heterotopy = normal tissue is misplaced
Abnormalities in pulley position have been shown in patients with alphabet patterns…occur a pulley displacement
Demer (2014):
A, Subject of Figure 1 with A-pattern exotropia demonstrating robust LR-SR band bilaterally, with rectus pulley
heterotopy. Lines connect centers of the horizontal and vertical rectus pairs at roughly the pulley locations, showing bilateral superior displacement
of the lateral relative to the medial rectus pulley, and lateral displacement of the inferior relative to the superior rectus pulley. B, Same subject of
Figure 3 with V-pattern exotropia showing robust LR-SR band bilaterally, with rectus pulley heterotopy. Lines connect centers of the horizontal and
vertical rectus pairs at roughly the locations of their pulleys, showing bilateral inferior displacement of the lateral relative to the medial rectus pulley,
and medial displacement of the inferior relative to the superior rectus pulley. C, Subject with adult-onset divergence paralysis esotropia. Note bilaterally
symmetric infraplacement of the lateral rectus pulleys with bilateral discontinuity of the LR-SR band ligaments. Horizontal line indicates centers
of the medial rectus muscles. D, Subject with adult-onset cyclovertical strabismus causing left hypotropia. Note asymmetric infraplacement of
the left lateral rectus pulley and bilateral discontinuity of the LR-SR band ligaments. Line indicates centers of the left horizontal rectus muscles.
describe muscle pulleys in x patterns
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)
LR pulley moved inferiorly on elevation & superiorly on depression
how does the shape and position of eye contribute to the type of alphabet pattern you have
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
what are other associations of alphabet patterns
Ocular syndromes
Duanes
Browns
DVD
what causes a v estotropia
superior oblique under action
inferior oblique over action
incyclophoira with compensatory inferior oblique over action
medial rectus over action
medial rectus insertion too high
superior insertion too posterior
what causes both a v esotropia and v exotropia
incylophoria with compensatory inferior oblique oversction
what causes a v exotropia
superior rectus underaction and inferior oblique overaction
lateral rectus overacton , lateral rectus insertion too low , inferior insertion too posterior
what causes an a esotropia and a a exotropia
excyclophoria With compensatory superior oblique over action
what causes an a esotropia and a exotropia
inferior inderaction superior obveraction
excyclophoria with compensatory superior oblique overaction
lateral recutus undevraction
left rectus insertion too high
inferior insertion too anterior
a esotropia inferior rectus under action superior over action , medial rectus under action and medial rectus insertion is too low
superior oblique insertion is too posterior
how would you define a v pattern
15 diopters difference between elevation and depression
how would you define an a pattern
10 diopters difference
how would you define an a pattern
10 diopters difference
what is the ateiology of a v pattern
eleavators - over action of inferior oblique and underaction of superior rectus
greater relative divergence
depresses under action of superior oblique and over action of inferior rectus
greater relative convergence
what causes an a pattern
A pattern
Elevators: u/a of IO and o/a of SR
Greater relative convergence
Depressors: o/a of SO and u/a of IR
Greater relative divergence
what are example measurements of an v exo
35 dioptres base in elevation
25 base in pp
10 diopters base in primary position
what is an example of an a exo pattern
10 diopters base in elevation
25 diopters base in pp
25 dioptres bi depression
what are typical measurement for an a eso
35 diopters base out elevation
25 diopters base out primary position
10 diopters base out
what are the typical measurments for an v eso
10 diopters base out elevation
25 diopters base out pp
35 diopters base out depression
what tests would you preform to diagnose an alphabet pattern
OM
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- useful guide for surgical management
what information is important to gain from the investigation
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 are the reasons for managing pattern
Reasons for managing 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 are the reasons for managing alphabet patterns
Reasons for managing alphabet pattern
Obtain/retain BSV
Create a larger and more useful field of BSV
Achieve better ocular alignment
what are the surgical management options for alphabet patterns
Surgery may depend on aetiology or the presence of significant oblique over-action
Surgical principle
If associated vertical muscle over- & under-actions: operate on vertical muscles
If no/ mild vertical muscle over- & under-actions: operate on horizontal muscles
what surgery is done for a v pattern with an inferior oblique over action
Aim weakening of the IO muscle allows more convergence on elevation i.e. cause SR over-action increased ad-duction
Surgical options
IO recession
IO myectomy
Anterior transposition of IO
Horizontal surgery (recess/resect) performed at same time or subsequent sitting
Oblique muscle placed more anterior weakens its ab-ducting force
what management is done for a v pattern with inferior oblique over action
Surgical options
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 is done for an a pattern with a superior oblique over action
Aim weakening the SO muscle allows more convergence on depression i.e. cause IR over-action increased ad-duction
Surgical options
SO posterior tenectomy
SO posterior tenotomy
SO z-tenotomy
SO split lengthening
SO tendon spacer (silicon expander)
Operate on both SO if moderate/marked o/a of SO
Alternative
Bilateral IR resection
what surgery is done for an a pattern with a superior oblique overaction
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:
Success rate of 60-90% (Lee and Rosenbaum, 2003;Ron et al. 2009)
what surgery is done for an a pattern with a superiorr oblique over action
Aim weakening of both SR muscles allows more divergence on elevation i.e. cause IO over-action increased ab-duction
Surgical option
Bilateral SR recession
what is transposition of horizontal muscles
MR always moved towards the apex!
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
When moving the insertion down it cause the action of that muscle to be more slack on depression
how are horizontal muscles transposed to correct alphabet patterns
V Eso
Transpose MR insertion downwards
A Eso
Transpose MR insertion upwards
V Exo
Transpose LR insertion upwards
A Exo
Transpose LR insertion downwards
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
why are muscle insertions are slanted
Bietti (1970) introduced the surgical technique of slanting horizontal muscle insertions
Advocated in the absence of marked over-actions of the oblique muscles
May combine horizontal surgery with slanting of muscle insertions (Boyd’s technique)
Complications
Correcting A-exo can result in SO weakening
Vertical displacement of horizontal muscles may induce torsion
what surgical options are there for the slanting of muscle insertions
Principle
Horizontal muscle tension is stronger at upper margin than lower margin on elevation
Surgical option
Upper margin of LR recessed > than lower margin to reduce V-exotropia
i.e. less ab-duction on elevation: close V
Lower margin of LR recessed > than upper margin to reduce A-exotropia
i.e. less ab-duction on depression: close A
Upper margin of MR recessed > than lower margin to reduce A-esotropia
i.e. less ad-duction on elevation: opens A
Lower margin of MR recessed > than upper margin to reduce V-esotropia
i.e. less ad-duction on depression: opens V
In what circumstances may surgery be modified to prevent an A exo post-operatively?
When performing horizontal muscle surgery
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
Consecutive exotropia may be associated with A pattern due to SO over-action
Combined horizontal muscle surgery with SO weakening procedure may reduce the risk of A exo post-operatively
Large recession of IR for TAO move insertions nasally will prevent A-exo post-operatively
i.e. moving insertion nasally increases ad-duction, moving insertion temporally decreases ad-duction
what surgical options are there for a esos and a exos
recess mr displace up and resect lateral rectus displace down
superior oblique weaken
transpose sr lateral
a exo - recess mr diplsace up and recess inferior lateral rectus - displace down
weaken superior oblique
transpose inferior rectus medial
what surgical procedure is done for v exos and v esos
resess medial rectus for v eso resect for v exo displace done and resect lateral rectus for v eso for v eso displace down and recess lateral rectul rectus
transpose vertical recti
weaken inferior oblique for both
antero positon inferior oblique muscles for both
