alphabet pattern

Question 1

what is a v pattern

Answer 1

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

Question 2

what is a pathological a pattern

Answer 2

more than 10 diopters difference from elevation to depression

Question 3

what are examples of a and v patterns

Answer 3

V Eso
5∆
Elevation

15∆
PP

30∆
Depression

V Exo
30∆
Elevation

15∆
PP

5∆
Depression

Question 4

what is an example of an eso in elevation primary position and depression

Answer 4

30 diopters elevation

15 diopters primary position

5 diopters depression

Question 5

what is an example of an a exo

Answer 5

5 dioptres elevation

15 diopters primary position

30 diopters depression

Question 6

what is the prevalence of a and v patterns

Answer 6

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

Question 7

what is the prevalence of a and v patterns

Answer 7

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

Question 8

what is the aetiology of a and v patterns

Answer 8

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

Question 9

what is the aetiology of a and v patterns

Answer 9

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

Question 10

what are the primary secondary and tertiary actions of the superior oblique muscle

Answer 10

depress , abbduct and intort

Question 11

what are the primary secondary and tertiary actions of the inferior oblique muscle

Answer 11

elevate abduct and extort

Question 12

what can a esotropia with an inferior oblique overaction be associated with

Answer 12

eso deviation greater on depression than elevation , elevate , abduct and extort - v pattern

Question 13

an exotropia with inferior oblique over action can have associated

Answer 13

v pattern

Question 14

an esotropia with a superior oblique over action can have associated

Answer 14

a pattern

Question 15

an exotropia with a superior oblique over action can have an associated

Answer 15

a pattern

Question 16

if you have a v eso what muscle weakness Is present

Answer 16

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

Question 17

if you have a v exo what muscle weakness do you have a

Answer 17

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

Question 18

if you have a a eso what muscle weakness do you have

Answer 18

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

Question 19

if someone has a A exo what muscle weakness do they have

Answer 19

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

Question 20

in what type of weakness do a or v patterns occur

Answer 20

a or v patterns occur most commonly in bilateral weakness

Question 21

what is abnormal horizontal muscle function caused by

Answer 21

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

Question 22

v exo can develop as a result of

Answer 22

over action of the lateral rectus

Question 23

an a type eso can develop as a result of

Answer 23

underaction of the medial rectus

Question 24

what can an a exo develop as a result of

Answer 24

under action of the lateral rectus

Question 25

what does abnormal insertion of horizontal muscles cause

Answer 25

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

Question 26

what does abnormal insertion of oblique muscle cause

Answer 26

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

Question 27

what does abnormal position of vertical rectus muscle insertion cause

Answer 27

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

Question 28

what is saggitlisation

Answer 28

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

Question 29

what does the saggitlisation of the inferior oblique cause

Answer 29

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

Question 30

what are the correlations between abnormalitieds in pulley position and alphabet patterns

Answer 30

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.

Question 31

describe muscle pulleys in x patterns

Answer 31

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

Question 32

how does the shape and position of eye contribute to the type of alphabet pattern you have

Answer 32

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

Question 33

what are other associations of alphabet patterns

Answer 33

Ocular syndromes Duanes Browns DVD

Question 34

what causes a v estotropia

Answer 34

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

Question 35

what causes both a v esotropia and v exotropia

Answer 35

incylophoria with compensatory inferior oblique oversction

Question 36

what causes a v exotropia

Answer 36

superior rectus underaction and inferior oblique overaction lateral rectus overacton , lateral rectus insertion too low , inferior insertion too posterior

Question 37

what causes an a esotropia and a a exotropia

Answer 37

excyclophoria With compensatory superior oblique over action

Question 38

what causes an a esotropia and a exotropia

Answer 38

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

Question 39

how would you define a v pattern

Answer 39

15 diopters difference between elevation and depression

Question 40

how would you define an a pattern

Answer 40

10 diopters difference

Question 41

how would you define an a pattern

Answer 41

10 diopters difference

Question 42

what is the ateiology of a v pattern

Answer 42

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

Question 43

what causes an a pattern

Answer 43

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

Question 44

what are example measurements of an v exo

Answer 44

35 dioptres base in elevation 25 base in pp 10 diopters base in primary position

Question 45

what is an example of an a exo pattern

Answer 45

10 diopters base in elevation 25 diopters base in pp 25 dioptres bi depression

Question 46

what are typical measurement for an a eso

Answer 46

35 diopters base out elevation 25 diopters base out primary position 10 diopters base out

Question 47

what are the typical measurments for an v eso

Answer 47

10 diopters base out elevation 25 diopters base out pp 35 diopters base out depression

Question 48

what tests would you preform to diagnose an alphabet pattern

Answer 48

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

Question 49

what information is important to gain from the investigation

Answer 49

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

Question 50

what are the reasons for managing pattern

Answer 50

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

Question 51

what are the reasons for managing alphabet patterns

Answer 51

Reasons for managing alphabet pattern Obtain/retain BSV Create a larger and more useful field of BSV Achieve better ocular alignment

Question 52

what are the surgical management options for alphabet patterns

Answer 52

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

Question 53

what surgery is done for a v pattern with an inferior oblique over action

Answer 53

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

Question 54

what management is done for a v pattern with inferior oblique over action

Answer 54

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

Question 55

what surgery is done for an a pattern with a superior oblique over action

Answer 55

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

Question 56

what surgery is done for an a pattern with a superior oblique overaction

Answer 56

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)

Question 57

what surgery is done for an a pattern with a superiorr oblique over action

Answer 57

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

Question 58

what is transposition of horizontal muscles

Answer 58

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

Question 59

how are horizontal muscles transposed to correct alphabet patterns

Answer 59

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

Question 60

why are muscle insertions are slanted

Answer 60

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

Question 61

what surgical options are there for the slanting of muscle insertions

Answer 61

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

Question 62

In what circumstances may surgery be modified to prevent an A exo post-operatively?

Answer 62

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

Question 63

what surgical options are there for a esos and a exos

Answer 63

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

Question 64

what surgical procedure is done for v exos and v esos

Answer 64

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