10 - Pattern Strabismus

Question 1

Définition du Pattern strabismus?

Answer 1

Pattern strabismus is a horizontal deviation in which there is a difference in the magnitude of deviation between upgaze and downgaze.

Question 2

Définition V pattern

Answer 2

The term V pattern describes a horizontal deviation that is more divergent (less convergent) in upgaze than in downgaze.
(Inverse du A pattern)

Question 3

Définition A pattern

Answer 3

The term A pattern describes a horizontal deviation that is more divergent (less convergent) in downgaze than in upgaze.
(Inverse du V pattern)

Question 4

Prévalence des A ou V pattern?

Answer 4

An A or V pattern is found in 15%–25% of horizontal strabismus cases.

Question 5

À quel pattern est associé une overaction du m. oblique inférieur?

Answer 5

Apparent inferior oblique muscle overaction (overelevation in adduction [OEAd]) is associated with V patterns.

Question 6

À quel pattern est associé une overaction du m. oblique supérieur?

Answer 6

Apparent superior oblique muscle overaction (overdepression in adduction [ODAd]) is associated with A patterns.

Question 7

Pourquoi un overaction des m. obliques supérieurs et/ou des m. obliques inférieurs sont associés à un V pattern et à A pattern respectivement? (Physiologie musculaire)

Answer 7

These associations
* May be due to the tertiary abducting action of these muscles in upgaze and downgaze, respectively;
* However, oblique dysfunction is frequently associated with ocular torsion that can also contribute to A or V patterns (see below).

Question 8

Étiologies de V pattern et A pattern?

Answer 8

• Oblique muscle dysfunction
• Orbital pulley system abnormalities
• Craniofacial anomalies
• Ocular torsion
• Selective innervation of superior or inferior compartments of the horizontal rectus muscles

Question 9

En plus d’un V ou A patterns, autre signe associé à un Orbital pulley system abnormalities?

Answer 9

Orbital pulley system abnormalities.
* Abnormalities (heterotopia) of the orbital pulley system have been described as a cause of simulated oblique muscle overactions and of altered rectus muscle pathways and functions that can result in A or V patterns.
* These pulley effects may help explain the observation that patients with upward- or downward- slanting palpebral fissures may show A or V patterns because of an under lying variation in orbital configuration, which is reflected in the orientation of the fissures.

Question 10

Étiologie d’un X pattern

Answer 10

Restricted horizontal rectus muscles.
* Contracture of the lateral rectus muscles in large- angle exotropia may result in an X pattern, with globe slippage in adduction.

Question 11

Étiologie d’un Y pattern

Answer 11

Anomalous innervation.
* Sometimes seen in isolation and sometimes associated with other congenital cranial dysinnervation disorders, this most commonly produces a Y pattern

Question 12

Comment mesurer un V ou un A pattern (positions)?

Answer 12

The presence of A and V patterns is determined by measuring alignment while the patient fixates on an accommodative target at distance, with fusion prevented with the prism alternate cover test, in primary position and in straight upgaze and downgaze, approximately 25° from the primary position.

Proper refractive correction is necessary during measurement because an uncompensated accommodative component can induce exaggerated convergence in downgaze.

The examiner should look specifically for apparent oblique muscle overaction (OEAd or ODAd) because of its frequent association with pattern strabismus.

Question 13

Que veut dire : OEAd?

Answer 13

OverElevation in adduction (contexte d’inferior oblique muscle overaction)

Question 14

Que veut dire : ODAd?

Answer 14

OverDepression in adduction (contexte de superior oblique muscle overaction)

Question 15

Déviation en prism diopters pour dire qu’un A pattern est cliniquement significatif?

Answer 15

An A pattern is considered clinically significant when the difference in measurement between upgaze and downgaze is at least 10 prism diopters (D).

Question 16

Déviation en prism diopters pour dire qu’un V pattern est cliniquement significatif?

Answer 16

For a V pattern, this difference must be at least 15D because there is normally some physiologic convergence in downgaze.

Question 17

Pourquoi un V pattern est-il cliniquement significatif à 15 prism diopters alors qu’un A pattern est cliniquement significatif à partir de 10 prism diopters?

Answer 17

For a V pattern, this difference must be at least 15D because there is normally some physiologic convergence in downgaze.

Question 18

Type de Pattern Strabismus le plus fréquent?

Answer 18

• V pattern is the most common type of pattern strabismus
• V pattern occurs most frequently in patients with infantile esotropia

Question 19

V pattern occurs most frequently avec quel autre type de strabisme?

Answer 19

V pattern occurs most frequently in patients with infantile esotropia.

Question 20

Onset du V pattern dans contexte d’esotropie infantile?
Survient-il en même temps que l’esotropie infantile?

Answer 20

The pattern is usually not present when the esotropia first develops but becomes apparent during the first year of life or later.

Question 21

Étiologies associées à V pattern (x3)

Answer 21

V pattern occurs in patients
* With infantile esotropia (most frequently)
* With superior oblique palsies (particularly if they are bilateral)
* With craniofacial malformations

Question 22

The second most common type of pattern strabismus?

Answer 22

A pattern is the second most common type of pattern strabismus

Question 23

Étiologies les plus fréquentes associées à A pattern (x2)

Answer 23

A pattern occurs most frequently in patients
* With exotropia
* With spina bifida

Question 24

Synonyme de Y pattern

Answer 24

Pseudo- overaction of the inferior oblique muscle
* Normal ocular alignment in primary position and downgaze
* But the eyes diverge in upgaze

Question 25

À quoi ressemble le Y pattern à l’E/O?

Answer 25

• Normal ocular alignment in primary position and downgaze
• But the eyes diverge in upgaze

Question 26

Cause du Y partten?

Answer 26

These patients appear to have overacting inferior oblique muscles, but the deviation is thought to be due to anomalous innervation of the lateral rectus muscles in upgaze.

Question 27

Clinical characteristics that help differentiate Y pattern strabismus vs inferior oblique overaction?

Answer 27

Clinical characteristics that help identify this form of strabismus include the following:
* The overelevation is not seen when the eyes are moved directly horizontally, but it becomes manifest when the eyes are directed horizontally and slightly into upgaze
* There is no fundus torsion
* There is no difference in vertical deviation with head tilts
* There is no superior oblique muscle underaction

Question 28

À quoi ressemble un X pattern à l’E/O?

Answer 28

In X- pattern strabismus, an exodeviation is present in primary position and increases in both upgaze and downgaze.

Question 29

Overelevation et/ou overdepression dans le X pattern?

Answer 29

This pattern is usually associated with overelevation and overdepression in adduction when the eye moves slightly above or below direct side gaze.

Question 30

X pattern occurs most frequently avec quel autre type de strabisme?

Answer 30

X patterns are most commonly seen in patients with large- angle exotropia.

Question 31

Qu’est-ce que le λ Pattern

Answer 31

This rare pattern is a variant of A- pattern exotropia.

Question 32

Caractéristique du λ- pattern strabismus à l’E/O?

Answer 32

• In λ- pattern strabismus, the horizontal deviation is the same in primary position and upgaze but becomes more divergent in downgaze.
• The λ pattern is usually associated with ODAd.

Question 33

Tx en général des Pattern strabismus?

Answer 33

Clinically significant patterns are typically treated surgically, in combination with correction of the under lying horizontal deviation.

Question 34

Règle générale pour déplacement des m. rectus médial et rectus latéral dans le Tx chirurgical d’un V pattern et A pattern?

Answer 34

For patients with no apparent overaction of the oblique muscles or a pattern inconsistent with oblique dysfunction, vertical transposition of the horizontal muscles is performed.
* The muscles are transposed from one- half to a full tendon width.
* The medial rectus muscles are always moved toward the “apex” of the pattern (upward in A patterns and downward in V patterns).
* The lateral rectus muscles are moved toward the open end (upward in V patterns and downward in A patterns).
* A useful mnemonic is MALE: medial rectus muscle to the apex, lateral rectus muscle to the empty space.

Question 35

Tx chirurgical d’un V pattern :
* With OEAd
* Without OEAd
* With dissociated vertical deviation (DVD)

Answer 35

• For V- pattern esotropia or exotropia associated with OEAd, weakening of the inferior oblique muscles is performed.
• For patients who also have dissociated vertical deviation (DVD), anterior transposition of the inferior oblique muscle may improve both the V pattern and the DVD.
• Because patients with V- pattern infantile esotropia who are younger than 2 years are at risk of developing DVD, anterior transposition of the inferior oblique may be considered preemptively for this group.
• For patients with V- pattern esotropia or exotropia not associated with OEAd, appropriate vertical transposition of the horizontal rectus muscles is performed.

Question 36

Tx chirurgical d’un A pattern :
* With ODAd
* Without ODAd

Answer 36

• For A- pattern exotropia or esotropia associated with ODAd, weakening of the superior oblique muscles is performed.
• Tenotomy of the posterior 7/8 of the insertions is an effective method for treating up to 20D of A pattern, without a significant effect on torsion.
• Lengthening of the oblique tendon by recession, insertion of a spacer, or a split- tendon lengthening procedure may also be used to weaken the superior oblique muscles.
• Bilateral superior oblique tenotomy is a very powerful procedure that may correct up to 40D–50D of A pattern.
• There is a risk of induced torsion with this procedure, which may be symptomatic for patients with binocular fusion.
• For patients with A- pattern exotropia or esotropia not associated with ODAd, appropriate vertical transposition of the horizontal rectus muscles is performed.

Question 37

Tx chirurgical d’un Y pattern

Answer 37

• Because Y patterns are not due to overaction of the inferior oblique muscles, weakening these muscles is not an effective treatment.
• Superior transposition of the lateral rectus muscles can improve this pattern but does not eliminate it.

Question 38

Tx chirurgical d’un X pattern

Answer 38

• X patterns are usually due to pseudo- overaction of the oblique muscles, which is caused by contracture of the lateral rectus muscles in large- angle exotropia.
• Recession of the lateral rectus muscles alone usually improves the pattern.

Question 39

Tx chirurgical d’un λ pattern :
* With ODAd

Answer 39

• These patterns are typically associated with ODAd.
• Appropriate superior oblique weakening procedures may be used in patients with this pattern.