10 - Pattern Strabismus Flashcards
Définition du Pattern strabismus?
Pattern strabismus is a horizontal deviation in which there is a difference in the magnitude of deviation between upgaze and downgaze.
Définition V pattern
The term V pattern describes a horizontal deviation that is more divergent (less convergent) in upgaze than in downgaze.
(Inverse du A pattern)
Définition A pattern
The term A pattern describes a horizontal deviation that is more divergent (less convergent) in downgaze than in upgaze.
(Inverse du V pattern)
Prévalence des A ou V pattern?
An A or V pattern is found in 15%–25% of horizontal strabismus cases.
À quel pattern est associé une overaction du m. oblique inférieur?
Apparent inferior oblique muscle overaction (overelevation in adduction [OEAd]) is associated with V patterns.
À quel pattern est associé une overaction du m. oblique supérieur?
Apparent superior oblique muscle overaction (overdepression in adduction [ODAd]) is associated with A patterns.
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)
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).
Étiologies de V pattern et A pattern?
- Oblique muscle dysfunction
- Orbital pulley system abnormalities
- Craniofacial anomalies
- Ocular torsion
- Selective innervation of superior or inferior compartments of the horizontal rectus muscles
En plus d’un V ou A patterns, autre signe associé à un Orbital pulley system abnormalities?
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.
Étiologie d’un X pattern
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.
Étiologie d’un Y pattern
Anomalous innervation.
* Sometimes seen in isolation and sometimes associated with other congenital cranial dysinnervation disorders, this most commonly produces a Y pattern
Comment mesurer un V ou un A pattern (positions)?
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.
Que veut dire : OEAd?
OverElevation in adduction (contexte d’inferior oblique muscle overaction)
Que veut dire : ODAd?
OverDepression in adduction (contexte de superior oblique muscle overaction)
Déviation en prism diopters pour dire qu’un A pattern est cliniquement significatif?
An A pattern is considered clinically significant when the difference in measurement between upgaze and downgaze is at least 10 prism diopters (D).