a-v pattern horizontal strabismus

A-V patternHorizontal strabismus

A R ZandiFeiz hospital

Change in magnitude of deviation in upgaze and downgaze

A-V pattern is a vertical incomittancy

More convergent in upgaze compared with downgaze

A pattern

More convergent in downgaze compared with upgaze

V pattern

An A or V pattern is found in 15%-25% of horizontal strabismus

Bilateral oblique muscle dysfunction

Cause

IO overaction is associated with V pattern

SO overaction is associated with A pattern

These associations reflect the ancillary abducting action in upgaze and downgaze

Horizontal rectus muscle dysfunction

Cause….

Vertical rectus muscle dysfunction

Cause….

Measurement of the alignment in downgaze and upgaze

Clinical features

When in 25` from the primary position at least 10^ difference in deviation is detected, the clinically significant A pattern is present

To be a clinically significant V pattern the difference must be at least 15^

Surgery for= Clinically significant pattern

Management

Most often in combination with correction of the underlying horizontal deviation

Surgery for pattern

Patients with large A or V pattern usually also have significant corresponding oblique muscle dysfunction

If the pattern is related to overaction of the oblique muscle,these are weakened as part of the surgical plan

Weakening the IO muscles or tucking the SO tendons corrects up to 15-25^ of V pattern

Bilateral SO tenotomy correct up to 35-45^ of A pattern(they produce 35-45^ esoshift in downgaze)

Displacing the horizontal rectus muscle insertions is indicated when there is no oblique dysfunction

The amount of displacement usually is ½ to a full tendon width

MR are always moved toward the direction where convergence is greater or divergence is less(upward in A pattern and downward in V pattern)

This displacement has no net horizontal,vertical or torsional effect in the primary position

For example for V pattern when MR is displaced downward(and LR upward) in downgaze MR will be relaxed and the LR will be tightened( thereby decreasing the V pattern)

MALE

The muscle is moved in the direction in which the muscle`s horizontal effect is to be lessened