A and V patterns

Strabismus

Key Points

•V-pattern requires ≥15 PD difference between upgaze and downgaze; A-pattern requires ≥10 PD — V-patterns are 3× more common than A-patterns
•The most common cause of V-pattern is inferior oblique overaction (IOOA); the most common cause of A-pattern is superior oblique overaction (SOOA)
•IO anteriorization (Elliot & Nankin) is the most versatile procedure — it collapses V-pattern, weakens IOOA, and treats DVD simultaneously
•Without oblique dysfunction, use horizontal rectus transposition — remember 'MALE': Medial rectus toward Apex, Lateral rectus toward Empty space
•Always measure deviations in 3 vertical gaze positions (upgaze, primary, downgaze) in every strabismus patient to detect A/V patterns

1. Definition

A and V patterns are significant changes in the horizontal deviation between upgaze and downgaze. A V-pattern exists when the horizontal deviation is more divergent (or less convergent) in upgaze compared to downgaze by at least 15 PD. An A-pattern exists when the deviation is more divergent (or less convergent) in downgaze compared to upgaze by at least 10 PD (von Noorden, Campos — Binocular Vision and Ocular Motility, 6th Ed).

2. Epidemiology

A and V patterns are found in 15–25% of all horizontal strabismus cases. V-patterns are approximately 3 times more common than A-patterns. V-pattern esotropia is the most common combination. A and V patterns are commonly associated with infantile esotropia (15–25%) and craniofacial syndromes (e.g., Crouzon, Apert). V-pattern is strongly associated with inferior oblique overaction (IOOA); A-pattern with superior oblique overaction (SOOA). No significant sex predilection. More commonly recognized in childhood but can persist into adulthood.

3. Aetiology and causes

Oblique muscle dysfunction (most common cause):

V-pattern: inferior oblique overaction (IOOA) — overacting inferior obliques abduct the eyes in upgaze, increasing divergence
A-pattern: superior oblique overaction (SOOA) — overacting superior obliques abduct the eyes in downgaze, increasing divergence

Horizontal rectus muscle anomalies:

V-pattern: lateral rectus muscles displaced upward or medial rectus muscles displaced downward relative to the horizontal meridian
A-pattern: lateral rectus muscles displaced downward or medial rectus muscles displaced upward

Structural/orbital factors:

Craniofacial anomalies (Crouzon, Apert, plagiocephaly): abnormal orbital geometry alters muscle planes
S-shaped lateral rectus path in craniofacial syndromes

Vertical rectus muscle dysfunction:

Superior rectus underaction or inferior rectus overaction can contribute

Idiopathic: no identifiable oblique dysfunction or structural abnormality in some cases

4. Pathogenesis

The horizontal deviation changes with vertical gaze because of the secondary actions of the oblique and vertical rectus muscles:

V-pattern mechanism:

Inferior oblique overaction: the IO's tertiary action is abduction. In upgaze, overacting inferior obliques excessively abduct both eyes, increasing the divergent component. In downgaze, inferior obliques are relaxed, and the convergent tone dominates.
Result: V-esotropia shows less esotropia in upgaze, more in downgaze. V-exotropia shows more exotropia in upgaze, less in downgaze.

A-pattern mechanism:

Superior oblique overaction: the SO's tertiary action is abduction. In downgaze, overacting superior obliques excessively abduct both eyes, increasing divergence. In upgaze, superior obliques relax.
Result: A-esotropia shows less esotropia in downgaze, more in upgaze. A-exotropia shows more exotropia in downgaze, less in upgaze.

Alternative mechanism (Knapp): abnormal insertion or displacement of horizontal rectus muscles changes their vertical-torsional vector, creating gaze-dependent horizontal deviation changes independent of oblique dysfunction.

5. Classification

By pattern:

V-pattern: horizontal deviation more divergent in upgaze vs. downgaze by ≥15 PD
A-pattern: horizontal deviation more divergent in downgaze vs. upgaze by ≥10 PD
X-pattern: more divergent in both upgaze and downgaze (rare)
Y-pattern: deviation increases sharply only in upgaze (lambda pattern is the reverse)
Diamond pattern: more convergent in both upgaze and downgaze (rare)

By associated horizontal deviation:

A-esotropia, V-esotropia
A-exotropia, V-exotropia

By etiology:

With oblique dysfunction: IOOA (V-pattern), SOOA (A-pattern)
Without oblique dysfunction: horizontal rectus malposition or idiopathic
Structural: craniofacial anomalies

Grading of oblique overaction (von Noorden):

+1: slight overaction
+2: moderate overaction
+3: marked overaction
+4: severe overaction (eye elevates above horizontal midline in adduction for IOOA)

6. Risk factors and associations

Infantile esotropia: V-pattern with inferior oblique overaction is very common.
Superior oblique palsy (unilateral or bilateral): most common cause of A-pattern.
Craniofacial syndromes: Crouzon, Apert, Pfeiffer — abnormal orbital anatomy creates V-pattern due to extorted orbits.
Down syndrome: V-pattern common.
Brown syndrome: can produce A-pattern due to superior oblique tendon restriction.
Plagiocephaly: asymmetric orbital geometry.
Previous strabismus surgery: altered muscle dynamics may create secondary A/V pattern.
Dissociated vertical deviation (DVD): often coexists with V-pattern in infantile esotropia.

7. Clinical features

Symptoms:

Abnormal head posture (AHP): chin-down position (to use upgaze where deviation is least) in V-esotropia or A-exotropia. Chin-up position in A-esotropia or V-exotropia.
Intermittent or variable diplopia in adults
Parents note deviation worse in certain gaze directions

Signs:

Measurement in 3 positions of gaze: primary position, 25-degree upgaze, and 35-degree downgaze
V-pattern: ≥15 PD difference (more divergent in upgaze)
A-pattern: ≥10 PD difference (more divergent in downgaze)
Assess oblique muscle function in all 9 positions of gaze:
IOOA: overelevation of the adducting eye in upgaze (V-pattern)
SOOA: overdepression of the adducting eye in downgaze (A-pattern)
Grade oblique overaction: +1 to +4
Fundus torsion: excyclotorsion (IOOA / SO palsy), incyclotorsion (SOOA)
Measure torsion: double Maddox rod, fundus photography, OCT
Associated DVD: slow upward drift of non-fixating eye
Head posture: document chin elevation/depression, face turn, and head tilt
Assess for associated horizontal strabismus and measure at distance and near

8. Investigations

Nine-position gaze measurements: prism cover test in primary, upgaze (25°), downgaze (25°), and side gazes to document the A or V pattern and oblique function.

Double Maddox rod test: quantify torsion — excyclotorsion in V-pattern with IOOA, incyclotorsion in A-pattern with SOOA.

Fundus photography or indirect ophthalmoscopy: assess foveo-disc angle for objective torsion measurement. Normal: fovea 0.3 disc diameters below disc center.

OCT: can quantify optic disc-foveal angle for objective torsion.

Synoptophore: measure subjective and objective angle in different gaze positions, assess torsion.

Hess/Lees screen: document pattern of muscle over- and underaction.

Forced duction test: intraoperatively to assess for restriction (Brown syndrome, restrictive strabismus).

CT orbits: in craniofacial syndromes to assess orbital geometry, muscle paths, and pulley positions.

MRI orbits (thin cuts): evaluate extraocular muscle size and path, especially in complex cases.

9. Differential diagnosis

Superior oblique palsy (unilateral or bilateral): produces A-pattern but is an incomitant deviation with hypertropia, head tilt, and positive Parks 3-step test — distinct from comitant A-pattern.

Brown syndrome: restricted elevation in adduction mimics superior oblique overaction; forced duction test is positive (restricted).

Inferior oblique palsy: rare, can produce A-pattern with limited elevation in adduction.

Dissociated vertical deviation (DVD): upward drift may be confused with inferior oblique overaction, but DVD is non-comitant, bilateral, and the hyperdeviation increases under cover.

Thyroid eye disease: restriction of inferior rectus can cause pattern strabismus.

10. Complications

Abnormal head posture (AHP): compensatory chin-up or chin-down position to maintain fusion in position of least deviation. Chronic AHP can cause cervical spine issues.
Diplopia: especially in adults if pattern creates misalignment in the reading position (downgaze)
Cosmetic concern: variable appearance of strabismus with gaze direction
Surgical undercorrection or overcorrection of the pattern element
Anti-elevation syndrome: after inferior oblique anteriorization, limitation of elevation in abduction (occurs in 20–25%)
New or worsened torsional symptoms after oblique muscle surgery
Consecutive A-pattern after V-pattern surgery and vice versa

11. Management

Principles: Treat the A or V pattern when ≥15 PD (V) or ≥10 PD (A) AND associated with compensatory head posture or significant functional impact.

1. Address oblique dysfunction first (if present):

V-pattern with IOOA:

Bilateral inferior oblique weakening: myectomy, recession (10–14 mm from origin), or anteriorization (Elliot & Nankin procedure)
IO anteriorization: most effective for collapsing V-pattern and simultaneously treating DVD. IO is repositioned to just temporal to the inferior rectus insertion
IO myectomy: simplest, effective for +2 to +3 overaction

A-pattern with SOOA:

Bilateral superior oblique weakening: SO tenotomy (free or controlled), silicone tendon expander, posterior 7/8 tenectomy
Caution: SO weakening in patients with pre-existing excyclotorsion can worsen torsional diplopia

2. Without oblique dysfunction — horizontal rectus transposition:

V-pattern: transpose both medial recti downward (half-tendon width) and/or both lateral recti upward
A-pattern: transpose both medial recti upward and/or both lateral recti downward
Mnemonic: 'MALE' — Medial rectus toward Apex, Lateral rectus toward Empty space of the pattern
Each half-tendon-width transposition corrects approximately 15–20 PD of A/V collapse

3. Combine with horizontal surgery:

Perform oblique surgery or transposition simultaneously with recession/resection for the horizontal deviation
Example: BMR + bilateral IO weakening for V-pattern esotropia

4. Craniofacial syndromes: may require customized approach based on CT orbital anatomy

12. Prognosis

V-pattern with IOOA: good surgical outcomes; IO weakening collapses V-pattern by 15–25 PD in 80–90% of cases.

A-pattern with SOOA: SO weakening collapses A-pattern effectively, though risk of iatrogenic SO palsy features (new torsion, Brown syndrome resolution creating IOOA).

Horizontal rectus transposition: effective in 70–80% for collapsing patterns without oblique dysfunction.

Head posture: usually improves significantly with successful pattern correction.

Recurrence: relatively low (10–15%) for isolated oblique surgery.

Anti-elevation syndrome after IO anteriorization: occurs in 20–25%, usually mild and well-tolerated. More pronounced if IO placed anterior to or at the level of the IR insertion.

Torsional outcomes: improved excyclotorsion after IO weakening in most cases.

Overall, pattern strabismus surgery is among the more predictable and satisfying strabismus procedures.

Clinical Pearls

Remember the mnemonic 'MALE' for horizontal rectus transposition: Medial rectus toward the Apex of the pattern, Lateral rectus toward the Empty space.

V-pattern threshold is ≥15 PD difference between upgaze and downgaze; A-pattern threshold is ≥10 PD — the 'V' has more letters than 'A', matching the larger threshold.

Inferior oblique anteriorization is a powerful procedure that simultaneously collapses V-pattern, weakens IO overaction, AND treats DVD — consider it as the first-line IO procedure in infantile esotropia.

Bilateral superior oblique palsy (e.g., after head trauma) produces an A-pattern with excyclotorsion, chin-down head posture, and V-pattern reversal on head tilt — don't confuse with simple A-pattern strabismus.

Always measure horizontal deviations in upgaze, primary position, AND downgaze in every strabismus patient — missing an A/V pattern leads to suboptimal surgical planning.

Exam Trap: V-pattern requires ≥15 PD difference between upgaze and downgaze — the most common cause is inferior oblique overaction (IOOA), which abducts the eyes in upgaze. Do not confuse the threshold with A-pattern (≥10 PD).

Exam Trap: A-pattern requires ≥10 PD difference between upgaze and downgaze — the most common cause is superior oblique overaction (SOOA), which abducts the eyes in downgaze. The lower threshold reflects the greater functional significance of downgaze (reading position).

Exam Trap: V-pattern esotropia — always check for craniofacial syndromes (Crouzon, Apert). These patients have shallow, extorted orbits that alter extraocular muscle planes, producing V-pattern even without primary oblique dysfunction. A CT orbit is mandatory.

Oral-exam questions

What is the threshold for a clinically significant V-pattern? — ≥15 PD difference between upgaze and downgaze. For A-pattern: ≥10 PD (von Noorden, Campos).
Why is V-pattern associated with inferior oblique overaction? — The IO's tertiary action is abduction. In upgaze, overacting IOs excessively abduct both eyes, increasing divergence in upgaze relative to downgaze.
What is the MALE rule? — For horizontal rectus transposition in patterns without oblique dysfunction: Medial rectus toward the Apex, Lateral rectus toward the Empty space of the letter pattern.
What is anti-elevation syndrome? — Limitation of elevation in abduction occurring after IO anteriorization, reported in 20–25% of cases. More pronounced if IO is placed anterior to or at the level of the IR insertion.
How do you differentiate DVD from IOOA? — DVD is a slow upward drift that increases under cover, does NOT follow Hering's law, and the hyperdeviation is variable and non-comitant. IOOA is overelevation in adduction that is comitant and follows Hering's law.
What procedure simultaneously treats IOOA, V-pattern, and DVD? — IO anteriorization (Elliot & Nankin procedure) — the IO is repositioned to just temporal to the inferior rectus insertion.

Mnemonics

MALE

M — Medial rectus toward the Apex of the pattern A — Apex L — Lateral rectus toward the Empty space E — Empty space

V-IOOA / A-SOOA

V-pattern = Inferior Oblique OverAction A-pattern = Superior Oblique OverAction IO tertiary action = abduction (increases divergence in upgaze → V) SO tertiary action = abduction (increases divergence in downgaze → A)

Comparison Tables

A-Pattern vs V-Pattern: Key Differences

A-Pattern vs V-Pattern: Key Differences
Feature	V-Pattern	A-Pattern
Threshold for significance	≥15 PD	≥10 PD
Relative prevalence	3× more common	Less common
Oblique dysfunction	Inferior oblique overaction	Superior oblique overaction
Most common combination	V-esotropia	A-esotropia
Direction of increased divergence	Upgaze	Downgaze
Chin position (ET)	Chin down (uses upgaze)	Chin up (uses downgaze)
Fundus torsion	Excyclotorsion	Incyclotorsion

Threshold for significance

V-Pattern: ≥15 PD
A-Pattern: ≥10 PD

Relative prevalence

V-Pattern: 3× more common
A-Pattern: Less common

Oblique dysfunction

V-Pattern: Inferior oblique overaction
A-Pattern: Superior oblique overaction

Most common combination

V-Pattern: V-esotropia
A-Pattern: A-esotropia

Direction of increased divergence

V-Pattern: Upgaze
A-Pattern: Downgaze

Chin position (ET)

V-Pattern: Chin down (uses upgaze)
A-Pattern: Chin up (uses downgaze)

Fundus torsion

V-Pattern: Excyclotorsion
A-Pattern: Incyclotorsion

Surgical Approaches for A/V Patterns

Surgical Approaches for A/V Patterns
Scenario	Procedure	Expected Correction	Notes
V-pattern with IOOA	Bilateral IO weakening (myectomy/recession/anteriorization)	15–25 PD collapse	IO anteriorization also treats DVD
A-pattern with SOOA	Bilateral SO weakening (tenotomy/tenectomy)	10–20 PD collapse	Risk of worsening torsion if pre-existing excyclotorsion
V-pattern without oblique dysfunction	MR transposition down + LR transposition up	15–20 PD per half-tendon width	MALE mnemonic: MR to Apex, LR to Empty
A-pattern without oblique dysfunction	MR transposition up + LR transposition down	15–20 PD per half-tendon width	MALE mnemonic applies
Combined pattern + horizontal deviation	Oblique surgery + horizontal recession/resection	Additive	Address oblique dysfunction in same sitting

V-pattern with IOOA

Procedure: Bilateral IO weakening (myectomy/recession/anteriorization)
Expected Correction: 15–25 PD collapse
Notes: IO anteriorization also treats DVD

A-pattern with SOOA

Procedure: Bilateral SO weakening (tenotomy/tenectomy)
Expected Correction: 10–20 PD collapse
Notes: Risk of worsening torsion if pre-existing excyclotorsion

V-pattern without oblique dysfunction

Procedure: MR transposition down + LR transposition up
Expected Correction: 15–20 PD per half-tendon width
Notes: MALE mnemonic: MR to Apex, LR to Empty

A-pattern without oblique dysfunction

Procedure: MR transposition up + LR transposition down
Expected Correction: 15–20 PD per half-tendon width
Notes: MALE mnemonic applies

Combined pattern + horizontal deviation

Procedure: Oblique surgery + horizontal recession/resection
Expected Correction: Additive
Notes: Address oblique dysfunction in same sitting

Inferior Oblique Weakening Procedures Compared

Inferior Oblique Weakening Procedures Compared
Procedure	Mechanism	Indication	Advantages	Complications
IO myectomy	Excision of 8–10 mm of IO	+2 to +3 IOOA	Simplest, fast	May under-correct +4 IOOA
IO recession	Reattach IO 2 mm posterolateral to IR	+2 to +3 IOOA	Graded, adjustable	Slightly more complex
IO anteriorization (Elliot–Nankin)	Reposition IO to temporal IR insertion	+3 to +4 IOOA, DVD	Treats IOOA + DVD + V-pattern	Anti-elevation syndrome (20–25%)
IO denervation-extirpation	Denervate and excise IO	Severe, recurrent IOOA	Maximal weakening	Risk of IR adherence

IO myectomy

Mechanism: Excision of 8–10 mm of IO
Indication: +2 to +3 IOOA
Advantages: Simplest, fast
Complications: May under-correct +4 IOOA

IO recession

Mechanism: Reattach IO 2 mm posterolateral to IR
Indication: +2 to +3 IOOA
Advantages: Graded, adjustable
Complications: Slightly more complex

IO anteriorization (Elliot–Nankin)

Mechanism: Reposition IO to temporal IR insertion
Indication: +3 to +4 IOOA, DVD
Advantages: Treats IOOA + DVD + V-pattern
Complications: Anti-elevation syndrome (20–25%)

IO denervation-extirpation

Mechanism: Denervate and excise IO
Indication: Severe, recurrent IOOA
Advantages: Maximal weakening
Complications: Risk of IR adherence

Self-Assessment (5)

MCQ

A 4-year-old child with infantile esotropia is found to have 35 PD esotropia at primary position, 20 PD in upgaze, and 40 PD in downgaze with bilateral overelevation in adduction. What pattern and associated dysfunction is present?

MCQ

In a patient with V-pattern esotropia WITHOUT oblique muscle dysfunction, horizontal rectus transposition is planned. In which direction should the medial recti be transposed?

MCQ

A child with V-pattern esotropia and +3 bilateral inferior oblique overaction also has dissociated vertical deviation. Which single procedure best addresses all three problems?

MCQ

An A-pattern exotropia patient has bilateral superior oblique overaction and is found to have excyclotorsion on double Maddox rod. What surgical concern should be considered before SO weakening?

MCQ

Which craniofacial syndrome is most commonly associated with V-pattern strabismus due to abnormal orbital geometry?

References

von Noorden GK, Campos EC. Binocular Vision and Ocular Motility: Theory and Management of Strabismus, 6th Edition. Mosby, 2002.
Wright KW, Spiegel PH, Thompson LS. Handbook of Pediatric Strabismus and Amblyopia, 2nd Edition. Springer, 2006.
Parks MM. The overacting inferior oblique muscle. Am J Ophthalmol. 1974;77(6):787-797.
Elliot RL, Nankin SJ. Anterior transposition of the inferior oblique. J Pediatr Ophthalmol Strabismus. 1981;18(3):35-38.
Knapp P. Vertically incomitant horizontal strabismus: the so-called A and V syndromes. Trans Am Ophthalmol Soc. 1959;57:666-699.
AAO Preferred Practice Pattern: Esotropia and Exotropia (2017)

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