on pattern strabismus in a simplified way

1. PATTERN STRABISMUS

2. Introduction
• Present when horizontal deviation change
in magnitude from up gaze to downgaze
• Type of Incomitant strabismus
• Described using alphabets
Alphabetical pattern

3. TYPES
• Types
1.A pattern
2.V pattern
3.X pattern
4.Y pattern
5.λ pattern

4. Defination:
• Measured in Primary gaze, 25 degree
upgaze, 35 degree downgaze
• V pattern: difference of ≥15 PD
• A-pattern: difference of ≥10 PD
Depending on primary gaze :
V or A Esotropia / Exotropia

6. Other patterns:
– X-pattern: Type 1DRS
– Y-pattern: LR aberrant innervation
– Lambda pattern : SOOA

7. PREVALANCE
A or V pattern: 12.5% -50 %
V-Esotropia – most common pattern associated
with Infantile Strabismus.
A pattern-most commonly seen in XT (Trisomy
21, Spina bifida)

8. THEORIES
ETIOLOGY
Vertical school
Structural
factors
Anomalies of
muscle
insertions
Horizontal
school

9. 1. HORIZONTAL THEORY
• Horizontal rectus muscles are the culprits
‘V’ ET – over action of MR
‘V’ XT – over action of LR
‘A’ ET – Under action of LR
‘A’ XT –under action of MR

11. 2.Oblique muscle dysfunction:
• Actions of Oblique muscle?
IO OA or SO underaction: V pattern
IO underaction or SO OA: A pattern

12. 3.Vertical rectus muscle dysfunction
SR underaction: less
adduction on elevation
IR overaction: more
adduction in depression
V-pattern

13. 4.Anatomical anomalies of orbits:
Cause dysfunction of Oblique Muscles
• Mongoloid features: IO underaction – A-pattern
• Antimongoloid features: IO overaction: V-pattern

15. • The trochlea acts as the functional
origin of superior oblique
• Sagittalisation– anterior positioning
of trochlea. Oblique muscles
become more parallel to the
antero-posterior axis
• De- sagittalisation– posterior
positioning of trochlea. Oblique
muscles become more parallel to
coronal plane

16. V pattern
SO weakening
IO overaction
De-sagittalisation
Plagiocephaly
A pattern
SO overaction
Sagittalisation
Hydrocephalus
Frontal bossing

17. 5. The Pulley effect
DISPLACED MUSCLE : Action BECOME WEAKER
Upward displacement of LR: weak abduction on elevation- A pattern
Downward displacement of LR: V pattern

18. Craniofacial anomaly with associated pattern:
Crouzon’s syndrome (mid facial hypoplasia)
This boy shows the classic “V” pattern seen in
Crouzon’s syndrome. There is overelevation and
underdepression of each eye in adduction.

19. Clinical presentation:
• Intermittent transient diplopia:
• Asthenopic symptoms: mainly during near work in V-Eso and
A-Exo
• Abnormal head posture : to attain BSV
V-Eso:
V-Exo:
A-Eso:
Chin depressed
Chin elevated
Chin elevated

20. WORK-UP
 Routine squint evaluation
 Measurement in 9 cardinal gaze.
 25 degree up and 35 degrees down gaze.(33cm)
 ‘V’ -15 Prism difference between up and down gaze.
 ‘A’ -10PD difference between up and down gaze.
 Clinical significance-Depends on with which it
interferes with normal binocular function in the
physiologically important positions of gaze

21. All cases of exo or eso deviations should be checked for A or V
patterns
A. Measurement of deviation
von Noorden’s technique
- 33 cm fixation distance
- full refractive correction
- 25 degree elevation &
35 degree depression

22. B. Version test
- most important for planning and management of A-
V pattern.
- overactions and underactions of oblique muscles
noted.
C. BSV in the primary and downward positions of gaze

23. Management
 Treatment of refractive error and amblyopia if present.
 Indications for the surgery
1. To improve , maintain or regain binocular single vision
2. Cosmetic improvement
3. Chin elevation or depression.

24. 1. OBLIQUE MUSCLE SURGERY :
• Done in presence of oblique muscle overaction
• V- pattern : weakening of overacting IO muscle
• A- pattern : weakening of overacting SO muscle

25. IO weakening
• Disinsertion
• Myectomy
• Recession
• Anterior transposition if
associated with DVD
SO weakening
• Tenotomy
• Recession
• Silicon expander
• Translational recession

26. IO Myectomy

28. 2.Horizontal Muscle surgery
Combined with vertical transposition of
their insertion.
Principle: to shift the muscle in the
direction you want to weaken them

29. • V- pattern :
LR shifted upwards and MR downwards
• A- pattern :
MR shifted upwards and LR downwards.