Pattern Strabismus
Michelle S. Go, MD
Laura B. Enyedi, MD
PREOPERATIVE CONSIDERATIONS
Clinical evaluation should include measurement of deviation in multiple positions of gaze with particular attention to the difference in deviation between primary gaze, downgaze (35 degrees chin elevation), and upgaze (25 degrees chin depression). Look for abnormal head position, overelevation or overdepression in adduction, and vertical deviations on lateral gazes. Assessment of fundus torsion can be performed by ophthalmoscopy or fundus photography (Fig. 51.1). Atypical location of muscle insertions may be seen by slit lamp examination or on MRI.
Anomalous head positions often indicate binocularity in that head position. Anomalous head positions can sometimes interfere with motor development in an infant and can cause neck muscular changes and/or neck pain in older children or adults.
Torsion may be a more reliable indicator of oblique overaction than versions.1 The normal fovea lines up with the lower 1/3 of the disc (upper 1/3 in the indirect view). The fovea will be lower (higher in the indirect view) with extorsion and higher (lower in the indirect view) with intorsion (Fig. 51.1).
 FIGURE 51.1. A. Indirect view of normal right fundus showing normal position of the fovea (white x) relative to the optic disc (within green dashed lines) and the location of the fovea with increasing amounts of intorsion or extorsion. B. Indirect view of right fundus with extorsion. C. Indirect view of right fundus with intorsion. |
Pattern Strabismus Etiologies1:
Oblique muscle dysfunction.
Anomalous orbits.
Heterotopy of muscle pulleys.
Neural mechanisms.
V-pattern:
Difference >15 prism diopters between upgaze and downgaze.
May be associated with inferior oblique overaction.
Examination findings:
Overelevation in adduction.
Left hypertropia on right gaze and right hypertropia on left gaze.
Fundus extorsion (Fig. 51.1B).
Abnormal head positions may be seen:
Chin up for V-pattern exotropia.
Chin down for V-pattern esotropia.
Associations include infantile esotropia, craniofacial anomalies, bilateral superior oblique palsy, Duane retraction syndrome, and Brown syndrome.
Y-pattern (subtype of V-pattern):
Divergence measures greater in upgaze, and there is a minimal change in deviation between primary and downgaze.
Examination may reveal bilateral inferior oblique overaction or pseudo-inferior oblique overaction (see sidebar).
Associations include Duane retraction syndrome and Brown syndrome.
Pseudo-inferior oblique overaction may present as V- or Y-pattern strabismus. It is thought to result from superior rectus and lateral rectus pulley instability vs cocontraction of the lateral rectus muscles as the eyes elevate in adduction. In pseudo-inferior oblique overaction, there is no hypertropia on direct side gaze, no difference in deviation with right vs left head tilt, and no torsion. Lateral rectus recession with superior transposition (or superior and lateral rectus transposition against the direction of instability) can be effective in normalizing the pattern.3,4,5 Inferior oblique weakening procedures are generally not successful.
Arrow pattern (subtype of V-pattern):
Greatest convergence occurs between primary gaze and downgaze (eg, ortho in upgaze, esotropia 5 prism diopters in primary position, and esotropia 20 prism diopters in downgaze).
May be associated with bilateral superior oblique palsy, especially when there is also extorsion on downgaze.
A-pattern:
Difference >10 prism diopters between upgaze and downgaze.
May be associated with superior oblique overaction.
Examination findings:
Overdepression in adduction.
Right hypertropia on right gaze and left hypertropia on left gaze.
Fundus intorsion (Fig. 51.1C).
Abnormal head positions may be seen:
Chin up for A-pattern esotropia.
Chin down for A-pattern exotropia.
Associations include bilateral Duane retraction syndrome, craniofacial anomalies, trisomy 21, and spinal column defects.
λ-Pattern (subtype of A-pattern):
Divergence measures greater in downgaze, and there is a minimal change in deviation between primary and upgaze.
Examination reveals overdepression on adduction.
May be associated with bilateral superior oblique overaction or inferior rectus underaction.
X-pattern:
Divergence increased in upgaze and downgaze compared to primary position.
Examination shows overelevation and overdepression on adduction.
Associated with longstanding exotropia and Duane retraction syndrome.
Possibly due to tight lateral rectus causing a leash effect or overaction of all four oblique muscles.
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