Optometry & Visual Performance 285 Volume 13 | Issue 4 | December 2025 Types of Strabismus (Each type has unique etiological, clinical, and diagnostic profiles.) Horizontal Strabismus - Exotropia (Divergent, 30% in peds. IXT most common in adults.) Subtype Prevalence Onset Angle & Pattern Key Associations Etiology Diagnostic Clues Intermittent 60% Distance > near Good initially Worsens with distance/fatigue/ light Fusional vergence weakness ACT distance > near; reduced reserves; NPC >10 cm. Constant 40% Basic (equal) or divergence excess (distance worse) Poor Amblyopia in 30-40% Innervational or sensory Large-angle (>30Δ) may show oblique pseudo-overaction. Convergence Insufficiency — Near exotropia — Asthenopia; improves with VT (60%) Vergence dysfunction Low fusional convergence. Vertical Strabismus (10%) Subtype Prevalence Presentation Etiology Diagnostic Clues Dissociated Vertical Deviation (DVD) 50-70% infantile esotropia Unilateral/bilateral upward/outward drift on occlusion (emerges >2 years); latent nystagmus Poor binocular fusion UCT shows drift (5-20Δ amplitude); no fixation preference. Latent manifestations during fatigue. 95% prevalence with amblyopia. Strong association with infantile esotropia and suppression. Oblique Muscle Dysfunction Common Inferior oblique overaction (bilateral asymmetric, V-pattern, overelevation adduction 1020Δ, graded 1+ to 4+); superior oblique overaction (A-pattern, overdepression). Etiology: Primary or secondary to antagonist weakness. Primary or secondary Versions grading; fundus torsion (extorsion 15° in inferior oblique). Pseudo-overaction in large-angle exotropia or TED. A side note on Dissociated Vertical Deviation (DVD) in Infantile Strabismus DVD is most commonly associated with congenital or infantile esotropia, but it can also appear in other conditions like intermittent exotropia or rarely in isolation. Key Characteristics • Appearance: When one eye is fixating, the other eye (the non-fixing or occluded eye) spontaneously drifts upward, sometimes with slight excyclotorsion. The deviation can be intermittent or constant and may alternate between eyes. • Trigger: It is elicited or worsened by covering the fixing eye, which dissociates the binocular input. Under binocular viewing, it may be partially suppressed. • Magnitude: The upward drift typically ranges from 2-20Δ, though it can vary. • Age of Onset: Usually presents in infancy or early childhood, often becoming noticeable between 6 months and 5 years of age. The exact cause of DVD is not fully understood, but it is thought to involve an imbalance in the neural control of vertical eye movements: • Shared Pathways Hypothesis: DVD may result from an abnormal connection or
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