Exotropia

Commonest childhood strabismus in South East Asia

Causes a crossed diplopia: right image comes from left eye and vice versa

Constant exotropias

• Infantile/congenital

  • Large deviation present at both near and distance
  • Presents at 2-6 months
  • Normal refraction
  • Often associated CNS abnormalities (in contrast with congenital eso)
  • DVD
  • Requires surgical treatment

• Basic exotropia

  • Exotropia equal for distance and near
  • Presents after 6 months
  • Surgical treatment

Intermittent exotropia

• Presents later (typically between 2 and 5 years)

• Intervening moments of normal alignment

• Often starts as an exophoria that decompensates with fatigue, inattention, bright light, illness

• Most common type of exo

• There is:

  • Suppression when the eyes are deviated
  • Good stereoacuity when aligned
  • Large convergence amplitudes
  • Amblyopia is rare

• Phases of intermittent exotropia (aim for surgery when they progress beyond 1)

  • 1. Exophoria at distance and orthophoria for near when the patient is tired or daydreaming
  • 2. Exotropic at distance and exophoric for near. Suppression prevents diplopia
  • 3. Exotropic for near and distance.

Simulated distance exotropia (aka pseudo-divergence excess)

• Appears worse for distance
• High AC:A
• Tenacious proximal convergence/fusion masks larger deviation for near: can be unmasked by 1 hour of monocular occlusion (patch test), prism adaptation testing or by using a +3.00D lens
  • If after the test the exo is equal for distance and near, then it is a pseudo-divergence excess

True distance exotropia (divergence excess)

• Rare
• AC:A may be normal or high (which carries risk of overcorrection after surgery)
• Deviation >10PD for distance

Near exotropia (convergence insufficiency)

• Exotropic for near, exophoric for distance
• Associated with myopia or presbyopia
• Affects young adults: aesthenopia, diplopia for reading

Convergence insufficiency: not a true exotropia

• Exophoric for near
• Causes aesthenopia, especially in teenagers

Treatment for intermittent exotropia

• Refractive error correction: myopic correction can relax divergence and correct exo.
  • Overminusing hypermetropes can also be considered
• Manage amblyopia
• Orthoptic exercises (eg. pencil push-ups) and diplopia awareness
• Occasionally prisms, botox
• Surgery