Esotropia

The commonest form of childhood strabismus

Esotropia causes an uncrossed diplopia: right image comes from right eye and vice versa

Accommodative esotropia

• Accommodation and convergence are linked neurologically

• AC:A varies between people eg. young hypermetropes will naturally accommodate to see clearly

• Primary factors

  • Uncorrected hyperopia
  • Accommodative convergence
  • Insufficient divergence

• Usually presents between 1 and 5 years of age, average of 2.5 years old

• No diplopia: the deviating eye is suppressed

• Patients may alternate fixation

• Less than half develop amblyopia

• There may or may not be a refractive component (or overlap/mixed)

  • Refractive

    • A physiological response in high hypermetropia due to the excessive amount of accommodation needed to focus on targets (even distant ones) which is linked to a proportional amount of convergence

    • Spectacles correct/improve alignment when there is a refractive component

    • Normal AC:A ratio

    • Normal BSV

    • Equal deviation at near and distance

    • Eso only arises intermittently at first with fatigue/illness

    • If only partially accommodative, surgery can be considered if there is potential for BSV

      • Partially accommodative cases are more associated with amblyopia and bilateral superior oblique weakness

    • The measured hyperopia usually increases until children are 5-7 years old, beyond which point the Rx can be decreased to stimulate fusional divergence

  • Non-refractive (ie. convergence excess): 20%

    • High AC:A ie. disproportionate convergence for every unit of accommodation

      • An esotropia of ≥10PD for near compared to distance confirms a clinically high AC:A

    • Managed with orthoptic exercises, bifocals (relieves accommodation and thus convergence), miotics (eg. phospholine iodide) temporarily if non-compliant with glasses, surgery (eg. bimedial recession, if potential for BSV or for cosmesis)

Non-accommodative

• Infantile esotropia

  • Most common non-accommodative subtype

  • Family history may be present

  • Presents <6 months, patient neurologically normal

    • Full extraocular muscle movements

• Large angle ie. > 30PD (similar for near and distance)

• Alternating fixation (therefore low risk of amblyopia)

• Low BSV potential

• Normal refractive correction for age (ie +1 to +2)

Treatment

• Treatment of amblyopia

• Correction of hypermetropia

• Surgery: timing of surgery can be challenging. Typically done between 6 and 12 months of age

  • Before 6 months: spontaneous recovery can occur (hence no surgery before then)
  • Early surgery may achieve better long-term alignment and chance for BSV/stereopsis
  • But carries increased GA risks and less accurate preoperative measurements eg. prism cover test
  • Options: bimedial recession, unilateral MR recession, LR resection, IO recession if IOOA
  • Target 10PD of residual eso

Microtropia

• Small angle (<10PD)

• Strong binocular cooperation compared to other forms of strabismus

• Typically asymptomatic

• Deviation may not be detectable on cover test in microtropia with identity (ie. ARC)

  • In microtropia without identity, the fixation point of the deviated eye does not align with the fovea of the fellow eye so there is a small movement on cover test

• Associated with anisometropia especially hypermetropia +/- astigmatism

• Abnormal retinal correspondence is present but normal fusional amplitudes

• Central suppression scotoma in the deviating eye

• Reduced but present stereopsis

• The 4PD test will produce movement when placed over the normal eye but no movement over the suppressed eye.

• Managed with refractive correction and treatment of amblyopia