Overview

Proper assessment should always include refraction

Pseudostrabismus

• Pseudoeso-

  • Epicanthic folds
  • Narrow IPD
  • Face -asymmetry
  • Proptosis/enophthalmos
  • Negative angle kappa (associated with high myopia)

• Pseudoexo-

  • Wide IPD
  • Positive angle kappa

• Dragging of the macula due to ROP or toxocara can cause pseudo-strabismus (revealed by the cover test)

• Eyelid retraction

Large angle kappa

• Produces pseudo-exotropia
• Occurs where there is temporal displacement of the macula
• Associated with
  • ROP
  • FEVR
  • Combined hamartoma of RPE/retina
  • Persistent posterior fetal vasculature

Phorias

• Latent deviations that are controlled by fusion
• Can decompensate eg. during certain tasks, fatigue, illness
• Patients may be phoric in certain instances and tropic in others

Causes of eso/exotropias

Esotropia

• Primary

  • Accommodative

    • Fully accommodative esotropia: normal AC:A ratio, resolves with hypermetropic correction
    • Partially accommodative esotropia: normal AC:A ratio, improves with hypermetropic correction
    • High AC:A ratio: convergence excess esotropia

  • Non-accommodative

    • Infantile/congenital esotropia: constant, onset < 6 months
    • Basic esotropia: constant, onset > 6 months
    • Near esotropia: only for near fixation (non-accommodative convergence excess)
    • Distance esotropia: only for distance fixation (divergence insufficiency)
      • Managed with orthoptic exercises
    • Cyclic esotropia: varies with time
    • Microtropia

• Secondary

  • Reduced VA eg. media opacities
  • Duane’s type 1
  • Mobius syndrome
  • Sixth nerve palsy
  • Thyroid eye disease
  • Myasthenia gravis

• Consecutive (post-surgery for exo)

Exotropias

• Primary

  • Constant
    • Infantile exotropia: onset < 6 months
    • Basic exotropia: onset > 6 months
  • Intermittent
    • Convergency insufficiency (near exotropia): worse for near fixation
    • Divergence excess
    • Simulated distance exotropia: worse for distance with a high AC:A ratio. Accommodative fusion prevent deviation at near
    • True distance exotropia: worse for distance and normal AC:A

• Secondary

  • Reduced VA eg. media opacities
  • Duane’s type 2
  • Thyroid eye disease
  • Myasthenia gravis
  • INO
  • Third nerve palsy

• Consecutive exotropia: following surgery for eso, amblyopia or longstanding eso- where fusion has not established

Krimsky test

• Prisms placed over the fixating eye
• Aim to center the light reflex over the pupil in the deviating eye
• Foveal fixation in the deviated eye is not needed (unlike the alternate-cover test with prisms, simultaneous prism-cover test and cover-uncover test with prisms)