Aetiology

Causes include:

• strabismus - normal acuity develops in the eye used habitually for fixation, amblyopia in the non-preferred eye. This is most common in esotropia and rare in exotropia and hypertropia. It does not usually occur if there is spontaneous alternation of fixation.
• anisometropia; the eye with the greater refractive error is at risk of amblyopia.
• combined strabismic and refractive
• less commonly
  • ametropia- if refractive error is large and symmetrical, may cause bilateral amblyopia
  • stimulus deprivation(rare) - amblyopia results from interruption of the formation of an image on the retina:
    • unilateral
      • monocular cataract
      • ptosis
      • hyphaema
      • opaque cornea
      • cloudy vitreous
      • iatrogenic - prolonged patching or prolonged atropine eyedrops
    • bilateral
    • nystagmus
      • cataract

Reference:

• (1) Jefferis JM, Connor AJ, Clarke MP. Amblyopia. BMJ. 2015;351:h5811
• (2) Bradfield YS. Identification and treatment of amblyopia. Am Fam Physician. 2013;87(5):348-52.