2-ametropia

• Development of fixation reflex in newborns

  Eyes follow light
• Development of eye movement in newborns

  1. Eyes follow large objects at 2 months

  2. Hold objects at 3 months

  3. Fixate on objects for 1-2 minutes at 6 months
• Vision at birth


  • No greater than 5/200 (subnormal VA)
  • Eye is normally hyperopic because the ciliary muscles are not yet fully developed
• Development of visual acuity

  1. 20/70 at 1 year old

  2. 20/20 at 3 years old
• Development of fusional mechanism

  Fully developed from 1 to 1.5 years of life
• Development of accommodation


  Develops with sharpening of visual acuity at 3 years old
• Emmetropia


  Parallel incident light is focused on the retina
• Myopia


  Parallel incident light is focused in front of the retina
• Presbyopia


  Age-related condition
• Hyperopia


  Parallel incident light is focused behind the retina
• Ametropia


  Parallel incident rays do not come to a focus on the retina
• Types of ametropia


  • Refractive ametropia (incorrect power of cornea and/or lens)
  • Axial ametropia (incorrect axial length of eyeball)
  • Combined ametropia (combination of refractive and axial)
• Subtypes of ametropia


  • Myopia without astigmatism
  • Myopia with astigmatism
  • Hyperopia without astigmatism
  • Hyperopia with astigmatism
• Astigmatism


  Focal planes and circle of least confusion
• Emmetropization


  1. Eye growth compensation during first 2 years of life

  2. Genetically programmed or visually influenced via feedback loop
• Astigmatism shows a significant decrease during the first two years of life
• Refractive status changes with age: hyperopic at birth, emmetropic at 10, myopic at 25, then hyperopic again at 60 and less hyperopic at 80