University of Edinburgh
 

Supporting VI children and young people in a mainstream school

Presented on Wednesday 16 September 2009

What do we use vision for?

Janis Sugden

What do we mean by vision?

  • Vision differs from eyesight.
  • Eyesight is our ability to see.
  • Vision is a learned process.

What do we use vision for?

  • For Communication
  • For information
  • For moving around in our environment

Effects of visual impairment on early development

  • Reduced vision may delay a child's development in all areas.
  • Cognitive
  • Language
  • Fine and gross motor
  • Social and emotional
  • Self-help and independence.

the human eye

How is the Eye formed?

The Outer Layer

  • Tough and provides protection.
  • It is made up of back 5/6 Sclera and front 1/6 Cornea.
  • Whilst remaining tough the Cornea must also stay transparent to allow light to enter. It also starts to bend the light rays.
  • The Sclera provides the anchor for the muscles which move the eye.

The Retina (innermost part)

  • Cone cells are responsible for detail and colour vision and though they are found throughout the retina are in the highest concentration in the Macula - the area of best vision most detailed, that is, central vision.
  • Rod cells react best in dim light and give peripheral vision - less detailed.
  • Chemical changes in these cells give off electrical impulses so information starts its journey to the brain for interpretation.

Pressure is needed within the eye to keep the retina in contact with the choroid (nutrition).

This is maintained by:
Vitreous Humour - a jelly-like substance which must remain transparent to allow light to reach the retina.

Production and drainage of the aqueous humour which brings nutrition to the lens and cornea as neither have their own blood supply as they need to remain clear.

The Lens
The lens is controlled by the suspensory ligaments and is responsible for the fine focusing of the eye, bringing the object of regard into focus on the retina (upside down and back to front).

Formation of the Eye (The middle)

  • The Iris which controls the size of the pupil to control the amount of light reaching the retina. The colour of the iris depends on the amount of pigment it contains.
  • The Ciliary body controls the suspensory ligaments and so the shape of the lens. It also secretes fluid called aqueous humour into the eye to nourish the lens and the cornea.
  • The Choroid is richly supplied with blood vessels and supplies nutrition to the innermost layer of the eye.

What can go wrong?

  • Errors of refraction
  • Field loss
  • Other difficulties

A visual problem can give rise to:

  • Less information coming in
  • Fewer facts on which to base judgement
  • Poorer quality information
  • Distorted picture of the world
  • Restriction on incidental learning
  • Risk of passivity
  • Need for intervention to ensure learner reaches their optimum potential.

Vision in the first years of life

  • Dependent on intact eye, optic nerve and brain
  • Dependent on being stimulated
  • Problem with either then visual function will not develop properly
  • From 5 years of age probably have adult-like visual function