University of Edinburgh

What do we mean by Visual Impairment?

[For non-specialist teachers and support workers to raise awareness - can be offered on outreach basis]

Presented on Thursday 22 January 2009

Common Visual Impairments

Janis Sugden

the human eye

sketch of a street scene

A scene as viewed through normal, healthy eyes.
Variations of this picture will follow to simulate some visual impairments.

Errors of refraction

  • myopia
  • hypermetropia
  • astigmatism

With myopia the rays of light from a distant object come to a focal point before they reach the macula so the image is blurred.

In a hypermetropia eye the focal point of the rays of light is behind the macula.



The top line of lettering above is as seen by a normal, healthy eye. The other lines show increasing amounts of Astigmatism, in descending order. The last line is a severe case.


A typical Coloboma of the Iris showing the 'keyhole' pupil.

keyhole pupil

coloboma image


View as might be seen by an eye with an Anterior Polar Cataract

cataract image

Retinitis Pigmentosa

View as might be seen by eyes with Retinitis Pigmentosa, where central vision has not yet been affected.

RP image


View as might be seen by eyes with right hemianopia.

Macular damage

macular damage


wavy line

Look at this wavy line. Start first at the top of the line, then follow the waves of it right down to the bottom.
Now do it again, but this time as fast as you can.
And now do it several times, as fast as you can, one after the other without a break.
You will now have some slight impression of how Ocular Nystagmus might affect your eyes.


Albinism is not a disease or disorder.
There are two types. Oculocutaneous Albinism and Ocular Albinism.
Oculocataneous Albinism.
Tyrosinase – VE negative
White hair, eyelashes, eyebrows
Iris thin and pale blue
Nystagmus, head nodding, myopic, astigmatism* (can also be longsighted) squint,
photophobia, reduced vision.
Lack of binocularity – can participate in most sports but not comfortable with fast moving balls.

Other impairments

  • strabismus
  • colour vision deficiency
  • muscle disorder
  • cerebral palsy
  • visual perception problems
  • visual agnosias
  • retinopathy of prematurity
  • detached retina

Cortical/cerebral visual impairment

  • Very short visual span
  • Associated neurological problems eg; motor disabilities.
  • Processing difficulties
  • Visual skills fluctuate.

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.

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.

Acknowledgement: The slides showing the visual simulations of impairments have been adapted from the illustrations shown in George Marshall's book The Eye.