University of Edinburgh

The Assessment of Visual Functions in Children with Visual Impairment

Presented on Saturday, 11 December 2010

Assessment of Visual Functions workshop

Visual Acuity (Distance)

1 Our ability to see detail is dependent on external factors such at the size of the target, the complexity of the target, the target surround contrast, target illumination and the distance at which the target is viewed. Measure monocular acuity using the test chart provided at a range of distances (8m/4m/2m/1m). For the purpose of this exercise, record acuity as the number of letters read (Plot number of letters read against test distance). Do this for a number of individuals, some of whom should remove their glasses.

2 Compare and contrast the different test charts provided. When and for what reason would you choose to use the different types of chart?

Visual Acuity (Near)

1 Time yourself as you read the 4 blocks of text (one at a time). Ask your partner to do the timing and another to observe your behaviour.

  • Comment on speed, fluency and strategy.
  • Plot time against text size and comment on the relationship.

2 Compare and contrast the different test charts provided and comment on when and why you might choose to use the various types of chart.

Visual Fields (Distance)

1 Using the BIC biros provided, measure each otherís visual fields under both binocular and monocular conditions. Why is it that we usually express fields in degrees?

2 Discuss how you feel visual field size may be affected by :

  • Congenital glaucoma
  • Cerebral vascular accident (stroke)
  • Uncorrected refractive error
  • Target size

3 Why is it that you as educationalists might want to know about visual fields as well as visual acuity?

Contrast Sensitivity (Distance?)

1 Measure the contrast sensitivity in all of the group members using the Berkeley Discs test.

  • Use a 2m working distance
  • Record the number of discs per side
  • Observe the strategy used when identifying the most difficult targets
  • Record the contrast threshold in log units.

2 Compare reading speed and fluency using the Collenbrander mixed contrast letter and text charts in both good and sub-optimal lighting. Comment on the reason for using high contrast text in visually impaired education.

Colour Vision (Near)

1 Why do you think there is such confusion in the population as a whole concerning 'colour blindness'?

2 Look at the range of colour vision tests available and comment on their various uses and the factors that may cause erroneous results.