University of Edinburgh

The Assessment of Visual Functions in Children with Visual Impairment

Presented on Saturday, 11 December 2010

Assessment of Visual Functions workshop

Understanding Refractive Error 1

Spherical Refractive Error

We can assess central resolution/visual acuity by measuring the number of letters that can be read when the acuity chart is presented at a fixed distance (2m). 

Let's think about the effect of myopia (short-sightedness) - Use positive lenses (+0.5/+1.0/+2.0/+4.0/+8.0) and a working distance of 2m. 

Now let’s think about hypermetropia (long-sightedness). Use negative lenses (-0.5/-1.0/-2.0/-4.0/-8.0) and users of different ages, and test at a fixed working distance of 2m.

  • Plot number of letters read against the strength of correction.
  • Think about when and where glasses for hypermetropia and myopia may be most useful.

Understanding Refractive Error 2

Astigmatism and Pinhole

1. a) Find a spot light and view it through a variety of cylindrical lenses
(-1.0, -2.0, -4.0, -6.0).
Compare the lenses and comment on the effect.

b) Do a similar exercise, only on this occasion look at the outline of individuals, windows and doors. Once again, comment on the effect. Rotate the lens and comment on what happens.

2. Place lenses in the trial frame that cause letters on the visual acuity chart to become very blurred. Now place a pinhole in front of the lens and comment on the effect.  Why do you think this occurs?

Understanding Refractive Error 3

Low Vision Aids

  • Using the reading chart provided, measure the best distance at which to place it in order to see the print clearly, when viewed through a collection of lenses (+1, +2, +4, +8, +16, +32).

Comment on the difficulties experienced when using the different lenses.

  • Many VI people require a range of low vision aids to undertake a range of activities. 

Using the range of LVAs provided, comment on the various benefits and disadvantages of the various types of LVAs.