Contrast Sensitivity

How contrast sensitivity/Irlen Syndrome causes reading difficulties

To read well your eyes must be working optimally. That is why I am peering at the screen through my new glasses now! So the first step (which should be routine anyhow with any child) is to get a complete checkup with a good optician.

But beyond this, there is a syndrome that some opticians may not check for, where the eye is sensitive to the contrast of a pure black on a white background. It is a bit like red on blue for the rest of us. Here is an example of that:

For me that is very hard to read. Some people find the same effect with black text on a white background.

If your child complains of “the text moving around” on the page, or that the white on the page hurts the eyes, that will be the reason.

The eye actually begins processing the visual image that is projected onto the retina while it is still in the eye. In fact the eye is effectively a part of your brain that has extruded itself out of the skull (mmm… freaky eh?!).

One of the most important elements of processing that happens in the eye is to look for shapes and the edges of shapes. There are around 100 million rods and cones in each retina and only 1 million neurons in each optic nerve. So the eye is aggregating the individual rods and cones and it is in the aggregating process that the eye is very sensitive to changes in intensity.

If it is too sensitive to a black/white contrast, you will get this effect, known as contrast sensitivity. It is also called visual stress or Irlen Syndrome after Helen Irlen who first discovered it in the 1980’s.

Symptoms of contrast sensivity

Some of the key symptoms are:

  • Sensitivity to strong sunlight and flourescent strip lights
  • Complaining about the text moving
  • Complaining about distortions of the page
  • Finding larger text easier (this can be related to eye-tracking too)
  • Eyes watering while staring at computer screens
  • Getting headaches while trying to read or do mathematics

How reading feels with contrast sensitivity

A child who had this visual issue may not realize they do not see letters on the page as most people do. Often they will see distortions on the page which make it almost impossible to focus and read individual words. Here are some examples of those distortions:

Copyright 1987 by Perceptual Development Corp/Helen Irlen. All rights reserved

The solution for contrast sensitivity

If you feel that your child may be suffering from this issue, the first thing to do is test some tinted acetate sheets placed over the page of text. If there is a clear improvement, rather than a mild one, then we recommend you get a screening test done. As part of the screening process, color overlays are chosen to eliminate distortions and provide immediate relief from the symptoms. If you feel your child may be having contrast issues, please contact us and we can refer you to a local screener.

The screener can then provide the right tone of tinted overlay or get some tinted glasses made for you. It will also help to print text on tinted paper instead of white paper.