Visual Stress is a term used to describe a visual perceptual condition responsible for problems with
reading. The condition is also known as Meares-Irlen Syndrome.
Symptoms of visual stress include:
•
Perceptual instability: letters or words appear to move
•
Illusory perception of colours or shapes in and around the letters
•
Blurring of letters
•
Eyestrain and headaches
Visual Stress is due to a sensitivity to light or photophobia, thought to arise from a hyperexcitability
of the visual cortex of the brain. Visual stress is not dyslexia, although its symptoms are often
confused with those of dyslexia and other forms of specific reading difficulty.
It is estimated that at least 20 percent of the population is affected by visual stress. Whilst visual
stress can affect poor readers, it can also affect good readers who are required to do extensive
reading.
Coloured overlays are often used as the first step in identifying the presence of visual stress.
Overlays are transparent coloured sheets of plastic. They come in a range of ten to twelve different
shades. They are placed in turn over a page of print and the reader selects the colour optimal for
clarity. It is important to sample at least ten colours and chose the best, because individuals differ
with respect to the colour that provides greatest clarity.
The effect of the overlay on reading can be assessed using the Wilkins Rate of Reading Test, which
requires the reader to read aloud randomly ordered common words. The random order means that
the words cannot be guessed from context: they have to be seen to be read. The passage is read for
one minute with the overlay, one minute without the overlay, again without and finally again with
the overlay. The number of words read in one minute provides a measure of reading speed. Any
improvement in reading speed with the overlay of more than 10% suggests that the overlay will be
helpful for general reading. Some individuals show no improvement in reading speed, but report
that the overlay makes reading more comfortable.
The optimum overlay can be used when reading, both in the classroom and the home.
Although overlays are often useful when reading from a book, precision tinted spectacles can be
used in a greater range of contexts, such as when copying from the board and using a computer.
Coloured spectacle lenses usually work more effectively than overlays, possibly because the colour
can be selected with greater precision. The coloured lenses are prescribed using the Intuitive
Colorimeter, which shines coloured light on text and varies the shade of colour. Over 10,000
different shades are available. The assessment finds the best shade rapidly and precisely.
Children who consistently use an overlay should be considered for coloured lenses provided they are
typically over the age of seven and old enough to undertake the Colorimeter examination.
The symptoms that are treated with coloured overlays and spectacle lenses are very similar to those
that result from more conventional problems with vision. It is therefore important that all children
with a reading problem undergo a full vision assessment before being prescribed tinted lenses. A list
of eyecare professionals who have specialised in vision and learning can be found at
http://www.ceriumoptical.com/vistech/specialists.aspx
Any requirement for an optical correction can be incorporated into the precision tinted lens.