A big problem for the visual stress hypothesis

Spatiotemporal function in Tinted Lens Wearers
Anital Simmers, Peter Bex, Fiona Smith, and Arnold Wilkins
Invest  Ophthalmol Vis Sci 2001;42:879-884

For once, a rather good study which comes from a reputable group at Imperial College London. You can download it here.
Proponents of visual stress as a factor in reading difficulties argue that the sort of discomfort and movement illusions that most of us experience in response to recurring geometric patterns, varies in the population from person to person. They go on to argue that in some susceptible individuals it can be brought on by print, resulting in distortions and movements of letters and words - so called visual stress.
The conditions that induce these symptoms, for geometric patterns, are said to be surprisingly specific and peak with high contrast square gratings between 2-8 cycles per degree. Proponents argue that text has spatial frequencies within this range see the figure below.

The text has been filtered to remove high spatial frequencies and the contrast exaggerated to make the stripes more apparent

Text obviously isn't a striped grating. However, like a piece of music which contains multiple frequencies of sound waves at the same time (which you don't notice as the music washes over you), text contains multiple spatial frequencies and it is those between 2-8 cycles per degree that are the said to be a problem in 'visual stress'.
If this is the case we would expect to see this effect in simplified settings using actual gratings rather than text. Such a study has been done on subjects with visual stress, in a reputable psychophysical laboratory. Even more interesting is that Arnold Wilkins was one of the authors although he does not emphasise the results of this study a great deal.
The subjects were twenty individuals with 'visual stress' who had successfully worn tinted lenses (prescribed with the intuitive colorimeter) for at least six months. Twenty control subjects were recruited from the staff and siblings of staff and students of the University of Exeter.
Subjects were tested with a range of psychophysical tests which are designed to assess visual processing in the range of frequencies that are said to be aversive in visual stress.  The participants with visual stress, they were tested with and without their lenses.
The tests included spatiotemporal contrast sensitivity, contrast increment thresholds, random dot motion coherence, and motion perception
Results
To put it simply, there was no difference between control subjects and visual stress subjects and just as important, in the group with visual stress there was no difference with and without their lenses.

Contrast sensitivity function for subjects with visual stress with without

 lenses

Despite this, some people (mostly with a vested interest) still claim that lenses prescribed with the intuitive colorimeter are the 'gold standard.
Will this study dent their confidence? I doubt it.