The trials they don't want you to know about (1)

Not only do proponents of the treatment of visual stress with coloured overlays and lens mis-represent their own trials, they keep quiet about a number of negative studies. This study is arguably the most rigorous trial to date and was performed by reputable scientists with no financial interest in coloured lenses and overlays.
The paper?
RitchieSJ, Della Sala S, McIntosh RD. Irlen colored overlays do not alleviate readingdifficulties. Pediatrics. 2011 Oct;128(4):e932–8.

Participants

75 below average readers were selected from a school setting in Glasgow.

These children were assessed by a qualified Irlen screener. 13 were unable to co-operate with the test and one moved out of the area. Therefore 61 children were assessed and  47 (77%) were diagnosed with Irlen syndrome (visual stress). Although the study has been criticised for the high number diagnosed it is entirely consistent with the case control studies published by Kruk et al and Kriss and Evans. Similarly, the observational study published by Tyrell and colleagues in 1995 found that 100% of well below average readers  and 75% below average readers chose an overlay

The study had a cross over design and subjects received a prescribed overlay, an overlay of a complementary colour and clear sheet.

Testing was with the Mini Mental State Exam MMSE, Wilkins Rate of Reading Test, and Gray Oral Reading Test.

The trial was rigorously conducted. Even though it was a cross over study, sequence generation was adequately generated and allocation concealment was was good so testers could not have foreseen whether subjects would have received experimental or placebo overlay first.

Steps were also take to ensure that subjects did no know which overlay was being used.

Data collection was complete and the analysis was on an intention to treat basis. In short there were no obvious sources of bias.

The results

 Irlen overlays had no demonstrable effect on reading compared to placebo overlays.

It can been seen from the figure on the left that the test retest variability for the WRRT was high and some individuals read more words per minute and some read fewer with their chosen overlay some as much as 30% fewer. 

Interestingly the two outliers shown in triangles both knew what their chosen tint was. Strong evidence for placebo effect.

WRRT reading rates for the Irlen group, non Irlen group and
3 children for whom the treatment was not masked

The pooled data doesn't look any better. Neither the Irlen group or the 'normals' read any better with overlays. The only group to do better were those who were not masked. Strong evidence for the placebo effect.

What about reading naturalistic text? - The Gray Oral Reading Test -here the study design was slightly different 22 of the subjects with visual stress received their chosen colour and 22 a clear overlay. There was no difference between the two groups.

Conclusions
The authors were unable to demonstrate any improvement in reading the WRRT or naturalistic text using Irlen overlays prescribed by a qualified Irlen practitioner.

There was also a one year follow up which will be discussed in a future post

2.Ritchie SJ, Della Sala S, McIntosh RD. Irlen Colored Filters in the Classroom: A 1-Year Follow-Up. Mind Brain Educ. 2012 Jun;6(2):74–80