Its really interesting reading this and that the use of overlays is still happening in schools. As a dyslexia assessor and teacher (and a SALT), Irlen syndrome/scotopic sensitivity is not supported by the scientific and clinical communities and the use of irlen related terminology is strongly discouraged by SASC and PATOSS. It was highlighted that Irlen (1983) used this term to promote her own method of teaching and learning, and was not robustly researched apart from within her own community. We, as assessors, are not allowed to conduct overlay assessments any more due to the lack of research.
I know its not directly related to your question but find it interesting anyway.