I have to gently disagree with the above. It is not an optical problem. It is a problem with the brain’s ability to process visual information. It also causes concentration difficulties. The overlays and glasses help, but they don’t take the problem away completely. And pupils struggling with irlens have not developed the same learning skills, often, as those without. Irlens is also a spectrum affecting some more severely than others. So although on its own Irlens doesn’t tick the extra time box, it may be part of a package of difficulties that do – the Irlen Institute suggest up to 43% of people with literacy difficties have Irlens and many with ASD, ADD, dyslexia also have the same neurological difference.