I don't think the condition that the modern-day filters correct is actual dyslexia, but a reading problem that was 'diagnosed' as dyslexia, if you see what I mean - I think dyslexia has been used a lot recently as a catch-all word by teachers/lazy doctors for a variety of sight problems. With Robespierre, though, I've come across suggestions that he may have had migraines, in which case symptoms are light sensitivity, aura, fogginess and other visual weirdness: then again, these people were working long hours by artificial light, so must have all been wrecking their eyes!