What are the causes of reading failure?

Language difficulties ( pollutants in the melting pot) which can be very real, possibly visual impairments, uncorrected, can add to eyestrain and difficulty in reading. I don"t like to bring this up but some so-called Word games as Jumble, grid puzzles, which utterly eschew grammatical structure ( allowing for back spellings, angles, etc) well, they should be labeled as ( eye irritants) they are not good for your eyes- any age group!