Research on reading development has focused on the linguistic, cognitive, and recently, metacognitive skills children must master in order to learn to read. Less focus has been devoted to how the text itself, namely the perceptual features of the words, affects children’s learning and comprehension. For second graders, decreasing font size, as well as increasing line length, yielded significantly lower comprehension scores. Line spacing had no effect on performance.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074061

Perhaps I can interest a classification of types of digital texts:

https://www.researchgate.net/publication/270575717_LA_INFLUENCIA_DE_LAS_TIC_EN_LA_FORMA_DE_LEER_TIPOLOGIA_DE_TEXTOS_DIGITALES

Article LA INFLUENCIA DE LAS TIC EN LA FORMA DE LEER: TIPOLOGÍA DE T...