Greg Lehnman is a physiotherapist and chiropractor, and has a popular blog.  He denounces the poor science of “text-neck” in this article, hinting that there isn’t really an “ideal posture”:

http://www.greglehman.ca/2014/11/22/text-neck-is-bad-science-and-fear-mongering/

This is also a good article, in which he questions the validity of the perhaps outdated “lower-crossed syndrome”.

http://www.greglehman.ca/2016/01/11/jandas-lower-crossed-syndrome-has-not-been-validated/