To be perfectly honest, I am not sure how central Bryan K. Marcia is in the movement, but at least he can serve as our Encyclopedia’s representative of one of the biggest, most insane crackpot phenomena out there: Iridology; the most famous proponent in the States, Bernard Jensen, is currently dead and thus disqualified). Marcia may even be Canadian (he probably is, but he got his educational degree from Hawaii – the cnri website emphasizes that his educational institution was accredited – so there is at least this justification for including him).
For the uninitiated, iridology is the study of the iris to diagnose disease. The governing idea is that every organ in the body has a corresponding location within the iris and that it can be determined whether an organ is healthy or not by examining the iris rather than the organ itself. The view has absolutely no scientific support, and tests show that even iridologists themselves fail miserably in distinguishing between healthy and unhealthy individuals (and the rate of agreement between individual iridologists is hardly better than chance either). See the perfectly insane responses to this article here. The utter silliness of the idea is well illustrated by this piece from a former iridologist - and he is not the only one.
Bryan Marcia is at least an iridologist and seems to be counted as something of an authority in the iridology movement, in particular for his educational work. He has also worked with the legendary Dr. Jensen, and seems to be primarily responsible for the “educational” institution cnri.edu. The course description for the iridology course can be found here or here. The first of those pages also includes a useful list of iridologists in the US and other countries, although many of the names return preciously few google hits.
Diagnosis: Über-crank who is mired in the deep end of the fluffy pool of altmed. The popularity of iridology is unclear, but as with all woo it has the potential to cause some real harm to real people.