We are waiting for the eighth season and I still have no idea why Dean’s eyes bled in “Bloody Mary”. Kripke said he would be explained … but it seems that spent too long to be revisited. We never know what was the real secret of Dean. Another storyline wasted, thrown away.
Kripke’s interview : http://eclipsemagazine.com/hollywood-insider/5633/
Oh, I think I have an inkling as to what Dean’s secret might be: