hamsters have very bad eye sight to start with, so it doesnt take much of an eye problem to totaly blind them, i have a dwarfie with cataracts, it could be he has ALWAYS had eye problems that have slowly been getting worse but his other senses have made up for it
the blood on his nose would have been effecting his whiskers so he couldnt sense you with those
as for the nose bleeds, it does sound like you hhave done some damage to the small blood vessals in his nose, and made it a little bit weaker, my guess would be the blood you have been seeing is when he has accidently run into something and knocked himself
loosing too much blood does not lead to blindness, loosing too much blood effects your bodies ability to absorb oxygen, it can send you very dizzy and leave your ears ringing (on a side note i do not advise giving blood when you havent eaten
) in which case you are most likely to fall over, or faint, and it is only very temporary