A glamour is a subjective event. Glamours don't actually change the physical appearance. Instead, they alter how you project yourself and the impressions you leave (or allow you not to leave none at all). With a glamour you can temporarily leave the impression that you are extremely attractive, taller, shorter, etc. Glamours are most effective upon strangers, and not everyone is susceptible to them.
Is it possible to change your eye colour with a spell? No. But with a glamour someone may remember you as having a different eye colour than you do. Again, it is a temporary thing.
