Twang,
I shoot with glasses and have no trouble. I draw 31 inches and anker my thumb behind my head also. You didn't say what kind of glasses you wear. I weare trifocals. I recently tried the new progressives and found I couldn't adjust to them. I am acustomed to turning my eyes rather then my head and with progressives you are required to look directly over your nose. A shift of 20 Degrees left or right and you loose focus. Hope this helps.