I found that the refraction of my glasses causes me to shoot off my mark. In the past I shot with either my glasses, or my contacts (when i finally got them). one year i tried shooting my bow, with glasses, and couldn't hit a thing. it was summer and i was sweating so I went into the house and put the contacts in. when i shot again i was hitting my mark. i then realized that i dialed the bow in wearing contacts and the glasses caused me to shoot off. practice alot with ur glasses on. you may have to site in the bow again.
if ur anything like my dad, he had alot of problems when he first got bi-focals. he found himself looking through the wrong lense more times than not.
practice, practice, practice.