well, yes. any change in your amsler grid should be discussed with your eye doctor and evaluated.
but i personally doubt that the coreg has anything to do with it. coreg does have some visual side effects, but none IMO that would change the appearance of an amsler grid.
you should also be doing your amlser grid WITH GLASSES. since its a central vision test, and acuity is obviously important in that type of testing. any amlser grid result done WITHOUT glasses (unless you are a spherical myope between -1.00 and -4.00) must be taken with a grain of salt.
the short version is, i doubt its your medication, but any change in your amsler grid is worth investigating.