Another approach is getting closer fitting/thinner glasses dedicated for hunting/birding. It can really help.
ER isn't a fixed number (well it is but how a given ER works for you isn't fixed). It all depends how far the bins are away from your pupils and that depends on how far away your eyeglasses are. Close fitting glasses bias the game in your direction though too close fitting with some bins: Nikon SE and some Bushnells comes to mind which already has a little long ER for the eyecups ... can cause blackouts!
Last edited by KevinPurcell; 01/03/09.