When I shoulder my rifle with my eyes closed, I can open my eyes and the sights are right there and on target. That is the beauty of a cast off stock and proper fit etc. Considering your vision troubles, you may be smart to hold out for a left hand rifle ....with a swamped barrel. Are you comfortable with the touch hole venting right out in front of your face ? Some folks use right hand guns while shooting "lefty" and don't mind, but it's something to consider. It sure would be nice if you could get a chance to shoulder and fire a few different rifles so you could feel the differences . A trim late Lancaster style rifle with a "B" weight 38 inch swamped barrel, or a nice Oct to round barrelled 38 or 42 in / 20 gauge smoothbore would be my final suggestions. My own 20 bore has a 38 in barrel and it is light and handles wonderfully. It has taken everything from partridge to deer and black bears