I am legally blind, there are two things you may want to ask CM about. The first is front row seating, at dlr it is usually not honored, at wdw they do a better job at it, but as people say, pick your own seat or tell the CM which will work best, with the card, I usually if ask nicely can seat anywhere although the card will say front row. In dlr the show alladin has cast members that come out as giraffes and elephants I think, because they can not see well looking down, they miss my dog, so I sit in second row, and some shows since I really do not see like you or others, I just see like a kaleidoscope I learn where to seat the best, like in Nemo, as long as I cam close enough it see a kaleidoscope, if to far off to side or in front I see nothing, so the card helps but I doubt a three year old is going to be able to tell you how much. Also be careful many times, they sit w/c in with blind, such as parades, and it actually defeats the purpose, especially for a three year old, he won't be able to see over a w/c and they will not let him sit in front of the w/c with a parent because that would defeat the w/c spot, catch 20/20.
The second thing you may want to explain is that he may need help with stairs or things, with one eye, if he has any depth perception problems he may need help on stairs and such.
Another thing, which I would consider is the w/c as a stroller, since he may not have adjusted enough with one eye if he just had surgery, this will keep him protected from walking into things, or uneven surfaces, or depth perceptions. If you get both stamps, he can stay in the stroller, but if it is a place that seats him all the way in back with w/c you can ask to sit up front with him on lap, at those events. That way you get the best of both worlds.