So, I probably wouldn’t pull this one out at a happy hour or summer BBQ but this is one of those tid-bits that can help 
further understand how binos work and how to make them work best for you.
Ok, so the techy part….Interpupillary Distance is the distance between the pupils of the eyes. Don’t worry, we’re not suggesting any surgery here….. In the world of binoculars, interpupillary distance is the distance between the centers of the two eye pieces.
The good news is, you can shift that distance by moving the barrels apart or together. When this distance is set correctly for your face, you see one circle in the viewing area (versus two or versus seeing parts of the inside of the barrel).
To set the distance, simply move the binocular barrels closer together or further apart until you see just one circle. I’ve noticed that in some binoculars, to get them set up properly I need to hold them closer to my eyes but in other binoculars I hold them a little off my face and they work better. When you select your binoculars you’ll want to try out a few pairs and get a good feel for where that distance from your face is so you can properly set the interpupillary distance.