Margin of error for interpupillary distance on binoculars

[timbernomad]

How essential is it for binoculars to be an exact fit for someone's IPD? My wife has an IPD of 56mm according to her optometrist. A lot of binoculars on the market start at 57mm or 58mm on the low end.

How much will the view be compromised if the IPD setting is one or two millimeters off? I am the primary user for the binoculars, but I'd hate to buy something that my wife can't also enjoy.

 

[Airohunter]

I also have a narrow IPD, around 55 seems to be my mark. I can tell you it makes a huge difference, 56's are just too wide and worthless to me regardless of the quality of optic.