This guide to confirm or even measure your far ipd, which is especially important for when you order a Bigscreen Beyond, but it also helps to set the lenses at a proper distance for other hmd’s, since most tend to set them too wide. Give it a try and experience peak clarity.
Or use an app; https://play.google.com/store/apps/details?id=com.sixoversix.copyglass
https://apps.apple.com/gb/app/eyemeasure/id1417435049
be warned those apps are not perfectly accurate. I used android apps that take a card as reference and also the one using iphone face scan measurements, they were 2 to 3mm wider than what my real far ipd ended up being. I even had an optometrist do multiple far ipd measurements, those lined right up with this paper method. To remove bias i also made sure to mix 10 papers at .5mm steps and checked them all.
So your optometrist is very likely correct, but the paper method is also, never trust an app.