Just like any piece of motocross gear every goggle will fit slightly different depending on the brand and the shape of your face.
When deciding on a new pair of goggles check the fitment and feel by holding the goggles against your face. You want the foam to be touching evenly against your face all the way around the frame and have the smallest amount of frame in your peripheral vision as possible.
If you wear prescription glasses there are also "OTG" goggles which have a deeper frame to allow room for your spectacles too!
See if you can try them on with the current helmet you are riding in as some brand goggles are more difficult to fit in certain helmet eye ports than others.