Tom,
You want to be very careful using other-than-prescribed eyewear at the lathe because you need to be fully aware of everything that is happening at the same time.
Jewellers' loupes are not really intended for use around moving machinery because they obscure your peripheral vision (things happening to the left and right side).
Sometimes I use a large magnifying glass mounted on a flexible arm but I twist it out of the direct line when the lathe is turning.
If you have an optometrist that you see regularly about your eyes (and possibly reading glasses) I would talk over with him/her what your needs might be. I know that costs money but it is well worth it to get a professional opinion of what you should use.