Unfortunately there isn't a way to actually physically correct double vision that is caused by MS. PastorDan makes a good suggestion re: seeing a neuro-ophtha about prisms. Although not therapeutic, meaning they won't actually 'fix' your eye, prisms can trick the eyes into seeing one image and make it much easier to cope with this frustrating symptom.
Speak to a neuro-ophthalmologist. Mine added prism to one of my lenses. The double images aren't quite fully merged now, but they are much better.