In my experience, diplopia has been a short-term MS symptom. I had severe double-vision during a particularly bad flare and needed to wear an eye-patch to counteract the nausea brought about by the double-vision. Once the flare eased, the vision returned to normal, or as near normal as it gets.
Cranial Nerve VI Palsy will often bring on diplopia. The sixth nerve controls the lateral rectus muscle which pulls the eye outwards. The cranial nerve VI arises in the Pons area of the brainstem which, apparently, is a favoured site for MS lesions.
Diplopia in Multiple Sclerosis
Diplopia may also be associated with damage to the cranial nerve III or the cranial nerve IV. The third (oculomotor) nerve controls four muscles to each eye including the medial rectus which pulls the eye inwards. The fourth (trochlear) nerve controls the superior oblique muscle which moves the eye down and out.
I have continued to have vision problems since my diagnosis with multiple sclerosis in 1994, but the symptom of double-vision or diplopia has not recurred in any especially noticable manner.
I was surprised to find eye problems given that, prior to MS, I had near perferct vision. But the optic nerve is considered to be part of the central nervous system (CNS) and multiple sclerosis, an autoimmune disease, attacks the central nervous system.
It is easy to assume hat MS is attacking the peripheral nervous system when so many of the symptoms affect the hands, arms and legs. But multiple sclerosis is active in the brain and spinal cord affecting many bodily functions.
Treatments for diplopia
Wearing an eye-patch or press-on prisms for spectacles can help eliminate the double-vision.
Steroids such as prednisolone will help accelerate recovery from a period of double-vision in the same way it helps with optic neuritis.