There are some very serious things that can cause double vision (brain tumors, myasthenia gravis, small strokes, etc). I would suggest you see either a eye muscle Eye MD (strabismus specialist/pediatric ophthalmologist) or a neuro-ophthalmologist. Find one at www.aao.org
JCH III MD
Is it unusual to need prism lenses then? I do have a large benign pineal cyst slightly pushing on my tectum. Could this be causing this?