lb2k04,

Your vision issue sounds like it may be an astigmatism. An optometrist can check for this. [ I often see a double image (fainter and to the upper right of the real image), especially with my left eye. ] I have worn lenses to correct for this for 50 years. The fact that it is apparent with just one eye suggests an astigmatism and not a convergence or other issue where both eyes need to work together.

If it only happens from time to time, it could be an occular migraine. Astigmatism would be all the time.

If it is an astigmatism, you may have had it all along but you were never sensitive to it. A concussion can cause the brain to become sensitized to this because the brain has lost the ability to filter out the shadow image.